
20221214: How Can Matter Be BOTH Liquid AND Gas?
 14:26: ... types; photonic matter; various spinbased states from ferromagnets to quantum spin liquids to time crystals; come to think of it, let’s not review all ...
 15:11: ... I can go back to the 1920’s and debate interpretations of quantum mechanics with Einstein and Schrödinger!” – well, then you’d need to ...
 16:53: Dark matter suffuses the nearvacuum of space, where we mostly just have the elementary quantum fields.


20221208: How Are Quasiparticles Different From Particles?
 05:51: But remember we’re at the quantum scale here.
 06:16: So now we have something like a particle  a quantum of vibrational energy moving around the lattice.
 06:25: ... through solids via these vibrations  so this makes the phonon a quantum of a sound wave, similar to how a photon is a quantum of light  of an ...
 07:07: As well as being a quantum of sound in solids, they are also the quantum of heat.
 07:30: ... understanding of the behavior of both sound and heat in solids at the quantum scale And phonons are also really important for your computer, which, as ...
 07:45: ...  and modeling this is needed for modeling the behavior of heat on the quantum ...
 12:47: But this means they act like photons in that many Cooper pairs can occupy the same quantum state.
 13:28: ... I had time for today  for example, quasiparticles appear in lattices of quantum spin, like are magnons  quanta of waves in that lattice, or skyrmions, ...
 13:51: In superfluids we have rotons  a quantum of a vortex in the fluid.
 14:20: After all, the elementary particles like electrons, photons, and quarks are just excitations in the elementary quantum fields.


20221116: Are there Undiscovered Elements Beyond The Periodic Table?
 09:23: The magic numbers are all even, and that’s because nucleons pair up according to their quantum spin, just like electrons in their shells.


20221109: What If Humanity Is Among The First Spacefaring Civilizations?
 16:59: Today’s comment responses are for the episode on the 2022 Nobel prize, which went to three scientists for their work on quantum entanglement.
 17:08: ... to wavefunction collapse when he said "spooky action at a distance" not quantum entanglement as is commonly ...
 17:37: ... together with Boris Podolsky and Nathan Rosen and basically discovered quantum entanglement in an effort to disprove wavefunction collapse through a ...
 18:28: It’s call transactional quantum mechanics.
 18:50: ... description implied by this interpretation is equivalent to standard quantum field theory, with the timereversed signals corresponding to negative ...
 19:50: Radar they plan to dress as a Quantum Entangled Particle this Halloween and so doing causing lots of spooky action at a distance.
 20:17: And then I figured it out  for my costume I entered a quantum superposition of both going and notgoing to all of the parties.


20221026: Why Did Quantum Entanglement Win the Nobel Prize in Physics?
 00:21: ... ingenious experiments that proved that the strangest prediction of quantum mechanics is actually ...
 00:34: ... the prediction that Einstein refused to accept  the idea that two quantum systems can be entangled  bound to each other such that they can ...
 00:58: ... our understanding and practical application of the phenomenon of quantum ...
 01:11: ... course, we’ve talked about quantum entanglement once or twice in the past, but today I want to tell ...
 01:58: Now imagine these are quantum balls with entangled “quantum” colors.
 02:03: ... to quantum mechanics, we not only don’t know which is which until the box is ...
 02:36: ... “quantum balls” could be any particle from subatomic to molecular scale, and ...
 03:01: Well, because quantum mechanics in it's standard form says so.
 03:07: Quantum systems are described by a mathematical object called the wavefunction, which evolves according to the Schrodinger equation.
 03:28: For our quantum balls to know their own color the whole time, there would need to be extra information not contained in their wavefunction.
 03:36: ... are a few different interpretations of quantum mechanics that allow this hidden information, and they’re collectively ...
 03:46: ... insisted that the wavefunction was the complete description of a quantum ...
 04:03: Quantum mechanics was just too successful, and Neils Bohr was aggressive in pushing his Copenhagen interpretation.
 06:12: Apparently Feynman thought it was pointless because standard quantum mechanics was clearly correct.
 06:42: ... possible electron transitions was between two states that had zero quantum spin, and which also resulted in the creation of two ...
 06:51: Spin is the quantum version of angular momentum.
 07:09: ... quantum mechanics says that those polarizations are undefined until ...
 07:33: ... was convincingly violated in their experiments, which means quantum mechanics was working exactly as expected, implying no hidden ...
 07:56: ... result of a quantum measurement depends on how you make the measurement  in the case ...
 08:35: ... direction the whole time and sort of conspire to look like standard quantum mechanics, even if they had real hidden ...
 10:35: There are two ways that the Bell inequalities could be violated without quantum entanglement being as spooky as Einstein feared.
 12:37: ... and Aspect's work was all about testing the fundamentals of quantum mechanics  about getting closer to what its weirdness is really ...
 12:50: They, and others like them, advanced our ability to create and manipulate entangled quantum states. And Zeilinger put these to good use.
 12:57: He may be the most famous for demonstrating quantum teleportation.
 13:02: This is a phenomenon in which a quantum state is transferred between two particles via an interrmediate particle that’s entangled with them both.
 13:13: ... teleportation and the corresponding ability to move around quantum information is critical for quantum ...
 13:21: ... of advances in manipulating entanglement, and has applied these to quantum cryptography and to the development of quantum ...
 13:38: Einstein because, one way or another, the quantum world is indeed quite spooky.
 13:43: ... Feynman was right in thinking that Clauser would never disprove standard quantum mechanics  but he was wrong in thinking that Clauser shouldn’t ...
 14:06: ... this case, our better understanding of quantum entanglement has brought us very close to the age of quantum ...
 19:16: ... in general a lot of problematic features appear in quantum field theory that have to be removed by hand  for example, ...


20221019: The Equation That Explains (Nearly) Everything!
 01:33: ... example, if we insist that the phase of the quantum wavefunction is fundamentally unmeasurable, then we need to add a term ...
 03:24: ... the path traveled by a ball through the air or the probability that two quantum particles will ...
 03:36: ... distance an object or system travels through the space of all possible quantum states. For classical physics it simplifies to just Kinetic Energy minus ...
 06:36: ... are actually shorthand for the separate interaction of each of the three quantum ...


20221012: The REAL Possibility of Mapping Alien Planets!
 15:45: ... Bang. First let me say that in the extremely early, the 3 quantum forces were coupled with a high joint interaction ...
 18:29: ... of that tiny patch of space, and that can change the way the quantum fields behave  including raising the fine structure ...


20220928: Why Is 1/137 One of the Greatest Unsolved Problems In Physics?
 00:19: This is the fine structure constant, and it appears everywhere in our equations of quantum physics, and we’re still trying to figure out why.
 00:48: But there’s something so weird and so compelling about this number that many of the founders of quantum mechanics obsessed over it.
 01:34: As with much of quantum mechanics, it started with us watching the light produced as electrons flicked between energy levels in atoms.
 02:04: ... spectral lines was a major driver of the development of quantum mechanics, and one of its first great successes, first with the ...


20220921: Science of the James Webb Telescope Explained!
 12:19: ... for the two recent episodes  the one about the strong force and quantum chromodynamics, and then the one about how the Higgs boson could tell us ...
 14:20: Quantum chromodynamics actually started to explain was going on, so it suplanted hadronic string theory.
 14:28: ... in size by about 20 orders of magnitude and developed into a theory of quantum ...
 17:09: ... quantum theorists of various colours can tell themselves that they’re hunting ...


20220824: What Makes The Strong Force Strong?
 00:00: Quantum mechanics gets weirder as you go to smaller sizes and higher energies.
 00:10: And today we’re going nuclear, as we dive into the weird world of quantum chromodynamics.
 01:20: The answers to these questions lie in the complex behavior of quarks and gluons via the rules of quantum chromodynamics.
 03:15: For the class of particles called fermions, no more than one particle can wear the same dress or occupy the same quantum state.
 04:52: And this colourful convention led to the naming of our science of strong force interactions: quantum chromodynamics.
 17:53: ... exist, but instead are a calculation tool to describe fluctuation quantum fields, what does that mean for Hawking ...
 18:28: Hawking’s original derived his radiation by calculating the disturbances on the quantum fields due to the appearance of an event horizon.
 21:07: ... don't get caught in the same trap as the proponents of theories of quantum consciousness, or that aliens built the pyramids, or that Elvis shot ...


20220817: What If Dark Energy is a New Quantum Field?
 05:18: ... that there are problems with the explanation where dark energy is due to quantum fluctuations. For example, it’s actually very difficult to get the ...
 05:50: ... energy density of dark energy. You can reduce that number if the quantum fields sort of cancel each other out. A perfectly symmetric canceling ...
 07:31: ... for a mechanism for accelerating expansion due being some other than quantum fluctuations. It’s because we know there must be one to explain cosmic ...
 10:55: ... us another explanation. The quintessence field could be coupled to the quantum fields responsible for radiation and matter, and its behavior could be ...
 11:51: ... a little bit ambiguous, and all of these could result from a new scalar quantum ...
 14:41: ... coincidental with a quintessentially consistent dark energy, or scalar quantum fields shift in a quintessencesaturated space ...


20220803: What Happens Inside a Proton?
 00:45: ... systems. That’s especially true when we study the quantum world, where the information density is obscenely high. As ...
 01:31: ... The messy interactions of quarks via gluons is described by quantum chromodynamics, or QCD, in the same way that quantum ...
 03:12: ... before we do the hard stuff, let’s review the comparatively “easy” quantum electrodynamics. Say we want to predict what happens ...
 07:07: ... general, if we can’t calculate what quantum chromodynamics predicts for the behavior of quarks, how can we even test ...
 07:53: ... that’s where lattice QCD comes in. It’s an effort to model how the quantum fields themselves evolve over the course of a strong force ...
 08:58: ... to do here. We want the probability for some wiggly quantum field wiggles between two states. Let’s go back to electromagnetism ...
 11:28: ... quantum field is a 3D pixelated lattice that evolves through time. As with ...
 12:15: ... the connections are the gluon field. Getting rid of the quantum probabilities means this isn’t really even a quantum problem any ...
 13:36: ... trick of transforming quantum fields into a lattice was first discovered by Ken Wilson all ...
 14:08: ... QCD even works gives us deep insights into the nature of the quantum fields. For one thing, because it doesn’t use ...


20220727: How Many States Of Matter Are There?
 07:00: The stuff of quarks is generically called quark matter or QCD matter  for quantum chromodynamics  the physics of quark and gluon interactions.
 08:00: But once you bring quantum mechanics into the picture, many strange states of matter become possible.
 08:07: ... in degenerate matter like neutronium or BoseEinstein condensates, all quantum states are occupied, leading to some surprising and useful emergent ...
 08:21: Time crystals are the latest and perhaps weirdest quantum state of matter.
 12:09: ... matter allows us to use the tools of our material sciences  for example quantum mechanics and condensed matter physics  to help us understand why we ...


20220720: What If We Live in a Superdeterministic Universe?
 00:33: These quantum superpositions only collapse into single states when we try to measure them.
 01:06: There have been many efforts to find a realist interpretation of quantum mechanics.
 01:34: Erwin Schrodinger, coinventer of quantum mechanics with Werner Heisenberg, was a big proponent of realism.
 01:55: Albert Einstein also came up with a scenario in which he tried to refute the nonrealist implications of pure quantum mechanics.
 02:20: ... “standard” quantum mechanics, the fundamental building block of reality is the ...
 02:55: This is quantum superposition.
 03:04: This is quantum entanglement.
 03:36: Standard quantum mechanics says that this is possible, but it leads to the seemingly absurd result of the EPR paradox.
 04:02: According to standard quantum mechanics, that spin is undefined until measurement.
 05:34: ... in a way that was somehow hidden from the wavefunction of standard quantum ...
 06:36: ... the beginning and contained within the electron  but false if standard quantum mechanics is right and spin is undefined until ...
 06:59: That test thoroughly supported standard quantum mechanics.
 07:52: There are ways to save realism in quantum mechanics by crossing Einstein and abandoning locality.
 08:04: On the other hand, Many Worlds interpretation of quantum mechanics saves local realism at the cost of requiring multiple realities.
 08:47: But quantum mechanics says that when Alice measures her electron, Bob’s electron is instantly affected.
 14:09: Quantum mechanics has been telling us that we are not that for 100 years.


20220630: Could We Decode Alien Physics?
 06:55: ... righthanded and lefthanded versions of all particles with quantum spin. If we build the device with positions that are ...
 07:38: ... put aside quantum spin for a minute to define this rule. Say you have an electron ...
 10:41: ... symmetry between left and right handed chirality for particles with quantum spin, and in our universe Psymmetry is broken in much ...


20220622: Is Interstellar Travel Impossible?
 15:08: We talked about how quantum mechanics can be derived as a model of our information about the world, rather than the world itself.
 15:31: Clay Farris Naff asks whether Zeilinger description of informational quantum mechanics is consistent with Hawking's lateinlife antirealist stance?
 16:09: But this is the philosophy behind Zeilinger’s interpretation of quantum mechanics.
 16:24: ... the waveparticle duality was explained in the context of informational quantum mechanics in that you couldn’t simultaneously extract answers to both ...
 16:41: ... know what questions are the most elementary, and so we don’t know if a quantum system’s waveparticle nature has a binary ...
 17:58: We have robust theories for the unification of the three quantum forces.
 18:03: And we even have ideas for black holes in theories of quantum gravity  for example, the fuzzball of string theory, which we did an episode on.
 19:30: Hawking’s original argument talked about perturbing the positive and negative frequency modes of the quantum vacuum.


20220615: Can Wormholes Solve The Black Hole Information Paradox?
 00:26: ... there’s an uncomfortable conflict between general relativity and quantum mechanics when we try to describe the tiniest scales and the ...
 01:40: ... This conflicts with the law of conservation of quantum information, which is a nonnegotiable constraint of quantum ...
 02:43: ... quantum version of entropy is called von Neumann entropy. This is the ...
 03:20: ... of the black hole are entangled. The black hole interior contains quantum information about the radiation. But when the black ...
 04:44: ... have largely focused on ways to encode Hawking radiation with that quantum information, so that each new particle is entangled ...
 06:54: ... the Page curve using only general relativity and accepted quantum mechanics  no string theories attached. To be fair, these ...
 07:24: ... papers pulls ideas from string theory, holography, quantum field theory, and quantum computing to name a few ...
 12:09: ... transitional geometries allow the radiation to leak quantum information from the black hole ...


20220601: What If Physics IS NOT Describing Reality?
 00:25: ... which laws work best. But actually, some of the founders of quantum theory were convinced that the role of physics was one step ...
 01:41: ... started talking about informational interpretations of quantum mechanics. Then we discussed one of the more radical ...
 02:20: ... right, but we can explore the power of informational quantum mechanics without committing to quite such a radical ...
 02:44: ... see if we can rebuild the world from those parts. In quantum mechanics, we have things like particles and fields which can only ...
 03:22: ... Anton Zeilinger has proposed an informational approach to quantum mechanics in which the world is broken up not into ...
 04:05: ... of wellchosen yesno questions. So Zeilinger says that any quantum system can be broken into the results of binary questions. ...
 04:56: ... simplest way to start is to look at a quantum system where the answer to a single binary question seems to ...
 05:53: ... by definition, that’s all the information that the elementary quantum system of spin can contain. That means the leftright orientation ...
 07:23: ... Quantum entanglement also fits this picture. When we prepared our ...
 08:49: ... we’ve seen how an elementary quantum system’s information content has to exist with respect to ...
 09:26: ... one of the original and most mysterious features of quantum mechanics  waveparticle ...
 10:33: ... both questions. So, they found that the waveparticle duality of quantum mechanics arises from the limited information, the ...
 11:24: ... one thing to use quantum information theory as a mathematical tool, but quite another to ...
 12:09: ... And it turns out that a lot of the weirdness we see in the quantum world make more sense if we pay attention to the fact ...


20220504: Space DOES NOT Expand Everywhere
 08:51: ... made out of, if anything. That’s the province of a longsought theory of quantum ...
 10:33: ... that at the smallest scales, general relativity comes into conflict with quantum mechanics. There is a smallest measurable length called the Planck ...
 14:34: ... of phrasing has led to all sorts of misunderstanding and quantum charlatanry. But I think the reason people like Wheeler and Bohr used ...
 15:31: ... electron thing from his advisor, and using it to help develop quantum electrodynamics. So what can we build using ideas from the participatory ...


20220427: How the Higgs Mechanism Give Things Mass
 01:48: ... can wiggle, twist, oscillate in different ways. A quantum field just represents one of these modes. And these wiggles are ...
 02:31: ... quantum mechanics, such a “redundant degree of freedom” leads to a gauge ...
 02:50: ... we enforce this requirement, we find that we have to add a new quantum field to the Schrodinger equation that lets the ...
 07:01: ... in a similar way. The equivalent of the simple valley exists. A quantum field can oscillate around some “zeropoint” value ...
 08:09: ... particular Lagrangian describes a simple quantum field made of massive particles which interact with each ...


20220420: Does the Universe Create Itself?
 00:59: ... then came the 20th century, and quantum mechanics. In quantum mechanics, not only does the act of measurement ...
 01:59: ... to go to these crazy lengths to explain the universe, let’s review some quantum weirdness. We’ll start with the good ol’ Schrodinger’s cat thought ...
 04:03: ... put the whole mess behind them and get on with the job of actually using quantum mechanics to invent the modern ...
 04:14: ... others. Wheeler was never completely satisfied with any of the proposed quantum interpretations. Although he started out as a pure realist, he came to ...
 05:56: ... or reflected by the beamsplitter. But remember I said that the quantum world appears to live in a state of uncertainty until it’s ...
 06:13: ... this case, quantum mechanics states that the photon is in a state of having been both ...
 11:11: ... power over reality, as claimed by some of the worst practitioners of quantum woo. But the role of consciousness was something Wheeler really ...
 12:27: ... In the broad category of “participatory realism” we have things like quantum bayesianism and relational quantum mechanics, in which the universe ...
 16:10: ... horizons will lead to a disconnection in the vibrational modes of the quantum fields in a way that looks like thermal radiation. That radiation has a ...


20220323: Where Is The Center of The Universe?
 10:45: Stand by for our theory of quantum gravity to resolve that one.


20220316: What If Charge is NOT Fundamental?
 00:37: The math that describes it  Maxwell's equations or quantum electrodynamics  seem to wrap it up nicely.
 01:39: As with much of modern physics, this story begins with Werner Heisenberg, whose epiphanies birthed quantum mechanics.
 02:23: For example electrons have this thing called spin  a quantum analogy to angular momentum.
 05:13: ... the same way that isospin followed the same mathematics as regular quantum spin, this new property seemed to obey the math for our old friend ...
 08:32: The quark model for nucleons led to a description of the strong nuclear force via this SU(3) stuff to give us quantum chromodynamics.
 09:07: The secrets of electric charge are actually hiding in the last, most obscure of the quantum forces  the weak force.
 09:32: ... it is  but it's the thing that's going to connect all of this back to quantum spin, which is sort of where we ...
 09:41: One consequence of quantum spin is this thing called chirality, which is sort of the projection of spin in the direction that a particle is moving.
 10:39: Only lefthanded particles have it, and so it has an intimate connection to the quantum spin.


20220308: Is the Proxima System Our Best Hope For Another Earth?
 17:13: But in general it means different branches of the wavefunction are able to influence each other, which is not the case in standard quantum mechanics.
 17:20: Check out our episode on the manyworlds or EverettWheeler telephone for juicy details on nonlinear quantum mechanics.
 17:45: ... that produce hopeless contradictions between general relativity and quantum ...
 17:58: ... quantum mechanics and quantum field theory assume a welldefined underlying ...
 18:22: Resolving that has been the major work of all of our searches for quantum gravity and theories of everything.


20220223: Are Cosmic Strings Cracks in the Universe?
 00:00: ... a nice, clear ice cube for your drinks, it’s important to consider quantum fields. First, boil to release dissolved gasses, ...
 00:58: ... Big Bang energy, formed from topological defects in the quantum fields, aka cosmic strings. They have subatomic thickness but ...
 04:51: ... just like a ball sitting at the top of a hill. But the slightest quantum jiggle would send the ball, or the Higgs, rolling down in a ...
 07:33: ... that’s for another time. OK, so we’ve managed to freeze the quantum fields amidst the first bawlings of the baby universe and woven ...
 12:19: ... about the origins of the universe, or the nature of quantum fields, or the validity of string theory. Many murky ...


20220216: Is The Wave Function The Building Block of Reality?
 00:03: ... the world of quantum mechanics, it’s no big deal for particles to be in multiple different ...
 00:49: ... quantum mechanics, particles don’t have definite properties. Rather they are ...
 01:24: ... decayed OR not, and the cat is alive or dead, not alive and dead. The quantum becomes classical at some point between the subatomic and the ...
 02:24: ... first proposed by Werner Heisenberg, one of the principle founders of quantum theory. Heisenberg and his friend Neils Bohr were convinced that this ...
 03:24: ... forever, splitting into parallel realities. And we have the idea of quantum decoherence, where different parts of the wave function simply become ...
 04:17: ... to become known as GRW theory  the first in a new class of alternate quantum theories called “objective collapse ...
 04:54: To understand how objective collapse theories work, we need just a little more quantum mechanics.
 06:04: ... collapse in just the right way to explain why subatomic systems could be quantum but large systems were always ...
 06:41: ... hits are very rare. It’s incredibly unlikely that a single isolated quantum particle will undergo collapse during the course of an ...
 06:53: ... wave function of the entire system. Any attempt to measure an isolated quantum system necessarily means bringing lots of particles into the picture  ...
 07:17: ... this “hitting” mechanism gives a potential explaination for the quantumclassical divide  it simply depends on the number of particles involved. Small ...
 08:55: ... explain two mysteries of physics. 1. What causes the transition from quantum to classical? And 2. Why can’t gravity be quantized like the other ...
 09:25: ... Quantum mechanics rules when things are small, but add enough mass, and the ...
 10:19: ... to the Schrödinger equation, they are not mere interpretations of quantum mechanics — they are distinct theories with unique predictions. This ...
 11:09: ... indirect signs of collapse models. For example, the models imply that a quantum wave function will be randomly tossed about and jostled by gravity or ...
 12:55: ... in physics. And one that we’ll be coming back to. What, in fact, is the quantum wave function? And how does this abstract system of shifting realities ...


20220210: The Nature of Space and Time AMA
 00:03: ... the planck time and we know this because general relativity and quantum mechanics come into impossible conflict below these planck units of ...


20220127: How Does Gravity Escape A Black Hole?
 03:17: First we’ll see what Einstein has to say on the matter, and then we’ll go deeper, into the speculative realm of quantum gravity.
 05:54: ... believe that general relativity needs to be replaced by a theory of quantum gravity to explain the behavior of gravity in these ...
 06:03: So can gravity escape from a “real” black hole of quantum gravity?
 06:08: Now in quantum mechanics  or more specifically quantum field theory  forces are mediated by particles, not by the geometry of spacetime.
 06:28: In theories of quantum gravity, the gravitational force should probably also have a mediating particle  usually called the graviton.
 07:55: That’s easy  these are virtual particles, and in quantum field theory, virtual particles are not restricted by the speed of light.
 08:39: ... talking about the classical gravity of Einstein or some deeper theory of quantum ...
 13:06: ... ingenious method for simulating the insane amount of information in the quantum wavefunction with density functional theory, and then went from the tiny ...
 13:25: Starting with the quantum, manonthedollar asks  given the incredible amount of power required to simulate quantum interactions...


20220119: How To Build The Universe in a Computer
 11:13: ... we discussed recently, a full quantum description of the world contains unthinkably more information ...
 11:23: No conceivable technology could fully simulate a quantum universe, except perhaps a cosmicallysized quantum computer.


