
20221116: Are there Undiscovered Elements Beyond The Periodic Table?
 11:08: ... doing this using computational techniques like density functional theory, which we explained in a previous ...


20221109: What If Humanity Is Among The First Spacefaring Civilizations?
 18:50: ... implied by this interpretation is equivalent to standard quantum field theory, with the timereversed signals corresponding to negative frequency ...


20221026: Why Did Quantum Entanglement Win the Nobel Prize in Physics?
 00:47: ... at a distance” as Einstein called it, is in seeming violation of his own theory of relativity, which tells us that no causal influence can travel faster ...
 03:36: ... hidden information, and they’re collectively known as hidden variable theories. ...
 04:10: It became dogma, and for a while it was career suicide to question the orthodoxy, for example by researching hidden variable theories.
 04:21: David Bohm got the worst of that with his pilot wave theory, which we talk about in another video.
 04:38: ... that information, or even testing a specific hidden variables theory. ...
 07:18: Hidden variable theories, on the other hand, allow the polarization to be set at the moment the photons are created.
 10:22: The Bell inequalities were also violated in Alain Aspect’s experiment, dealing another blow to hidden variable theories.
 13:53: Because science only moves forward when we try to push its theories to the breaking point.
 18:42: ... could be eliminated with a more elegant formulation of the theory. ...
 19:16: ... in general a lot of problematic features appear in quantum field theory that have to be removed by hand  for example, various infinities ...


20221019: The Equation That Explains (Nearly) Everything!
 00:00: ... Standard Model of particle physics is arguably the most successful theory in the history of physics. It predicts the results of experiments with a ...


20221012: The REAL Possibility of Mapping Alien Planets!
 04:12: ... first let’s review gravitational lensing. Einstein’s general theory of relativity tells us that gravity is due to curvature in ...


20220921: Science of the James Webb Telescope Explained!
 13:29: Robin Saunders reminds us that there’s a relationship between gluon flux tubes and string theory.
 13:37: ... string theory actually began as an attempt to understand QCD, before being abandoned ...
 13:46: And asks whether the methods of string theory are being brought back to understanding gluons again?
 13:56: The core mechanics of string theory were developed to describe the very stringy onedimensional gluon bonds between quarks, particularly in mesons.
 14:20: Quantum chromodynamics actually started to explain was going on, so it suplanted hadronic string theory.
 14:28: ... modes of these strings looked like the graviton, so the entire theory was shrunk in size by about 20 orders of magnitude and developed into a ...
 14:41: We explain everything in our string theory episodes.
 14:45: ... now, decades later, with string theory still failing to produce a slamdunk testable prediciton, people are ...


20220914: Could the Higgs Boson Lead Us to Dark Matter?
 07:34: ... is a whole family of potential theories of how the Higgs could interact with dark matter, these all fall under ...


20220824: What Makes The Strong Force Strong?
 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 ...


20220817: What If Dark Energy is a New Quantum Field?
 13:27: ... on itself. But this flexibility makes it hard to actually falsify the theory  it’s just too easy to come up with a behavior of the field that fits ...


20220803: What Happens Inside a Proton?
 00:22: ... how the universe should behave  that lets us test our theories and basically become wizards capable of predicting the ...
 00:45: ... about the hack that lets us do it anyway  density functional theory. ...
 02:06: ... with a gluon. Instead we need to figure out what the theory predicts about properties of hadrons that are actually measureable. ...
 07:07: ... for the behavior of quarks, how can we even test the theory? Well, we need to abandon Feynman diagrams. In fact, we need ...


20220720: What If We Live in a Superdeterministic Universe?
 01:12: Pilot wave theory, objective collapse models, and even the Many Worlds interpretation all seek to describe a reality that exists sans observers.
 07:24: According to the Bell theorem, any localrealist theory must obey the Bell inequality.
 07:40: ... a local realist theory, every point in space and time  every event  can only be influenced by ...
 07:59: Things like pilot wave theory and objective collapse models try to do that.
 09:52: In Bell’s theorem, his inequality is satisfied in localrealist theories  but there is another condition to the validity of the theorem.


20220622: Is Interstellar Travel Impossible?
 15:43: In his book The Grand Design” Hawking says, and I quote, “There is no picture or theoryindependent concept of reality.
 15:52: ... view that we will call modeldependent realism: the idea that a physical theory or world picture is a model and a set of rules that connect the elements ...
 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.
 18:26: Could this, for example, show us how black holes deviate from theory?
 18:42: Actually, simply gaining information about the interior of the black hole this way is counter to the orthodox black hole theory.


20220615: Can Wormholes Solve The Black Hole Information Paradox?
 00:26: ... come when we noticed inconsequential seeming inconsistencies in our theories. The fact that Maxwell’s electromagnetism didn’t square ...
 05:20: ... radiation is our information escape route from the black hole. Any theory trying to solve the black hole information paradox has ...
 06:01: ... advanced form of this is AdS/CFT correspondence, a branch of string theory that reveals that a particular type of universe with three ...
 06:54: ... relativity and accepted quantum mechanics  no string theories attached. To be fair, these US teams, dubbed the “eastcoast” and ...
 07:24: ... tidal wave of math in these papers pulls ideas from string theory, holography, quantum field theory, and quantum ...
 11:25: ... this equation. The island rule had already been derived in string theory. The researchers were surprised to find that you don’t need string ...


20220601: What If Physics IS NOT Describing Reality?
 00:25: ... work best. But actually, some of the founders of quantum theory were convinced that the role of physics was one step further ...
 05:53: ... “quanta of information”, we see the indeterminacy of quantum theory arises naturally. Zeilinger even managed to derive the ...
 08:49: ... idea leads us naturally to some other staples of quantum theory  like the Heisenberg uncertainty principle. In a previous ...
 09:26: ... fact, by bringing to bear the tools of information theory we can derive an even tighter uncertainty relation  something ...
 11:24: ... one thing to use quantum information theory as a mathematical tool, but quite another to claim that ...


20220504: Space DOES NOT Expand Everywhere
 00:19: ... away from us, and interpreted through the lens of Einstein’s general theory of relativity, this only makes sense if all distances everywhere are ...
 08:51: ... tough one  in fact an impossible one because we don’t have an accepted theory for what that the fabric of space is actually made out of, if anything. ...


20220427: How the Higgs Mechanism Give Things Mass
 04:37: ... to each other. To see if we can duplicate that in our theory we need to combine the U(1) and SU(2) symmetries so that ...


20220420: Does the Universe Create Itself?
 00:59: ... himself. We’ve talked about this debate between the founders of quantum theory before, and of some of the supposed resolutions, which I’ll come back ...
 01:59: ... in the behavior of the wavefunction, such as de BroglieBohm pilot wave theory or objective collapse interpretations. Still others sought to explain ...


20220330: Could The Universe Be Inside A Black Hole?
 00:19: Einstein’s ridiculously successful general theory of relativity has never failed.


20220323: Where Is The Center of The Universe?
 02:57: His general theory of relativity explains gravity as the warping of space and time due to the presence of mass and energy.
 10:45: Stand by for our theory of quantum gravity to resolve that one.


20220316: What If Charge is NOT Fundamental?
 03:14: In this theory the proton would be the “up” state with isospin 1/2, and the neutron would be the down state with isospin 1/2.


20220308: Is the Proxima System Our Best Hope For Another Earth?
 16:39: ... doing comments on the last two episodes: the one on objective collapse theories, where wavefunction collapse is explained as a real, physical ...
 17:58: ... quantum mechanics and quantum field theory assume a welldefined underlying framework, upon which all the quantum ...
 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?
 12:19: ... a cosmic superstring? You’ve probably heard of string theory  we’ve certainly talked about it enough on this show. It’s ...


20220216: Is The Wave Function The Building Block of Reality?
 02:24: ... proposed by Werner Heisenberg, one of the principle founders of quantum theory. Heisenberg and his friend Neils Bohr were convinced that this wave ...
 03:24: ... all of these ideas in the past. We also have de BroglieBohm pilot wave theory, where particles already have defined properties that are hidden within ...
 03:59: ... function as the fundamental building block of reality, unlike pilot wave theory. And one which avoids multiple universes by insisting that collapse does ...
 04:17: ... Weber published a paper that outlined what was to become known as GRW theory  the first in a new class of alternate quantum theories called ...
 04:36: ... objective collapse theories, wave functions are real, physical entities that literally collapse when ...
 04:54: To understand how objective collapse theories work, we need just a little more quantum mechanics.
 08:02: ... was a revolutionary theory that inspired many subsequent models, like Continuous Spontaneous ...
 09:25: ... into a classical object. Instead of gravity being quantized, Penrose’s theory predicts quantum mechanics will be “gravitized.” For example, consider a ...
 10:19: ... are not mere interpretations of quantum mechanics — they are distinct theories with unique predictions. This means that, unlike other interpretations ...


20220210: The Nature of Space and Time AMA
 00:03: ... brave efforts to try to figure it out the emerging generations of theories of quantum gravity theories of the theme some of them try to answer ...


20220127: How Does Gravity Escape A Black Hole?
 00:35: ... 1915 Einstein presented to the world the equations behind his general theory of relativity, which describe gravity not as a traditional force, but ...
 00:48: Einstein’s theory predicted the existence of the ultimate gravitational object: the black hole.
 01:01: ... to Einstein’s theory, any object that reaches such a density has to collapse to a pointlike ...
 01:21: ... = \kappa T_{\mu\nu} so they would be consistent with his special theory of relativity, which describes how lengths and times and other ...
 05:43: But we know that GR is not the final theory.
 05:54: ... physicists believe that general relativity needs to be replaced by a theory of quantum gravity to explain the behavior of gravity in these ...
 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: ... we’re talking about the classical gravity of Einstein or some deeper theory of quantum ...
 13:06: ... of information in the quantum wavefunction with density functional theory, and then went from the tiny to the enormous, exploring how we do ...
 13:42: ... with our reality, is an indicator that there's a much simpler underlying theory on the order of complexity of that small ...
 14:21: We said that in density function theory you start with a makebelieve system of noninteracting electrons.


20220112: How To Simulate The Universe With DFT
 08:49: ... stands for density functional theory, and it’s perhaps the most successful approach to tackling the extreme ...
 09:01: ... of atoms comprising the capsid of a virus done using density functional theory, and here’s resonant excitation in the many electrons of a ...
 11:54: The secret sauce that makes this work is something called the energy functional  it’s the functional in density functional theory.
 12:51: ... functional theory has now been used to model the intricate quantumlevel behavior of ...


20211220: What Happens If A Black Hole Hits Earth?
 10:44: ... made by regular old rocks is hard, but not impossible thanks to some new theory work. Recently, some scientists have calculated how the shape of a black ...
 14:10: ... an explanation for dark matter, and the one on fuzzballs  the stringy theory version of the black ...
 14:26: ... all this complexity. "Let's just add a few more fields to GR so that our theory fits the data.” Well to that I’ll let Einstein respond: “It can scarcely ...
 17:55: ... tested. Actually, this might be the most testable prediction of string theory. There are simulations that suggest that the gravitational waves created ...


20211210: 2021 End of Year AMA!
 00:02: ... that massive bodies bend the paths of light according to einstein's theory of general relativity so when you look out there you see you know ...


20211117: Are Black Holes Actually Fuzzballs?
 00:18: String theory, in fact.
 00:20: ... in the black holes of string theory  fuzzballs  are perhaps even weirder than the regular type Einstein’s ...
 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.
 04:39: But such a theory didn’t exist back then in the 70s and still doesn’t.
 05:22: And it turns out that our most advanced theory of quantum gravity can do this quite neatly.
 05:28: Black hole paradoxes may be solved by string theory.
 05:32: In string theory, black holes are not hairless at all  in fact all of those strings make them positively fuzzy.
 05:43: First a spot of string theory.
 05:52: ... string theory, all elementary particles are oscillations in 1dimensional strands that ...
 06:01: ... theory immediately solves the problem of the black hole singularity, because ...
 06:17: It turns out that though, that string theory can make sense of the black hole event horizon also.
 06:22: ... when Andrew Strominger and Cumrun Vafa created a black hole using string theory  in theoryspace, not ...
 07:04: The infinitesimal strings and branes of string theory might be the analog of the molecules that store the entropy of our room full of air.
 07:13: ... a decisive step and it gave us a compelling reason to think that string theory might explain where the microstates of black holes ...
 08:00: This was another stunning match to theory, and also a way for stringy black holes to leak out their information.
 08:39: This property of black holes is actually quite hard to reproduce in theories of quantum gravity.
 09:52: The ability for strings to maintain structure in this extreme gravity comes down to an effect specific to string theory called fractionation.
 10:10: ... in string theory, when you merge a large number of strings, the tension of the resulting ...
 12:20: In string theory we have extra compact dimensions  spatial dimensions that are coiled up on the Planck scale so we can’t see them.
 13:00: ... emergence of fuzzballs in string theory radically changed our vision of what a black hole could be and provided ...


20211110: What If Our Understanding of Gravity Is Wrong?
 01:34: After all, if your scientific theory doesn’t fit observations we should reject our theory, right?
 01:39: ... for dark matter, others have been hunting for an alteration to our theory of gravity that can explain the effect of dark matter without the actual ...
 02:52: ... the gravitational field gets too strong  there you need his general theory of relativity, which explains gravity as the curvature in the fabric of ...
 08:50: ... laws were obeyed, and because this was a relativistic theory it was possible to see if it gave the right result for the bending of ...
 12:25: Modified gravity theories still can’t explain the Bullet Cluster  and I don’t have time to get into that and we’ve covered it before.
 12:54: At this point the two theories are in a bloody theoretical knife fight, where the knife is Occam’s razor.
 13:44: But Bekenstein was no slouch, nor are many of the others who have supported MOND theories.
 15:45: ... quantum mechanics and relativity, what's missing to make this a theory of ...


20211102: Is ACTION The Most Fundamental Property in Physics?
 05:24: ... then it should apply well beyond classical mechanics and into our modern theories  in particular general relativity and quantum mechanics. And perhaps in ...
 05:52: ... start with Einstein’s General Theory of Relativity, which, as we’ve discussed before, describes the force of ...
 12:59: ... to the evolution through quantum states underpins modern quantum theory. Back to Paul Dirac just for a moment. His eponymous equation was derived ...
 15:27: ... get into your comments on our recent episode on constructor theory. This was a contentious one. Many of you were dubious that constructor ...
 15:51: Nestor de Buen asks: Isn’t this more of an epistemological framework than a theory?
 15:58: ... of science collaborated more. So my sense is that constructor theory does try to bring a philosophical perspective shift, which in principle ...
 16:26: ... of the math  Corbin Simpson and Skooks say that constructor theory sounds like category theory. I only learned about category theory while ...
 17:15: This is all some pretty obtuse stuff, and some of you did better at explaining the point of constructor theory than I did, so let me just summarize.
 17:24: ... Andy points out that constructor theory seeks to narrow down the space of all possible functions that might ...
 17:54: ... spacetime, invariance, quantum etc.) then constructor theory gives us insights as to what math is possible, and what math should be ...
 18:34: ... notes that constructor theory feels like alchemy. Relatedly, Cluebcke says “Rough shade on Newton with ...
 18:52: ... lines of inquiry would be “fruitful” without exploring them? Constructor theory might be another alchemy, or it might be another Newtonian mechanics. ...


20211020: Will Constructor Theory REWRITE Physics?
 00:00: ... and from simple statements about reality they built up their incredible theories. ...
 01:30: ... a set of equations for each separate aspect of the world  but if these theories are really true then they should ultimately come together into some ...
 01:43: ... and Newtonian mechanics and electromagnetism and so on from two master theories: quantum mechanics and Einstein’s general ...
 01:53: But the master theory that unifies those last two has so far eluded us.
 01:58: ... come up with dynamical laws that describe all of nature  a mechanistic theory of ...
 02:15: One such approach is constructor theory, developed by David Deustch and Chiara Marletto at Oxford University since 2012.
 02:31: In constructor theory, the fundamentals are simpler  they are binary facts about whether or not a particular process is possible.
 02:40: ... uses theories like general relativity and quantum mechanics, along with more ...
 03:05: Constructor theory is inspired by information theory and the theory of quantum computation.
 03:11: ... process in physics, then all of physics can be expressed in terms of the theory of quantum ...
 03:54: ... constructor theory is about something called a counterfactual  which in constructor theory ...
 04:21: The power of constructor theory is that it allows us to explore physics without having to solve the detailed equations of motion.
 04:47: Before we get to how constructor theory is going to explain everything, let’s look at a simple example to define some of these concepts.
 05:18: In the constructor theory view, we ask what tasks are possible and impossible for the apple given its input state.
 05:57: This just serves to give an idea of the perspective shift in constructor theory.
 07:38: An aim of constructor theory is to formalise our statements about what is possible and impossible into a sort of “algebra of possibility”.
 07:47: At its heart, constructor theory is based on information theory and uses related tools like set theory in its formalism.
 07:58: ... means that constructor theory can be applied even when we don’t know the dynamical laws of a system  ...
 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.
 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.
 10:02: ... it pares down the facts that we need to assume about the mechanistic theory in order to make the argument  in this case, just the way informational ...
 10:15: ... Deustch has said that constructor theory may be the most fundamental way to describe reality  in which case the ...
 10:28: That’s a lofty claim, but consider how previous great theories emerged.
 10:42: ... general theory of relativity came from asking what were the inevitable implications of ...
 11:04: ... has called such efforts “antecedents” of constructor theory, which sounds presumptuous, but it gets to the spirit of the effort: to ...
 11:52: ... would be impossible, which in the language of constructor theory makes you a counterfactual. We are humbled and grateful ...


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 may be possible, while ...
 05:27: ... we’ve said before, his theory of special relativity explains that if you move faster than light, you ...
 07:45: ... the Schrodinger equation, which doesn’t incorporate Einsteins’s special theory of relativity and so has no speed limit baked into ...
 11:45: The spins were altered by pretty much the same amount that theory predicted they would be.
 12:02: The point is that the theory and the experimental tools are now converging on a way to answer our questions once and for all.


20211005: Why Magnetic Monopoles SHOULD Exist
 02:18: Well, according the classical theory we shouldn’t.
 03:54: ... not forbidden is compulsory." meaning that if the math of our physical theory allows it, then it exists in ...
 04:21: At least according to classical theory.
 04:26: ... quantum theory first appeared it quickly revolutionized our understanding of ...
 05:09: ... particular, the magnetic field emerging from the quantum theory must have zero divergence  its field lines can never end  so it can’t ...
 09:08: With that squared away, physicists were working to bring the strong nuclear force into the fold with the socalled Grand Unified Theories.
 09:37: ... in electroweak theory, the Higgs field is a scalar field  it takes on a numerical value ...
 09:55: In the simplest grand unified theory, the Higgs field has three degrees of freedom instead of two.
 10:55: And it turns out these knots in the Higgs field in GUT theories behave as massive particles with magnetic charge  magnetic monopoles.
 11:12: ... turns out that GUT theories generically predict these magnetic monopoles, and that they should be A) ...
 11:29: The fact that magnetic monopoles should exist in these theories was both exciting and problematic.
 11:54: This conflict with reality might have ruled out both monopoles and the grand unified theories that predict them.
 13:13: ... lower than is needed to produce the monopoles predicted by grand unified theories. ...
 13:42: Their discovery would mean cracking open the grand unified theories and revealing mysteries far beyond.
 17:56: Physicists hope to understand these things someday, perhaps with twistor or string theory.
 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.


20210907: First Detection of Light from Behind a Black Hole
 11:33: ... of the black hole  30 million Suns  to verifying Einstein’s general theory of ...


20210818: How Vacuum Decay Would Destroy The Universe
 08:30: ... For example, there may be weird fields within string theory that exist in false vacuum states. The decay of those could ...


20210810: How to Communicate Across the Quantum Multiverse
 02:29: ... of measurement, leaving only one reality; or de BroglieBohm pilot wave theory, which says that particles are particles and waves are waves  and the ...
 02:56: ... is perfectly consistent with the equation that lies at the heart of the theory  that’s the Schrodinger ...


20210803: How An Extreme New Star Could Change All Cosmology
 17:08: ... with a brutal analysis of the psychology of pseudoscience conspiracy theories. I will just say this: if electromagnetism really does govern everything, ...


20210713: Where Are The Worlds In Many Worlds?
 03:39: Quantum mechanics is a theory about waves.


20210707: Electrons DO NOT Spin
 04:40: ... and has all the weirdness you’d expect from the weirdest of theories. But before we dive into that weirdness, let me give you one more ...
 08:28: ... equation  in this case to make it work with Einstein’s special theory of relativity  something we’ve discussed before. Dirac wasn’t ...
 15:31: ... about quantum gravity and inflation and whatever other crazy theory we haven’t figure out yet. But what we do know is that at some ...
 17:29: ... named after Dr, Shannon, the founder of the field of information theory. As with many of these things, the word has been corrupted over ...