20220112: How To Simulate The Universe With DFT
 00:00: ... in the observable universe to solve the schrodinger equation and do full quantum simulation of some chunk of the universe, how big would that chunk ...
 00:18: That’s how insanely information dense the quantum wavefunction really is.
 00:38: Quantum mechanics allows us to predict the behavior of the subatomic world with truly incredible precision.
 01:12: But for almost every practical use you’d need to do that math for multiple quantum particles interacting  and then the blackboard doesn’t cut it.
 01:48: ... describes how the wavefunction of a quantum particle  that’s this psi thing  changes over space, assuming the ...
 02:30: ... time independent Schrodinger equation isn’t the be all and end all of quantum mechanics  it’s an approximation that works for slower moving particles ...
 02:39: But it’s where we start learning quantum mechanics, and it works for a lot of simple cases.
 05:39: ... in quantum mechanics often means finding a solution to a problem that’s much ...
 05:52: ... to solve the impossible case of many interacting quantum particles, we should start by thinking about the completely solvable ...
 06:48: In quantum mechanics, we’re dealing with the wavefunction, and the wavefunction fills all of configuration space.
 06:59: ... only that, but quantum mechanics contains nonlocal correlations which arise because the ...
 08:02: But if we want to keep the quantum behaviour of quantum mechanics we can’t throw away most of configuration space like we do in Newtonian mechanics.
 08:22: Doing so destroys quantum correlations.
 08:26: ... equation for more than a few particles, researchers still manage to do quantum simulations of some extremely complex ...
 08:49: ... to tackling the extreme dimensionality problem when solving realistic quantum ...
 09:01: ... an example, here’s a quantum simulation of the millions of atoms comprising the capsid of a virus ...
 09:41: And through a very mysterious quality of the quantum world, it's possible to map that fake solution to real answers.
 12:51: ... functional theory has now been used to model the intricate quantumlevel behavior of chemical reactions, of complex molecules even as far as DNA ...


20211220: What Happens If A Black Hole Hits Earth?
 17:30: ... principle, which we covered previously. It, says that vibrations in a quantum field on the surface of a 4D hyperbolic space are equivalent to objects ...
 18:16: ... potentially detect deviations from general relativity in the form of quantum fluctuations near the event horizon that might be amplified by ...
 19:14: ... 3+1 in my experience. And for that matter all hairballs are technically quantum. This teaches us one important lesson: next time you clean up after your ...


20211210: 2021 End of Year AMA!
 00:02: ... the so so so we have this strange uh description of of the forces in quantum mechanics in particular in quantum field theory where two particles ...


20211117: Are Black Holes Actually Fuzzballs?
 01:00: At the central singularity, the known laws of physics break down  general relativity comes into irreconcilable conflict with quantum mechanics.
 03:34: And that violates a very deep and fundamental law  the law of conservation of quantum information.
 03:40: This threat of erasure of quantum information in a hairless black hole is the black hole information paradox.
 04:17: Ultimately, the black hole paradoxes stem from the disagreement between quantum mechanics and general relativity.
 04:23: The impossibility of the central singularity is the most obvious place where we need a theory of quantum gravity.
 04:32: A theory of quantum gravity would have really helped Stephen Hawking in deriving his eponymous radiation.
 04:49: ... pure general relativity but then analyze its effect on the surrounding quantum fields, which only worked if the gravity at the horizon was relatively ...
 05:09: ... gravity starts to get quantum even above the event horizon, then it may be possible to actually encode ...
 05:22: And it turns out that our most advanced theory of quantum gravity can do this quite neatly.
 08:39: This property of black holes is actually quite hard to reproduce in theories of quantum gravity.
 09:09: ... and branes, like the hairball coughed up from some hyperdimensional quantum ...
 09:39: ... most amazing element of the fuzzball paradigm is the discovery that quantum gravity effects might not just be important at the center of the black ...
 13:26: I should also add that fuzzballs are not the only quantum extension of the GR black hole.
 13:38: And they’re one of our best hopes for understanding the union of general relativity with the quantum.


20211110: What If Our Understanding of Gravity Is Wrong?
 15:45: ... if the configuration space Lagrangian seems to bridge quantum mechanics and relativity, what's missing to make this a theory of ...
 16:31: Check our episodes on Noether’s theorem, quantum invariance, and the electroweak force for some details, but we probably need to go even deeper.


20211102: Is ACTION The Most Fundamental Property in Physics?
 05:24: ... and into our modern theories  in particular general relativity and quantum mechanics. And perhaps in these we’ll find clues as to what the action ...
 08:31: OK, it seems like we’re getting somewhere. Let’s see if quantum mechanics will get us any deeper, or perhaps just make everything more confusing.
 08:39: ... with the famous double slit experiment, as we so often do when talking quantum mechanics. In it, a stream of quantum particles are launched at a ...
 09:56: ... Dirac very nearly figured this out. He realized that a quantum analog of the action existed that was related to the integrated time ...
 10:26: ... along some hypothetical path. Feynman realized that the path of a quantum object could be determined by adding together all possible paths that ...
 11:12: ... is Feynman’s path integral formulation of quantum mechanics, and it exactly reproduces the predictions of previous ...
 11:59: ... to guess, particles tend to end up near the stationary points of the quantum action. In the path integral, this happens for paths that take the ...
 12:16: ... spacetime, where the shortest path minimizes proper time. In quantum mechanics configuration space could mean phase space  the space of ...
 12:59: ... application of the quantum action principle to the evolution through quantum states underpins ...
 13:16: Well it turns out that this equation is just the Lagrangian for a spin½ quantum field.
 13:23: ... there’s a Lagrangian for each quantum field which describes how that field and its particles tend to evolve. ...
 17:54: ... assumptions (infinite/finite, discrete/continuous spacetime, invariance, quantum etc.) then constructor theory gives us insights as to what math is ...


20211020: Will Constructor Theory REWRITE Physics?
 01:43: ... mechanics and electromagnetism and so on from two master theories: quantum mechanics and Einstein’s general ...
 02:40: ... uses theories like general relativity and quantum mechanics, along with more fundamental conservation laws, or principles, ...
 03:05: Constructor theory is inspired by information theory and the theory of quantum computation.
 03:11: ... David Deutsch says, if a quantum computer can, in principle, simulate any process in physics, then all of ...
 04:42: For example, understanding the union of quantum mechanics and general relativity.
 05:44: Again, this task is impossible, since it’s ruled out by the laws of quantum mechanics and the principle of conservation of energy.
 08:07: For example Chiara Marletto has used constructor theory to describe a scenario for testing whether gravity is quantum in nature.
 08:16: And we certainly don’t have a mechanistic theory for quantum gravity.
 08:20: ... systems of information  called information media  and how systems of quantum information  or superinformation media  must differ from regular ...
 08:34: For example, for systems of quantum information there’s a particular task that is possible that is impossible for classical systems.
 08:43: That task is entanglement between the information elements  the qubits in the quantum case.
 09:17: From the definitions of what an information medium is, Marletto argues that this chain of quantum elements is equivalent to a quantum field.
 09:27: And she argues that only a "superinformation medium"  aka a quantum field  could mediate the entanglement of two spatially separated qubits.
 09:35: ... could induce entanglement between separated qubits, then gravity has quantum ...
 09:47: This is cool because it gives us an experimental test of quantum gravity that has absolutely no dependence on a particular theory of quantum gravity.
 09:55: It doesn't need the dynamical laws of such a theory, or even of quantum mechanics or general relativity as they currently stand.
 10:51: ... Heisenberg came up with the first version of quantum mechanics by stripping away all but the bare facts about the nature of ...
 12:21: Last time we talked about the latest ideas on the weird world of quantum tunneling. Let’s see what you had to say.
 12:30: ... a particle tunnel through .. nothing. As in could it quantum teleport even through empty space in Fact do particles even travel ...


20211013: New Results in Quantum Tunneling vs. The Speed of Light
 00:10: ... efforts in quantum tunneling  both theory and experiment  show that superluminal motion ...
 00:26: Quantum tunneling is one of the weirder phenomena in the generally very weird world of quantum mechanics.
 00:32: It describes how quantum particles are able to move across seemingly impenetrable barriers  for example, when atomic nuclei decay.
 00:40: ... it’s not just the Houdinilike power that makes the quantum world weird  it’s also that the tunneling motion may move particles ...
 00:55: Now we covered quantum tunneling a long long time ago  in fact it was the first video we did on quantum mechanics.
 01:05: I mean, we’ve learned a lot on this show and so we can dig deeper into the FTL aspect of quantum tunneling.
 01:12: ... are bringing us closer to understanding the superluminal prospects of quantum ...
 01:25: But first, a quick recap of quantum tunneling.
 01:51: ... similar thing happens in the world of quantum mechanics, where particles are pushed and pulled by the fundamental ...
 02:30: This is quantum tunneling.
 02:31: The key to the escape is quantum uncertainty.
 02:35: Between observations, quantum particles don’t have well defined properties  and that includes their positions.
 04:31: ... to determine the socalled tunneling time because, in the fuzzy world of quantum mechanics, it’s hard to even define what we mean by tunnelling time or ...
 06:30: ... if this was a quantumtunneling train, then only the front carriage would make it through the tunnel, ...
 06:45: It’s hard to measure the travel time of a quantum train OR a quantum wavefunction because it’s hard to define the start and end points.
 08:22: Can quantum tunneling really speed up the transmission of the information contained in that message?
 08:50: ... cutoff front end of the old wavefunction, or the first carriage of the quantum ...
 10:40: In 2020, a paper was published in the journal Nature that used the swiveling axis of a particle’s quantum spin as the clock hand.
 12:28: All signals in our universe, whether via quantum tunneling or quantum entanglement, seem to be bound by the same limits imposed by relativity.
 13:38: ... as a scientist I may not know everything about the depths of quantum tunneling, but as a New Yorker I know that every tunnel needs a name so ...
 13:59: ... goes through solid bedrock so there’s a low probability that your quantum wavefunction will make it through  but if you do then the trip is ...
 16:55: It's hypothesized that portkeys are based on wormhole technology, but actually they may well use quantum tunneling.
 17:04: And that process actually evades Hogwart's security wards because the wizards are rubbish at quantum mechanics.


20211005: Why Magnetic Monopoles SHOULD Exist
 04:24: But what about quantum mechanics?
 04:26: ... quantum theory first appeared it quickly revolutionized our understanding of ...
 04:37: ... arose automatically from requiring that the equations of quantum mechanics had a particular symmetry  the measurements they predict are ...
 05:09: ... particular, the magnetic field emerging from the quantum theory must have zero divergence  its field lines can never end  so it ...
 05:27: Quantum mechanics, as the saying goes, forbids it.
 06:52: In quantum mechanics, this works by shifting the phase of the particle’s wavefunction.
 08:45: Charge turns out to be quantized, so quantum mechanics doesn’t actually forbid monopoles.
 14:55: ... week we talked about how quantum spin leads to the universe as we know it  for example all the structure ...
 15:08: We represented very distinctly separated electron energy levels in our explanation of how fermion’s can’t occupy identical quantum states.
 15:16: ... it’s possible to have two electrons at the same energy but different quantum states by allowing for opposite spin ...
 15:29: ... more careful I would have said that we were trying to represent separate quantum states, not energy levels in an ...
 15:39: ... that we don’t need to keep talking about spin as this incomprehensible quantum property that has no intuitive analogy  reminding us that Hans Ohanian, ...
 16:49: Fermions never occupy the same quantum states.
 16:51: When degeneracy pressure is broken it’s because new space in quantum states opens up.
 18:01: Or maybe you could just use USBC  they’re spin2 bosons like gravitons, so easily understood with a basic theory of quantum gravity.


20210921: How Electron Spin Makes Matter Possible
 00:26: ... now we’ve established that quantum spin is very weird. We talked all about that recently  how electrons ...
 01:44: ... no limit to the number of photons you can add  all of them in the same quantum state. But not fermions  no two fermions can share the same quantum ...
 03:19: ... degrees. So a spinor’s rotational weirdness is not necessarily all that “quantum”  it’s a natural function of how it’s connected to the universe. So ...
 05:59: ... Well electrons don’t really rotate in the classical sense. They’re quantum objects described by a quantum wavefunction. A wavefunction is this ...
 08:00: ... just doing addition and subtraction here. Let’s think about the quantum state of an electron. We’ll call it Psi. Psi gives the distribution of ...
 10:32: ... atom, but this works for any two possible wavefunctions  two possible quantum states  that our electrons could have. If electron A is in the ground ...
 12:37: ... vanish electrons  so the transition of an electron into an occupied quantum state is ...
 13:03: ... anti symmetric wavefunctions cannot have multiple particles in the same quantum ...
 13:25: ... fact that you need to use spinors in the Dirac equation  which is the quantum equation of motion for electrons and other spin½ ...
 18:44: ... tells us that Space Time made him realize that he’s more interested in quantum physics than astrophysics. Hey, at least you didn’t devote decades of ...


20210915: Neutron Stars: The Most Extreme Objects in the Universe
 04:04: ... of the fermion family can’t occupy the same quantum state. The matter has become what we call degenerate, and ...


20210907: First Detection of Light from Behind a Black Hole
 12:26: Blinkist has an array of categories – from the science of Quantum Mechanics to philosophy to futurism.
 12:37: ... telephone, where we explored how to send messages across the quantum ...


20210818: How Vacuum Decay Would Destroy The Universe
 00:21: ... universe is largely defined by the properties of the quantum fields that pervade all space. The quantum fields give rise to the ...
 01:15: ... that expands at the speed of light, rewriting the nature of the quantum fields as it ...
 01:24: To understand whether and when this might happen, we first need to understand the quantum fields that it threatens.
 01:31: ... axes, or deform or more complex ways. We can think of each quantum field as a set of these modes of oscillation. And each quantum ...
 02:18: ... like the deformed ring, a quantum field wants to return to its equilibrium position. ...
 02:52: ... most quantum fields, the minimum energy is where the field value is ...
 03:11: ... there’s one quantum field that breaks these rules. That’s the Higgs field. The minimum ...
 04:00: ... dips in our graph of energy versus field strength. A quantum field with multiple minima like this will tend to find its ...
 04:42: ... in  well, pretty much everything, but certainly in the value of a quantum field. This results in fluctuations in the field strength ...
 06:08: ... field in a false vacuum. At a single point in space, a quantum tunneling event drops the field into the true vacuum. This creates ...
 07:01: ... true vacuum. This is vacuum decay. It’s a phase transition of the quantum fields. In fact it has a lot of similarities with ...


20210810: How to Communicate Across the Quantum Multiverse
 00:00: ... Hello There. I’m Matt from a different quantum timeline. I figured out the secret truth behind quantum mechanics and ...
 01:23: Everything I just described is real, but it’s also an analogy for the quantum multiverse.
 01:29: ... principle. This principle also applies to the wavefunction in quantum ...
 01:46: ... the Many Worlds interpretation of quantum mechanics, the universal wavefunction is the reality, encompassing all ...
 02:29: ... are other ways to interpret the math of quantum mechanics that don’t require a multiverse. For example there’s the ...
 02:56: ... now approaching 100 years since the discovery of quantum mechanics, and we still don’t know which of these  if any  are right. ...
 03:30: ... Schrodinger equation describes how the wavefunction of a quantum system changes over space and time  and so it should completely ...
 03:55: ... and even the ability to send messages between the worlds of the quantum multiverse  if it turns out that actually ...
 06:28: ... equation as we usually write it is a perfectly linear equation, and in quantum mechanics it’s always assumed that linearity and the superposition ...
 09:36: ... so he stumbles upon a way to communicate between the worlds of the quantum multiverse. And this time he actually tells us how to do it, inventing ...
 09:57: ... spin by whether the particles are deflected to the north or south pole. Quantum particles will always be found to have a spin in the direction that you ...
 11:53: You’ve now successfully transmitted a single bit of information between quantum timelines.
 12:00: ... idea really just serves as a proof of concept that in a nonlinear quantum mechanics, actions can influence the entire wavefunction  spanning ...
 12:47: ... to summarize: either quantum mechanics is perfectly linear and you should forget I said anything, OR ...


20210803: How An Extreme New Star Could Change All Cosmology
 06:21: ...  they’d have to occupy the same energy states. But that’s forbidden by quantum mechanics  specifically, by the Pauli exclusion principle, which tells ...
 08:05: ... known white dwarf it must also be the most massive. Doing a little quantum mechanics, it was found that it must weigh in at 1.32 times the Sun’s ...
 14:14: ... enthusiasm, we’d probably have sunk to spacethemed reaction videos and quantum mechanics based pranks. As always, thanks for everything. And today’s ...


20210721: How Magnetism Shapes The Universe
 13:47: ... we’re covering comments from our episode on the weirdness of quantum spin, and then our episode that tried to answer the question where ...
 15:15: For example Zapp Brannigan asks what percentage of quantum interactions separate into worlds versus recombining again.
 16:27: The number of distinguishable worlds depends on the rate at which distinct decoherence happens  so far, far fewer than the number of quantum wiggles.
 17:10: ... probabilities must be reflected in the number of worlds for each quantum outcome  because in the many worlds interpretation, an observer is more ...
 18:20: ... Barefoot also point out that this divide isn’t needed for quantum mechanics to work  its perhaps only helpful in making us less freaked ...
 18:42: Really, that entire series can be framed as an alternative interpretation of quantum mechanics.


20210713: Where Are The Worlds In Many Worlds?
 00:00: ... many worlds interpretation of quantum mechanics proposes that every time a quantum event gets decided, the ...
 00:20: ... one branch of the splitting quantum multiverse a radioactive nucleus decay, in another it doesn’t; in one ...
 00:44: We’ve talked before about this interpretation of quantum mechanics, and whether it’s plausibly true.
 03:13: But the superposition principle seems to always hold for the waves that drive quantum mechanics.
 03:20: ... the ability for the quantum wavefunction to coexist and overlap without being affected by that ...
 03:35: And by jump through a pond I mean learn some quantum mechanics.
 03:39: Quantum mechanics is a theory about waves.
 03:57: It represents the shifting distribution of possible results you might get if you were to try to measure a certain property of a quantum system.
 04:32: The actual mechanics of quantum mechanics is all about determining the shape and evolution of the wavefunction.
 05:22: ... most mainstream interpretation of quantum mechanics  the Copenhagen Interpretation  tells us that the ...
 12:01: On a quantum scale, worlds  or wavefunction components  recombine all the time.
 12:26: But that’s for another time  and I’ll do my best to bring it to every future branch of our splitting quantum space time.


20210707: Electrons DO NOT Spin
 00:00: ... Quantum mechanics has a lot of weird stuff  but there’s one thing that ...
 01:26: ... of an electron is far more fundamental than simple rotation  it’s a quantum property of particles, like mass or the various charges. But it doesn’t ...
 04:40: ... they act like they have angular momentum. And this is how we think about quantum spin now. It’s an intrinsic angular momentum that plays into the ...
 07:02: ... the direction of the underlying magnetic momentum is fundamentally quantum. The direction of this "spin" property is quantized  it can only take on ...
 07:30: ... than that. To understand why we need to see how spin is described in quantum mechanics. It was again Pauli who had the first big success here. ...
 10:33: ... us the law of the conservation of momentum. For related reasons in quantum mechanics position and momentum are conjugate ...
 11:26: Some physicists think that spin is more physical than this. Han Ohanian, author of one of the most used quantum textbooks.
 11:44: ... the quantum field surrounding the Dirac spinor aka the electron, ...
 12:02: ... say that particles described by spinors have spin quantum numbers that are halfintegers  ½, 3/2, 5/2, etc. The electron itself ...
 12:44: ... with each other. Bosons, for example, are able to pile up in the same quantum states, while fermions can never occupy the same ...
 13:49: ... time we talked about the connection between quantum entanglement and entropy  this was a heady topic to say the least, but ...
 15:09: ... it was at its minimum at the Big Bang, does that mean there was no quantum entanglement at the Big Bang? To answer this we’d need to know why ...
 15:31: ... beginning of time, because that moment lost in our ignorance about quantum gravity and inflation and whatever other crazy theory we haven’t ...


20210623: How Quantum Entanglement Creates Entropy
 00:27: ... black hole information paradox—a solution that may one day unite quantum physics with ...
 02:13: ... is often the case, getting more fundamental means getting quantum  and there is indeed a type of entropy that applies to ...
 05:19: ... brand of entropy. Von Neumann entropy. Its the entropy of quantum systems, and because everything else is made of quantum systems, it ...
 05:55: ... entropy is at least incredibly powerful. It’s at the heart of quantum information theory, enabling us to calculate how much ...
 06:38: ... von Neumann entropy is about, let’s think about information in quantum mechanics. Quantum systems are described by what we ...
 06:56: ... an example, imagine you have a quantum coin. It has a wavefunction that just describes which side is up  ...
 07:14: ... the way, the quantum coin is just like the both aliveanddead Schrodinger’s ...
 07:44: ... a counterintuitive thing about superposition: after you flip the quantum coin, you actually DO know its current unrevealed ...
 08:59: ... case superposition wasn’t weird enough, let’s bring in quantum entanglement. That means we need a second quantum coin. ...
 09:22: ... you flip your pair of entangled quantum coins. There are two ways this can turn out  either the ...
 10:23: ... viewed WITH its entangled partner, the coin exhibits quantum weirdness like superposition. That could be revealed in ...
 11:00: ... similarity between the entangled but isolated quantum coin is no coincidence. Its entanglement is the first step ...
 11:50: ... the entanglement is between the coin’s countless constituent quantum parts and every particle they’ve ever interacted with. That network ...
 12:35: ... about the detailed quantum states of all particles becomes increasingly ...
 13:09: ... of thermodynamics AND the emergence of the classical world from the quantum. And, as an extra trick, it also defines the arrow of time which ...
 16:39: ... with good answers  Daemonxblaze points out that quantum teleportation, aka quantum tunneling, is basically moving ...


20210616: Can Space Be Infinitely Divided?
 00:00: ... coordination and the ability to localize my palms to the quantum level. 15 halvings gets them to within a cell’s width. ...
 01:16: ... the final year of the 19th century, Max Planck ushered in the quantum age by thinking about hot pokers. He found the ...
 02:38: ... the scale at which space itself is thought to “become quantum”. I say “thought” because we’ve never been able to ...
 05:08: ... But it turns out that the Planck constant defines a new source of quantum uncertainty that you can’t ever physics away. And we hit that ...
 10:55: ... define distances. We think that space AND time  spacetime  “go quantum” at that scale  but we just don’t know in what way. ...
 11:26: ... length, at least for any intuitive conception of space. Quantum uncertainty thwarts our attempt to understand the ...


20210525: What If (Tiny) Black Holes Are Everywhere?
 00:50: ... in 1974, a young genius named Stephen Hawking showed that if you bring quantum mechanics into the equation, quite literally, then the black hole is ...
 01:07: In a way quantum mechanics saves us from the eternal black hole … except perhaps that it doesn’t.
 01:16: ... the evaporation of the black hole all the way to the very last instant  quantum mechanics may well play a second trick and save that final speck of the ...
 01:51: It came from thinking about how black holes interact with the quantum fields from which all elementary particles arise.
 01:57: Now to do this properly, you really need a theory of quantum gravity, which we don’t even have now and certainly didn’t in 1974.
 02:06: ... if an event horizon forms in a vacuum, then the vacuum states of the quantum fields have to be ...
 04:02: Researchers have come up with different hacks for combining general relativity and quantum mechanics and they reached the same conclusion.
 04:19: One big assumption is that the space near the event horizon isn’t TOO strongly curved compared to the smallest quantum scale.
 04:37: ... falls apart when the black hole has shrunk down to the tiniest quantum ...
 04:49: At that point you need a proper theory of quantum gravity to describe the process.
 05:31: So a large black hole is like our entire poker  there are many ways that the quantum fields can fluctuate around it.
 06:48: ... is the sizescale where general relativity and quantum mechanics come into hopeless conflict, and is sometimes thought of as ...
 09:28: So you completely evaporate a black hole and then all the quantum information that went into it is deleted from the universe.
 09:36: That breaks one of the most sacred rules of quantum mechanics  the conservation of quantum information.
 14:24: ... to create squeezed states of light, they’re used in all sorts of other quantum optics applications like the various quantum eraser ...