20210623: How Quantum Entanglement Creates Entropy
 00:27: ... supreme position among the laws of Nature... if your theory is found to be against the Second Law of Thermodynamics I can give ...
 03:45: ... it took the invention of information theory to really see the connection between information and entropy. It was Claude ...
 04:50: ... he first came up with this theory, though, Shannon didn’t fully realize its importance. As ...
 05:55: ... least incredibly powerful. It’s at the heart of quantum information theory, enabling us to calculate how much quantum information is contained ...


20210616: Can Space Be Infinitely Divided?
 10:55: ... scale  but we just don’t know in what way. We need a theory of quantum gravity to answer this. We’ll come back to what ...


20210525: What If (Tiny) Black Holes Are Everywhere?
 00:41: At least, that’s the black hole as it appears in the mathematics of Einstein’s general theory of relativity.
 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.
 04:49: At that point you need a proper theory of quantum gravity to describe the process.
 04:53: ... that theory, we have no way to describe the final stage of black hole evaporation  ...
 07:16: But assuming that they a[re allowed in the theory, are they also allowed in the real universe?


20210511: How To Know If It's Aliens
 14:35: ... covering comments from the last two episodes: our update on warp drive theory, and the one about whether dark matter can be explained by enormous ...
 14:48: ... pure general relativity, and we know for sure that GR is not our final theory of nature because it doesn’t perfectly gel with quantum mechanics. So ...
 18:32: ... to check. I like this a lot. Looking for dark matter in, say, string theory, before you check whether it’s black holes is like looking for your keys ...


20210421: The NEW Warp Drive Possibilities
 00:31: In 1915, Albert Einstein’s general theory of relativity revealed that the fabric of space and time is mutable and dynamic.
 02:30: His special theory of relativity just says that it takes infinite energy to accelerate anything with positive mass all the way to light speed.
 03:29: It’s a sp acetime geometry that is a valid solution to the equations general theory of relativity. The Einstein Field Equation.
 08:54: OK, let’s move on to the second paper by Erik Lentz: “Breaking the Warp Barrier: HyperFast Solitons in EinsteinMaxwellPlasma Theory”.
 10:53: ... assert for Alcubierre’s bubble  it can exist at superluminal speeds in theory, but there’s no known way to get it to those speeds in the first ...
 11:36: ... warp fields exist in theory, and there’s a very tentative hints that the worst dealbreaker can be ...
 12:37: They’ll continue to try to “make it so” by exploring Einstein’s theory  hoping to build starship, but in the process learning how our universe works.


20210413: What If Dark Matter Is Just Black Holes?
 00:44: ... are trying to find holes in Einstein’s theory of gravity  the general theory of relativity  that might explain dark ...


20210407: Why the Muon g2 Results Are So Exciting!
 00:00:  When a theory makes a prediction that disagrees with an experimental test.
 00:04: Sometimes it means we should throw that theory away.
 00:07: But what if that theory has otherwise produced the most successful predictions in all of physics.
 00:47: In fact, it doesn't play nice with Einstein's entire theory of gravity, which itself is clearly right in its own way.
 00:54: Our search for a theory of everything which will bring these theories together is perhaps the next great question physics.
 01:00: To find the path forward, we need to find glitches in these theories.
 01:11: These theories are woven pretty tight but there is one glitch, one stray thread that is just begging to be tugged.
 04:33: In this theory, electromagnetic interactions result from charge particles communicating by exchanging virtual photons.
 09:05: Until now, it had been measured precisely enough to claim a 3.7 sigma difference, compared to theory.


20210323: Zeno's Paradox & The Quantum Zeno Effect
 05:07: ... can be halted if you continuously measure the state  again, in theory. ...
 07:23: In theory, if these “measurements” are fast enough they should stop the wavefunction from evolving.


20210309: How Does Gravity Affect Light?
 00:28: That fact is guaranteed by Einstein’s general theory of relativity.
 01:17: ... assumed that Isaac Newton’s theory of gravity was the full picture, and that light behaves like any other ...
 07:31: Huygens’ wave theory of light advanced the field of optics enormously.
 09:41: As you might expect from a theory called “relativity”, stuff is relative.


20210224: Does Time Cause Gravity?
 00:34: ... as surely as 1+1=2 if we accept the two axioms of Einstein’s relativity theory: that the speed of light is constant for all observers, and that the ...


20210217: Gravitational Wave Background Discovered?
 00:00: ... particles well many maybe most physicists working in the area think a theory of quantum gravity will reveal that the gravity field spacetime ...


20210210: How Does Gravity Warp the Flow of Time?
 01:13: Einstein had his happy thought in 1907, a couple of years after he started his scientific revolution with the special theory of relativity.
 01:22: It took him another 8 years and a lot of help to grow this simple idea into his full theory of gravity  the general theory of relativity.


20210126: Is Dark Matter Made of Particles?
 05:52: ... a dark matter particle may be our best for finding a bigger, deeper theory than the standard ...
 06:25: The other delves deep into theory  in speculative mathematics beyond the standard model for signs of new particles.


20210119: Can We Break the Universe?
 00:09: ... was already rocking our understanding of the universe with his special theory of ...
 00:17: ... theory started with the simple assumption that the speed of light was the ...
 12:05: ... so we make sense of this deeply strange, but unfailingly selfconsistent theory of Einstein’s ...
 15:12: ... of Tokyo reported on a new experiment that helped validate this theory. ...
 15:40: This is the first time the flourescence has been directly observed, so it lends credence to the theory.


20210112: What Happens During a Quantum Jump?
 01:56: ... 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 observed ...
 03:14: ... quantum jumps, I am sorry that I ever had anything to do with quantum theory.” Schrödinger became bedridden with an illness during that visit  ...
 03:40: ... twopart essay titled “Are there quantum jumps?” wherein he compared the theory of quantum jumps to that of epicycles—the long dead theory about the ...
 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.
 09:47: And that transition appeared to be perfectly described by theory  in this case quantum trajectory theory.


20201222: Navigating with Quantum Entanglement
 02:52: ... theories have suggested that birds have iron structures in their beaks which help ...


20201215: The Supernova At The End of Time
 05:27: ... failed to incorporate the effects of Albert Einstein’s relativity theory, which predicted that the world looks very different to things traveling ...


20201208: Why Do You Remember The Past But Not The Future?
 12:23: ... highlights a real mystery with the big bang theory The distribution of matter and energy in the early universe does appear ...


20201118: The Arrow of Time and How to Reverse It
 09:39: ... not the future, we need to delve deeper. In fact it involves information theory and quantum entanglement, so we need another episode. Or more than one. ...
 10:20: ... now we’re looking at comments from the last two episodes  electroweak theory and our discussion on free will in ...
 10:34: ... electroweak theory Marik Zilberman has a really good comment. If the current fundamental ...
 13:36: ... quantum electrodynamics, which comes from ontology: 1. A physics theory with a cool abbreviation is inherently better than a physics theory ...
 13:58: therefore Quantum electrodynamics is better than other physics theories.


20201111: Can Free Will be Saved in a Deterministic Universe?
 10:42: You can get this sort of singular hard determinism with things like DeBroglieBohm pilotwave theory.


20201104: Electroweak Theory and the Origin of the Fundamental Forces
 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.
 04:02: Anyway, this new gauge theory of the weak interaction seemed to be okay with parity violation, and it wasn’t only accurate at low energies.
 04:28: At least assuming that the symmetries of gauge theory remain intact.
 04:44: To get all of this we need to do a quick recap of what a gauge theory actually is.
 05:54: So that is gauge theory in a nutshell: it explains a force by imposing symmetries on the equations of motion.
 07:56: Quantizing this field gives 3 bosons which are *almost* exactly what we need to make a gauge theory of the weak field work.
 14:10: ... because it causes unreconciled conflicts with other physics  quantum theory in this ...


20201027: How The Penrose Singularity Theorem Predicts The End of Space Time
 00:00: ... is much deeper  it leads us to the limits Einstein’s great theory and to the origin of the ...
 00:34: ... holes have haunted our theories of gravity since the 1700s. When John Mitchell and ...
 01:17: ... often than not they turn out to be a glitch in the theory. Einstein himself doubted that the black holes could form in the ...
 03:18: ... out how to describe a rotating black hole in Einstein’s theory. In it, the central point of infinite gravity is spun out into ...
 03:38: ... new advances in general relativity, half a century after the theory was ...
 11:10: ... should be dubious when we see infinities and singularities in our theories. Penrose showed us that singularities are unavoidable ...
 13:38: ... equation. Other interpretations  Copenhagen, pilot wave theory, etc. actually add things to the pure evolution of the ...


20201020: Is The Future Predetermined By Quantum Mechanics?
 00:00:  Einstein's Special Theory of Relativity combines space and time into one dynamic unified entity, spacetime.
 11:10: ... should make an honorable mention de BroglieBohm pilot wave theory, This is an entirely deterministic interpretation that doesn't have ...
 11:27: ... universe of pilot wave theory is really a block universe but unfortunately, no one has convincingly ...
 11:51: So does the future already exist according to quantum theory?


20201013: Do the Past and Future Exist?
 05:53: ... his special theory of relativity, Einstein showed that there’s no absolute way to define ...


20200928: Solving Quantum Cryptography
 15:06: The theory just isn’t there.
 15:35: Well, first let me say that magnetic monopoles may well exist  in fact mainstream grand unified theory candidates routinely predict them.


20200921: Could Life Evolve Inside Stars?
 12:12: ... tor Sabine’s own words read the book and check out our Theories of Everything livestream from a month ago, also with Lee Smolin and Eric ...
 12:21: ... the importance of mathematical beauty, by some, perhaps by many, in the theoryofeverything ...
 13:43: ... the epicycles in Ptolemy’s theory, Ry706 says “adding epicycles upon epicycles can represent any motion is ...


20200908: The Truth About Beauty in Physics
 00:37: ... been argued that modern theoretical physics, and in particular string theory, has been overly transfixed by the allure of beauty for decades, and that ...
 06:45: ... a good time for a quote from Einstein himself: “The supreme goal of all theory is to make the irreducible basic elements as simple and as few as ...
 08:58: Nobel laureate physicist Frank Wilcek talks about a form of mathematical beauty that he calls the exuberance of a theory  its productivity.
 09:42: ... off a roof, or a photon bouncing between mirrors  but the resulting theory predicts black holes, gravitational waves, and even the big ...
 10:01: ... couple of years after Einstein presented his general theory of relativity  Weyl found a simple, elegant way to unify Einsteinian ...
 10:22: But Weyl’s theory made some predictions that simply did not reflect the real universe  ultimately it was just plain wrong.
 10:29: ... had a hard time accepting that such a beautiful theory could be wrong, and he modified his idea to fix the issues  added some ...
 10:44: So now we come to string theory.
 10:46: The first compellingly beautiful aspect of string theory is that gravity, in the form of the Einstein field equations  automatically emerged from it.
 10:54: But there are other things too  for example, disparate versions of string theory seem to miraculously converge into one master theory.
 11:15: So did string theory fall for the same sort of misguided obsession with beauty as did Weyl?
 12:11: And so perhaps the mathematical wonders of string theory DO reflect something true about reality, but we’re struggling with how to interpret it all.