20210519: Breaking The Heisenberg Uncertainty Principle
 00:00: Quantum mechanics forbids us from measuringthe universe beyond a certain level of precision.
 00:25: ... the recent g2 experiment for measuring the muon’s interaction with quantum fields is good to to one part in a billion And also pretty recently we ...
 00:47: ... become so precise that we’re starting to run up against the absolute quantum limit  the limit defined by the Heisenberg Uncertainty ...
 01:41: ... quantum mechanics, we call these pairs of properties complementary variables, ...
 01:58: Werner Heisenberg discovered the uncertainty principle when he was inventing his version of quantum mechanics back in the 1920s.
 03:02: Heisenberg took his new idea to Niels Bohr  his mentor and one of the cofounders of quantum mechanics.
 03:18: ... when trying to reconcile the perplexing apparent contradictions in quantum ...
 03:31: ... example, how can a quantum object sometimes be a “wave” and some times be a “particle?” In a sense ...
 03:45: A quantum object can project its nature up to our classical world in one way or another, but not both.
 04:10: The Heisenberg uncertainty principle prevents us from being able to know everything about a quantum state all at once.
 04:40: That’s not as easy as it sounds  normal quantum states tend to share the uncertainty between complementary partners fairly evenly.
 04:47: ... theoretical and engineering tricks that enable us to manipulate quantum states to push the limits of the uncertainty ...
 06:32: Quantum fluctuations result in a low level of noise  a flickering signal where you should see darkness.
 06:44: ... quantum fluctuations in the phase of the laser beams are larger than the change ...
 07:15: That would enable us to line up those waves more perfectly to reduce quantum fluctuations.
 07:55: By playing quantum tricks on the light, we can squeeze the uncertainty in one direction at the cost of greater uncertainty in the other.
 08:30: This phase squeezing is achieved by using quantum entanglement.
 08:54: ... they’re recombined, they still have quantum fluctuations in the phase, but the fluctuations between the two beams ...
 09:56: The use of squeezed light is just one example of how quantum mechanics can be used to increase measurement precision.


20210511: How To Know If It's Aliens
 14:48: ... Randlepp asks whether understanding quantum gravity might be helpful for developing warp drives. Good insight. All ...
 16:32: ... when people talk about wimps they’re referring to some undiscovered quantum particle, but actually a micro black hole would have all the properties ...


20210421: The NEW Warp Drive Possibilities
 04:48: We can summarize this by saying that it requires a negative energy density, which should be impossible except perhaps on the tiniest, quantum scales.
 11:07: Both of these papers are peer reviewed and published in the reputable journal Classical and Quantum Gravity.
 13:55: Okay, onto today’s comments we’re covering two episodes  there’s the quantum Zeno effect and the recent result from Fermilab’s muon g2 experiment.
 16:15: OK, onto the quantum Zeno Effect, and the idea that you can freeze a quantum system by observing it.
 16:40: Actually, in quantum mechanics, velocity isn’t just change in position with time.
 16:54: For Flensdude the quantum Zeno effect reminds them of a poem composed by the Norse god Odin.
 17:14: So we can conclude that Odin knew quantum mechanics.
 17:17: I mean, stopping an arrow with the power of observation is a spell they teach you in undergrad quantum.
 17:47: So maybe Odin learned his quantum mechanics watching space time like the rest of us.
 17:54: ... Turner asks the real question: If the Quantum Zeno Effect plays a role in birds' ability to see magnetic fields, then ...
 18:08: ... tiny but nonzero number of worlds where the freezing of cryptochrome quantum states randomly failed in all avian ...


20210407: Why the Muon g2 Results Are So Exciting!
 01:56: ... particles with electric charge interact via the electromagnetic force, quantum ...
 03:01: Let's start by talking about quantum spin.
 03:09: Every particle with electric charge also has quantum spin.
 03:15: ... particles with quantum spin do generate a magnetic field, same as if you send an electric ...
 04:23: Quantum electrodynamics, tells us exactly what this difference is.
 05:14: For a deeper dive in Feynman diagrams, virtual particles, and quantum electrodynamics, we have you covered, episode list in the description.
 07:23: They have the same exact charge, interact with the same forces, and have the same quantum spin.
 07:29: They have a different gfactor because there are slowly different ways that the muon can interact with the quantum fields.
 07:43: The quantum vacuum is seething with an incredible variety of possible virtual particles.
 11:56: And that dance, may just have revealed to us the next step on our path to a more complete understanding of our quantum space time.


20210323: Zeno's Paradox & The Quantum Zeno Effect
 00:04: This has now been proven true by quantum mechanics.
 01:07: That’s what a mathematician might tell you  but quantum mechanics also has a thing or two to say about extremely tiny distances and time intervals.
 01:15: ... fact, if we’re talking about a quantum arrow, there may be a way to freeze its motion simply by looking at it, ...
 01:27: ... quantum Zeno effect predicts that certain quantum events  like the electrons ...
 01:43: But first, let’s see if the Quantum Zeno Effect can save us from being shot by a quantum arrow.
 01:50: ... we’ll give our arrow a few weird behaviours befitting a good quantum object: we have quantization  certain properties of our arrow can only ...
 02:04: In this case let’s say our quantum arrow’s position is quantized  it can exist only at the start and end of its path, but not in between.
 02:19: One way to do that is by executing a quantum jump, which we discussed in our recent episode.
 02:24: OK, the next quantum property we need is superposition.
 02:28: Just like Schrodinger’s cat, our quantum arrow can exist in multiple states at once.
 02:52: In the language of the Copenhagen interpretation of quantum mechanics, we say that the “wavefunction collapses” on observation.
 03:18: ... superposition thing actually gives our quantum arrow a way to travel its path smoothly and gradually, but still without ...
 03:32: Here’s the scenario: someone shoots a quantum arrow at you.
 04:10: Two ways this can play out: the arrow leaves the quantum bow with a quantum twang.
 04:15: ... it allows the arrow’s wavefunction to evolve smoothly into the state of quantum ...
 04:41: ... observing it and keep resetting it back again through the magic of the Quantum Zeno ...
 04:54: So the message is clear  if anyone ever tries to shoot you with a quantum arrow, don’t blink.
 05:01: Of course arrows don’t really behave this way, but it seems that this is exactly what real quantum systems should do.
 05:23: ... for radioactive decay, even chemical reactions The basic idea of the quantum Zeno effect was first proposed by Alan Turing, but it got a full ...
 05:47: These were some of the same people who first demonstrated quantum jumps, and using a similar scheme that we described in that episode.
 06:09: Just like our quantum arrow, sometimes an electron is in state 1, sometimes state 2, but in between it’s a smoothlyvarying superposition of both.
 07:02: ... like a measurement  and remember, measurement should be able to freeze quantum arrows and presumably also electron transitions via the Quantum Zeno ...
 07:41: Long story short: it appears you can freeze a quantum state by measuring it continuously.
 07:47: ... studies have claimed successful observation of the quantum Zeno effect, including various studies of atomic energy levels, as well ...
 08:02: ... even been proposed that the quantum Zeno effect plays a role in the photochemical reactions that give birds ...
 08:13: Quantum Zeno effect verified?
 08:29: ... argued that it’s not the abstract act of measurement that causes the quantum Zeno effect, but rather it’s a physical consequence of interacting with ...
 08:43: ... objection gets to the very foundations of quantum mechanics: what exactly do we mean by a “measurement” and what do we ...
 09:21: ... to achieve a true quantum Zenolike freezing you’d need to hit the atom with many, many photons  ...
 09:30: ... to have proved that it’s perturbation, not measurement, that causes the quantum Zeno effect by demonstrating that with the right type of “jiggling” a ...
 10:09: We would say that the wavefunction for different electron states or quantum arrow positions are in phase with each other, or “coherent”.
 10:32: In fact, as argued by Ballentine, you can force a quantum system back to its starting state without true decoherence.
 10:38: ... to get a full quantum Zeno effect  a perfect freezing of your electron or quantum arrow  you ...
 11:04: Obviously we’ve talked about decoherence and many worlds before, but let’s talk about what the quantum Zeno effect looks like in this picture.
 11:32: For example, by forcing the electron or quantum arrow out of its superposition.
 12:01: Like I said, if someone shoots you with a quantum arrow, don’t blink.
 12:05: The quantum Zeno effect appears to be very real  but its interpretation is still hotly debated.
 12:17: ... quantum zeno experiments are difficult, and perhaps future brilliant tests will ...
 12:27: So there you have why a watched quantum pot never boils. And it's because you did watch space time.
 13:04: ... the course you’ll explore everything from time in quantum mechanics to black hole entropy and learn what cuttingedge science has ...


20210316: The NEW Crisis in Cosmology
 16:28: ... principle feels like Feynman's path integral formulation of quantum mechanics. For those who don't know, the path ...


20210309: How Does Gravity Affect Light?
 11:59: Light isn’t really a simple plane wave  it’s a much weirder quantum waveparticle thing.


20210224: Does Time Cause Gravity?
 07:11: ... truly occupies only a single, perfectly defined position in space  quantum uncertainty means that everything is always at multiple places at once, ...
 07:25: But actually general relativity doesn’t need quantum mechanics to explain gravity.
 10:04: ... asks whether gravitational waves can be used to test ideas in quantum ...
 10:56: ... inflation it’s believed that quantum gravitational effects would have been very important, so if we can get ...


20210217: Gravitational Wave Background Discovered?
 00:00: ... the edge of absolute collapse into black holes supported only by weird quantum forces neutron stars tend to channel jets of high energy particles due ...


20210210: How Does Gravity Warp the Flow of Time?
 11:03: ... the photon  or whatever lightspeed quantum components make up matter  actually do have to travel further  between ...


20210126: Is Dark Matter Made of Particles?
 02:27: A more technical way to think about this stuff is in terms of quantum fields  where each particle and force is a vibration in its own field.
 02:51: But gravity is a little different to the other forces  it’s not part of the Standard Model, and we don’t even know if it has a quantum field.
 12:03: ...  interacting by dark forces, all of them oscillations in their own dark quantum fields  perhaps with their own complexity and ...


20210119: Can We Break the Universe?
 13:01: ...  the protein not the browser bitcoin wallet  may give birds quantum ...
 13:13: And also our episode on what happens during quantum jumps.
 13:20: Regarding the experiment which showed that quantum jumps could be predicted, tracked, and even reversed in an artificial atom.
 13:38: So the answer I think is that we don't yet know  but it's important to point out that the system used in the experiment IS a genuine quantum system.
 13:48: The energy levels are represented by a very small number of photons in a cavity  0 to 5  so quite quantum.
 13:56: Transitions involve quantum tunneling in a superconducting circuit  so entirely quantum.
 14:15: ... possible question: Could it be that asking which interpretation of quantum mechanics is "true" is like asking if light is made up of particles or ...
 15:10: And on to quantum magneto reception in birds.


20210112: What Happens During a Quantum Jump?
 00:00: Since the very beginning of quantum mechanics, a debate has raged about how to interpret its bizarre predictions.
 00:06: ... at the heart and origin of that debate is the quantum jump or quantum leap  the seemingly miraculous and instantaneous ...
 00:24: The notion of a quantum jump or quantum leap is one of the founding concepts of quantum mechanics.
 00:28: It’s really the OG of quantum weirdness  so much so that it’s become part of common lexicon, with very loose fidelity to the original meaning.
 00:52: But one of the principal founders of quantum mechanics thought otherwise.
 00:56: Erwin Schrodinger himself never accepted the idea of the quantum jump  but could also never prove it wrong.
 01:07: However they exist now  and the reality of the quantum jump has finally been tested.
 01:56: ... result was the Bohr model of the atom  the very first attempt at a quantum theory, and it very neatly explained the specific frequencies of light ...
 02:25: But one thing remained mysterious  what was actually happening during the quantum jump, and what determined when a quantum jump would occur?
 02:34: To address questions like this, Bohr and Heisenberg teamed up to develop the “Copenhagen interpretation” of quantum mechanics.
 02:41: Copenhagen describes transitions in quantum states as fundamentally random  the dice are rolled, and the system transitions instantaneously.
 02:55: ... with the environment causes the state transition  causes the quantum ...
 03:14: ... said “If we are still going to have to put up with these damn quantum jumps, I am sorry that I ever had anything to do with quantum theory.” ...
 03:40: ... 1952, Schrödinger published a twopart essay titled “Are there quantum jumps?” wherein he compared the theory of quantum jumps to that of ...
 03:54: ... claimed that both epicycles and quantum jumps were “ingenious constructs of the human mind” that nevertheless ...
 04:04: So why did Schrodinger hate quantum jumps so much?
 04:07: Simply put, they seemed unnatural and unphysical  a hack added to cover up a phenomenon that quantum theory could not yet properly explain.
 04:16: The debate over quantum jumps was just one part of the larger discussion about the quantum nature of reality.
 04:54: He argued that most “spooky” quantum phenomena could be explained by classical resonance phenomena.
 05:24: ... states during each transition, rather than undergoing instantaneous quantum ...
 05:54: ...  and in 1952 we had never seen a single photon produced by a single quantum jump in a single ...
 06:21: And in 1986, almost simultaneously, three different teams observed quantum jumps in such an atom.
 07:14: ... wasn’t a direct observation of individual quantum jumps  that required an extra level of cleverness, as well as an extra ...
 07:58: In this way, physicists were able to gain fairly direct evidence of a single quantum jump.
 08:30: ... has advanced to the point that we can not only see individual quantum jumps  we can monitor their progress, and even interrupt them ...
 08:48: The 3 different energy levels of this artificial atom corresponded to the number of electromagnetic quanta of energy stored in the circuits.
 08:56: ... 1 using the notation from the previous experiment) corresponded to zero quanta in either circuit, states 2 and 3 corresponded to 1 quantum in either ...
 09:28: They could actually zoom in on a quantum jump and finally figure out whether it truly was an instantaneous transition.
 09:47: And that transition appeared to be perfectly described by theory  in this case quantum trajectory theory.
 10:11: And that ability to predict also allowed them to reverse the quantum jumps midflight by adjusting the microwave field during the process.
 10:19: ... that the quantum jump onset was predictable, and that its trajectory was extremely well ...
 10:47: They explain this noninstantaneous quantum transition in terms of something called the Quantum Zeno Effect.
 11:10: ... theorists showed how quantum states can transition very predictably through a series of superposition ...
 11:31: The weaker the measurement, the less likely a true quantum jump is to occur.
 11:44: For the longest time, physicists have shied away from asking which interpretation of quantum mechanics is correct.
 12:06: ... and Schrodinger started the argument, we may be on the verge of the next quantum leap  to learning whether quantum jumps are instantaneous or ...


20201222: Navigating with Quantum Entanglement
 00:00: ... often think of quantum mechanics as only affecting only the smallest scales of reality, with ...
 00:08: ... in his 1944 book, What is Life?, the quantum physicist Erwin Schrödinger suggested that “incredibly small groups of ...
 00:29: Because it turns out we might need all the weirdness of quantum mechanics to explain birds.
 01:52: How do they do it and what does quantum mechanics have to do with all of this?
 03:03: ... that proposes birds can in a sense see the Earth’s magnetic field due to quantum weirdness happening inside their ...
 03:19: Before we get into all the cool quantum stuff, a quick review on Earth’s magnetic field is in order.
 05:33: And this is where quantum mechanics comes in.
 06:03: A quick review of quantum entanglement is in order here, although we’re talked about it before..
 06:08: When two particles are entangled, it means one or more of their quantum properties are correlated.
 06:29: The entangled properties are the quantum spins of the two valence electrons in two separate radical molecules.
 06:58: ... electrons have the same spin direction  either both up, both down, or a quantum superposition of both at the same ...
 09:40: This “avian compass” presents a tantalizing possibility of quantum biology.
 09:45: It’s strange to think of quantum effects being relevant in living organisms.
 09:49: ... to observe the strange behavior of the quantum world we need to perform incredibly careful experiments in highly ...
 10:07: Quantum entanglement is very quickly destroyed in such environments  but birds may have found a workaround.
 10:12: ... entanglement is destroyed the subsequent chemical reactions remember the quantum state, and so remember the magnetic ...
 10:24: So is this true quantum biology?
 10:33: The team’s calculations showed that only a full quantum description of the process could produce the required sensitivity to magnetic fields.
 10:54: So Erwin Schrodinger’s ideas about quantum mechanics influencing living organisms may be right.
 10:59: And quantum magnetoreception in birds isn’t the only example of what we sometimes call “quantum biology”.
 11:06: We know for sure that it happens in some cases  like the quantum tunneling that drives enzyme catalysis.
 11:12: There are other contentious, but intriguing cases  like the idea that longrange quantum coherence may drive photosynthesis.
 11:19: ... there are some highly contentious ideas  like quantum entanglement in the brain’s microtubule proteins as a key ingredient in ...
 11:27: The quantum magnetoreception of the avian compass sits somewhere in the middle  not yet proved, but more and more favoured.
 11:40: ... swallows  european especially  birds of many a feather using quantum physics to flock together to navigate the hidden lines of a geomagnetic ...
 14:02: For more detail we would indeed need a whole episode Quantum fields asks what about neutron stars.
 14:12: ... are two broad scenarios  first, if protons do NOT decay then quantum tunneling will cause the neutron star to collapse into a black hole over ...
 15:21: So yeah, Russell’s teapot either evaporates as its protons decay, or quantum tunnels into an iron teapot  is that a kettle?


20201215: The Supernova At The End of Time
 01:39: ... hyperdense crystalline ball of quantum weirdness has supported itself against gravitational collapse by the ...
 03:37: The new science of quantum mechanics had shattered our classical understanding of the world in many ways.
 03:43: ... and then those electrons are crammed so close together that all possible quantum states are ...
 03:58: Now electrons can’t overlap  can’t occupy identical quantum states  a weird quantum fact that had only been recently discovered.
 08:14: Suddenly it’ll find itself one row over  teleported due to fundamental quantum uncertainty in its position.
 08:22: This quantum tunneling lands the nucleus close enough to its neighbor that the two fuse into a heavier element.
 09:20: ... quietly become black holes themselves through countless aeons of more quantum tunneling  something like 10^10^75 ...
 15:21: This one depends entirely on your choice of interpretation of quantum mechanics.


20201208: Why Do You Remember The Past But Not The Future?
 05:16: We’re totally ignoring quantum indeterminacy, or that any information might be lost from the internal structure of the proton.
 06:45: ... through in exactly the right way to erase their tracks, seemingly random quantum jiggling ejects these embedded clumps, and so on, until we’re left with ...
 11:14: ... want to talk about how entropy is also connected to the spreading of quantum entanglement. If you have a universe of only pure quantum states they’ll ...
 13:18: Ryan Christopherson asks whether the random nature of quantum mechanics isn’t a larger hurdle to the reversibility of time than entropy.
 13:33: ... answer is that yes, IF quantum mechanics is fundamentally random, and IF the wavefunction collapse is a ...


20201118: The Arrow of Time and How to Reverse It
 00:24: ... describe a universe in rewind. That’s true from the subatomic realm of quantum mechanics to the cosmic realm of Einstein’s general relativity. But if ...
 09:39: ... we need to delve deeper. In fact it involves information theory and quantum entanglement, so we need another episode. Or more than one. Because on ...
 11:16: ... Dr Diagrams also points us to Scott Aaronson’s essay "The Ghost in the Quantum Turing Machine”, which I’m going to go and read ...
 13:36: ... back to matters quantum. Zahaquiel reminded us of the best proof regarding quantum ...
 13:53: 2. Quantum electrodynamics has a pretty cool abbreviation.
 13:58: therefore Quantum electrodynamics is better than other physics theories.


20201111: Can Free Will be Saved in a Deterministic Universe?
 02:03: Yes, we will mention the quantum, but importantly, that is not to say that free will or consciousness are necessarily related to it.
 02:15: But understanding the implications of quantum mechanics is key to unraveling determinism and its connection to predictability.
 02:22: Quantum mechanics seems to tell us that one of the following is true.
 02:26: ... the outcomes of quantumscale events are fundamentally random or the outcomes of quantum events are ...
 02:46: One of the most important rules of quantum mechanics is the principle of conservation of quantum information.
 02:51: It just says that quantum information can never be destroyed or created out of nothing.
 03:00: Let's paint a cartoon representation of quantum information in a block universe.
 03:15: Each bit of quantum information can be represented as a thread.
 03:19: Threads are evolving quantum states.
 03:21: These may transform and become entangled with each other, but if quantum information is conserved, a thread can never vanish nor start out of nothing.
 04:23: ... form of a decision, either one, incorporates an entirely new thread of quantum information, in violation with the conservation principle, or two, that ...
 05:37: Now, creating brand new information explicitly violates conservation of quantum information.
 05:42: That said, the most mainstream interpretation of quantum mechanics has the same problem.
 05:47: The Copenhagen interpretation insists that the apparent randomness of quantum events is really random.
 05:52: The quantum information in the state of the wave function before collapse is destroyed, but information is also created.
 05:59: The outcome of quantum interactions are chosen in fundamentally unpredictable ways.
 06:21: Think about a new thread of quantum information starting from nothing, let's say emerging from a packet of space time where no information enters.
 07:19: On the surface, the idea of randomly generating new streams of quantum information within a brain doesn't seem to help the cause of free will.
 09:40: ... even the allknowing Laplace demon may be out of luck, especially if quantum randomness or quantum indeterminacy is magnified to brainlevel ...
 09:50: Again, not saying consciousness is quantum.
 10:17: All possible futures exist and develop according to the laws of quantum mechanics.
 11:12: So this nexus of quantum information processing may truly be an unpredictable black box decisionmaking machine, at least some of the time.


20201104: Electroweak Theory and the Origin of the Fundamental Forces
 01:36: While the brand new field of quantum mechanics could describe the behaviour of electrons, nuclear processes remained mysterious.
 01:46: Enrico Fermi made the first attempt at a full quantum description of beta decay with his ‘four fermion’ interaction.
 02:36: ... effort was quantum electrodynamics, in which charged particles interact not by actually ...
 02:56: QED is what we call a gauge theory  its forcecarrying fields and particles arise from the symmetries of the quantum equations of motion.
 04:50: ... try an example: In quantum mechanics, the wavefunction determines the probabilities of certain ...
 05:01: Quantum mechanical equations of motion like the Schrodinger equation describe how the wavefunction evolves through space and time.
 05:50: That resulted in a new quantum field and a corresponding particle.
 06:49: The ‘U’ stands for unitary and tells us that elements of this group preserve vector length, or in our case quantum probability.
 14:10: ... it’s bad because it causes unreconciled conflicts with other physics  quantum theory in this ...


20201027: How The Penrose Singularity Theorem Predicts The End of Space Time
 11:10: ... points. The resolution must be the union of general relativity and quantum mechanics  a theory of quantum gravity, from which both ...
 12:51: ... and the block universe, but this time weaving in what quantum mechanics had to say about the whole mess. Quantum mechanics ...
 13:38: ...  AKA branches of the wavefunction. That’s exactly what a quantum interference experiment is seeing  multiple possible “realities” ...


20201020: Is The Future Predetermined By Quantum Mechanics?
 02:38: We need to see what quantum mechanics says about determinism and how it plays with relativity and the block universe.
 02:46: According to quantum mechanics, physical systems, parts of the universe evolve as wave functions.
 03:24: The big question is what causes the transition from this world of quantum indeterminacy to the solid singular reality of the macroscopic world.
 03:50: ... is the socalled Copenhagen interpretation, which states that a quantum system is literally in a state of undefinedness until ...
 04:23: ... function evolves in a precise way, perfectly defined by the equations of quantum mechanics but at the moment of measurement, a single reality is randomly ...
 04:45: Another popular interpretation of quantum mechanics is the ManyWorlds Interpretation, which simply states that the wave function never collapses.
 04:53: Instead all possible states of the quantum system continue to exist.
 04:57: ... than choosing one reality out of many, when we observe a quantum system, we sort of just become part of one of the realities and lose ...
 08:15: Sometimes the quantum multiverse of ManyWorlds is depicted as this branching tree, in which the realities multiply as time progresses.
 08:24: In the block universe picture, it's tempting to depict this as the entire block multiplying with every quantum event.
 08:32: A division in the block universe can only propagate as quickly as the result of that quantum event can become known.
 08:46: Really what's happening here is that parts of the universe become entangled with each other, correlated at a quantum level.
 08:55: Each such web defines a set of properties of the universe correlated with some prior quantum decision.
 09:07: Here we are bringing in the concept of decoherence and quantum Darwinism, which we've covered before.
 09:23: According to the decoherence explanation, the quantum multiverse isn't a cleanly divided set of alternate realities.
 09:59: However, light speed signaling is the surest way to transfer quantum correlations so this is still a useful picture.
 11:06: Copenhagen and ManyWorlds aren't the only interpretations of quantum mechanics in town.
 11:51: So does the future already exist according to quantum theory?
 11:55: The answer depends on your favorite flavor of quantum interpretation.
 12:00: ... ride the dice of Copenhagen into an unknown future or surf the splitting quantum multiverse into all futures of which you will become just ...


20201013: Do the Past and Future Exist?
 01:44: Now quantum mechanics might argue otherwise, depending on which quantum mechanics you prefer, but we’ll come back to in an upcoming episode.
 12:00: To rescue materialism without demanding a perfectly defined personal future we need quantum mechanics.
 12:07: ... Quantum mechanics tells us that all this stuff outside our past lightcone  and ...
 12:17: Depending on how you interpret quantum mechanics, that could be evidence in favor of this solipsistic denial of external reality.
 12:24: ... quantum can also save materialism and determinism if you like but to do so you ...
 12:35: ... these ideas before  the Copenhagen and Many Worlds interpretations of quantum mechanics  but soon we’ll dive back in, to see what these idea imply ...


20201005: Venus May Have Life!
 14:02: ...  possible solutions to the impending cryptographycracking powers of quantum computers that don’t themselves require quantum ...
 15:19: Which I guess you don’t need a quantum computer for.
 15:35: Really, there were doubts that any saladbased protocols would be meaty enough to resist quantum decryption.


20200928: Solving Quantum Cryptography
 00:10: ... math problem is prime number factoring, and the new era of quantum computers may lay bare your indiscretions, as well as collapse the ...
 00:31: ... said that quantum computers will threaten the security of our digital civilization because ...
 01:08: ... Peter Shor developed an algorithm  Shor’s algorithm  that could use a quantum computer to factor a prime number in, well, a human lifetime, or a human ...
 01:23: ... Quantum computers did not exist in 1994, but just last year, Google’s quantum ...
 01:33: ... to the researchers, Sycamore performed calculations to simulate another quantum system exponentially faster than would have been possible with a pure ...
 01:51: ... quite  quantum computers need to become far more reliable  have better “fault ...
 02:07: One option is to match quantum decryption with new quantum encryption techniques to replace prime factoring.
 02:15: We talked about all this in our episode on quantum key distribution  and we’ve also talked about the challenges.
 02:21: To distribute a quantum key, you also need a quantum internet to transport quantum states.
 02:29: ... Quantum states are insanely fragile and difficult to transport, and the quantum ...
 02:41: Fortunately there is another option  and one that’ll be a lot cheaper than building a quantum internet.
 02:48: It turns out there are some ingenious nonquantum ways to thwart the hacking powers of quantum computers.
 02:55: Enter postquantum cryptography, or quantum resistant algorithms  which might replace our vulnerable prime factoringbased cryptography.
 03:04: ... understand why some algorithms are vulnerable to quantum computing attacks while others are thought to be quantum resistant, we ...
 04:21: It works great except for its vulnerability to Shor’s algorithm and quantum computers.
 04:36: To understand that, we need a brief word on how quantum computers do their magic.
 05:24: It turns out there’s a structure to factorization that can be exploited by quantum computers.
 06:27: This is where quantum weirdness comes in.
 06:35: ... Quantum computers store information in qubits, which, until they give an output, ...
 06:59: ... across different computers, you’re processing in different parts of the quantum wavefunction  or in different parallel realities if you’re into the ...
 07:23: ... you tried to use a quantum computer to guess the factors of a prime number, you’d read out one of ...
 07:38: ... of qubits holds these repeating moduli of Shor’s algorithm  one per quantum state in the ...
 08:20: So far, quantum computers are stuck under 100 qubits and none have managed to factor a number higher than 21 with Shor’s algorithm.
 08:31: Does that mean I’m a quantum computer?
 08:37: ... current technology isn’t there yet, when we figure out how to build quantum computers with thousands of qubits even the very high digit RSA keys ...
 09:15: In 2022, NIST is expected to narrow it down to one or two quantum resistant algorithms.
 09:20: ... signatures—and they’ll hopefully be able to protect our data from quantum computing ...
 11:53: To be secure against quantum attacks for the foreseeable future, McEliece would need an 8 Mb public key—8,000 times larger.
 12:45: So far there’s no known classical or quantum algorithm that solves it quickly for large lattices.
 12:58: ... is the question is whether these algorithms are really robust against quantum and classical ...
 13:34: ... true that these quantum resistant algorithms seem like they will be hard, if not impossible for ...
 13:58: ... at the end of the day, quantum key distribution proponents would rather put their faith in fundamental ...
 14:11: ... the meantime, postquantum crypto may be our only hope as black hat quantum hackers attempt to decrypt your embarrassing emails across the parallel ...


20200921: Could Life Evolve Inside Stars?
 03:00: Quantum fields should also be able to develop topological defects.
 03:16: But here, the quantum fields themselves changed state due to the rapidly dropping temperature.
 10:14: So are the stars filled with thriving ecosystems of critters built from fractured quantum fields?


20200908: The Truth About Beauty in Physics
 07:19: ... Dirac, one of the principal founders of quantum mechanics, said “It is more important to have beauty in one's equation ...
 07:49: He sought to develop a quantum mechanical wave equation that agreed with Einstein’s special relativity.
 08:11: The resulting Dirac equation is the entirely correct relativistic quantum description of the behavior of the electron.
 11:30: His idea of introducing a new symmetry to space was translated to adding a new symmetry to the wavefunction in quantum mechanics.


20200901: How Do We Know What Stars Are Made Of?
 00:39: A hundred years ago, we were starting to plumb the deepest mysteries of the universe with Einstein’s relativity and with quantum theory.
 06:04: The brand new field of quantum mechanics was emerging in Europe, and a young astrophysicist named Cecilia Payne had just arrived at Harvard.
 06:13: ... was widely read and so she knew about some groundbreaking work in early quantum theory that she could use to decode the complex patterns of absorption ...
 07:00: ... her research, Indian astrophysicist Meghdad Saha had used early ideas in quantum theory to crack the ionization ...


20200824: Can Future Colliders Break the Standard Model?
 03:29: Finally we’d reached collision energies needed to test predictions of the still relatively new quantum electrodynamics.
 03:36: This was huge in solidifying our understanding of the quantum world.
 05:25: ... masses of the known particles and what we expect their masses to be from quantum field theory ...
 06:02: ... cancel out the interactions of the known particles with the elementary quantum fields on which those particles live, eliminating most of their mass in ...


20200817: How Stars Destroy Each Other
 11:50: ... think a theory of quantum gravity probably prevents the singularity from really forming  but ...


20200810: Theory of Everything Controversies: Livestream
 00:00: ... for the past century after the great revolutions of relativity and quantum mechanics so together with professor brian keating astrophysicist and ...


20200728: What is a Theory of Everything: Livestream
 00:00: ... a hugely broad range of interests including string theory and loop quantum gravity in principle we could do this entire conversation just with ...


20200720: The Boundary Between Black Holes & Neutron Stars
 06:17: That ball of neutrons is a fundamentally quantum mechanical object.
 11:08: Each will be rich in information on the nature of stars, and gravity, and strange quantum states of matter.


20200708: Does Antimatter Explain Why There's Something Rather Than Nothing?
 04:05: ... universe of matter, and would undo a lot of what we think we know about quantum mechanics. So, good news bad news I ...
 05:19: ... besides the charge and spin thing — it must have the same mass, the same quantum energy levels, and the same interactions with its ...
 09:19: ... and even the strength of the coupling between the particles and the quantum fluctuations of the vacuum. Any difference in these properties in ...


20200622: Building Black Holes in a Lab
 05:25: ... involves the black hole scattering the vibrational modes of the quantum fields that have wavelengths similar to the black hole’s event ...
 06:12: This perturbs the quantum fields in a way that look likes escaping particles if you’re very far away from the black hole.
 06:20: ... case of an analog watery black hole you just replace “vibration in the quantum field” with “ripple on surface of water” and viola, same deal. ...
 09:19: ... useful as classical analogs are, Hawking radiation is ultimately a quantum mechanical effect. Deeper insights may require an analog quantum black ...
 10:37: Besides rubidium gas, there are other quantum systems which physicists are using as analogs.
 10:44: ... are even quantum optical analogs, in which light sees an apparent horizon—usually caused ...
 11:04: ... Hawking radiation need not necessarily depend on a specific theory of quantum gravity. Proponents of this line of thought have triumphantly pointed to ...


20200615: What Happens After the Universe Ends?
 07:16: ... electrons and positrons, and neutrinos, as well as gravitons  the quantum particles of ...
 07:53: ... particles  they come from the interactions of those particles with quantum fields  the Higgs field in the case of the ...
 12:54: This is another issue with the CCC model  most physicists think quantum information can’t be destroyed.


20200608: Can Viruses Travel Between Planets?
 16:13: Well I’d accuse you of propogating quantum woowoo, except that this theory is actually supported right at the top.


20200527: Does Gravity Require Extra Dimensions?
 11:58: This is the negative pressure due to the exclusion of quantum vacuum modes, or virtual particles, between two very closely separated plates.
 13:49: ... through black holes has nothing to do with the multiverse predicted by quantum ...
 14:04: ... quantum multiverse is what you get when you accept Hugh Everett's many worlds ...
 14:24: ... say the second multiverse is less likely to be real than the quantum multiverse  it's almost certainly a mathematical figment, arising from ...


20200518: Mapping the Multiverse
 14:50: Will that next step be as surprising as relativity and the quantum revolution?
 15:40: ... higher precision using other methods  lasers, vacuum chambers, strange quantum mechanical states of light  you name ...


20200511: How Luminiferous Aether Led to Relativity
 12:25: ... aether” could explain the near vacuum state of spacetime in which quantum physicists believe particle pairs are quickly born and destroyed. In ...
 13:18: ... But that death helped spark the revolutions of relativity and then quantum theory that revealed a much weirder, but still totally luminiferous ...


20200504: How We Know The Universe is Ancient
 16:59: ... She loves crawling into boxes whenever possible, I assume to test quantum theory. Miraculously emerging definitely alive every time. She's become ...


20200428: Space Time Livestream: Ask Matt Anything
 00:00: ... in the late 1900s late 1800s actually in the era of relativity and quantum physics and this is kind of you know Astro 101 except for the fact ...


20200422: Will Wormholes Allow Fast Interstellar Travel?
 09:44: ... plates that are brought very close together will block components of the quantum vacuum from existing in that region. The gap between the plates will ...
 11:03: ...  paths back to your own past  except in useless circumstances like on quantum scales or if they’re hidden by an event horizon. Combined with Roger ...
 12:17: ... your needs. And there is one place natural wormholes might exist: in the quantum vacuum. This was another idea of John ...
 13:26: ... Maldecina have speculated that the EinsteinRosen bridge may explain quantum entanglement  itself first described by Einstein and Rosen, along with ...


20200331: What’s On The Other Side Of A Black Hole?
 11:37: ... comments for the last two episodes which are on rotating black holes and quantum darwinism. Let’s see what you had to ...
 12:02: ... is the principle of monogamy of entanglement, which states that a given quantum state can only be maximally entangled with one other quantum state. The ...
 13:01: ... this idea: the macroscopic "world" is a filter function which selects quantum states immune to entanglement diffusion. So that's almost it, but ...
 14:15: ... points out that the way quantum states become increasingly entangled with their environment seems ...
 14:25: ... connected. I've been meaning to get around to a whole episode on quantum entropy  aka von neumann entropy, and how it relates to entopy. We'll ...


20200316: How Do Quantum States Manifest In The Classical World?
 00:04: ... from the information flowing through an impossibly complex network of quantum entanglement, that just happens to mutually agree that you and I exist ...
 00:20: ... the quantum world things are routinely in multiple states at once  what we call a ...
 00:44: ... Quantum mechanics tells us that the atom’s wavefunction can be in a ...
 00:57: ... seems absurd  but quantum mechanics appears to allow this. In fact the idea of superposition is ...
 01:48: ... states. But that doesn’t tell us why certain states that exist in the quantum world can survive this decoherence and become manifest in the classical ...
 02:39: ... to lay out are mostly due to Wojciech Zurek, who calls this framework quantum darwinism  and you’ll see why. To get there we need to start by talking ...
 02:56: ... quantum particles have a property called quantum spin. That spin has an axis ...
 03:37: ... the value for quantum spin depends on how you choose to measure it  it depends on your ...
 04:28: ... came up with to demonstrate an apparent absurdity predicted by pure quantum mechanics. This is the socalled EinsteinPodolskyRosen, or EPR ...
 10:14: ... a chain of quantum systems between that original atom and the pointer. Information spreads ...
 10:41: ... as more and more particles join our entanglement web, information about quantum states get spread amongst ...
 10:53: ... environment  it’s no longer bounded, and so the information about most quantum states can’t be ...
 11:11: ... there are certain very special quantum states whose information does NOT get hopelessly mixed through this ...
 11:30: ... our dial’s pointer  are strongly correlated with these states of our quantum ...
 11:48: ... what determines whether a quantum state can be a pointer state? Well to some extent the way you set up the ...
 12:04: ... for environmentally induced superselection. And he coined the term quantum darwinism too, because we have these more “fit” states surviving and ...
 12:33: ... important example of a pointer state is the position of a particle. Most quantum interactions depend heavily on the relative location of interacting ...
 13:22: ... this fully solves the measurement problem it only tells us why certain quantum states are observable on macroscopic scales while Schroedinger Cat ...
 13:47: ...  object positions, feline mortality statuses, even the results of quantum measurements  do NOT exist in the underlying quantum objects. Quantum ...
 15:28: ... about a thought experiment to test the many worlds interpretation of quantum mechanics  quantum immortality, aka quantum suicide, in which a ...
 16:29: ... had an excellent insight. If every possible combination of quantum events exists and if the increase of entropy is probabilistic, then is ...
 18:58: ... declines our offer of quantum immortality, saying "I'll stick with classical immortality, thank you". ...


20200303: Does Quantum Immortality Save Schrödinger's Cat?
 00:11: If the quantum multiverse is real there may be a version of you that lives forever.
 00:22: In the last couple of episodes we’ve been delving into a key mystery of quantum mechanics  why don’t we have quantum magical powers?
 00:30: Or, more scientifically, what causes the divide between the weird behavior of quantum world and our largescale, macroscopic world?
 00:39: ... particular, what causes quantum systems to transition from simultaneously existing in many states at the ...
 00:53: We’ve been exploring decoherence as a mechanism for this quantumclassical transition  and we’re not done yet.
 01:18: ... in one of them, we need to embrace one of the interpretations of quantum ...
 02:17: We’ll call this test quantum immortality.
 02:33: ... of the radioactive decay over a certain period of time  that means the quantum wavefunction of the atom splits equally  the atom is simultaneously ...
 04:33: ... which tells us that there’s ultimately only a single result from each quantum event, so a single result from the “Schrodinger’s physicist” ...
 05:21: ... is right because the chance survival under any other interpretation of quantum mechanics is basically ...
 05:31: Many Worlds, on the other hand, guarantees their survival in at least one branch of the quantum wavefunction.
 05:59: This thought experiment is sometimes called quantum immortality.
 06:04: ... that any process leading to mortality is ultimately a sequence of quantum events  so there are timelines in which those incremental steps towards ...
 06:25: Hugh Everett, who first came up with the many Worlds interpretation, actually believed in this sort of quantum immortality.
 06:43: Max Tegmark makes a good point regarding quantum immortality  which is that death is an incremental process, not a single quantum event.
 07:19: ... Many Worlds might be wrong  I say live as though this is your one quantum timeline While we’re discussing dubious methods for predicting survival ...
 10:45: ... tried to make sure all correct answers got a prize in at least one quantum timeline  so if you didn’t see your name here, please congratulate the ...
 10:59: I have a feeling it’s going to be a hell of a ride, even if we’re not a quantumimmortal in branch.
 11:51: ... to address both our episodes on the role of conscious observation in quantum mechanics and on quantum decoherence as a better path to understanding ...
 12:55: ... won't see multiple outcomes at the same time  you don't see macroscopic quantum ...
 13:12: We're going to explore this in much more detail next week, when we look at the role of quantum entanglement in decoherence.
 13:20: eddybox on the spacetime discord asked about the quantum eraser, as did several people in the comments.
 13:33: ... answer is essentially yes  in a typical quantum eraser experiment you use entangled photon or other particle pairs  one ...
 13:59: ... in the quantum eraser, we haven't reached true decoherence  relative phase information ...
 14:10: ... exact mechanism varies by quantum eraser experiment, but this is true even in the infamous delayed choice ...
 15:44: ... channel is pleased that we share his annoyance at horrible missuse of quantum mechanics to promote pseudoscientific ...
 15:55: As Nick says, "Quantum mechanics is not magic!".
 16:11: ... taking advantage of that fact  whether to sell snake oil, or books on quantum healing, or $80 crystal infused water ...
 16:41: ... that a more interesting question than does consciousness influcence quantum mechanics is the other way around: "Does quantum mechanics influence ...
 16:54: Despite my fascination with the subject, I've dosed off in MANY quantum mechanics lectures.
 17:00: Quantum UNconsciousness achieved.


20200224: How Decoherence Splits The Quantum Multiverse
 00:00: On the quantum scale, we can see these multiple histories play out and even talk to each other.
 00:11: Many physicists believe that the answer lies in a process known as quantum decoherence.
 00:29: Sure  but it’s also the elusive dividing line between the quantum and classical worlds.
 00:35: ... the measurement problem  the question of why and where the blurry quantum wavefunction collapses into welldefined measurement ...
 00:48: We focused on a simple question: does conscious observation of a quantum system cause the wavefunction to collapse?
 01:25: ... why is it that we can see these multiple histories play out on the quantum scale, and why do lose sight of them on our macroscopic ...
 01:36: Many physicists believe that the answer lies in quantum decoherence.
 01:41: ... Quantum decoherence is a deep and developing subject, and today we’re going to ...
 01:52: ... quantum systems are described by this wavefunction thing  it’s the mathematical ...
 02:20: Over time the histories of a quantum system separate to represent every possible future the laws of physics allow.
 02:44: This fact is also reflected in Richard Feynman’s path integral formulation of quantum mechanics.
 03:33: The best way to illustrate quantum coherence is with the good ol’ doubleslit experiment.
 03:38: ... you remember it from last week  a quantum particle seems to pass through two slits simultaneously as a probability ...
 04:04: This time we'll use particles of light  photons as our quantum particle.
 06:53: And this is one of the weird, multiple history aspects of quantum mechanics that we can directly observe.
 07:03: These also have a known phase relation, so they have quantum coherence relative to each other.
 07:09: ... potentially bring those branches back together again to produce the same quantum state  for example by cutting slits in the second screen and producing ...
 09:54: We can think about the photon wavefunction becoming mixed with the wavefunctions of the quantum particles along this chain.
 12:59: ... order to do quantum experiments we need to isolate a slice of the global wavefunction and ...
 13:34: That includes yourself and your measuring device, unless you know the exact quantum state of all of the particles of both.
 13:55: There’s a lot more to discuss  including the connection to quantum entanglement and to entropy.
 14:19: ... argue that it does  in the context of the Many Worlds interpretation of quantum mechanics, in which there is no wavefunction collapses at ...


20200218: Does Consciousness Influence Quantum Mechanics?
 00:00: If I focus really hard do my power of quantum mechanics allow me to manifest reality?
 00:08: No, but then why did some of the founders of the theory seem to think that consciousness and quantum mechanics were inextricably linked.
 00:22: The behavior of the quantum world is beyond weird.
 00:36: The rules governing the tiny quantum world of atoms and photons seem alien.
 00:41: ... set of rules that give us incredible power in predicting the behavior of quantum system  rules encapsulated in the mathematics of quantum ...
 00:52: ... its stunning success, we are now nearly a century past the foundation of quantum mechanics and physicists are still debating how to interpret its ...
 01:04: ... not surprising that the profound weirdness of the quantum world has inspired some outlandish explanations  nor that these ...
 01:18: One particularly pervasive notion is the idea that consciousness can directly influence quantum systems  and so influence reality.
 01:25: Today we’re going to see where this idea comes from, and whether quantum theory really supports it.
 01:32: ... we're going to need to go back to one of the earliest interpretations of quantum mechanics  the Copenhagen interpretation, often associated with Neils ...
 03:45: So when does the quantum transition to the classical actually happen?
 04:59: The first electron to become excited in the detector is also a quantum object.
 05:34: But all of these things are made of atoms  the “von Neumann chain” from detector to mind is a chain of quantum objects.
 05:42: With no clear boundary between the quantum and the classical, where does the collapse of the wavefunction happen?
 06:01: Another of the greats of early quantum theory agreed with him.
 06:44: ... step in our von Neumann chain  before it the information about this quantum experiment reaches your conscious awareness, it has to pass through your ...
 07:04: From your perspective, your friend’s entire brain exists in a quantum superposition of all possible results of the experiment.
 08:49: With the greats of quantum physics inclined to speak in mystical terms, it’s not surprising that the idea stuck around.
 08:56: ... Wu Li Masters drew parallels between eastern mystical traditions and quantum physics  which on its surface seems like a nice idea  poetic ...
 09:40: ... as Richard Feynman said, "If you think you understand quantum mechanics, you don't understand quantum mechanics." The more you know ...
 09:56: And yet the most confident claims about quantum mechanics seem to be the mystical ones.
 10:21: The weird behavior of the quantum world demanded the courageous and openminded speculation that characterizes a great scientist.
 12:00: ... universal wavefunction  but that’s not going to give you any powers of quantum ...
 12:09: ... the Measurement Problem  at least not with full consensus, modern quantum theory has come a very, very long way since its ...
 12:44: We need to learn about quantum decoherence and the quantum multiverse.
 12:49: ... is that your own future wavefunction includes a deeper dive into the quantumclassical divide, on an upcoming episode of Space ...
 15:01: ... and Francisco Martinez asked whether we would get new quantum fields and new particles if other fundamental constants turned out to ...
 15:25: Would it be a quantum field with particles?
 15:49: ... constant are just scaling factors and so varying them shouldn't lead to quantum particles  but perhaps other constants could give us a ...


20200211: Are Axions Dark Matter?
 02:35: ... best theoretical description of the strong force is quantum chromodynamics  QCD. That’s a deep and rich subject that will get its ...
 03:42: ... before we can see how that happens, we need to understand why quantum chromodynamics predicts a CP violation in the first place. Compared to ...
 03:59: ... You might ask how can a vacuum, aka “nothing” have structure? Well, in quantum field theories, the vacuum isn’t really nothing. “Vacuum” is the word we ...
 04:33: ... between these different states. But because they're all the same energy, quantum weirdness allows the QCD vacuum to sort of simultaneously occupy all of ...
 06:32: ... and so this solution is not generally accepted  turning theta into a quantum field is the most promising ...
 06:54: ... you might recall that in quantum field theory a particle is just an oscillation in a quantum field. So ...


20200203: Are there Infinite Versions of You?
 03:38: The properties of each region are effectively random  set in the beginning of the universe by quantum processes.
 06:08: It means that every particle, or chunk of quantum field, or whatever elementary pixel of reality  has matching properties between the two regions.
 08:40: For example, you could argue that fundamental quantum randomness will cause even identical starting configurations to produce different results.
 09:00: In fact, quantum randomness could allow different starting conditions to evolve into a universe that looks like this one.
 12:19: ... first up we got the threebody problem and then we'll do our episode on quantum hacking with the smatrix ...
 14:48: But in smatrix theory and quantum field theory, time and space in the interaction region are fuzzy.
 16:21: ... depiction of the proton being made of lego bricks as a viable theory  quantum lego dynamics, as Steve Plegge puts ...


20200127: Hacking the Nature of Reality
 00:54: ... mathematical insights, with the final result being the birth of modern quantum theory and first complete formulation of quantum mechanics  matrix ...
 01:08: ... representations of quantum mechanics soon followed  for example, the wave mechanics driven by the ...
 01:53: ... its importance in the foundation of quantum mechanics, and being championed by Bohr and Heisenberg, most physicists ...
 02:16: ... search for the underlying clockwork of reality led to quantum field theory, in which all particles are described by vibrations in ...
 02:41: Early quantum theory was plagued by problems  for example, how do you compute infinite interactions?
 02:55: ... tame the infinities and yielded the incredibly accurate predictions of quantum electrodynamics, which describes the interactions of the electromagnetic ...
 03:14: At the beginning of the 1960s the atom was understood as fuzzy, quantum electron orbits surrounding a nucleus of protons and neutrons.
 04:55: The idea was invented by John Archibald Wheeler in the late 30s as a convenient way to express the possible results of a quantum interaction.
 05:03: In fact, it's still a very important tool in quantum mechanics today.
 06:47: Remember, that quantum field theory fastidiously adds together a complete set of virtual interactions that contribute to the real interaction.
 07:12: ... include things like conservation of energy and momentum, the behavior of quantum properties like spin, and the assumption of a family of particles that ...
 08:28: In regular quantum field theory you’d need to add up all the different versions of both these two channels separately.
 09:11: ... Smatrix approach to solving problems in quantum mechanics based on these global consistency conditions and taking ...
 09:35: It presented severe challenges on par with those plaguing quantum field theory  and, as it happened, physicists solved the QFT challenges first.
 09:45: ... actually approach infinite strength as was once feared, and so a full quantum field theoretic description of the strong nuclear force was possible ...
 10:01: The result is quantum chromodynamics  our modern description of subnuclear physics.
 10:10: ... the results was that Smatrix theory was sidelined, and quantum field theory reigns supreme to this day as our reductionist description ...
 10:41: Quantum field theories like QCD surely gives us insights into the nature of the fundamental workings of the universe.
 10:47: ... theory  but it turns out that it has led to deep insights that even quantum field theories could not ...
 11:35: ...  at first as a description of strong nuclear force interactions before quantum chromodynamics took over  but then as a theory of quantum ...
 12:13: ... in the universe today  galaxies and galaxy clusters  as collapsed from quantum fluctuations in the extremely early ...
 12:56: ... the amplituhedron doesn’t just eliminate the fiddly mechanics of quantum field theory, it removes the very concepts of space and ...
 13:17: ... ourselves up by our bootstraps towards a better understanding of the quantum weirdness of space ...