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.
 01:43: ... solar eclipse expedition in which he verified Einstein’s new general theory of ...
 06:13: ... read and so she knew about some groundbreaking work in early quantum theory that she could use to decode the complex patterns of absorption lines in ...
 07:00: ... Indian astrophysicist Meghdad Saha had used early ideas in quantum theory to crack the ionization ...
 07:19: Saha and others began to apply this theory to stellar absorption lines.
 09:29: ... real”  that it was likely the result of not understanding the atomic theory of hydrogen and helium well ...
 10:20: ... what stars are made of, he and others were able to develop a detailed theory of stellar ...


20200824: Can Future Colliders Break the Standard Model?
 00:02: ... by omelet I mean a theory of everything, and by eggs I mean a billion billion subatomic particles ...
 00:47: The hope is that this will open the window to brand new physics  and perhaps break the current deadlock in our quest for a theory of everything.
 05:25: ... known particles and what we expect their masses to be from quantum field theory ...
 07:07: ... general, to get closer to a theory that unifies our understanding of the Standard Model’s motley zoo of ...


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


20200810: Theory of Everything Controversies: Livestream
 00:00: ... today from loop quantum gravity which is one of the founders to string theory to the foundations of quantum mechanics and the philosophy of physics ...


20200728: What is a Theory of Everything: Livestream
 00:00: ... it still relevant this conjecture to pursue these fanciful ideas about theories of everything and whether they exist so part of the motivation is to ...


20200720: The Boundary Between Black Holes & Neutron Stars
 01:04: ... waveform, and based on calculations using Einstein’s general theory of relativity, the masses of those bodies were ...
 07:19: ... not because our theories are wrong  it’s because the calculations required to understand the ...


20200708: Does Antimatter Explain Why There's Something Rather Than Nothing?
 04:48: ... asymmetry problem. So, if there exists some underlying more fundamental theory, maybe string theory for example, then CPT symmetry may no longer be a ...


20200622: Building Black Holes in a Lab
 11:04: ... holes. True Hawking radiation need not necessarily depend on a specific theory of quantum gravity. Proponents of this line of thought have triumphantly ...


20200608: Can Viruses Travel Between Planets?
 14:22: ... theory is modified newtonian dynamics  MONDS  in which gravity doesn’t drop ...
 14:44: ... from the stars and therefore can’t be due to just having the wrong theory of ...
 15:49: ... and for the most part that dependency agrees with socalled lifshitz theory, which is based on this altered vacuum energy ...
 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?
 01:18: ... the mysteries about why gravity works the way it does, our current theories still describe how gravity behaves remarkably ...
 01:28: ... general theory of relativity has a perfect track record predicting the behavior of ...
 01:37: But even Newton’s old theory works great in almost all situations.
 05:57: ... most famous example of compactified extra dimensions is in string theory, and in modern superstring theory there are 6 additional spatial ...
 06:10: ... the idea of compact extra dimensions is much older than string theory  first proposed by Oscar Klein in the 1920s as part of what became ...
 11:23: And while that may seem anticlimactic, it’s actually extremely useful, ruling out some theories and constraining the space of possibility from others.
 11:32: ... being able to probe the sizescale of the extra dimensions from string theory though, and so string theorists can keep on ...


20200511: How Luminiferous Aether Led to Relativity
 00:00: ... satisfied with the state of their science. The great edifice of physical theory seemed complete. A few minor experiments remained to verify everything. ...
 01:09: ... death of the aether helped open the way for the acceptance of Einstein’s theory of ...
 02:33: ... The Dutch physicist Christiaan Huygens developed a detailed mathematical theory around this idea that gravity results from the fluid dynamics of the ...
 04:06: ... was sitting in Cambridge making life difficult for Huygens. First his theory on universal gravitation conflicted with the predictions of Huygens’ ...
 11:42: ... of light and the Lorentz transformation are fundamental to his special theory of relativity, which was published 8 years after the MichelsonMorley ...
 13:18: ... that death helped spark the revolutions of relativity and then quantum theory that revealed a much weirder, but still totally luminiferous space ...


20200504: How We Know The Universe is Ancient
 03:09: ... makes perfect sense in the context of Einstein’s thennew general theory of ...
 04:40: ... Lemaître himself disagreed, stating: “As far as I can see, such a theory remains entirely outside any metaphysical or religious question.” So if ...
 07:07: ... years old! So there was a problem  but it wasn’t a problem with the theory, it was a problem with the observations. Edwin Hubble had got the ...
 16:59: ... loves crawling into boxes whenever possible, I assume to test quantum theory. Miraculously emerging definitely alive every time. She's become a pretty ...


20200428: Space Time Livestream: Ask Matt Anything
 00:00: ... know Astro 101 except for the fact that I dearly love these old wrong theories I think they're so colorful and cool you know the the one electron ...


20200422: Will Wormholes Allow Fast Interstellar Travel?
 01:09: ... along with Nathan Rosen, expanded on Flamm’s idea  but not into a theory of wormholes  instead as a theory of particles. Einstein and Rosen ...
 14:59: ... matter interactions with the black hole. I'm afraid I don't know of any theory of dark matter that would do that. But who knows  dark matter is weird. ...


20200414: Was the Milky Way a Quasar?
 09:12: Unfortunately, there’s a problem with this theory too.
 09:43: So what  two nice theories and neither of them work?
 15:12: ... Current theories on the creation of the Universe state that, if it was created at all and ...


20200407: How We Know The Earth Is Ancient
 03:30: ... can thank Hutton and his 1788 book the Theory of the Earth for opening scientific eyes to the possibility of an ...
 05:38: ... ideas gave Darwin the millions of years he needed for his theory of evolution, and its painfully slow mechanism of natural selection. But ...


20200331: What’s On The Other Side Of A Black Hole?
 01:53: ... just a couple of months after Einstein published his general theory of relativity. It allows us to calculate the path of an object moving in ...


20200324: How Black Holes Spin Space Time
 00:21: ... months after Einstein presented his complete general theory of relativity in 1915, a young German physicist named Karl Schwarzschild ...
 05:14: ... B measured the Earth’s frame dragging and it was exactly as Einstein’s theory predicted  incredibly weak in Earth’s case. But in the case of a Kerr ...


20200316: How Do Quantum States Manifest In The Classical World?
 15:05: One exciting new course is the Theory of Everything hosted by our friend, Dr. Don Lincoln.
 15:11: ... learn what cutting edge science is doing to reconcile these two great theories. ...


20200218: Does Consciousness Influence Quantum Mechanics?
 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.
 01:25: Today we’re going to see where this idea comes from, and whether quantum theory really supports it.
 06:01: Another of the greats of early quantum theory agreed with him.
 09:40: ... you don't understand quantum mechanics." The more you know about this theory, the less likely you are to pretend you fully understand its deepest ...
 10:01: ... tend to be made by people who have never studied the theory deeply, but nonetheless have great surety in cherrypicking and ...
 12:09: ... Measurement Problem  at least not with full consensus, modern quantum theory has come a very, very long way since its ...


20200211: Are Axions Dark Matter?
 03:02: ... weaker than predicted by a CPviolating QCD. This discrepancy between theory and experiment is known as the strong CP problem and is currently ...
 03:59: ... how can a vacuum, aka “nothing” have structure? Well, in quantum field theories, the vacuum isn’t really nothing. “Vacuum” is the word we use to describe ...
 06:54: ... you might recall that in quantum field theory a particle is just an oscillation in a quantum field. So with a new ...
 08:45: At least in theory  so far several experiments have not confirmed axions this way, at least so far.


20200203: Are there Infinite Versions of You?
 12:19: ... and then we'll do our episode on quantum hacking with the smatrix theory. ...
 12:29: Ilavenya rightly points out that no nice analytical solutions to the 3body problem exist in general relativity  Einstein's modern theory of gravity.
 14:48: But in smatrix theory and quantum field theory, time and space in the interaction region are fuzzy.
 16:21: ... in our 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: ... insights, with the final result being the birth of modern quantum theory and first complete formulation of quantum mechanics  matrix ...
 02:16: ... search for the underlying clockwork of reality led to quantum field theory, in which all particles are described by vibrations in elementary fields ...
 02:41: Early quantum theory was plagued by problems  for example, how do you compute infinite interactions?
 02:55: ... clever hacks  perturbation theory and renormalization  worked in many cases to tame the infinities and ...
 03:50: ... and time should break down at those scales, and our even best field theory hacks seemed to ...
 04:10: ... atomic nucleus  not by modeling all the cogs and wheels of the field theory of the internal nucleus, but rather by understanding the observables ...
 05:52: ... the Smatrix and his antireductionist philosophy and developed Smatrix theory. ...
 06:47: Remember, that quantum field theory fastidiously adds together a complete set of virtual interactions that contribute to the real interaction.
 06:56: ... theory sought to avoid this, and instead tries to model a scattering experiment ...
 07:23: But in order to avoid those sums of Feynman diagrams, Smatrix theory also relies on symmetries between those virtual interactions.
 08:28: In regular quantum field theory you’d need to add up all the different versions of both these two channels separately.
 09:30: So Smatrix theory looked extremely promising … until it didn’t.
 09:35: It presented severe challenges on par with those plaguing quantum field theory  and, as it happened, physicists solved the QFT challenges first.
 10:10: ... the results was that Smatrix theory was sidelined, and quantum field theory reigns supreme to this day as ...
 10:41: Quantum field theories like QCD surely gives us insights into the nature of the fundamental workings of the universe.
 10:47: ... their astounding predictive success, Smatrix theory now seems less fundamental  it seems like an emergent set of ...
 11:05: So I said that Smatrix theory got sidelined  that’s not exactly true.
 11:35: ... so string theory was born  at first as a description of strong nuclear force ...
 11:48: So our leading, and perhaps only current contender for a theory of everything was first derived as a bootstrap model, an Smatrix theory.
 12:56: ... doesn’t just eliminate the fiddly mechanics of quantum field theory, it removes the very concepts of space and ...
 16:28: But you should take all of this with a grain of salt; as rjw elsinga notes: there are a lot of holes in this theory


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.
 04:27: Perhaps the configuration of the geometry string theory’s extra dimensions gets shifted  this would do the job.
 10:33: Now perhaps the extra .17 can be factored into the uncertainties of the theory...


20191209: The Doomsday Argument
 01:57: ... number of theories in physics from string theory to eternal inflation predict that the ...


20191202: Is The Universe Finite?
 02:59: Albert Einstein’s general theory of relativity allows for three simple geometries for our universe.
 12:12: If you want to dive deeply into understanding the building blocks of space time then you need to study quantum theory.
 12:25: Honestly, the best way to wrap your head around quantum theory is to play with it.
 12:30: ... of physics, and systems of measurement based on the algebra of quantum theory. ...


20191118: Can You Observe a Typical Universe?
 17:37: If it can't be solved then we should ultimately dismiss the theory.


20191111: Does Life Need a Multiverse to Exist?
 00:43: We can’t determine the values of these constants from pure theory  we have to measure them in the real universe.
 01:02: ... the general theory of relativity and the standard model of particle physics, there are ...
 01:24: Or perhaps they’re connected and controlled by some master dial or dials  whose nature awaits discovery in the longsought theory of everything.
 09:29: ... is, when we try to calculate the strength of this vacuum energy from our theory we get an enormous number  10^60 to 10^120 larger than actually seems ...
 11:24: ... example we have string theory: this candidate theory of everything suggests that the values of the ...


20191104: Why We Might Be Alone in the Universe
 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.
 12:39: The strings of string theory have a somewhat physical interpretation  the fact that they can hold energy and vibrate and exist in space.
 13:48: And this was NOT observed in the light from a distant gamma ray burst, which presents a challenge for the theory.


20191021: Is Time Travel Impossible?
 00:41: ... special and general theories of relativity changed the way we think about time forever, and believe ...
 03:00: This is an example where the equations of a theory technically allow something to be true, but there’s still no good reason to believe that it is.
 03:16: ... we still have the general theory of relativity, which incorporates special relativity, but also explains ...
 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 ...
 11:47: Approximate theories can make bad predictions – like the possibility of time travel.


20191015: Loop Quantum Gravity Explained
 00:06: And can it really defeat string theory in our quest for a Theory of Everything?
 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 ...
 00:42: But string theory isn’t the only game in town  or so some physicists believe.
 00:47: ... to reconcile 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 ...
 01:46: ... mechanics, and indeed most theories in physics, involve a set of equations describing how stuff moves ...
 02:54: In string theory, a type of background independence emerges in an abstract space of moving strings and with that comes a gravitational field.
 03:24: The challenge really gets us to the fundamentals of what a quantum theory actually is.
 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.
 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.
 06:52: A contender for a theory of quantum gravity.
 08:47: In this formalism, the “space of metrics” looks just like a space of fields in quantum field theory.
 10:03: It’s general relativity – our modern theory of gravity – cast in terms of very abstract building blocks.
 11:20: ... theory has some other successes, for example, the theory seems to predict ...
 11:31: However there are also many who identify serious, fundamental issues the theory.
 11:54: ... generally, for this theory to be successful it needs give you the equations of good old general ...
 13:16: Loop quantum gravity is an intriguing alternative to the more popular string theory.


20190930: How Many Universes Are There?
 07:20: People have also invoked the anthropic principle plus eternal inflation to explain a conundrum in string theory.
 07:27: ... we’ve talked about before, modern string theory is difficult to pin down because there are countless possible ...


20190903: Is Earth's Magnetic Field Reversing?
 05:21: And dynamo theory not only explains geomagnetism, but also why Earth’s field sometimes reverses its polarity.


20190819: What Happened Before the Big Bang?
 00:43: These days, the best accepted description of the time before the Big Bang is given by inflation theory.
 01:07: ... further back in time and explore a stunning implication of inflationary theory. ...
 05:49: Now, the behavior of this field depends on some unverified physics But a suitable inflaton field fits with some grand unified theories.
 05:59: Those are theories that combine the strong nuclear force with electromagnetic and weak forces.
 06:04: As well as theories which also unify gravity, like string theory.
 06:09: These theories predict phase transitions in the behavior of fields as the temperature of the universe changes.
 06:23: Very flat potential energy slopes are also possible in these theories, enabling slow roll inflation or a combination of both.
 06:32: ... more episodes, so, for now take my word for it that inflation fits some theory even if that theory is also entirely ...
 10:04: ... are also deep possible connections between inflation and string theory and with the holographic principle, as described in one of Stephen ...
 12:15: ... the standard Big Bang Theory doesn't explain the initial expansion at all, it includes an expansion ...


20190806: What Caused the Big Bang?
 02:26: First up, the equations of Einstein's general theory of relativity.
 02:31: Our modern theory of gravity can be used to predict the behavior of the universe as a whole.
 04:42: We need some quantum physics. In fact, we need some quantum field theory.


20190718: Did Time Start at the Big Bang?
 00:25: ... and Vesto Slipher, combined with Einstein's  then  brandnew general theory of relativity, revealed that our universe is expanding and if we reverse ...
 01:22: ... keep changing their minds  they don't know anything", or "the Big Bang Theory is just a theory" Let me be very clear, the evidence for a hot dense ...
 01:56: ... growth spurt solves a couple of the big problems with the Big Bang Theory, but it doesn't change the fact that Rewinding the expansion of the ...
 08:14: ... Any time you encounter a singularity in the mathematics of a physical theory you have good reason for skepticism It's probably telling you that your ...
 09:52: ... isn't anywhere near enough matter to do that unless we bring in string theory the SteinhardtTurok model suggests that our universe floats in a higher ...


20190715: The Quantum Internet
 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.
 01:09: ... plainold nonquantum information theory  the study of the creation, storage, and transmission of information, ...
 01:21: ... Shannon started it all with his 1948 paper “A Mathematical Theory of Communication”, which quantified the rate of digital information that ...
 01:37: ... theory has since blossomed into a full science, ultimately connecting the ...
 01:49: Quantum information theory parallels classical information theory, but instead of using classical bits, it deals bits of quantum information  qubits.


20190509: Why Quantum Computing Requires Quantum Cryptography
 00:22: Quantum theory may seem like an obscure subject of questionable relevance to the average person.
 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.


20190501: The Real Science of the EHT Black Hole
 08:55: ... the addition of the warped spacetime of a black hole using Einstein’s theory of general ...
 10:17: ... the black hole looks just like we predict based on Einstein’s general theory of ...


20190424: No Dark Matter = Proof of Dark Matter?
 00:03: ... to an unknown source of gravity but due to a failure of gravitational theory itself the first such proposal was Mons modified Newtonian dynamics ...


20190410: The Holographic Universe Explained
 01:02: We’ve moved from quantum field theory to black hole thermodynamics to string theory.
 04:06: ... laid out the first steps towards how this could be achieved using string theory, but ultimately it was Juan Maldacena who figured out a concrete string ...
 04:26: Let’s ignore string theory for the moment and just think about how to create an extra dimension.
 04:45: Those rules are a field theory, the lattice itself is the field, and the cells are some elementary component of the field.
 05:08: Probably the rules between cells – the field theory – depends on this scale.
 05:33: We’re going to say our field theory is scaleinvariant.
 05:53: We also see it in string theory, which I’ll come back to.
 05:57: A field theory with this property is called a conformal field theory.
 06:09: A conformal field theory has this property.
 06:25: By making this a conformal field theory we’ve added a symmetry –invariance under local changes in scale – also known as Weyl invariance.
 07:42: But for the details we need string theory.
 07:47: Even from the beginning string theory had hints of this scale invariance and dimensional weirdness.
 07:54: ... first iteration of the theory, around 1970, tried to model the strong force between pairs of quarks – ...
 08:44: This and other glitches led to string theory being abandoned as a model for the strong force.
 08:49: ... it was quickly rejigged to make it a theory of quantum gravity, and the scale invariance of the strings becoming a ...
 09:02: We now have a several versions string theory that try to explain how vibrating strings can lead to the familiar particles of this universe.
 09:10: These were tentatively united by Ed Witten’s Mtheory, which showed that different types of string and string theories were all related by dualities.
 09:19: A duality is when two seemingly different theories prove to represent the same underlying physical reality.
 09:52: Maldecena imagined a set of string theory objects called branes.
 10:23: ... a Minkowski spacetime of 3+1 dimensions on which their lived a field theory that arose from interactions between ...
 10:37: ... itself that field theory wasn’t stringy– rather it was a quantum field theory like the ones that ...
 10:49: It was also a conformal field theory – a CFT  so it was invariant to the scaling of grid sizes.
 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.
 11:38: As with the other dualities in string theory, this one was extremely useful for calculations.
 11:46: ... interactions in the lower dimensional field theory are extremely strong – we would say the fields are strongly coupled  ...
 12:37: The lower dimensional CFT space is the surface of the AdS space because the field theory exists where the new dimension becomes infinite.
 13:23: The rules of interactions between cells on the surface is a quantum field theory.
 13:28: But those rules translate to interactions in the volume – in the bulk – and there they are a theory of gravity.
 15:28: ... AdS/CFT correspondence, the volume exhibits gravity via a type of string theory, while the surface exhibits no gravity  only a quantum field theory ...
 16:20: That surface contains only a conformal field theory and no gravity.


20190403: The Edge of an Infinite Universe
 02:29: At least the three basic types described by Einstein’s general theory of relativity.
 07:16: Only lightspeed paths – or in the language of quantum field theory “massless fields” can access these diagonal boundaries.
 14:04: ... realized that if you define a conformal quantum field theory in a 3+1dimensional Minkowski space, that corresponded to an ...
 14:20: That structure looked exactly like a string theory with gravity and everything.
 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.


20190328: Could the Universe End by Tearing Apart Every Atom?
 00:25: ... with the cosmological constant in the equations of Einstein's general theory of relativity but what if dark energy is not constant what if the energy ...
 14:16: Sounds cool, but be cautious of theories that seem crafted to give happy endings.
 14:28: I'm guessing the save the universe theories are more numerous than their plausibility warrants.


20190220: Secrets of the Cosmic Microwave Background
 07:42: ... and that gives us the exact physical size that we expect from our theory from our standard ruler then that's a good indication that our universe ...


20190207: Sound Waves from the Beginning of Time
 14:12: ... isn't a hard rule, it's a good guiding principle to be dubious of new theories that contradict extremely well tested old ...
 14:33: Remember that things like general relativity and much of quantum field theory are verified to stunning precision.
 14:39: If a new theory says, "Nuhuh, that all wrong", it better be able to also explain how those theories appear to be so right while being wrong.
 14:49: ... scientists sort through the overwhelming flood of poorly thoughtout "theories" that they get bombarded with all the ...