20200113: How To Capture Black Holes
 12:17: ... ridiculously large universe that multiplies the density of a highenergy quantum field powering inflation. Check out our episodes on cosmic inflation to ...


20191217: Do Black Holes Create New Universes?
 03:48: The details of how this happens is presumably buried in the asyetunknown theory of quantum gravity.
 07:16: ... proposed that if a universe lasts forever then in the distant future, quantum fluctuations of that near vacuum will cause black holes to spontaneously ...
 07:38: ... by the biggest universes  more space means more chances for these quantum ...
 07:56: ... be extrapolated to the insanely long timescales required for these quantum fluctuations to ...


20191209: The Doomsday Argument
 01:57: ... 120 orders of magnitude higher according to the crudest predictions of quantum field ...
 13:11: ... the future of humanity, the nature of space and time, the weirdness of quantum mechanics  you name ...


20191202: Is The Universe Finite?
 12:12: If you want to dive deeply into understanding the building blocks of space time then you need to study quantum theory.
 12:18: Brillaint.org has a fun course called quantum objects that include interactive challenges and problems to solve.
 12:25: Honestly, the best way to wrap your head around quantum theory is to play with it.
 12:30: ... this course you can explore the experiments of quantum mechanics and use them to construct equations of motion, laws of ...


20191111: Does Life Need a Multiverse to Exist?
 09:04: ... quantum fields, which fill all of space and whose oscillations produce the ...
 09:16: ... with themselves even when there are no particles around, resulting in a quantum buzz of energy everywhere in the universe that would accelerate its ...
 10:02: One possibility is that the zeropoint energies of unknown quantum fields cancel out the known contributions.


20191104: Why We Might Be Alone in the Universe
 12:21: We skipped comment responses last episode, so today we're covering two episodes  loop quantum gravity and time travel.
 12:30: A few of you wondered if there's a connection between the loops of loop quantum gravity and the closed strings of string theory.
 12:52: Which brings us to the most common question  what actually ARE the loops of loop quantum gravity?
 13:17: But that doesn't mean the loops are physical, they're just a way to parameterize the quantumscale geometry of space.
 13:37: ... Receiver asked about the experiment to test Loop Quantum Gravity So LQG predicts that light of different wavelengths travels at ...
 14:00: ... the very shortest wavelengths of light to be slightly perturbed by these quantum cells of space  sort of like traveling through cracked glass  they ...
 14:15: Wavelengths longer than this quantum scale can ignore this fragmentation and so travel at normal speed.
 15:16: Surely as time travelers you could have reminded me in the loop quantum gravity comments the week before.


20191021: Is Time Travel Impossible?
 10:54: ... alternative lies in Hugh Everett’s manyworlds interpretation of quantum mechanics, in which every possible universe exists, splitting off in an ...
 11:17: ... be one fundamental law of physics that prohibits it  for example, the quantum vacuum may be unstable in the infinitely iterating loops of a closed ...
 11:36: ... actual fact we can’t know until we have a full theory of quantum gravity – until then we’re working with the approximate theories general ...


20191015: Loop Quantum Gravity Explained
 00:00: It’s time we talked about loop quantum gravity.
 00:28: To connect quantum physics with Einstein’s general theory of relativity.
 00:32: ... search for a theory of quantum gravity is a century old, and we’ve talked about it quite a bit already, ...
 00:47: ... the physics of the tiny and the gigantic  another way to a theory of quantum gravity that avoids a lot of conceptual baggage like tiny wiggling ...
 01:03: That other way would be loop quantum gravity, and today we’re going to find out exactly what it is.
 01:09: Back in the day we talked about why combining quantum mechanics with general relativity was so hard.
 01:16: ... example, there’s the fact that general relativity  or perhaps quantum mechanics breaks down when we think about the extreme densities of the ...
 01:34: ... thing because this is what really inspired the invention of loop quantum ...
 01:46: ... Quantum mechanics, and indeed most theories in physics, involve a set of ...
 02:06: In quantum mechanics that stage is flat and static and isn’t influenced by the actors.
 02:11: It requires some giant hacks to even attempt regular quantum calculations in a nonflat geometry.
 02:18: In short: quantum mechanics is NOT background independent.
 03:10: ... quantum gravity tries to quantize general relativity with no strings attached, ...
 03:24: The challenge really gets us to the fundamentals of what a quantum theory actually is.
 03:30: So just quickly, let’s review all of quantum mechanics.
 03:50: But in quantum mechanics, things aren’t so straightforward.
 04:06: In the first formulations of quantum mechanics, that wavefunction describes the distribution of possible positions and momenta of, say, a particle.
 04:30: ... all, the position and momentum of quantum mechanics literally describes location on a spatial coordinate system ...
 04:43: There are other ways to formulate quantum mechanics, like quantum field theory, but these ultimately have the same issue But it gets worse actually.
 04:51: In quantum mechanics, time is treated completely separately to other variables  there is no “time wavefunction” or “time operator”.
 05:13: A quantum theory of gravity needs to fix both of these issues  but we’re going to focus on background independence for now.
 05:19: ... equations of quantum mechanics let you calculate changing properties of a particle  like ...
 05:35: So maybe instead of thinking about the quantum fuzziness of position and momentum we can think about the quantum fuzziness of the metric itself.
 05:45: ... instead of an equation that describes the quantum evolution of the properties of an object in spacetime, maybe there’s an ...
 06:43: So the WheelerdeWitt equation quantizes these  turns them into quantum operators.
 06:48: The result is a quantum equation for the fabric of space.
 06:52: A contender for a theory of quantum gravity.
 07:16: ... what loop quantum gravity does  it takes us down the abstraction rabbit hole  past our ...
 08:20: ... something called a spinor  a vectorlike thing that also represents a quantum of angular momentum  or ...
 08:47: In this formalism, the “space of metrics” looks just like a space of fields in quantum field theory.
 08:59: And now we get to the loops of loop quantum gravity.
 10:01: The result, of course, is loop quantum gravity.
 10:10: Not with chunks of spacetime but with quantum circuits of gravitational field.
 11:01: ... big success of loop quantum gravity is that it manages to combine general relativity and quantum ...
 12:41: ... quantum gravity seems to predict that the speed of light should depend very ...
 13:10: If there was any difference it was barely measurable, and that doesn't look great for loop quantum gravity.
 13:16: Loop quantum gravity is an intriguing alternative to the more popular string theory.
 13:58: David, we already spent all of your money ... on aspirin, after loop quantum gravity broke our brains.


20190916: Could We Terraform Mars?
 16:31: This is the simplest type of quantum field, consisting of only a single scalar value at all points in space.


20190819: What Happened Before the Big Bang?
 02:17: This is actually the simplest type of quantum field because it's described by a single number, a scalar everywhere in space.
 02:50: I mentioned last time that quantum fields can hold energy without actually having particles.
 05:07: But it wouldn't end as a random process, it wouldn't require quantum tunneling to get started.
 06:49: I mentioned that quantum fields fluctuate due to the intrinsic randomness of the quantum world.
 07:53: But seeding all of the structure in our universe is probably the least impressive thing those quantum fluctuations did.
 08:06: ... differences in when the inflation ends from one point to the next But quantum fluctuations come in all sizes and a rare strong fluctuation would force ...
 09:34: Assuming a quantum field of the right type and that speck will start inflating.


20190806: What Caused the Big Bang?
 02:14: In the case of inflation part of the appeal is that it fits extremely nicely into our modern understanding of gravity and quantum mechanics.
 04:42: We need some quantum physics. In fact, we need some quantum field theory.
 04:55: There's some more homework for you. For now, a review: the universe is filled with quantum fields.
 05:09: The field strength determines how much force a quantum field exerts on other fields and particles.
 05:22: ... this field strength  a little packet of energy held by the field. If a quantum field has energy in the form of particles and if space is expanding  as ...
 05:45: ... quantum field can contain an intrinsic energy even without particles. In that ...
 06:14: ... we graph a quantum field potential energy versus field strength, it might look something ...
 06:55: If such a quantum field found itself near that local minimum then it would roll to the bottom and get stuck there.
 08:29: ... super cooling would go on forever if the inflaton field stays stuck. But quantum fields have a tendency to randomly fluctuate to different values, thanks ...
 08:51: ... going to quantum tunnel and on that other side, it sees a deeper truer minimum  perhaps ...
 10:26: ... are unstable and they very quickly disperse their energy into the other quantum fields. The inflatons decay into the familiar particles of the standard ...


20190718: Did Time Start at the Big Bang?
 08:52: ... Bang singularity, and just after, GR comes into terrible conflict with quantum mechanics We've talked about that conflict and its possible resolutions ...
 11:12: ... ways to get a new universe out of an old one for example an extreme quantum fluctuation could initiate a new Big Bang given infinite time or The ...
 11:36: ... nothing moments physicists have a thing or two to say about that from quantum fluctuations from nothing  Stephen Hawking's timeless interpretation of ...


20190715: The Quantum Internet
 00:00: When we finally have a quantum internet you’ll be able to simultaneously like and dislike this video.
 00:43: ... classical cryptography, but one day soon this may not be enough and so quantum cryptographic methods and algorithms are being ...
 01:00: To understand what needs to be done we need to get to the foundations of quantum mechanics  we need to talk about quantum information theory.
 01:37: ... and certain fundamentals of physics  such as entropy, and also quantum ...
 01:49: Quantum information theory parallels classical information theory, but instead of using classical bits, it deals bits of quantum information  qubits.
 01:58: ... enjoy all of the weirdness of quantum mechanics  they can be in a superposition of many states at once, ...
 02:21: Those restrictions, on top of all the weirdness, define the challenge of transmitting and storing quantum information.
 02:27: But first, a reminder why we want to muck around with quantum info in the first place.
 02:33: ... there’s the whole quantum computer thing  in those, the ability for a qubit to hold many ...
 02:43: Partly motivated by the cryptographiccracking power of the quantum computer, we also want to think about a quantum internet.
 02:53: ... our episode on quantum key distribution we talked about two schemes for sharing cryptographic ...
 03:03: ... these only work if you can actually send entangled quantum states between parties  that means transmitting qubits over long ...
 03:19: We can already send photons of light very long distances using lasers or fiber optics  and those photons are pretty quantum.
 03:27: The problem is that to transmit quantum information we have to pay attention to individual photons  quanta of light.
 03:52: It’s much harder to transmit single photons in a way that perfectly maintains their quantum state.
 04:09: It simply states that: “you cannot take a quantum state and copy it perfectly and end up with two copies of the same state existing at the same time”.
 04:18: ... is connected to the law of conservation of quantum information, which we’ve talked about before  it comes from the fact ...
 04:34: That prohibits a quantum state vanishing, but also splitting in two  or being copied.
 04:40: ... such a way that you will never end up with two exact copies of the same quantum ...
 04:53: ... you could copy it, you wouldn’t really be able to transmit an entangled quantum state because the act of reading in the state to copy it would destroy ...
 05:32: But quantum information DOES allow us to massively extend the range over which we can send an intact qubit.
 05:41: Think of it this way: Two people, let’s say Bill and Ted, are connected by a classical channel and a quantum channel.
 05:49: ... optic cable, a telephone wire, the Pony Express, whatever, while the quantum channel needs to carry intact quantum states  so it's probably fibre ...
 06:00: A pair of entangled particles are created, and Bill and Ted receive one each via the quantum channel.
 07:18: ... this point the original quantum state of photon C, which contains the message, has been almost ...
 07:36: The remaining information of the quantum state is actually obtained by observing the outcome of the process that generated the entanglement itself.
 08:16: Combined with a quantum key distribution protocol, this can give a mechanism for secure communication.
 08:22: It can also be used to transmit quantum information over longer distances than we could normally send entangled particles.
 08:29: Just position repeaters along the quantum channel between Bill and Ted.
 08:33: ... copy of the original qubit C. In principle this can be done without the quantum channel ever becoming ...
 09:01: Quantum states have to somehow be stored – by Bill, by Ted, and by the repeaters in between.
 09:07: ... typically means transferring a quantum state between a photon and a matter particle – say, an electron whose up ...
 09:18: But storing delicate quantum states for any length of time is hard work – especially if you don’t want insanely expensive supercooled devices.
 09:27: ... a number of ingenious solutions, ranging from storing entangled photon quantum states in a cloud of caesium atoms, a kind of quantum atomic disk drive, ...
 10:00: This could also be done between many individuals in a centralized node – a sort of quantum switchboard.
 10:14: These are great because they’re much, much faster than repeaters that have to transfer quantum states between photons and matter particles.
 10:22: So the current state of the art is that entangled quantum states have been transmitted with photons using fibre optics and lasers.
 10:34: ... serve as repeaters to extend the range and connect a network of these quantum ...
 10:57: ... streams of 1’s and 0’s round the world, but if we could build truly quantum networks we’ll also be able to build the next generation of ...
 11:18: The quantum information age is around the corner.
 11:21: ... guessing we’ll go with “quantum age”  as the quantum internet enables us to take advantage of the ...


20190617: How Black Holes Kill Galaxies
 11:24: ... problems so whether you wanna learn about special relativity, quantum physics or brush up on your complex algebra and differential equations ...


20190606: The Alchemy of Neutron Star Collisions
 13:02: ... Grumpy's wavefunction  can't Has Cheezburger just by talking about it quantum mechanics forbids that anyway I'm sure grumpy is now in meme heaven ...


20190516: The Cosmic Dark Ages
 13:07: ... time we talked about some quantum encryption  ways to secure messages using the weirdness of quantum ...
 13:23: ... Ellen and EebstertheGreat note that both prime numbers in your quantum key need to be large numbers, not just one of them, as we stated. ...
 13:43: ... others also point out that internet security isn't doomed in the wake of quantum computers without us also having quantum cryptography. There are a ...
 14:26: ... as others mentioned, that condition is a big one  maintaining a quantum state over long distance is very difficult, requiring relays to ...
 14:38: ... revert to classical information while being boosted. We'll talk about quantum relays in an upcoming ...
 14:48: ... that episode we'll probably conclude that a real quantum internet is a long way off. That said, the entire point of talking about ...
 15:04: ... Areani, regarding the quantum internet quips: "You might or might not have mail!" Nice. In ...


20190509: Why Quantum Computing Requires Quantum Cryptography
 00:03: Quantum computing is cool, but you know what would be extra awesome  a quantum internet.
 00:12: And the first step to the quantum internet is quantum cryptography.
 00:22: Quantum theory may seem like an obscure subject of questionable relevance to the average person.
 00:27: But in fact much of our technological world depends on our understanding of the quantum properties of the subatomic universe.
 00:35: ... soon, perhaps very soon, we’ll be interacting with the weirdness of quantum mechanics even more directly – with the coming of quantum computing and ...
 00:48: Specifically quantum cryptography and quantum key distribution – the foundations of the prospective quantum internet.
 00:56: We may come back to quantum computers in detail – but for now just a word on why their advent will demand a quantum internet.
 01:04: The logic gates of a quantum computer exist in a state of quantum superposition of many simultaneous configurations.
 01:21: For example, a quantum computer can calculate the prime factors of large numbers extremely quickly.
 03:01: Once quantum computers can factorize public keys quickly the entire public key system falls apart.
 03:45: A metaphorical quantummechanical bridge, which allows the sharing of a secure private key.
 03:52: Enter quantum key distribution.
 04:21: Each highlights a different fundamental weirdness of quantum mechanics – the Heisenberg uncertainty principle and quantum entanglement.
 04:29: These will be the keys to unbreakable cryptography of a quantum internet.
 04:52: Another example is the polarization of a photon, a quantum of electromagnetic wave.
 06:26: In fact here’s an quantum experiment you can do at home.
 06:37: You just switched between different quantum representations of reality and then back again, and so invoked the uncertainty principle.
 07:16: This is the basis of one of the first quantum key distribution algorithms developed in 1984 Bennett and Brassard and known as BB84.
 08:44: If he doesn’t, they know something was up  and this is where the quantum part becomes useful.
 10:34: So that’s BB84, and it's one path to a secure quantum internet.
 10:40: Another way to generate secure keys using quantum mechanics was developed by Artur Ekert in 1991.
 10:46: It uses a similar choiceofquantumbasis mechanism but with the added frill of quantum entanglement.
 10:58: Here we definitely have to direct you to our full episode on quantum entanglement for the details.
 11:04: ... the superbrief summary: create a pair of particles with a quantum property that is correlated between the two – for example, electrons ...
 13:13: Which to be fair will still be the case in a quantum internet.
 13:16: But come quantum computers even the smartest classical security protocols will be compromised.
 13:23: Then we’ll also need a quantum internet … which we know how to do in theory, but it’s a different matter to actually build one.
 13:34: Quantum states – and particularly entangled states – are notoriously fragile and so it’s hard to transmit them across large distances.
 13:42: We’ll show you how to construct a vast, planetspanning network of encrypted quantum states real soon.


20190410: The Holographic Universe Explained
 01:02: We’ve moved from quantum field theory to black hole thermodynamics to string theory.
 01:27: A black hole’s entropy represents the amount of quantum information of everything that ever fell into it.
 02:11: ... information paradox, because this radiation was expected to erase the quantum information of everything that fell into the black ...
 02:23: But destroying quantum information would break the foundations of quantum mechanics.
 08:23: ... weird thing is that when you write the quantum wave equation for the gluon strand with length expressed as a separate ...
 08:49: ... it was quickly rejigged to make it a theory of quantum gravity, and the scale invariance of the strings becoming a central ...
 10:37: ... itself that field theory wasn’t stringy– rather it was a quantum field theory like the ones that gives us our standard model of particle ...
 11:24: The conformal field theory in the original space included no gravity, but in the higherdimensional space it became a full quantum theory of gravity.
 13:23: The rules of interactions between cells on the surface is a quantum field theory.
 15:28: ... a type of string theory, while the surface exhibits no gravity  only a quantum field theory similar to the field theory behind the standard ...
 17:50: Personally, I'd always thought of him as a Jedi master  especially with all that dubious quantum consciousness stuff.


20190403: The Edge of an Infinite Universe
 07:16: Only lightspeed paths – or in the language of quantum field theory “massless fields” can access these diagonal boundaries.
 07:25: ... then we can do something that seems impossible – we can track a quantum field to infinite distance and calculate its behavior ...
 08:01: That’s handy because flat space is the only space where quantum mechanics is fully solvable.
 08:15: ... connected a quantum field between two points at infinite distance – past and future  where ...
 08:26: Then he placed a black hole in between these points and calculated how it perturbed the balance of a quantum field traced between them.
 14:04: ... realized that if you define a conformal quantum field theory in a 3+1dimensional Minkowski space, that corresponded to ...
 14:31: Quantum mechanics in the form of a conformal field theory in one space is a theory of quantum gravity in a space with one higher dimension.
 14:49: Every particle, every gravitational effect in the bulk is represented by quantum fields on an infinitely distant surface.


20190313: Will You Travel to Space?
 13:51: Electrons escape their orbits by quantum tunneling, and protons themselves may eventually decay.


20190306: The Impossibility of Perpetual Motion Machines
 06:50: In fact, quantum mechanics forbids it.
 06:55: Due to the intrinsic quantum randomness of all particles, as expressed by the Heisenberg uncertainty principle, everything moves.
 08:41: One popular source of free energy is the zeropoint energy of the quantum vacuum, and it’s the most fun to debunk.
 08:48: ... going to have to refer you to our entire playlist on the quantum vacuum for the physics, but the important point is that any energy of ...


20190207: Sound Waves from the Beginning of Time
 03:51: ... bit less there, These fluctuations probably were the remnants of random quantum fluctuations From when the universe was subatomic in ...
 13:26: ... the probability of collapsing into a big crunch due to everything quantum tunneling towards a single ...
 13:50: Almost certainly, there could be no quantum tunneling big crunch, but there is some smaller size that can eventually collapse that way.
 13:58: ... you need to wait 10^(10^25) years for the first quantum tunneling to turn iron stars into black holes, and way, way longer than ...
 14:33: Remember that things like general relativity and much of quantum field theory are verified to stunning precision.


20190130: Perpetual Motion From Negative Mass?
 03:48: ... note, and at the risk of getting way too technical, this is also what quantum field theory predicts: fields with even spin have to work in the ...
 12:23: I’m pretty sure that breaks quantum field theory as well as general relativity.


20190124: The Crisis in Cosmology
 15:47: ...as demonstrated by the different forward/backward reaction rates in certain quantum interactions.
 16:41: ...and is used in, for example, Feynman's path integral formulation of quantum mechanics.


20190116: Our Antimatter, Mirrored, TimeReversed Universe
 00:03: ... foundations of quantum theory rest on its symmetries for example it should be impossible to ...
 02:02: ... of charge parity and time and this symmetry lies at the foundations of quantum field theory physics must work the same if we flip all of these ...
 03:02: ... decay of neutral Kaons these things are extra weird and usual k on is a quantum mix of its own particle and antiparticle there are two ways to do this ...
 08:43: ... don't we absolutely require time reversal symmetry in order to conserve quantum information which itself is required for all of quantum mechanics to ...
 10:26: ... with Richard Feynman  it's essential to his path integral approach to quantum mechanics and to Feynman diagrams maybe that's why he was so into ...
 10:54: ... then there's the whole entropy business although it's connection to quantum mechanics is still not well understood like I said this simple ...
 16:49: ... of string theory is connected to the extreme energy scale of quantum gravity and that problem is not unique to string theory. Now we do talk ...
 17:15: ... of physicists. We blasted through several reality layers from atoms to quantum fields in the past hundred years or so but maybe the next layer will ...


20181220: Why String Theory is Wrong
 01:06: ... old idea did work when translated to the very particular case of a quantum string, which is part of what got string theory going in the first ...
 01:35: ... seemed so beautiful, the effortlessness of its inclusion of quantum gravity, its promise to unify all particles under one umbrella, and ...
 03:37: Klein realized that you can get a sensible quantum theory if you compactify that extra dimension.
 07:50: Our tiny quantum strings can roam that small dimension.
 14:34: ... entire field of gauge theory upon which much of our understanding of the quantum world ...
 14:48: It also gave us the sought after quantum electromagnetism in the end, just with a slightly different symmetry.
 15:37: ... whether you want to learn about special relativity in quantum physics or brush up on your complex algebra and differential equations ...


20181212: Quantum Physics in a Mirror Universe
 00:02: ... in spacetime and even the rather abstract phase of the wave function in quantum mechanics so it might be surprising to learn that with all the weird ...


20181121: 'Oumuamua Is Not Aliens
 13:37: Whether you want to learn about astronomy, quantum physics, or even artificial neural networks, you can learn more at brilliant.org/spacetime.