20190130: Perpetual Motion From Negative Mass?
 03:48: ... the risk of getting way too technical, this is also what quantum field theory predicts: fields with even spin have to work in the opposite way to ...
 05:47: ... of a much more complete description of gravity: Einstein’s general theory of ...
 10:10: With this sort of highly speculative science, you really have to dig down and look at the assumptions in ALL of the theory.
 12:23: I’m pretty sure that breaks quantum field theory as well as general relativity.


20190124: The Crisis in Cosmology
 14:57: When a theory leads to these  sort of  pathological predictions, it's a big red flag.
 17:42: Mr. Nation [?] has his own unified theory of the Dark Sector.


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: ... and time and this symmetry lies at the foundations of quantum field theory physics must work the same if we flip all of these properties if not ...
 03:02: ... the 1950s was also the decade of the foundations of quantum field theory an SQFT emerged it became clear that there is a certain symmetry that's ...
 13:52: ... version of Canada. The last episode before the break was, "Why string theory is Wrong". Today, I want to address the comments to that episode or ...
 15:29: ... it provides an answer to the hierarchy problem and gives us super string theory it will be odd if supersymmetry existed as part of super string theory ...
 16:06: ... other point is that the large undefined parameter space of string theory  the so called 'String landscape' is no more of a problem for string ...
 16:49: ... FieldStrength's final point is that the untestability of string theory is connected to the extreme energy scale of quantum gravity and that ...
 17:15: ... yeah string theory is apparently not yet testable, but I disagree with those who say that ...


20190109: Are Dark Matter And Dark Energy The Same?
 00:10: But perhaps one astronomer has just fixed it, with a theory that says perhaps actually they are they same stuff.
 00:58: Farnes 2018, “A unifying theory of dark energy and dark matter: Negative masses and matter creation within a modified LambdaCDM framework”.
 01:08: As with any new theory combining dark matter and dark energy, probably it helps to know what they are first.
 02:25: According to Einstein’s general theory of relativity, any such positive energy produces an inwardpulling gravity.


20181220: Why String Theory is Wrong
 00:07: There's this idea that beauty is a powerful guide to truth in the mathematics of physical theory.
 00:13: String theory is certainly beautiful in the eyes of many physicists, but is it beautiful enough to pursue even if it's wrong?
 00:35: Weyl had tried to explain electromagnetism by imposing on Einstein's general theory of relativity.
 00:57: But sometimes it can be hard to let go of the sense that a beautiful theory must be right.
 01:03: Could this also be the case with string theory?
 01:06: ... particular case of a quantum string, which is part of what got string theory going in the first ...
 01:18: We talked about this in detail in our episode on why string theory is right.
 01:23: Which itself was a sequel to our primer on the basics of string theory.
 01:27: In those episodes, we saw some of the remarkable ways that string theory promised to converge on a theory of everything.
 01:35: ... umbrella, and there's also the convergence of many versions of string theory into a single picture with a very specific number of extra dimensions. ...
 01:55: ... promise of being so right do more and more physicists think that string theory is after all either woefully incomplete or just plain ...
 02:07: Modern string theory is the convergence of many beautiful ideas in physics, each of which feel right in their own way.
 02:14: ... see where string theory ultimately fails, we need to rewind to look at some of these a bit ...
 02:27: In 1919, not long after Einstein published his great theory of gravity, Theodor Kaluza discovered something strange.
 03:37: Klein realized that you can get a sensible quantum theory if you compactify that extra dimension.
 03:52: In the resulting in Kaluza–Klein theory, the fifth dimension is looped into a tiny circle.
 04:36: Probably wrong, and it's not the only problem with the first version of Kaluza–Klein theory.
 04:57: These may have seemed like fatal flaws, but we can thank this wrongness for the later development of string theory.
 05:12: There are many KaluzaKlein inspired theories out there.
 05:16: String theory is just the most famous.
 05:18: So, start with KaluzaKlein, add vibrating strings and exactly the right extra special dimensions, and you have string theory.
 05:40: It also introduces fermions to the boson only version of string theory to give super string theory.
 06:03: Superstring started out with incredible promise, and so there was a proliferation of different versions of super string theory.
 06:59: The various superstring theories exhibited what we call dualities.
 07:04: A duality in physics is when two apparently different mathematical theories proved to represent the same physical process.
 07:12: These dualities reveal that certain classes of string theory were actually the different ways of expressing exactly the same theory.
 07:20: Perhaps there was a glimmer of hope for these divergent versions of string theory after all.
 07:25: ... looks like, let's go back to the good old simplicity of Kaluza–Klein theory, or at least at the simplicity of just one extra circular spatial ...
 09:07: ... you can construct a theory in which momentum increases with the size of the compact dimension, or ...
 09:19: ... sounds weird but this may just have saved string theory. I just described a type of duality, in this case tduality, short for ...
 09:48: Tdualities prove that some of these different versions of string theory are actually different expressions of the same theory.
 09:54: The other main type of duality in string theory is sduality, strongweak duality.
 10:18: Sduality provided the final linchpin that demonstrated that the five different types of string theory were all manifestations of the same theory.
 10:31: ... a string conference in '95, Witten showed that the disparate string theories were all just different perspectives, different limits or special cases ...
 10:42: This was mtheory, where M stands for really what have you want it to: membrane, magic, mother theory.
 10:51: ... to Witten is to be decided when the full nature of the theory is understood. We'll come back to Mtheory in real detail, but the ...
 11:08: So whereas the original superstring theories were ten dimensional with six compactified, Mtheory is 11D, with seven hidden dimensions.
 11:24: Whoa Well, that all sounds a bit arbitrary. Your theory not working? Just add an extra dimension.
 11:32: Actually, the realization that superstring theory could be 11 dimensional was a revolution. It sparked the second superstring revolution.
 11:41: See, in parallel to the development of super string theory, other physicists have been working on super gravity.
 11:49: ... gravity should be the low energy, largescale limit to super string theory. So it was incredibly exciting that string theory appeared to have an 11 ...
 12:14: ... convergence of the superstring theories with each other and with super gravity restored the sense of beauty to ...
 12:36: It's not solvable using perturbation theory, which doesn't leave much room to explore its implications.
 12:43: In all superstring theories the extra spatial dimensions are wrapped, not in simple loops, but in complicated geometries called CalabiYau manifolds.
 13:00: For example, sections of these manifolds that can be approximated as simple tubes, like in KaluzaKlein line theory.
 14:00: Essentially all string theories require supersymmetry in order to work.
 14:16: But string theories are still rightly concerned. Their elegant theory which was converging so beautifully has stalled.
 14:34: ... general relativity was wrong, but it inspired the entire field of gauge theory upon which much of our understanding of the quantum world ...
 15:00: ... wrong or incomplete as current string theory may be, it may also be the inevitable early step as we seek an even more ...
 15:14: ... the physics required to understand string theory is tough thankfully there are online tools that can help like brilliance ...


20181212: Quantum Physics in a Mirror Universe
 00:02: ... to seem heavily and yeah we'll be covering that after we do why string theory is wrong because you guys haven't stopped complaining that it isn't up ...


20181121: 'Oumuamua Is Not Aliens
 15:28: Well, actually, modern string theory relies on supersymmetry so it's already included.
 15:34: Was it called Ting theory before that?
 15:37: Actually, the name string theory originally applied to what we call bosonic string theory.
 15:51: The result is superstring theory.
 15:53: And these days some form of superstring theory is implied when people talk about string theory.


20181114: Supersymmetric Particle Found?
 00:03: ... Hadron Collider running out of places to look for clues to a deeper theory of physics, we're going to need a bigger particle ...
 00:28: Historically, no matter how crazy our theories got, there were always new ways to test them.
 00:34: Your theory predicts a new particle.
 01:02: There must be a more fundamental theory that explains the origin of this rich family of particles.
 01:08: Proposals for such grand unified theories proliferate unconstrained by even the tiniest hint of new physics from the LHC.
 01:17: One potentially very important ingredient for grand unification theories is supersymmetry.
 01:30: ... extension to the standard model, designed to fix certain issues with the theory, the most serious issue being that the standard model can't explain the ...
 02:08: It's a key feature in some grand unified theories as well as modern string theory, leveling it up to superstring theory.
 12:33: ... below to subscribe to "Two Cents." Last week, we talked about why string theory is so compelling to so many ...
 12:51: Many of you have some interestingly passionate hate for string theory on the grounds that it's so far proved unfalsifiable.
 13:04: String theory may be wrong, but it's not testable due to the limits of current facilities.
 13:25: The thing that makes string theory less sciencey is that its modern version, Mtheory, is not particularly welldefined.
 13:39: String theory is not precise enough yet to be confirmed wrong, which means it might be right or not.
 14:24: So how can you get world sheets?" Yes, it is a pain keeping the number of dimensions straight in string theory.
 14:47: So yeah, the math of string theory only works for 1D objects because these trace 2D world sheets.
 15:32: But this has no bearing on the compactified extra dimensions of string theory.
 16:06: And to end on a funny, Dash to the Max points out that string theory is literally like playing a sad song on the world's smallest violin.
 16:16: And if it proves wrong in the end, at least we have the perfect instrument for a requiem to string theory.


20181107: Why String Theory is Right
 00:06: ... see string theory as the one great hope for a theory of everything that will unify quantum ...
 00:20: Others see string theory as a catastrophic dead end, one that has consumed a generation of geniuses with nothing to show for it.
 00:29: So why are some of the most brilliant physicists of the past 30plus years so sure that string theory is right?
 00:37: [MUSIC PLAYING] Why has string theory been the obsession of a generation of theoretical physicists?
 00:59: ... short, the strings of string theory are literal strands and loops that vibrate with standing waves simply by ...
 01:21: In this episode, I'm going tell you why string theory is right, at least why so many of those geniuses think it is.
 01:52: I also want to give you a teaser on why string theory is actually wrong.
 02:01: The greatest criticism of string theory is that it's never made a testable prediction.
 02:06: ... space of possible versions of string theory is so vast that nothing can be calculated with certainty, so string ...
 02:22: They might say, maybe half jokingly, that string theory does make one great prediction.
 02:41: But the fact is when you start to work out the math of string theory, gravity appears like magic.
 02:47: You don't need to try to fight gravity into string theory.
 02:50: ... it will be difficult to remove it, and the quantum gravity of string theory is immune to the main difficulty in uniting general relativity with ...
 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 bolts ...
 03:40: In quantum theories of gravity, the gravitational force is communicated by the graviton particle.
 04:22: OK, let's switch to string theory where particles are not points.
 05:06: ... illustrate why quantum gravity isn't hopelessly broken in string theory, and that's a huge point in favor of string theory, but these world ...
 05:20: And this is the second point in string theory's favor.
 05:22: ... out that tiny vibrating quantum strings automatically reproduce the theory of general relativity and, in the same mechanism, seem to promise to ...
 05:39: This stuff appears a little too naturally in the math of string theory to be a coincidence, or so a string theorist might tell you.
 06:36: A while ago, we talked about Paul Dirac developed a wave equation for the electron that took into account Einstein's special theory of relativity.
 08:11: So, we expect the phase of the quantum wave function to be a gauge symmetry of any quantum theory.
 09:02: ... turns out that exploring a very different symmetry of string theory both makes it possible to quantize the theory and gives us a very ...
 09:14: So, like I was saying, when we try to quantize string theory, of course it's a huge mess.
 09:43: Hermann Weyl actually came up with this symmetry right after Einstein proposed his general theory of relativity.
 11:44: ... you use string theory to write down the gravitational field in what we call the lowenergy ...
 11:57: ... right particles, including the graviton and the photon, out of string theory for a very specific number of spatial dimensions, nine to be ...
 12:11: In fact, if string theory makes any predictions, it's the existence of exactly this number of extra dimensions.
 12:18: And this is where string theory starts to look less attractive.
 12:25: ... that seems like a hell of an extra thing to add in order to make your theory ...
 12:43: And that's just the first of many problems of string theory.
 12:49: ... were lead to string theory by the elegance of the math and the fact that it appeared, at least in ...
 12:58: ... convergence is also seen in the union of different string theories by M theory and in the discovery of AdS/CFT correspondence again, for ...
 13:26: Perhaps we're now overly distracted by the elegance of string theory.