20181107: Why String Theory is Right
 00:06: ... theory as the one great hope for a theory of everything that will unify quantum mechanics and gravity and so unify all of physics into one great, ...
 02:50: ... fact, it will be difficult to remove it, and the quantum gravity of string theory is immune to the main difficulty in uniting ...
 03:07: ... did talk about this and other problems with developing a quantum theory of gravity in a recent episode, but before we get to the nuts and ...
 03:40: In quantum theories of gravity, the gravitational force is communicated by the graviton particle.
 05:06: ... illustrate why quantum gravity isn't hopelessly broken in string theory, and that's a huge ...
 05:22: ... see, it turns out that tiny vibrating quantum strings automatically reproduce the theory of general relativity and, in ...
 05:54: ... flying through the air or a vibrating rubber band and turning it into a quantum ...
 06:05: ... follow a standard recipe to turn them into wave equations with various quantum weirdness added in like the uncertainty relation between certain ...
 07:46: A really important type of symmetry in quantum mechanics is gauge symmetry.
 08:11: So, we expect the phase of the quantum wave function to be a gauge symmetry of any quantum theory.
 08:54: So in a way, electromagnetism was discovered in its quantum form by studying the symmetries of quantum mechanics.
 10:25: That's on the 2D dimensional world sheet of a quantum string.
 10:41: ... we can smooth out that surface mathematically and write a nice, simple quantum wave equation from the equations of motion, but only for 1D strings ...
 11:28: So, with our quantized equations of motion in hand, you can predict the quantum oscillations of our string.
 11:35: These are particles, and the first mode looks like the graviton, a quantum particle in the aforementioned gravitational field.
 14:14: ... week we talked about one of the most misunderstood concepts in quantum mechanics, the idea of virtual particles and their tenuous connection to ...
 14:37: These fundamental forces are mediated by fluctuations in the quantum fields of the relevant forces.
 16:03: David Ratliff asks if a quantum tree falls in a vacuum and nobody is around to measure it, does it still have energy?
 16:39: Quantum mechanics can't tell us whether anyone cares.


20181031: Are Virtual Particles A New Layer of Reality?
 01:15: That math hack turned out to represent the very real quantum nature of the photon.
 01:22: This insight led to the discovery of all quantum physics.
 01:30: ... started out as a trick to make impossible calculations in quantum field theory possible possible, at least, for the sort of people who ...
 01:47: Now, we're going to go pretty deep in this one, but it will bring us closer to a better understanding of the quantum nature of reality.
 02:01: So quantum field theory is the machinery behind the standard model of particle physics.
 03:16: In that sense, virtual particles are the building blocks of our approximation of the behavior of quantum fields.
 03:25: ... field, transferring between them energy momentum and one photon worth of quantum properties in a single packet that we call a virtual ...
 04:58: ... diagrams are an absolutely essential tool in most modern quantum field theory calculations, but they also add to the misconception about ...
 05:18: ... share some properties with their real counterparts in particular, quantum numbers like charge and spin, but they don't need to obey Einstein's ...
 05:45: Virtual particles are our mathematical representation of the quantum mechanical behavior of fields, and that behavior is weird.
 06:00: One electron throws a virtual photon at the other one causing them to be deflected from each other like a game of quantum dodgeball.
 07:09: ... one of these infinite possible virtual particles represents a quantum of energy in a single possible vibrational mode of the underlying ...
 08:03: ... a bit like the photon starts out moving in the wrong direction and then quantum tunnels between the particles, kicking them towards each other like a ...
 08:40: Did I mention that quantum mechanics is weird?
 08:52: ... might have heard the quantum vacuum described as his roiling ocean of virtual particleantiparticle ...
 09:06: So the quantum fields are composed of these vibrational modes of all different frequencies/momenta that can be excited to become particles.
 09:20: ... mode should have 0 energy in a vacuum, but in quantum mechanics, nothing can be so exact thanks, again, to the Heisenberg ...
 10:27: ... a quantum state in a superposition of "yep particles" and "nope, no particles." ...
 11:28: In his actual mathematical derivation, he instead talks about vibrational modes of the quantum vacuum being cut off by the event horizon.
 11:44: A similar perturbation of the quantum vacuum is also seen in the Casimir and Unruh effects.
 12:00: So to recap, virtual particles are best thought of as a mathematical device to represent the behavior of quantum fields.
 12:08: ... tool in perturbation theory as we tried to approximate the behavior of quantum ...
 12:18: ... in the case of Max Planck discovery of the quantum nature of photons, it turned out that a mathematical artifact ...
 12:31: ... there was no way to express his Planck law without an artifact of that quantum nature namely, the Planck ...
 12:45: If they represent a physical reality, then there should be no way to do quantum field theory calculations without them.
 12:53: It turns out there is a version of quantum field theory that doesn't use virtual particles at all.
 13:17: There is no good reason to believe that virtual particles exist outside the math we use to approximate the behavior of quantum fields.
 13:25: At best, they can be interpreted as a small component of possibility space for a quantum field doing something real.
 13:32: That said, for something that doesn't exist, they're surprisingly useful for describing the weird underlying machinery in our quantum spacetime.


20181018: What are the Strings in String Theory?
 02:32: A lot of work went into figuring out a quantum theory for the strong interaction based on the physics of strings.
 02:39: The theory had some success but kind of got stuck and was ultimately replaced by quantum chromodynamics.
 02:58: What's a vibrational mode in a quantum field?
 03:08: But the only hypothetical massless spin2 particle is the graviton, the conjectured quantum particle of the gravitational field.
 03:16: ... the gravitational field is made of quantum particles, which it might be we really don't know, but if it is then ...
 03:45: What if the math of this theory could be used in a theory of quantum gravity?
 05:29: To understand quantum strings, first we need to look at regular strings.
 06:38: But this sort of behavior, where only specific, discrete energy modes are allowed, sounds very quantumlike.
 06:48: Niels Bohr came up with the first quantum model for electron orbits by thinking of them as ringlike standing waves around the hydrogen atom.
 06:57: But quantum strings are much more ambitious than boring electron orbits.
 09:10: ... you remember from our episode on quantum gravity, if you try to describe gravitational interactions on the ...
 11:16: Very tiny objects like quantum strings could explore that extra dimension, and importantly, oscillate in it.


20181010: Computing a Universe Simulation
 00:44: ... or nonexistence like if the tiniest chunks of space time or chunks of quantum field or elements in the abstract space of quantum mechanical states can ...
 02:01: That includes most formulations of quantum mechanics and proposals for theories of everything.
 06:36: Every quantum state must be processed into the following state.
 06:40: There's a fundamental limit to the speed with which quantum states can change.
 06:46: ... MargolusLevitin theorem tells us the maximum rate at which the quantum states of a system can shift into completely independent quantum states ...
 07:04: The more energy in the system, the quicker it's quantum states can evolve.
 07:16: For example, a simple quantum system would be a group of electrons with spins pointing up or down, corresponding to a single bit the information each.
 07:35: This sort of quantum spin array is exactly the system used in most quantum computers.
 07:41: ... MargolusLevitin theorem also gives us the speed limit of operations in quantum computing, in fact, for any computing, but only quantum computing can ...
 11:41: ... of physics, in particular very standard ideas on general relativity and quantum mechanics, to figure out the computational properties of our ...
 11:53: This will be important as quantum computers develop.


20181003: How to Detect Extra Dimensions
 06:07: ... structures of potentially any number of dimensions on which the quantum field and their corresponding particles can ...
 12:23: ... in physics, exploring the conflicts between general relativity and quantum theory towards the development of a theory of quantum ...
 12:47: Theories of quantum gravity go in both directions.
 13:14: An example is loop quantum gravity.
 13:22: If spacetime is indefinitely divisible, then you get hopeless conflicts with quantum theory.
 14:14: For the simplest attempts at quantum gravity, you need infinite measurements.
 14:43: ... quickfire answers John Gibbs yes, if general relativity and quantum mechanics are both right, then we should have Plancklength virtual ...
 14:57: ... the difference between deleting quantum information and just removing it from the universe, e.g., by dropping it ...


20180920: Quantum Gravity and the Hardest Problem in Physics
 00:00: [MUSIC PLAYING] MATT O'DOWD: Between them, general relativity and quantum mechanics seem to describe all of observable reality.
 00:40: Then the quantum revolution of the '20s and '30s overturned all of our intuitions about the subatomic world.
 00:47: Together, general relativity and quantum mechanics have allowed us to explain nearly every fundamental phenomenon observed.
 01:12: ... discussion of the great quest for this union, the quest for a theory of quantum gravity and for a theory of ...
 01:29: What exactly are the conflicts between general relativity, or GR, and quantum mechanics?
 02:17: Where general relativity describes the universe of the large and the massive, quantum mechanics talks about the subatomic world.
 03:06: Nowadays, modern quantum field theories fully incorporate the melding of space and time predicted by special relativity.
 03:44: That's a big conflict with quantum theory right there, which tells us that quantum information should never be destroyed.
 04:14: Hawking, actually, derived the latter by finding a way to unite general relativity and in quantum field theory.
 04:30: In fact, it's very possible to shoehorn the curved geometry of general relativity into the way quantum field theory deals with space and time.
 04:50: For that, you need a true quantum theory of gravity.
 07:41: ... that tells us that something is missing in our description of either quantum theory or general relativity, or both, at the smaller ...
 07:54: Standard quantum theories treat the fabric of spacetime as the underlying arena on which all the weird quantum stuff happens.
 08:01: Given that sensible underlying structure, it's relatively routine to apply quantum principles, or quantize, most of the forces of nature.
 08:10: For example, classical electromagnetism becomes quantum electrodynamics when you quantize the electron field and the electromagnetic field.
 08:19: But in the resulting math, the new quantum fields still lie on top of a smooth, continuous grid of space and time.
 09:08: In quantum gravity, gravity itself becomes an excitation in our quantized spacetime.
 09:26: This type of selfinteraction or selfenergy is seen in other quantum field theories and is hard to deal with, even there.
 09:33: ... example, in quantum electrodynamics, the electron has a selfinteraction due to its electric ...
 10:05: So perturbation theory is applied throughout quantum field theories of the standard model.
 10:31: ... example, measurement of the mass and charge of an electron renormalizes quantum electrodynamics to allow incredibly precise calculation of the ...
 10:46: When you have strong gravitational effects on the quantum scale, the selfenergy corrections blow up to infinity.
 10:53: But unlike other quantum field theories, there are no simple measurements you can do to renormalize those corrections.
 11:27: Generations of physicists, starting with Einstein himself, spent their lives trying to fix this to unite quantum mechanics and general relativity.
 11:54: ... leading example of this is loop quantum gravity, or you just assume that GR and, indeed, the mutable fabric of ...
 12:11: ... crack the greatest problem in modern physics, the quest for a theory of quantum ...
 15:27: No real quantum states means no information except, perhaps, whatever information you need to track the bulk properties, like vacuum energy.


20180912: How Much Information is in the Universe?
 00:25: ... stars and galaxies, not to mention space itself, with its fluctuating quantum fields, dark energy, blah blah, stuff ...
 03:10: ... we can describe the universe completely if we go through all of its quantum voxels, and answer the yes/no question of whether it's full or ...
 04:21: ... will be better to use the number of grid points in a quantum phase space, which includes position, but also other degrees of freedom, ...
 04:30: In other words, we should count all possible quantum states in the universe.
 04:44: OK, so 10 to the power of 180 or so bits is the minimum if you want to describe every 3D quantum voxel completely independently.
 15:41: ... that a metaphor for quantum fluctuations in impossibly distant futures spontaneously generating a ...


20180905: The Black Hole Entropy Enigma
 01:09: They cause all sorts of problems with quantum theory, which we've talked about before and we'll review in a sec.
 02:25: But a fundamental tenet of quantum mechanics is that quantum information can never be destroyed.
 02:30: ... we also covered, this evaporation should destroy a black hole's internal quantum information, giving us the black hole information ...
 05:24: If quantum information is stored on the surface of the black hole, can't we store entropy there also?
 08:30: It's as though each of these minimumpossible quanta of area each contain a single bit of information.


20180823: How Will the Universe End?
 04:11: This is matter that is fully collapsed in a quantum mechanical sense.
 04:15: It's so densely packed that all possible quantum states are completely filled and no further collapse is possible, short of becoming a black hole.
 09:41: The fate of these depends on quantum mechanisms.
 09:48: By a process called quantum tunneling, everything eventually reaches the lowest possible energy state.
 09:54: ... the remaining matter in the universe, quantum tunneling allows the elements lighter than iron to fuse together, while ...
 10:26: The same process of quantum tunneling eventually transport a star's material toward its center.
 10:46: Quantum tunneling may actually bring on the Black Hole Era much earlier.
 10:53: ... small, stable black holes are possible, then quantum tunneling should allow small regions within larger bodies to collapse ...
 12:29: Or quantum fluctuations may spawn new universes from the void.
 13:55: ... electron should have been equal to 1 in the classical case and 2 in the quantum ...
 15:25: ... the answer is, essentially, that as far as quantum mechanics is concerned, size is a property of composite particles, ...
 15:43: All they have is their quantum wave function, which tells the probability of the particle's location, momentum, spin, direction, et cetera.
 15:50: Now, we can think of a quantum wave function as having a size because it can be spread out over space.
 16:03: If we know with 100% certainty the position of an electron, then the size of its quantum wave function becomes zero.


20180815: Quantum Theory's Most Incredible Prediction
 00:07: Let's talk about the best evidence we have to the theories of quantum physics truly represent the underlying workings of reality.
 00:17: [MUSIC PLAYING] Quantum field theory is notoriously complicated, built from mindbendingly abstract mathematics.
 00:43: We know this because the predictions of quantum field theory stand up to experimental test time and time again.
 00:50: Quantum field theory describes a universe filled with different quantum fields in which particles are excitations, quantized vibrations.
 00:59: We've talked about QFT many times before, starting with the very first quantum field theory, quantum electrodynamics.
 03:32: As we'll see, their nature is predicted by quantum theory, measure electromagnetic moments, and you verify your quantum picture of reality.
 04:02: Nonetheless, electrons do have a sort of intrinsic, angular momentum, a fundamental quantum spin that is as intrinsic as mass and charge.
 04:12: Despite not being the same as classical rotation, this quantum spin does grant electrons a dipole magnetic field.
 05:23: This difference between the quantum versus classical magnetic moments for the electron is called the G factor.
 05:42: This equation is the origin of quantum electrodynamics and the first to correctly capture the notion of quantum spin.
 05:49: It describes electrons as weird, four component objects with quantum spin magnitudes of half.
 06:19: It doesn't consider the quantum nature of the field.
 06:23: Only the fully developed quantum electrodynamics, the first true quantum field theory, does this.
 06:29: And QED tells us that the quantum electromagnetic field is a messy, messy place.
 06:35: It seethes with a faint quantum buzz, infinite phantom oscillations that add infinite complication to any electromagnetic interaction.
 07:13: But in fact, we can calculate its effect extremely precisely and test this through experiments, showing the underlying truth of quantum theory.
 07:22: So one way to think about this quantum buzz is with virtual photons.
 07:27: Quantum field theory describes the interactions between particles as the sum total of all possible interactions that can lead to the same result.
 07:36: In the case of electromagnetism, those interactions are mediated by virtual photons, which are just a mathematical way to describe quantum buzz.
 08:02: So yeah, quantum field theory is a type of madness.
 08:08: In particular, we've been at Feynman diagrams, which are our best tool for dealing with the absurd complexity of quantum fields.
 08:17: They represent the possible interactions of the quantum field by way of virtual photons.
 08:54: ... now the electron undergoes an additional interaction with the buzzing quantum ...
 10:54: Electron spin axes are always slightly misaligned with an external magnetic field, due to quantum uncertainty in the spin direction.
 12:16: The theory of quantum electrodynamics has been pushed to the experimental limit and come out unscathed.
 12:23: That means that it and the quantum mechanical principles on which it is founded are good representations of reality.


20180725: Reversing Entropy with Maxwell's Demon
 11:04: That's quantum entropy, also known as Von Neumann entropy.
 11:09: It describes the hidden information in quantum systems, but more accurately, it's a measure of the entanglement within quantum systems.
 11:17: ... fact, the evolution of quantum entanglement may be the ultimate source of entropy, the second law, the ...
 13:20: ... him think of the game of Life and wonder whether the universe is a giant quantum cellular automata, which led him to a Wikipedia page on digital physics, ...


20180718: The Misunderstood Nature of Entropy
 10:22: ... the laws of motion, whether Newtonian or quantum mechanical, don't care about the direction of time, and yet, the second ...
 10:45: ... the most profound insights into the working of both the largescale and quantum ...


20180711: Quantum Invariance & The Origin of The Standard Model
 00:03: ... theory ever developed, describing with stunning accuracy the fundamental quantum building blocks of our ...
 02:24: The standard model is ultimately based on quantum field theory, but we're going to use the Schrodinger equation.
 02:31: That's the most basic equation of motion of quantum mechanics.
 03:40: The function is an oscillation in quantum possibility, moving through space and time.
 04:56: The equations of quantum mechanics have what we call global phase invariance.
 08:05: By discovering how it fits into the Schrodinger equation, we've unlocked its quantum behavior.
 08:53: At this point, we only need a couple of extra steps to produce the full description of electromagnetism in the quantum world.
 09:00: Quantum electrodynamics, or QED.
 09:13: ... we need to apply quantum principles to our field, like considering its internal or self energy ...
 10:29: ... the greatest mystery here is not the nature of the quantum field nor the connection between symmetry and the fundamental forces, ...


20180704: Will A New Neutrino Change The Standard Model?
 02:10: ... of particle physics, electric charge and antimatter, the bizarreness of quantum chirality and the Higgs mechanism, and finally, why all of this points ...


20180620: The Black Hole Information Paradox
 00:12: But that same radiation threatens the very foundations of quantum mechanics.
 00:59: The apparent destruction of quantum information by Hawking radiation defies our current understanding of quantum mechanics.
 01:33: First, we looked at the law of conservation of quantum information.
 01:37: We saw that the very foundations of quantum mechanics demand that quantum information be preserved forever.
 02:57: The gravitational field of a black hole is expected to distort the surrounding quantum fields.
 03:59: ... his radiation, Stephen Hawking found a way to erase quantum information, which is in severe violation of one of the foundational ...
 04:18: After all, without a theory of quantum gravity, Hawking had to hack both general relativity and quantumfield theory to do the calculation.
 04:41: ... So it turns out that if we assume that both general activity and quantumfield theory are correct as we currently understand them, then Hawking ...
 05:08: A deeper understanding of general relativity or of quantumfield theory must resolve this.
 06:49: To resolve the bet, physicists had to figure out how quantum information could be transferred to Hawking radiation.
 07:07: And two, if it did, it would break quantum mechanics as surely as the old information paradox.
 07:16: ... turns out that by transferring quantum information to Hawking radiation, you may still violate the law of ...
 07:43: Specifically, it would violate the quantum nocloning theorem.
 08:11: ... might remember that there are certain pairs of quantumobservable complimentary observables, like position and momentum, that can't both ...
 09:16: ... Hooft realized that the threedimensional gravitational and quantummechanical interior of a black hole could be fully described by interactions on a ...
 09:29: This led him to realize that the union of quantum mechanics and gravity may require that the entire 3D universe be a projection on a 2D structure.
 10:09: ... Hawking himself has also jumped into that game, suggesting that quantum tunneling from within the black hole could interact with the holographic ...
 14:01: But quantumfield theory imagines the electromagnetic force as being transmitted by virtual photons.
 14:11: Virtual particles in general are just a way to mathematically account for the infinite ways a quantum field can communicate its influence.


20180613: What Survives Inside A Black Hole?
 01:21: ... conjecture with everything we learned recently about the conservation of quantum ...
 10:31: We discussed recently why quantum mechanics demands the conservation of quantum information.
 10:37: It's fundamental to quantum mechanics that the universe keeps track of its quantum states, which also means the types of particles it contains.
 11:44: In our last episode we looked at what might be the most fundamental rule in quantum mechanics, the conservation of quantum information.
 12:18: ... particle creation and annihilation is described by quantumfield theory, and unitary evolution and the conservation of probability and ...
 12:28: QFT describes the evolution of quantum fields in which particles are excited states.
 12:54: Peter K. asks how the universe can be deterministic given the fundamental probabilistic random nature of the quantum world.


20180523: Why Quantum Information is Never Destroyed
 00:36: Newton's equations for classical mechanics, Maxwell's equations for electromagnetism, and the Schrodinger equation for quantum mechanics.
 01:16: Today, we learn why conservation of information is such a fundamental requirement of quantum mechanics.
 04:33: Actually, quantum mechanics forbids this.
 04:45: To get at this, let's think about the basic equation of motion of quantum mechanics.
 05:02: ... in quantum mechanics, that means the probability distribution of all of its ...
 05:19: ... evolution of a given wave function in any given environment, or in quantum speak, in any given ...
 05:51: ... the conservation of information, as do the more advanced formulations of quantum mechanics, like the Dirac equation and quantum field ...
 06:49: And this unitarity is a foundational assumption in all formulations of quantum mechanics and quantum field theories.
 07:05: ... to explain without getting into some hairy math, but the upshot is that quantum states must remain independent of each other in order to preserve ...
 07:16: Two independent quantum states can't evolve into the exact same quantum state.
 07:27: ... to our first example, quantum states A and B can't both become quantum state C. The sum of the ...
 07:41: The only type of evolution that preserves probability and unitarity is the evolution that also preserves the number of quantum states.
 07:49: ... the preservation of quantum states means preservation of information, because you can trace a ...
 07:58: But all of this talk of quantum mechanics being deterministic seems a bit at odds with the idea of quantum randomness and the uncertainty principle.
 08:26: But that's not really what we mean by quantum information.
 08:29: Quantum information refers to the full information content of the wave function, not just what we measure.
 08:41: ... the collapse of the wave function in the Copenhagen interpretation of quantum mechanics actually does mess with conservation of ...
 09:14: ... interpretations of quantum mechanics, for example, Everett's manyworlds or the de BroglieBohm ...
 09:43: There is one situation where timereversibility appears to be broken regardless of your favorite interpretation of quantum mechanics.
 09:54: Stephen Hawking's eponymous radiation appears to destroy quantum information leading to the famous black hole information paradox.
 10:02: In an upcoming episode, we'll see whether quantum information really can be deleted from the otherwise perfect memory of space time.
 13:34: Black hole memory leaks, quantum rounding errors, and it took 10 billion years to compile the first life form.


20180516: Noether's Theorem and The Symmetries of Reality
 06:32: ... Fermat's principal to any object moving on any path or indeed any system quantummechanical to cosmological evolving between two ...
 06:43: ... of classical mechanics to Feynman's path integral formulation of quantum ...
 07:15: As long as we can identify that system's symmetries, this is useful in cosmology, but it's also useful in quantum physics.
 07:42: That symmetry is the phase of the quantum field.
 07:45: ... can rotate the complex phase of an oscillation in a quantum field by any amount, and the observable properties of that field, like ...
 07:59: This quantum symmetry is just the simplest of a large number of symmetries exhibited by quantum fields, the socalled gauge symmetries.
 08:14: For example, the color charge of quantum chromodynamics describes the strong interaction between quarks and gluons.
 08:26: It's founded on the fundamental symmetries of quantum fields.
 09:01: ... Weyl, also a giant in the mathematical foundation of quantum mechanics, said in her memorial address, I was ashamed to occupy such a ...
 12:47: ... "Space Time," we only ask that you start with a passing familiarity with quantum physics and the etymological foundations of the languages of ...


20180502: The Star at the End of Time
 06:00: ... helium and will quietly contract into a helium white dwarf, supported by quantum mechanical electron degeneracy ...


20180425: Black Hole Swarms
 11:11: Well, to answer that, I'd need a theory of quantum gravity so let me get back to you.


20180411: The Physics of Life (ft. It's Okay to be Smart & PBS Eons!)
 11:38: That emission looks like a straightforward quantum process, analogous to photon emission by an accelerating electric charge.
 11:49: ... there's a type of friction between the accelerating observer and the quantum field which should inhibit that acceleration by creating a type of ...


20180404: The Unruh Effect
 00:44: They were independently studying how the nature of quantum fields appears to change depending on whether or not an observer is accelerating.
 01:00: As we saw in our episode on horizon radiation, the presence of horizons distorts the quantum vacuum in a way that can create particles.
 01:19: To understand this, we don't need general relativity with its spacetime curvature and conflicts with quantum mechanics.
 06:00: And just as with Hawking radiation, that horizon cuts off your access to certain fundamental frequency modes of the quantum vacuum.
 08:02: This particle is coupled to the quantum field of interest, meaning it can exchange energy with that field.
 08:08: That means the particle can be excited into a higher energy quantum state when it encounters a particle associated with that field.


20180315: Hawking Radiation
 00:20: He made profound contributions across physics from quantum theory to cosmology.
 01:31: ... this and in a followup 1975 paper, he attempted a new union of quantum mechanics and general relativity to show that black holes should not be ...
 02:40: ... if you think you're ready, let's take a deep dive into the quantum field theory of curved space time to glimpse the true nature of Hawking ...
 02:52: Space is filled with quantum fields.
 03:14: They fluctuate in energy due to quantum uncertainty.
 03:25: They're really just a tool for calculating the infinite ways in which a fluctuating quantum field can behave.
 03:32: One way that quantum fields are very different to guitar strings is they can have both positive and negative frequencies.
 03:51: ... a quantum field is in a vacuum state, there's a balance between positive and ...
 04:11: But spatial curvature can mess with the balance of the underlying quantum field modes by introducing horizons.
 04:18: Horizons cut off access to certain modes of the quantum fields, disturbing the balance that defines the vacuum.
 04:25: Stephen Hawking knew that black holes with their insane spacetime curvature would wreak havoc on quantum fields in their vicinity.
 04:35: To answer that properly, he would need a full union of general relativity and quantum mechanics, a theory of quantum gravity, a theory of everything.
 05:21: Hawking imagined a simple quantum field tracing this path, a field that is in a perfect vacuum state before the formation of the black hole.
 05:54: ... flat space far from the black hole, regions where the nature of vacuums, quantum fields, and particles are perfectly well ...
 06:06: But to understand the effect of the close encounter with the black hole, he required an uneasy marriage of quantum mechanics and general relativity.
 06:14: In the absence of a theory of quantum gravity, Hawking needed a hack.
 06:23: These can be used to approximate the effect of curved spacetime on quantum fields by smoothly connecting regions of flat space.
 06:49: Certain modes of the quantum field are scattered or deflected by the gravitational field of the forming black hole.
 07:23: The quantum field that emerges is distorted in the same wavelength range.
 08:27: And for the escaping modes, there exist a corresponding set of modes linked by quantum entanglement that are trapped behind the event horizon.
 09:00: And they tell us that there is an enormous quantum uncertainty in the location of these particles.
 10:17: ... thinking about particles escaping from beneath the event horizon through quantum ...
 10:29: The common thread is quantum uncertainty.
 11:13: Without a full quantum theory of gravity, the origin of Hawking radiation will remain mysterious.
 11:32: ... radiation appears to destroy what should be a conserved quantity quantum ...
 11:49: ... by the brilliant mind of Stephen Hawking and a mysterious quirk of quantum ...


20180228: The Trebuchet Challenge
 00:00: [JINGLE PLAYING] Energy is a powerful tool for predicting the behavior of our universe, from quantum to cosmological scales.
 03:04: We could get into fluid or stellar dynamics, or even quantum mechanics.


20180221: The Death of the Sun
 03:52: While the stars outer layers of hydrogen are expanding and cooling, the core continues to collapse until it hits a quantum mechanical limit.
 04:08: ... rule that says is that fermions, like electrons, can't occupy the same quantum state as each ...


20180214: What is Energy?
 08:43: The concept of energy is so versatile that Hamilton's approach was even adapted to quantum mechanics.
 08:50: ... quantum Hamiltonian operator describes the total energy of a quantum system and ...
 09:05: Actually, Lagrangian mechanics makes a quantum comeback here.
 09:19: Lagrangian mechanics is the inspiration behind Feynman's path integral approach to quantum mechanics.
 09:26: And the Lagrangian quantum field theory is the basis for highenergy particle physics.


20180124: The End of the Habitable Zone
 11:09: Actually, all quantum fields are affected by the presence of a space time horizon.


20180117: Horizon Radiation
 00:00: ... The most successful theory in physics combines the weirdness of quantum mechanics with, well, the weirdness of special relativity, to give ...
 02:22: ... idea of observer dependent particles and vacua, we're going to need some quantum field theory, and we're going to need to draw heavily on this recent ...
 02:33: In QFT, we think about each particle type as having its own quantum field that exists at all locations in space.
 02:40: If the field vibrates with a single quantum of energy, we see a particle.
 03:26: That means everyone has to agree on the fundamental nature of the quantum fields that describe these particles and the way they interact.
 03:37: In fact, quantum field theory is what we call Lorentz invariant.
 04:08: To see how this happens, we need to think about how particles, interactions, and vacuums are described in quantum field theory.
 04:17: Imagine the simplest type of quantum field.
 04:42: That oscillator can increase in energy in discrete chunks in quanta.
 04:47: And we interpret each quantum of energy as representing a single particle.
 05:35: Quantum wave functions and quantum fields can be described in terms of variation with position or variations with momentum.
 05:56: So let's take our spatial quantum field our drum skin, with its single, localized particle, and transform to momentum space.
 06:59: Now it starts out with no oscillations, analogous to the vacuum state in quantum field theory.
 08:42: There's a nice mechanism in quantum field theory for doing this.
 09:46: OK, so what happens when we add a horizon to our infinite quantum field?
 11:53: So this year, keep your eye on the horizon the event horizon and the strange things it does to the quantum contents of space time.
 13:44: ... wonders whether stars may actually be speaking, considering Penrose's quantum brain hypothesis, which states that any sufficiently complex system ...
 14:00: ... would be regarding Penrose's idea that neurons perform a sort of quantum computation, and that this is the source of ...
 14:17: It feels like it's in the family of, we don't understand it, so it must be quantum mechanics.


20171206: Understanding the Uncertainty Principle with Quantum Fourier Series
 00:07: Sometimes intuitive, largescale phenomena can give us incredible insights into the extremely unintuitive world of quantum mechanics.
 00:16: ... really understanding Heisenberg's uncertainty principle, and ultimately, quantum fields and Hawking ...
 00:28: [MUSIC PLAYING] One of the most difficult ideas to swallow in quantum mechanics is Werner Heisenberg's famous uncertainty principle.
 00:44: We've discussed it in earlier videos on quantum mechanics, but it's time we looked a little deeper.
 01:44: We cannot simultaneously know both position and momentum for a quantum system with absolute precision.
 02:10: It's, instead, a statement about how much information we are ever able to extract from a quantum system.
 02:16: To understand the origin of the uncertainty principle, we don't need to know any quantum mechanics, at least not to start with.
 02:24: See, quantum mechanics is a type of wave mechanics.
 06:02: So how does this relate to the quantum world?
 06:04: Well, before we get back to quantum fields, let's think about the wave function.
 06:09: The solution to the Schrodinger equation that contains all of the information about a quantum system.
 06:49: In the early days of quantum mechanics, it was realized that photons are electromagnetic wave packets whose momentum is given by their frequency.
 09:43: It's a statement about how much of a quantum system's information is accessible at a fundamental level.
 10:12: So what does this oldschool quantum mechanics have to do with quantum field theory and Hawking radiation?
 10:18: Well, the key to understanding these things is to be able to switch between thinking about quantum fields in terms of position versus momentum.
 10:26: ... a single particle, a quantum field vibration, perfectly localized at one spot in space, can so be ...
 11:01: ... only by manipulating quantum fields in this strange momentum space, by adding and removing these ...
 11:53: Now, our recent discussions about the quantum world are leading up some pretty mindblowing episodes.
 11:59: ... yourself even better, you could check out Benjamin Shoemaker's series, "Quantum Mechanics," which includes a great episode on the uncertainty ...


20171129: Citizen Science + ZeroPoint Challenge Answer
 06:00: There were two, both quizzing you on the zeropoint energy of the quantum vacuum.
 06:06: The first question was about practical uses of the quantum vacuum.


20171122: Suicide Space Robots
 10:42: ... past couple of episodes have continued discussion of the quantum vacuum and zeropoint energy, including some discussion of the ...
 11:30: And just quickly regarding the objections of vacuum diagrams to some of my statements in this whole quantum vacuum series doctor diagrams, vacuum.
 12:00: You say that quantum field theory makes no prediction about the energy of the vacuum.
 12:12: QFT may not make a prediction about the zeropoint energy, but it does predict the existence of a fluctuating quantum vacuum.
 12:34: But as you mention on the subreddit, I'm more of a gravity guy than a quantum guy.
 15:07: Now sometimes the path to truth is extremely surprising, like the invariance of the speed of light the quantum nature of subatomic world.


20171108: ZeroPoint Energy Demystified
 00:00: ... PLAYING] The mysterious zeropoint energy, the quantum vacuum, has been a misrepresented subject of science fiction and ...
 00:32: ... is the prediction of quantum field theory, that there exists an energy of the vacuum resulting from ...
 01:17: Despite this minor glitch, quantum field theory is arguably the most successful theory in all of physics in terms of sheer predictive power.
 01:54: Today I want to debunk some of the nonsense surrounding the quantum vacuum.
 03:29: And this would be the case even with an extremely energetic quantum vacuum.
 05:46: ... popular use for the quantum vacuum is as a medium to push against for propulsion engine systems, ...
 06:10: Virtual particles, and hence, the quantum vacuum, mediate all forces.
 06:33: In the case of the EM drive, the proposal is that microwaves within the drive's resonant cavity push against the quantum vacuum.
 07:20: That said, the quantum vacuum does have its uses.
 07:56: Geckos literally manipulate quantum vacuum energy to climb walls.
 08:21: How many geckos do you need to catch and put on a leash in order to drag you up any wall, using only the power of the quantum vacuum?


20171102: The Vacuum Catastrophe
 00:03: The most successful theory in all of physics is arguably quantum field theory.
 00:32: The quantum vacuum is a seething ocean of activity.
 00:51: ... tells us that there's a quantum fuzziness in the amount of energy contained at every point in space a ...
 01:13: Quantum field theory predicts that the energy of the vacuum should be up to 120 orders of magnitude greater than the measured value.
 01:30: From the perspective of quantum field theory, every point in space is represented by a quantum oscillator, one for each elementary particle type.
 03:24: Until we develop a theory of quantum gravity, we can't say whether the photons above this energy are possible.
 03:49: ... even if it were infinite we may not notice, at least according to quantum ...
 04:12: In fact, in both quantum mechanics and classical mechanics, a particle's equations of motion depend only on changes in energy.
 04:39: Long story short a crazily high, even infinite, vacuum energy doesn't affect the predictions of quantum field theory.
 05:53: ... realization of this fact in the early days of quantum field theory was the beginning of what would become the vacuum ...
 07:39: Compare that to the number predicted by quantum field theory.


20171019: The Nature of Nothing
 01:21: Fix a particle's position, and its momentum, and so its motion, becomes a quantum blur of many possible momenta.
 01:55: Our modern understanding of the quantum nature of space is described by quantum field theory.
 02:08: In short, space itself is comprised of fundamental quantum fields, one for each elementary particle.
 02:28: Now these fields are quantum fields, which means their oscillations can't just have any old energy.
 02:41: In each quantum state, so each combination of particle properties, there is a ladder of energy levels, a bit like electron orbitals in an atom.
 02:50: Each new rung of the ladder represents the existence of one additional particle in that quantum state.
 02:57: In fact, the math of quantum field theory is all about going up and down this particle ladder, using socalled creation and annihilation operators.
 03:12: ... bottom of this energy ladder corresponds to these quantum oscillators having no energy, which means there are no particles in a ...
 03:51: ... more tightly we try to define the time window for the behavior of a quantum oscillator, the less certain we can be of its energy state in that time ...
 04:00: On extremely short time scales, a quantum field exists as a blur of many energy states.
 04:20: ... of all particle interactions in the universe, at least as described by quantum field ...
 05:24: For example, quantum conservation laws must be obeyed, so most virtual particles are created in particleantiparticle pairs.
 06:23: ... and that no such particles actually exist, or that they are only the quantum possibilities of particles, which somehow govern the interactions of ...
 08:20: ... if quantum fields are abuzz with particles popping into and out of existence, then ...
 09:32: ... found to be drawn together by a force that matched the predictions of quantum field ...
 10:53: ... Quantum field theory, with its dependence on virtual particles and vacuum ...


20171011: Absolute Cold
 00:11: We'll always have quantum fluctuations to warm our chilly bones.
 01:06: Doing so has revealed some bizarre quantum states of matter.
 01:11: But quantum mechanics may also prevent us from ever reaching absolute zero.
 01:17: Understanding the limit to cold will lead us to an understanding of the nature of the quantum vacuum itself.
 02:05: Those particles are quantum creatures.
 02:15: This quantum nature is revealed when we look at the spectrum of light produced as those particles hop between energy levels.
 02:27: It's mathematical form was our first hint at the quantum nature of the subatomic world.
 02:34: The influence of the quantum world becomes far more apparent in the strange states of matter that exist at the cold end of the heat spectrum.
 02:53: Once nearly all particles occupy that one quantum state, they share a single, coherent wave function.
 04:07: Now bosons are able to occupy the same quantum state as each other unlike the halfinteger spin fermions, which cannot.
 04:30: The unfreezability of helium reveals an even deeper quantum mystery.
 04:59: However, the most fundamental law of quantum mechanics forbids this.
 05:11: For example, the more precisely a quantum particle's position is defined, the less defined is its momentum.
 05:26: So try to fix a particle's position perfectly, try to hold it still, and its momentum enters a state of quantum haziness.
 05:38: At the lowest temperatures, particle motion acquires a sort of quantum buzz.
 05:55: We call the lowest possible energy of a quantum system it's zeropoint energy.
 06:14: All the quantum systems also have nonzero zero points, and that leads to even strange phenomena.
 06:21: For example, the quantum fields that fill our universe also fluctuate due to the Uncertainty Principle resulting in what we know as vacuum energy.
 06:31: And some quantum fields have an intrinsic nonzero zero point before even bringing Heisenberg into it.
 06:56: We'll need another episode to explore the quantum nature of nothing as we peer deeper into the coldest, darkest, and emptiest patches of Space Time.
 07:24: For example, Brian Greene's Exploring Quantum History delves much more deeply into the Heisenberg Uncertainty Principle.


20170928: Are the Fundamental Constants Changing?
 03:42: In the language of quantum field theory, it's the coupling strength between the electromagnetic field and a charged field like the electron field.
 05:17: Now, quantum spin gives electrons what we call a magnetic moment.


20170920: The Future of Space Telescopes
 12:14: Basically, the electrons are crammed as close together as quantum mechanics allows.


20170913: Neutron Stars Collide in New LIGO Signal?
 02:22: They are mostly composed of neutrons at the density of an atomic nucleus and are held up by a quantum mechanical force called degeneracy pressure.
 02:32: We talk about the bizarre physics of these quantum and gravitational monsters in this video.


20170810: The OneElectron Universe
 01:46: ... path integral formulation and the following spacetime interpretation of quantum mechanics, which won him the 1965 Nobel Prize in ...
 04:58: In a quantum field theory that's consistent with Einstein's special relativity, all particles must be symmetric under what we call CPT transformation.
 06:22: ... antimatter as timereversed matter is extremely useful in simplifying quantum field theory calculations, because it massively cuts down the number of ...


20170802: Dark Flow
 09:54: Last week, we talked about the actual rules by which Feynman diagrams can be used to describe real interactions in quantum electrodynamics.


20170726: The Secrets of Feynman Diagrams
 00:42: ... to Feynman's approach to quantum mechanics, every conceivable happening that leads from a measured ...
 00:57: To calculate the probability of any quantum system evolving between two states, we need to sum over every conceivable intermediate state.
 01:51: Then, you are going to apply them to do some quantum field theory yourself.
 02:00: We're going to stick to quantum electrodynamics.
 02:02: The first and most predictively powerful quantum field theory, QED, talks about the interaction of the electron field with the electromagnetic field.
 10:02: ... fact makes Feynman diagrams an incredibly powerful tool in simplifying quantum field theory calculations, vastly reducing the number of contributing ...


20170719: The Real Star Wars
 14:40: ... week when we talked about tricks for solving the impossible equations of quantum field ...


20170712: Solving the Impossible in Quantum Field Theory
 00:06: Quantum field theory is stunningly successful at describing the smallest scales of reality, but its equations are also stunningly complex.
 00:27: ... PLAYING] The equations of quantum field theory allow us to calculate the behavior of subatomic particles ...
 00:42: ... even the most elegant and complete formulations of quantum field theory, like the Dirac equation or Feynman's path integral, become ...
 01:26: ... give you an idea of how messy quantum field theory can be, let's look at what should be a simple phenomenon ...
 01:58: But in quantum field theory, specifically quantum electrodynamics, or QED, the story is very different.
 03:08: ... developed these pictorial tools to organize the painful mathematics of quantum field theory, but they also serve to give a general idea of what these ...
 04:24: Unfortunately, real electron scattering at a quantum level is a good deal more complicated than this.
 04:45: The quantum event around the scattering is a mystery.
 05:53: With infinite possible interactions behind this one simple process, a perfectly complete quantum field theoretic solution is impossible.
 06:07: This is the philosophy behind perturbation theory, an absolutely essential tool to solving quantum field theory problems.
 08:54: ... try to calculate the selfenergy correction to an electron's mass using quantum electrodynamics, you get that the electron has infinite extra ...
 09:27: The answer probably lies within a theory of quantum gravity which we don't yet have.
 10:27: ... trick can be used to eliminate many of the infinities that arise in quantum field theory for example, the infinite shielding of electric charge ...
 11:01: Nonetheless, renormalization saved quantum field theory from this plague of infinities.
 11:26: ... these rules make Feynman's doodles an incredibly powerful tool for using quantum field theory to predict the behavior of the subatomic ...
 12:07: The twoepisode documentary "The Ultimate Formula" gives a really nice history of the development of quantum field theory.
 13:12: Last week, we talked about Richard Feynman's brilliant contribution to the development of quantum field theory with his path integral formulation.
 13:35: So the deal is that Schrodinger's equation is a special case of a more general formulation of quantum mechanics.


20170707: Feynman's Infinite Quantum Paths
 00:00: ... PLAYING] Quantum mechanics seems to imply that all possible properties, paths, or events ...
 00:13: ... description of this crazy idea led to the most powerful expression of quantum mechanics ever devised Richard Feynman's path integral ...
 01:03: You might also want to catch up on the first two in our quantum field theory playlist because we are going to be building on that.
 01:46: There's a story about a quantum mechanics professor explaining the doubleslit experiment to a class.
 02:45: And he'd just outlined the basics of what was to become the path integral formulation of quantum mechanics.
 02:53: But it led to the most elegant formulation of quantum mechanics ever devised and became a key to quantum field theory.
 04:28: From that, it was possible for him and others to rederive all of quantum mechanics.
 05:20: However, in the quantum universe, there is no single path.
 05:24: Feynman instead used quantum action to assign an importance, a weight, to each of the infinite paths that a single particle could take.
 07:51: ... equivalent to and more powerful than earlier derivations of quantum ...
 08:37: But Feynman's solution produced a quantum mechanics that didn't need fixing.
 08:42: But perhaps the greatest power of the path integral is that it very naturally converts into a true quantum field theory.
 09:44: Instead of adding up all possible paths that particles can take, you instead add up all possible histories of quantum fields.
 10:04: The quantum action principle gives the probability amplitude of changes in the state of the field.
 10:25: ... the quantum field version of path integrals, we can describe all possible paths and ...
 12:56: OK, now let's get to your comments on our episode on quantum electrodynamics, the first quantum field theory.
 13:04: Jakub asks, what is the difference between the electromagnetic field of quantum field theory and the aether?
 15:00: A few of you asked whether quantum field theory and string theory are the same thing.
 15:07: Quantum field theory describes particles as a field vibration in 4D spacetime.


20170628: The First Quantum Field Theory
 00:17: I'm talking about quantum electrodynamics the first true quantum field theory.
 00:24: [MUSIC PLAYING] Quantum mechanics is perhaps the most unintuitive theory ever devised.
 00:41: Simply by following the math of quantum mechanics, incredible discoveries have been made.
 00:46: Its wild success tells us that the mathematical description provided by quantum mechanics reflects deep truths about reality.
 00:55: And by far the most successful, most predictive formulation of quantum mechanics is quantum field theory.
 01:07: And the first part of quantum field theory that was derived, quantum electrodynamics, is the most precise, most accurate of all.
 01:18: ... Quantum Field Theory, QFT, describes all elementary particles as vibrational ...
 01:30: Quantum ElectroDynamics, QED, provides this description for one such field, the ElectroMagnetic field.
 01:55: Now before we start thinking about vibrating quantum fields or even fields at all, let's talk about vibrations.
 03:42: OK, let's go quantum.
 03:47: If this were a quantum mechanical guitar string, then there'd be a minimum amplitude for the vibration that depended on its frequency.
 04:36: The electromagnetic field is a quantum field and so these oscillations have a minimum amplitude.
 04:51: Quantum physics may have started with Planck's discovery of the quantum nature of light.
 04:56: However, the first full formulation of quantum mechanics was Schrodinger's equation and it couldn't account for light at all.
 05:52: It follows the changing position and momentum and generally the physical quantum state of every individual particle but that's extremely inefficient.
 06:08: If you take a pair of electrons or photons in two quantum states and make them swap places, then nothing changes.
 06:15: ... the quantum state of every individual particle is like trying to do your finances by ...
 06:32: But bean counting in this way is not just inefficient in quantum mechanics.
 06:38: ... given quantum event or interaction can happen in multiple different ways and the ...
 07:31: ... complicated but it has to be built up from a number of minimum amplitude quantum oscillations, which is to say, ...
 07:43: So Dirac described a space of quantum states, including position and momentum/frequency, like an infinite array of springs.
 07:53: His mathematics, then, kept track of the number of particles, or quantum oscillations, in each of these states.
 08:00: ... of the movement of individual photons only the shifting number in each quantum ...
 08:21: He named the resulting theory quantum electrodynamics.
 08:26: He also coined the name second quantization for the process of counting the changing number of quantum oscillations, or particles per state.
 08:36: Schrodinger's approach of tracking the changing quantum state of each particle became the first quantization.
 09:29: The resulting quantum electrodynamics describes the interactions of matter and radiation with stunning success.
 10:26: ... that you can only have one fermion, or electron quark, et cetera, per quantum state, rather than infinite particles in the case of the ...
 11:10: This is the postulate of quantum field theory.
 11:43: The calculations of QED and of all quantum field theory are about counting the number of ways a quantum phenomenon can occur.
 11:58: In fact, a huge part of quantum field theory is about taming the infinities that arise in any calculation.
 12:45: ... you want to learn more about the relationship and the conflict between quantum mechanics and relativity, check out the course, The Theory of ...
 13:21: Last week, we began our discussion of quantum field theory by looking at the amazing Dirac equation and how it predicts the existence of antimatter.
 14:26: ... 100 asks, "Why was it possible to make quantum mechanics compatible with special relativity when we're still struggling ...
 14:46: ... work for the infinities you get when you think about curved space on the quantum ...
 15:11: And I guess it's possible there are quantum timelines where I missed it on the first attempt but it wasn't this one.


20170621: AntiMatter and Quantum Relativity
 00:24: And the emerging field of quantum mechanics had radically altered our understanding of the fundamental building blocks of the universe.
 00:31: Yet, this year, 1928, one brilliant insight would bring these theories together and unveil the quantum fabric of reality.
 01:21: ... change over time, and allowed physicists to predict the evolution of quantum systems, such as the strange interference pattern in the famous ...
 02:42: But spin does result in a sort of quantum angular momentum.
 03:00: The discovery of quantum spin starts with an Austrian physicist named Wolfgang Pauli.
 03:16: It states that no electron can occupy the same quantum state as another electron.
 03:24: In the case of electrons in atoms, it suggests that we should only find one electron per atomic orbital, if we count each orbital as a quantum state.
 03:38: And so Pauli realized there must exist a hidden quantum state.
 03:53: ... down, to occupy the same atomic energy level, without occupying the same quantum state and therefore violating the Pauli exclusion ...
 04:05: ... physicists soon figured out that this new quantum state represented spin and the up and down degrees of freedom were the ...
 05:02: He then used quantum mechanical expressions for energy and momentum.
 05:55: It contains the marks of both quantum mechanics, in the Planck constant, and relativity, in the speed of light.
 08:31: But it was one of the first attempts to describe something very real, the idea of a quantum field.
 09:02: Now, quantum field theory is a very deep topic.
 09:34: Well, it's a vibration in the same quantum field as its regular matter counterpart.
 10:20: So all elementary particles have a quantum field and all have an antimatter counterpart.
 10:53: ... incredible insight in combining quantum mechanics and relativity reveal an entire flip side of our universe, ...
 11:03: ... was also a key step in the discovery of quantum field and quantum field theory and the development of the standard model ...
 11:17: And that's a quantum rabbit hole that we'll jump into very soon, right here on "SpaceTime." I'd like to thank Skillshare for sponsoring this episode.
 15:04: This is the "Quantum Divide" by Chris Gerry and Kimberley Bruno.
 15:08: It explores the key concepts in quantum physics through a description of the most important quantum experiments ever made.