20181031: Are Virtual Particles A New Layer of Reality?
 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 can do quantum ...
 02:01: So quantum field theory is the machinery behind the standard model of particle physics.
 02:57: That's where perturbation theory comes in.
 04:58: ... diagrams are an absolutely essential tool in most modern quantum field theory calculations, but they also add to the misconception about virtual ...
 12:08: ... of virtual particles came about as a calculation tool in perturbation theory as we tried to approximate the behavior of quantum ...
 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.
 12:59: That will be the family of lattice field theories in which spacetime itself is defined on discrete grid.
 13:05: It doesn't rely on perturbation theory, and so it doesn't use virtual particles while ultimately giving the same results.


20181025: Will We Ever Find Alien Life?
 13:18: Last week we dipped our toes into string theory.
 13:38: Add it to string theory and you get superstring theory.
 13:47: Now, the details are way beyond a comment response, but look into superstring theory and supersymmetry.
 13:54: ... response to me saying that string theory has only one tunable parameter, Michael Murphy sarcastically points out ...
 14:43: Korbus Barkly and some others ask whether, if string theory makes no testable predictions, shouldn't it be just called string hypothesis?
 15:05: ... scientific theory is an explanation of an aspect of the natural world that can be ...
 15:20: ... actually we've always used the word theory to mean again, quoting Dr. Diagrams some framework that, loosely ...
 15:41: ... to put another way, in colloquial science speak, a scientific theory is a welldeveloped suite of ideas, laws, models, and predictive tools ...
 16:01: ... no separate word for a theory that's not wellaccepted, but there's still a huge difference between ...
 16:13: A scientific theory is selfconsistent and welldeveloped.
 17:13: [INAUDIBLE] wonders why M theory is represented by five interlocking Pringles.
 17:18: Well, rumor has it that Ed Witten came up with M theory while he was eating Pringles late one night.
 17:25: He was struck by the potential of multidimensional Pringles to unify string theory.


20181018: What are the Strings in String Theory?
 00:07: You may have heard the usual pop psy description of string theory.
 01:10: So surely there exists a deeper set of cogs and wheels, a theory that brings all observable phenomena into the same mechanical framework.
 01:20: That would be a theory of everything, and this is the great hope of string theory.
 01:26: In the following episodes, we're going to explore the gory details of string theory.
 01:32: But today it's String Theory 101.
 01:45: What exactly are the strings of string theory?
 01:48: First let's do a quick primer on the origins of 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.
 02:46: ... of the reasons this strong force version of string theory got stuck is that it predicted the existence of unexpected and unwanted ...
 03:45: What if the math of this theory could be used in a theory of quantum gravity?
 04:20: This was socalled Bosonic string theory.
 04:23: If it worked, it would have been a candidate for a grand unified theory combining all known forces.
 04:48: ... resulting superstring theory sought to become an allencompassing mechanism to explain the underlying ...
 05:05: ... in 1995, Ed Witten brought the many forms of superstring theory together into the single framework of mtheory, all for the low price of ...
 07:29: So this is the great promise of string theory.
 07:47: It sure sounds closer to a fundamental theory.
 08:51: These last properties are important because it gives a mechanism for the particles of string theory to interact and to decay into other particles.
 09:00: This picture of strings coming together jointly and splitting apart is a huge strength of the theory.
 09:31: String theory fixes this because the graviton is a loop, not a point particle.
 10:13: In fact, the theory only works in precisely nine spatial dimensions, plus one for time, plus one for M theory, which we'll come back to.
 10:34: It's a theory that works in a universe that is clearly not our own with its measly three dimensions of space.
 11:37: Voila, string theory is saved.
 11:40: Modern M theory proposes an additional large spatial dimension.
 11:54: ... theory unites different string theories because it demonstrates some ...
 12:19: In fact, the single free parameter in string theory becomes the configuration of the extra dimensions.
 12:43: Right now string theory appears to be at an impasse.
 13:08: In coming episodes, we'll look deeper into both the successes, the failures, and the profound weirdnesses of string theory.


20181010: Computing a Universe Simulation
 02:01: That includes most formulations of quantum mechanics and proposals for theories of everything.
 13:57: Science works by forcification, and null results rule out huge chunks of theory space, greatly advancing our certainty.


20181003: How to Detect Extra Dimensions
 05:15: Many would like to find a "theory of everything" which merges the forces of nature into the same über force.
 06:15: They're used in string theory, where they typically have a large number of dimensions.
 06:20: But in string theory, all but three spatial dimensions of the brane are inaccessible.
 06:55: ... your theory just right, and you get normal physics for matter and radiation in three ...
 07:59: ... on how you tweak the theory, gravity can obey an inverse square law on galactic scales, where it's ...
 11:16: This ruled out or constrained various alternative theories to general relativity.
 12:23: ... 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.
 12:50: ... theories of everything try to quantize gravity by placing it within the same ...
 13:00: These are grand unified theories.
 13:02: And string theories are an example.
 13:05: Other theories treat gravity very differently to the other forces.
 13:22: If spacetime is indefinitely divisible, then you get hopeless conflicts with quantum theory.
 13:45: So when you use perturbation theory to calculate an interaction in field theories, feedback effects give infinite loops of interactions.


20180920: Quantum Gravity and the Hardest Problem in Physics
 00:13: They must be united in a deeper, yet undiscovered, theory.
 01:00: And yet these two theories contradict each other in fundamental ways.
 01:12: ... begin our discussion of the great quest for this union, the quest for a theory of quantum gravity and for a theory of ...
 01:41: General relativity, GR, is Einstein's great theory of gravity.
 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: ... 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.
 08:38: That leaves no clean coordinate system on which to ground your theory.
 09:26: This type of selfinteraction or selfenergy is seen in other quantum field theories and is hard to deal with, even there.
 09:42: In QED, the mess is fixed with something called perturbation theory.
 10:05: So perturbation theory is applied throughout quantum field theories of the standard model.
 10:53: But unlike other quantum field theories, there are no simple measurements you can do to renormalize those corrections.
 11:54: ... fabric of spacetime itself are emergent phenomena from a quantum theory deeper than our currently accepted ...
 12:08: That's exactly what string theory seeks to do.
 12:11: ... to crack the greatest problem in modern physics, the quest for a theory of quantum ...
 13:06: It'll really help us constrain some black hole theory.


20180905: The Black Hole Entropy Enigma
 00:40: At least they are inevitable according to the equations of Einstein's general theory of relativity.
 00:46: That theory is one of the most thoroughly tested in all of physics, which means we should probably believe in black holes.
 01:01: And yet if black holes exist, which apparently they do, they contradict other theories in physics that are as sacred as general relativity.
 01:09: They cause all sorts of problems with quantum theory, which we've talked about before and we'll review in a sec.
 01:30: ... an entire new way of thinking about the universe in terms of information theory and ultimately led to the holographic principle, which I promise we're ...
 11:24: You just need to add a little bit of string theory.
 11:34: It might also be true, and obviously we'll be back before too long to talk about string theory and the holographic nature of spacetime.


20180830: Is There Life on Mars?
 05:10: Lowell wrote three books on the subject, the last presenting his full theory on the subject of life on Mars.


20180823: How Will the Universe End?
 06:37: Theory says that if protons decay at all, this halflife could be up to 10 to the power of 37 years.
 14:39: Dirac's theory, however, predicts exactly twice that value, g equals 2.
 14:59: That's the classical theory, which is wrong and also suggested that electrons should spin faster than light.
 16:36: We try to pull theory out or our out of nowhere to try to match to our observations, and we keep those theories that work.
 16:44: But the key here is that we don't keep the theories if they only fit one observation.


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.
 01:41: Well, because it makes some predictions that clash with the classical theory.
 01:53: ... we're going to talk about the theory and experiments behind one of these tests, measuring the G factor, or in ...
 03:32: As we'll see, their nature is predicted by quantum theory, measure electromagnetic moments, and you verify your quantum picture of reality.
 06:23: Only the fully developed quantum electrodynamics, the first true quantum field theory, does this.
 07:13: But in fact, we can calculate its effect extremely precisely and test this through experiments, showing the underlying truth of quantum theory.
 07:27: Quantum field theory describes the interactions between particles as the sum total of all possible interactions that can lead to the same result.
 08:02: So yeah, quantum field theory is a type of madness.
 10:34: However, the ultimate arbiter of any physical theory is experiment.
 12:04: ... those theories are good, they're able to predict things beyond the observations on ...
 12:16: The theory of quantum electrodynamics has been pushed to the experimental limit and come out unscathed.
 12:31: We have to conclude that we are getting closer and closer to the truth in our search for theories to explain the underlying mechanics of space time.


20180725: Reversing Entropy with Maxwell's Demon
 09:42: Claude Shannon, the father of information theory, was deeply inspired by the close connection between entropy and information.


20180718: The Misunderstood Nature of Entropy
 00:54: ... thermodynamics that encapsulates the second law is the only physical theory of universal content which I am convinced will never be overthrown." And ...
 01:45: In 1824, Sadi Carnot published his "Reflections on the Motive Power of Fire," in which he revealed the theory for perfect engine efficiency.
 03:46: ... mechanics, founded by the great Ludwig Boltzmann with his kinetic theory of ...
 03:57: This theory explained thermodynamic behavior as the summed result of the individual motion of tiny particles under Newton's laws of motion.
 11:11: Stunningly, its foundations are in probability theory.