20170607: Supervoids vs Colliding Universes!
 02:22: We think that they came from random quantum fluctuations from the very first instant after the Big Bang.


20170503: Are We Living in an Ancestor Simulation? ft. Neil deGrasse Tyson
 03:43: Let's avoid the idea that the entire universe is simulated, right down to every atom, electron, or vibrating quantum field.
 14:04: The truth of that statement depends on which interpretation of quantum mechanics you want to go with.


20170329: How Time Becomes Space Inside a Black Hole
 11:53: It refers to any quantum systems whose internal interactions result in a periodic change from one state to another and then back again.


20170315: Time Crystals!
 03:23: ... arguments that time translational symmetry can't be broken by a quantum system in ...
 04:07: These atoms have spin values, quantum mechanical angular momenta from their electrons.
 08:30: Time crystals could have their first application in quantum computing.
 08:34: ... the most popular approach to building a quantum computing memory element is to use electron spins, which can represent ...
 08:45: One of the most serious challenges is that these quantum states are really hard to maintain.
 09:00: Time crystals with their resilient spinflip cycle could be the next step in building stable quantum memory.
 09:08: Time crystals could also help bridge the gap between quantum mechanics and general relativity.
 09:21: And unlike in relativity, quantum mechanics treats space and time very differently to each other.
 09:29: ... in time just like in regular crystals, perhaps it's a first step in a quantum union of space ...


20170111: The EM Drive: Fact or Fantasy?
 06:56: This isn't something we can get into properly without first doing some quantum field theory, so I'll keep it brief.
 07:02: The paper invokes pilot wave theory as a way to justify treating the quantum vacuum as a sort of plasma with which it can exchange momentum.
 07:19: Our understanding of the quantum vacuum in standard quantum field theory doesn't allow you to push off it, like you might row a boat on a lake.
 07:59: Instead, they invoke pilot wave theory to justify treating the quantum vacuum as a deformable medium.
 08:05: ... which he argues demonstrates that such a medium can reproduce certain quantum observables, like the energy levels of the hydrogen ...
 08:18: ... the quantum vacuum is some sort of almost classical medium, then they argue that the ...
 08:29: ... very different than described by the otherwise amazingly successful quantum field ...
 09:01: A distant third is that it's something brand new, like this quantum vacuum stuff.


20161208: What Happens at the Event Horizon?
 15:57: In the Copenhagen interpretation, the uncertainty principle describes the intrinsic randomness of the quantum world.
 18:47: ... just don't know whether the reality that drives the strange results of quantum experiments is actually deterministic in the way that we understand ...
 18:57: ... theory can at least go some way towards predicting the results of quantum ...
 19:07: Personally, I'm agnostic towards the relative truth behind the Copenhagen, manyworlds, pilot wave, or the other interpretations of quantum mechanics.


20161130: Pilot Wave Theory and Quantum Realism
 00:00: ... PLAYING] There is one interpretation of the meaning of quantum mechanics that somehow manages to skip a lot of the wildly extravagant ...
 00:26: ... PLAYING] Misinterpretation of the ideas of quantum mechanics has spawned some of the worst quackery pseudoscience hooha ...
 00:47: There are some pretty out there explanations for the processes at work behind the incredibly successful mathematics of quantum mechanics.
 01:13: The weird results of quantum experiments seem to demand weird explanations of the nature of reality.
 01:19: But there is one interpretation of quantum mechanics that remains comfortably, almost stodgily, physical.
 01:47: Pilotwave theory is perhaps the most solidly physical, even mundane, of the complete and selfconsistent interpretations of quantum mechanics.
 02:08: And the founding fathers of the Copenhagen interpretation of quantum mechanics Niels Bohr and Werner Heisenberg were radicals.
 02:16: ... quantum theory was coming together in the '20s, they were fervent about the need ...
 03:11: ... and Heisenberg there needed to be a full theory that described how a quantum object could show both wave and particlelike behavior at the same time ...
 03:25: ... that matter could be described as waves right at the beginning of the quantum ...
 03:36: De Broglie's theory reasoned that there was no need for quantum objects to transition in a mystical way between nonreal waves and real particles.
 04:13: That's the equation at the heart of all quantum mechanics that tells the wave function how to change across space and time.
 04:21: This means that pilotwave theory makes the same basic predictions as any other breed of quantum mechanics.
 06:21: See, although pilotwave theory makes all of the usual predictions of quantum mechanics, it has some really fundamental differences.
 08:00: But hidden variables have a bad rap in quantum mechanics.
 09:39: But quantum entanglement experiments show that this sort of "spooky" action at a distance is a very real phenomenon.
 10:17: But we see many of the familiar quantum phenomena appear in this macroscopic system of a suspended oil droplet following its own pilotwave.
 10:56: While regular mechanics has quantum field theory as its relativistic version, pilotwave theory hasn't quite got there yet.
 11:05: Quantum field theory pretty explicitly requires that all possible particle trajectories be considered equally real.
 11:21: This is not consistent with quantum field theory, and so there isn't a complete relativistic formulation of Bohmian mechanics yet.
 11:33: Now let's not even start talking about gravity no version of quantum mechanics has that sorted out.
 11:55: ... it shows us that it's possible to have a consistent interpretation of quantum mechanics that is both physical and deterministic, no hooha ...


20161116: Strange Stars
 01:02: What happens to the resulting ultradense material depends on quantum theory.
 01:08: ... already talked about how quantum processes save a neutron star from collapse, but ultimately also doom ...
 01:18: But just shy of that final transition, and on the fringe of our understanding of the quantum universe, a star may become very strange indeed.
 03:19: Degenerate matter is so compressed that particles can't get any closer together without occupying the same quantum states.
 05:40: It has three quark types instead of two, and that means more particles can occupy the lowest quantum energy states.


20161109: Did Dark Energy Just Disappear?
 13:17: I want to respond to some of your thoughts on both colonizing Mars, as well as on the Many Worlds interpretation of quantum mechanics.


20161102: Quantum Vortices and Superconductivity + Drake Equation Challenge Answers
 00:02: ... three researchers for major breakthroughs in understanding the strange quantum behavior of very, very cold ...
 00:44: However, at extremely cold temperatures, this thermal motion is so small that quantum effects can dominate the behavior of certain materials.
 00:53: Thouless, Kosterlitz, and Haldane massively advanced our understanding of these quantum phases by showing how topology drives this weird behavior.
 02:11: ... behind a strange quantized magnetic field observed in the mysterious "quantum hole effect." These findings will lead to some spectacular applications ...
 02:36: ... are very likely, and it may even be possible to build a topological quantum computer that uses entanglement between ...


20161026: The Many Worlds of the Quantum Multiverse
 00:09: A huge outstanding question is when and why does the weirdness of quantum mechanics give way to classical physics.
 00:27: [MUSIC PLAYING] One of the strangest features of the quantum description of reality is the idea of superposition.
 00:53: Mathematically, this is encapsulated in the wave function of a quantum particle or system of particles.
 01:00: The best illustration of why we need to describe the quantum world this way is the famous doubleslit experiment.
 01:24: Quantum mechanics very successfully predicts this result by describing each particle's journey as a superposition of all possible trajectories.
 02:04: ... the original Copenhagen interpretation of quantum mechanics, the act of measurement was thought to collapse possibility ...
 02:19: That collapse signifies the transition between the quantum and classical realms.
 02:24: One of the founders of quantum mechanics, Erwin Schrodinger, found this ridiculous.
 02:51: That radioactive decay is a purely quantum process.
 03:04: But doesn't that mean that the entire macroscopic system attached to that quantum event is also in superposition?
 03:22: And from its point of view, is the physicist outside also a quantum blur until the box is opened?
 03:42: It's that quantum superposition doesn't extend to macroscopic scales.
 03:48: It disappears when different quantum scale histories diverge.
 03:55: ... the wave functions describing quantum systems overlap sufficiently in other words, they are coherent it's ...
 05:06: However, there is another way to interpret the transition between the quantum and classical worlds.
 05:33: ... box and find that the cat is alive, it's because we're part of an entire quantum timeline in which the radioactive decay and subsequent poisoning never ...
 05:52: This sounds outrageous, but it's a very serious interpretation of the mathematics of quantum mechanics.
 07:07: ... invites the idea that reality splits into different branches every time quantum states diverge into different possibilities for example, at every ...
 07:43: But remember, the Copenhagen interpretation itself proposes multiple worlds in the superposition of paths or properties of a quantum system.
 08:18: ... may, in fact, be the more pure interpretation of the mathematics of quantum mechanics because there's nothing in that math that requires the ...
 08:29: ... is more economical in the number of unsupported concepts it adds to quantum mechanics, even if it isn't particularly economical in the number of ...
 09:29: There's no more evidence for many worlds than there is for other mainstream interpretations of quantum mechanics.
 09:47: ... so although it is supported by the incredibly successful mathematics of quantum mechanics, it has not yet added a prediction that might distinguish it ...
 10:23: It explains the apparent randomness of quantum mechanics with a sort of observer bias.


20161012: Black Holes from the Dawn of Time
 02:43: Back then, quantum fluctuations caused a sort of static fuzz across the minuscule cosmos.


20160929: Life on Europa?
 09:31: ... next week on "Space Time." Last week we talked about the weirdness of quantum entanglement and the implications its results have for the nature of ...
 09:57: ... between the predictions of a local hidden variable theory versus pure quantum mechanics is if you measure the spins of both particles with the same ...
 10:10: In that case, the pure quantum, nohiddenvariable prediction is that you'll always measure opposite spins.
 10:29: ... one spin in one direction and the other at 90 degrees, then the pure quantum prediction is that the second particle is aligned one way 50% of the ...
 11:13: So I've done this in a couple of the quantum videos before, but it bears repeating.
 11:18: The definition of observer sort of depends on what interpretation of quantum mechanics you're going with.
 11:30: Rather, observation may just mean any interaction that destroys quantum coherence between the entangled particles.
 11:37: ... with a macroscopic system so complex that we no longer observe clean quantum ...


20160921: Quantum Entanglement and the Great BohrEinstein Debate
 00:00: [MUSIC PLAYING] Is there a hidden physical reality that underlies the strange behavior of the quantum world?
 00:12: The weird phenomenon of quantum entanglement gives us quite startling clues to the answer.
 00:25: But they're actually surprisingly good at quantum mechanics.
 01:27: But quantum mechanics is so bizarre that it still has scientists wondering if we need to reject even this basic premise.
 01:34: This was the source of one of the most heated debates at the advent of quantum mechanics.
 01:48: ... the intervals between measurement, quantum systems truly exist as a fuzzy mixture of all possible properties what ...
 02:29: He insisted that the wave function, and by extension quantum mechanics, is incomplete.
 02:40: ... idea, Einstein along with Doris Podolsky and Nathan Rosen proposed a quantum scenario that showed that in order to abandon the assumption of realism, ...
 03:13: The Einstein Podolsky Rosen, or EPR, paradox introduces one of the most mysterious ideas in quantum mechanics quantum entanglement.
 03:30: And yet we refrain from measuring these properties to preserve quantum uncertainty.
 03:36: ... Quantum mechanics requires that we describe the particle pair with a single ...
 05:10: But in quantum mechanics, measurement actually affects the thing you are measuring.
 05:15: In the case of quantum spin, that measurement effect is especially weird.
 05:31: We always find that the observed quantum spin aligns itself with our chosen measurement axis.
 07:13: ... that we'd expect to see in the case that Einstein was right and quantum mechanics needs local hidden ...
 07:42: It's a tricky experiment because entangled quantum states are hard to produce, but even harder to sustain.
 08:41: ... delayed choice quantum eraser, which we already covered, is yet another example of this strange ...
 09:02: Do we live in a peekaboo universe that vanishes into quantum abstraction when we aren't looking at it?
 09:09: Are babies really better at quantum mechanics than Einstein?
 10:04: ... those measurements are compared, just as we saw with the delayed choice quantum ...
 10:23: The Copenhagen interpretation remains consistent with all quantum observations.


20160907: Is There a Fifth Fundamental Force? + Quantum Eraser Answer
 02:06: That transition meant a difference in energy, but also a difference in some of the quantum stuff, spin parity and isospin.
 03:59: OK, on to the solution to the quantum eraser challenge.
 04:03: ... impossible to send any real data back in time using the delayed choice quantum eraser experiment, and so cheat on the ...
 06:59: But there's still time for a minirant about the role of consciousness in quantum mechanics.


20160824: Should We Build a Dyson Sphere?
 10:58: ... I travel and then coming back the following week with the answer to the quantum eraser lottery challenge and some intriguing physics ...
 11:36: A couple of weeks ago, we talked about the mysterious delayed choice quantum eraser.
 13:17: We'll go into all of this in more detail in the challenge question answer and also when we come back to quantum entanglement.


20160817: Quantum Eraser Lottery Challenge
 00:00: [MUSIC PLAYING] The quantum eraser experiment tantalizes us with the apparent instantaneous flow of information between entangled photon pairs.
 00:11: In fact, the delayed choice quantum eraser seems to show that information can travel backwards in time.
 00:31: First, though, you really should go back and watch that quantum eraser episode, unless you memory is incredible.
 05:12: ... detailed explanation to PBSSpaceTime@gmail.com with the subject line "Quantum Eraser Challenge Question." Be sure to use exactly these words because ...


20160810: How the Quantum Eraser Rewrites the Past
 00:09: That's the unsettling implication of the delayed choice quantum eraser experiment.
 06:26: This is quantum mechanics.
 06:29: This extra stuff is the quantum eraser.
 08:57: Now the delayed choice quantum eraser double slit experiment doesn't tell us whether the wave function is physical or not.
 09:15: In fact, the solution may lie in this fascinating phenomenon of quantum entanglement.


20160803: Can We Survive the Destruction of the Earth? ft. Neal Stephenson
 12:21: Well, wave functions for macroscopic objects are incredibly complicated because they're comprised of countless quantum particles.
 13:03: Some of you wondered why we didn't talk about what happens when you try to measure which slit the particle went through or talk about quantum eraser.


20160727: The Quantum Experiment that Broke Reality
 00:13: It's one of the most stunning illustrations of how the quantum world is very, very different from the largescale world of our physical intuition.
 05:47: We also saw this waviness in position when we talked about quantum tunneling.
 05:52: In fact, several quantum properties, like momentum, energy, and spin, all display similar waviness in different situations.
 06:00: ... function." Describing the behavior of the wave function is the heart of quantum ...
 07:42: In fact, the answers aren't known but the various interpretations of quantum mechanics do try.
 07:49: Let's talk about the view favored by Werner Heisenberg and Niels Bohr, who pioneered quantum mechanics at the University of Copenhagen in the 1920s.
 09:36: ... theory of quantum mechanics produces stunningly accurate predictions of reality and it's ...
 09:54: ... we know that light is a wave in the electromagnetic field and quantum field theory tells us that all fundamental particles are waves in their ...
 10:50: I have recently been exploring The Great Courses Plus quantum mechanics content.


20160720: The Future of Gravitational Waves
 06:49: And that's actually close to the number you get from doing this with quantum mechanics so that's cool.


20160706: Juno to Reveal Jupiter's Violent Past
 10:28: We recently talked about the origin of quantum theory with Max Planck's derivation of an equation to describe the black body spectrum.
 11:33: A few of you rightly know that quantum mechanics isn't needed to resolve Zeno's paradox of Achilles and the tortoise.


20160629: Nuclear Physics Challenge
 00:06: We've been talking about quantum mechanics recently, and I think we're ready to do a bit of recreational nuclear physics.
 00:13: A few episodes ago, we delved into quantum tunneling.
 00:31: One consequence of this uncertainty in position is the phenomenon of quantum tunneling.


20160622: Planck's Constant and The Origin of Quantum Mechanics
 00:03: ... physics of our macroscopic reality gives way to the weirdness of the quantum ...
 00:15: You might not expect the quantum behavior of the microscopic to be observable on all scales of the universe, but it is.
 00:23: In fact, you can see the effect of this quantum behavior and even measure the Planck constant just by observing the color of sunlight.
 01:14: As your distance to the tortoise becomes unthinkably small, there arises a quantum uncertainty in your location.
 01:22: Get close enough to it, and this quantum blurriness means it's impossible to say whether your location is really behind or in front of the tortoise.
 01:45: The tiny Planck constant, at 6.63 by 10 to the minus 34 joule seconds, sets the scale of this quantum blurriness.
 01:59: In many ways, it defines the divisibility of the quantum world.
 02:04: In fact, the Planck constant appears in essentially all equations that describe quantum phenomena.
 02:36: It may define the scale of quantum reality, but the influence of the Planck constant can be seen even on our scale.
 02:56: In fact, the mystery of why hot things glow the color that they do led us to discover the quantum universe in the first place.
 04:23: But he didn't realize that the relative brightnesses of those colors held the key to the quantum world.
 09:52: ... the existence of the photon part wave, part particle, carrying a quantum of energy equal to the now familiar frequency of the wave times the ...
 10:20: These discoveries sparked a frenzy of sciencing that led to the quantum revolution of the 1920s.
 10:27: And that little number that Max Planck came up with in his moment of desperation the Planck constant remains at the heart of all things quantum.
 10:36: But not just quantum.


20160615: The Strange Universe of Gravitational Lensing
 09:51: We recently started talking about quantum physics by looking at the bizarre phenomena of quantum tunneling.
 10:05: ... can't quantum tunnel to the moon, because to properly tunnel, you need to ...
 10:54: ... of possible locations is only true for the Copenhagen interpretation of quantum ...
 11:19: ... interpretation was one of the early interpretations of some of the weird quantum effects developed in the ...
 12:30: Mystyc Cheez and others ask, what is really meant by an observation in quantum mechanics?
 12:39: ... a quantum system means doing something to it that collapses its wave function into ...
 12:58: ... so hopelessly mixed with those of other particles that its observable quantum behavior can't be ...


20160601: Is Quantum Tunneling Faster than Light?
 00:08: According to quantum mechanics you are, at least a little bit.
 00:12: [THEME MUSIC] Quantum mechanics is a spectacularly weird theory.
 00:41: ... more accurately, until a quantum object interacts with something, all possible states are just as real as ...
 00:52: There is a distribution of probabilities for each of an object's quantum properties.
 01:19: For now, let's just look at the strange consequences of quantum uncertainty in an object's location.
 01:26: This is one of the early realizations in the development of quantum theory.
 03:33: But quantum objects aren't at all like balls.
 04:38: This process is called quantum tunneling.
 04:48: Quantum tunneling also goes in the other direction.
 04:52: Protons, neutrons, electrons, and alpha particles can quantum tunnel into nuclei in various types of fusion and particle capture phenomena.
 05:01: In fact, without quantum tunneling, stars could not fuse hydrogen into heavy nuclei.
 06:11: In the absence of quantum tunneling, that barrier should reflect its photon 100% of the time.
 07:04: To make that work you need to use a second, and perhaps even weirder feature of quantum mechanics, quantum entanglement.
 08:13: Well, this apparent violation of relativity only occurs deep within the quantum realm.
 09:28: But in the quantum realm, Heisenberg uncertainty does seem to allow instantaneous motion, and even perhaps causality violation within quantum limits.
 09:39: Stay tuned for the implications of this on both quantum and cosmic scales of space time.


20160302: What’s Wrong With the Big Bang Theory?
 04:20: See, at this point, general relativity comes into serious conflict with quantum mechanics.
 04:26: And we need a theory of quantum gravity, a socalled theory of everything, to go further.


20160224: Why the Big Bang Definitely Happened
 02:56: While general relativity is incredibly successful, it doesn't contain the machinery to describe the quantum scale gravity of that first speck.


20160203: Will Mars or Venus Kill You First?
 10:11: For one thing, we don't have a theory of quantum gravity to get us into the Planck era.


20160127: The Origin of Matter and Time
 07:28: We're extrapolating the validity of space time diagrams, and these tiny lifelike segments into the quantum realm.
 10:04: ... basic vibrations of their quantum fields the time that the electron or quark feels is felt by the ...


20160106: The True Nature of Matter and Mass
 09:32: There's a quantum blur surrounding the current state of the electron.


20151216: The Higgs Mechanism Explained
 01:01: To understand how all this works, we're going to need to learn a bit of quantum field theory.
 02:02: ... its incredible success, it was strange that quantum field theory, as it stood in the 1950s, gave a perfect description of ...
 02:35: ... has this type of intrinsic quantum spin that we call chirality, and this can either be clockwise or ...
 05:06: While most quantum fields hover around zero in empty space, the Higgs field has a positive strength at all points in the universe.
 05:17: ... some stunning quantum weirdness, this complex, multicomponent field not only carries the weak ...
 06:04: Well, something like this must be true, because all of the rest of quantum field theory hangs together too well.


20151209: How to Build a Black Hole
 00:06: To make one, we need both general relativity and quantum mechanics.
 01:04: We need quantum mechanics.
 02:33: Now, beneath the thin atmosphere of ion plasma, a neutron star is a quantum mechanical entity.
 02:39: And it's a quantum phenomenon that saves it, for the moment, from final collapse.
 02:44: It's also a different quantum phenomenon that will let us push it over the edge, creating a black hole.
 02:51: ... understand how space works for a quantum object like this, we need to think not in regular 3D space or even 4D ...
 03:15: ... the exact way that the matter of a neutron star fills this 6D quantum phase space depends on two important principles of quantum theory, the ...
 03:48: Now, by place, I mean location in quantum phase space.
 03:52: So two fermions can apply the same physical location just fine, as long as their momenta or any other quantum property is different.
 04:53: Two fermions just can't ever occupy the same quantum state.
 05:04: Fortunately, there's another quantum phenomenon that let's us get around the Pauli exclusion principle.
 05:10: The Heisenberg uncertainty principle tells us that the properties of a quantum entity are fundamentally uncertain.
 05:17: The details may be a topic for another episode, but in short, quantum mechanics describes matter as a distribution of possibilities.
 05:55: This is the weirdest, coolest aspect of quantum mechanics.
 07:31: This is a quantum effect, even though it's happening on the scale of a star.


20151028: Is The Alcubierre Warp Drive Possible?
 03:44: We can create something like it, a negative pressure, on quantum scales via Casimir effect.
 04:04: Except Stephen Hawking chronology protection conjecture states that quantum mechanics will always stop causalitybreaking actions.
 04:13: It suggests that there's something in the deeper union of GR and quantum mechanics, the theory of everything, that prohibits the warp drive.
 04:21: One possible quantum disaster is that the extreme spacetime curvature of the warp bubble walls would roast the interior with crazy Hawking radiation.
 06:02: Quantum scale manipulation of the vacuum energy a la the Casimir effect may be enough.
 08:32: Quantum mechanics began as an abstract musing on the nature of reality.
 08:36: ... that this crazy theory would lead to the invention of the transistor, a quantum mechanical device, let alone the computer, the smartphone, the Apple ...


20151022: Have Gravitational Waves Been Discovered?!?
 06:08: Even quantum fluctuations in the photon rate causes noise.


20151015: 5 REAL Possibilities for Interstellar Travel
 11:50: Jai Kolra and others ask, what about quantum entanglement?


20151007: The Speed of Light is NOT About Light
 02:26: The first clues to the bizarre quantum nature of reality had emerged.


20150923: Does Dark Matter BREAK Physics?
 06:58: Sinking down into the depths of quantum field and string theory, you can find all sorts of strange fish, WIMPs, axions, neutralinos.


20150819: Do Events Inside Black Holes Happen?
 00:24: That means no Hawking radiation, no string theory, and no quantum anything baby steps.


20150805: What Physics Teachers Get Wrong About Tides!
 10:09: ... may have heard that in quantum field theory, forces are described as being mediated by some kind of ...
 10:33: ... field, you're quantization something different when you talk about the quantum version of general ...
 10:53: ... when you start looking at very small scales, like what the quantum version of gravity tells you on very small scales or very high energies, ...
 11:07: But from the philosophical perspective of quantum field theory, you should be able to quantize anything.
 11:41: ... field theory versions of something and then add to them the machinery of quantum mechanics to sort of get a quantized version of the ...


20150429: What's the Most Realistic Artificial Gravity in SciFi?
 10:30: Does quantum mechanics bring back free will since it attaches some inherent randomness to the future.