20180711: Quantum Invariance & The Origin of The Standard Model
 00:03: ... model of particle physics is the most successful, most accurate physical theory ever developed, describing with stunning accuracy the fundamental ...
 01:07: To appreciate the theoretical whirlwind that is the standard model, we need to introduce the idea of a gauge theory.
 01:14: ... simple terms, a gauge theory is one that has mathematical parameters or degrees of freedom that can ...
 01:57: But it turns out that these gauge symmetries are an important feature of most of our physical theories describing the universe.
 02:16: A theory that has these gauge symmetries is called a gauge theory.
 02:24: The standard model is ultimately based on quantum field theory, but we're going to use the Schrodinger equation.
 10:49: And following those mathematical labyrinths reveals physical theory with stunning predictive power, like the standard model of particle physics.


20180704: Will A New Neutrino Change The Standard Model?
 10:17: ... in our understanding of physics, and glitches between experiment and theory are exactly how new physics gets ...


20180620: The Black Hole Information Paradox
 00:17: It may very well be the loose thread that leads to a theory of everything.
 03:59: ... is in severe violation of one of the foundational tenets of quantum theory. ...
 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: ... turns out that if we assume that both general activity and quantumfield theory are correct as we currently understand them, then Hawking radiation must ...
 05:08: A deeper understanding of general relativity or of quantumfield theory must resolve this.
 05:27: ... a slight modification of general relativity called EinsteinCartan theory, it's predicted that the formation of a rotating black hole gives birth ...
 09:39: Leonard Susskind formalized this idea in the context of string theory in what we now know as the holographic principle.
 11:11: ... me how one little loose thread, a seemingly insignificant quirk in the theory, can lead to massive discoveries and complete reframing of ...
 11:22: ... the nature of information and entropy, exploded the field of string theory, and hinted at the possible holographic nature of ...
 11:44: Einstein's general theory of relativity reveals them to be regions of frozen time and cascading space.
 12:45: Last week we talked about the nohair theory of black holes, and you all had some hairy questions.
 14:01: But quantumfield theory imagines the electromagnetic force as being transmitted by virtual photons.


20180613: What Survives Inside A Black Hole?
 03:24: In Einstein's general theory of relativity, we think of the gravitational field as curvature in the fabric of spacetime.
 12:18: ... particle creation and annihilation is described by quantumfield theory, and unitary evolution and the conservation of probability and ...


20180523: Why Quantum Information is Never Destroyed
 05:51: ... of quantum mechanics, like the Dirac equation and quantum field theories. ...
 06:02: That guarantee arises from a really fundamental foundational quality of these theories.
 06:49: And this unitarity is a foundational assumption in all formulations of quantum mechanics and quantum field theories.
 09:14: ... for example, Everett's manyworlds or the de BroglieBohm pilot wave theory preserve this time ...
 09:35: And in the case of pilot wave theory, the wave function contains hidden information that is carried with the final measured particle.


20180516: Noether's Theorem and The Symmetries of Reality
 01:03: When it was published in 1915, Einstein's general theory of relativity opened as many questions as it answered.
 08:22: The entire standard model of particle physics is what we call a gauge theory.


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.


20180418: Using Stars to See Gravitational Waves
 08:40: ... Einstein was able to derive his general theory of relativity, which predicted the existence of gravitational waves, he ...
 08:51: He needed to understand Newton's theory of gravity well enough to see where it failed.


20180404: The Unruh Effect
 08:36: ... they perform the relativistic field theory calculation to understand the coupling between the detector particle and ...


20180315: Hawking Radiation
 00:20: He made profound contributions across physics from quantum theory to cosmology.
 00:34: ... PLAYING] Soon after Einstein revealed his great general theory of relativity in 1915, physicists realized that it allowed for the ...
 01:07: Once formed, there was nothing in theory or imagination that could bring material consumed back to the outside universe.
 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 ...
 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.
 06:14: In the absence of a theory of quantum gravity, Hawking needed a hack.
 11:13: Without a full quantum theory of gravity, the origin of Hawking radiation will remain mysterious.


20180214: What is Energy?
 08:50: ... to complex interactions of particles and fields in quantum field theories. ...
 09:26: And the Lagrangian quantum field theory is the basis for highenergy particle physics.
 10:53: ... of energy is generally invalid in the context of Einstein's general theory of relativity due to the potential time evolution of ...


20180124: The End of the Habitable Zone
 13:03: ... when we're covering topics from topology to cryptography to number theory. ...


20180117: Horizon Radiation
 00:00: ... PLAYING] The most successful theory in physics combines the weirdness of quantum mechanics with, well, the ...
 00:12: This theory tells us that particles can be created and destroyed during interactions.
 00:26: [MUSIC PLAYING] Both theories of relativity, special and general, tell us that many things are observer dependent.
 02:22: ... 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 ...
 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.
 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.


20171206: Understanding the Uncertainty Principle with Quantum Fourier Series
 10:12: So what does this oldschool quantum mechanics have to do with quantum field theory and Hawking radiation?


20171122: Suicide Space Robots
 12:00: You say that quantum field theory makes no prediction about the energy of the vacuum.
 12:20: ... current, beyond standard model theory, has a lot of trouble explaining why it produces the tiny energy density ...


20171108: ZeroPoint Energy Demystified
 00:32: ... is the prediction of quantum field theory, that there exists an energy of the vacuum resulting from the nonzero ...
 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.
 01:26: This means we should take the idea of zeropoint energy seriously and are justifiably perplexed at the mismatch between theory and measurements.


20171102: The Vacuum Catastrophe
 00:03: The most successful theory in all of physics is arguably quantum field theory.
 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: ... if it were infinite we may not notice, at least according to quantum theory. ...
 04:39: Long story short a crazily high, even infinite, vacuum energy doesn't affect the predictions of quantum field theory.
 04:57: Einstein's theory tells us that any form of energy produces gravity, and what matters is the absolute amount of energy, not relative deviations.
 05:37: ... that, if vacuum energy really did have the enormous value predicted by theory, then our gently expanding geometrically flat universe would not ...
 05:53: ... realization of this fact in the early days of quantum field theory was the beginning of what would become the vacuum catastrophe, but it ...
 06:46: But perhaps a yet deeper theory allows perfect canceling down to 0.
 07:39: Compare that to the number predicted by quantum field theory.
 08:56: But of course, it may be that advances in theory will resolve this catastrophe without requiring us to invoke the anthropic principle.


20171025: The Missing Mass Mystery
 02:56: There's a huge discrepancy between the amount of baryonic matter our surveys find and the amount that our theories say should be out there.
 03:06: And those theories are pretty solid.
 05:50: And yet, when we add up the mass from those galaxies, most of the baryonic matter predicted by a theory is missing.
 12:55: Eliran Cohen suggests that, instead of presenting lame theories, we should travel 1,000 years into the future and bring back exact answers.
 13:08: Unfortunately, there's still no theory of everything in 1,000 years and still not flying cars, would you believe?
 13:17: Maybe we'll at least get some evidence for the string theory or something.


20171019: The Nature of Nothing
 01:55: Our modern understanding of the quantum nature of space is described by quantum field theory.
 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.
 04:20: ... interactions in the universe, at least as described by quantum field theory. ...
 07:26: According to the best existing theory of the time, those orbitals should have had exactly the same energy.
 09:32: ... drawn together by a force that matched the predictions of quantum field theory. ...
 10:44: This crazy discrepancy between theory and observation is considered by some to be one of the greatest unsolved mysteries in physics.
 10:53: ... field theory, with its dependence on virtual particles and vacuum fluctuations, is one ...
 11:18: ... episode, we'll look deeper into this perplexing mismatch between our theory and our observation of the behavior of nothing and what it might tell us ...


20171011: Absolute Cold
 04:40: In theory, absolute zero temperature means no thermal energy so no internal motion of particles whatsoever.


20171004: When Quasars Collide STJC
 11:17: These are like the tunable knobs of the theory.
 11:24: And presumably a deeper theory explains this, and may connect to them.
 11:29: In this theory, the value of some constants may prove to be tied to the values of other constants.


20170928: Are the Fundamental Constants Changing?
 01:21: The answer lies in a deeper underlying theory, a socalled grand unified theory.
 01:28: But some proposed grand unified theories predict something unsettling.
 01:41: Now, we're not going to get into the nitty gritty of the theory today.
 02:13: It's been suggested that a changing speed of light might be an alternative to inflation theory, or even to the apparent expansion of the universe.
 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.
 09:38: Well, any measurement of a change in Alpha may provide evidence to constrain the grand unified theories that predict such changes.
 11:45: ... speaking of grand unified theories, I wanted to give a special shout out to Don Lincoln's excellent series, ...


20170913: Neutron Stars Collide in New LIGO Signal?
 15:42: And Hot Fuzz is obviously a reference to black hole singularities in string theory.


20170830: White Holes
 00:37: ... the idea first emerged from Einstein's general theory of relativity, physicists wondered how seriously to take this ...
 02:31: ... a few months after Einstein published his general theory of relativity, Karl Schwarzschild solved its equations for a very ...


20170810: The OneElectron Universe
 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: ... as timereversed matter is extremely useful in simplifying quantum field theory calculations, because it massively cuts down the number of Feynman ...


20170726: The Secrets of Feynman Diagrams
 01:51: Then, you are going to apply them to do some quantum field theory yourself.
 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: ... diagrams an incredibly powerful tool in simplifying quantum field theory calculations, vastly reducing the number of contributing interactions ...


20170719: The Real Star Wars
 14:40: ... about tricks for solving the impossible equations of quantum field theory. ...


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 by expressing ...
 00:42: ... even the most elegant and complete formulations of quantum field theory, like the Dirac equation or Feynman's path integral, become impossibly ...
 01:26: ... give you an idea of how messy quantum field theory can be, let's look at what should be a simple phenomenon electron ...
 01:58: But in quantum field theory, specifically quantum electrodynamics, or QED, the story is very different.
 03:08: ... pictorial tools to organize the painful mathematics of quantum field theory, but they also serve to give a general idea of what these interactions ...
 06:07: This is the philosophy behind perturbation theory, an absolutely essential tool to solving quantum field theory problems.
 08:09: Perturbation theory, with the help of Feynman diagrams, make the calculation possible, but that doesn't mean we're done.
 09:27: The answer probably lies within a theory of quantum gravity which we don't yet have.
 09:33: But just as with perturbation theory, physicists found a cunning trick to get around this mathematical inconvenience.
 10:27: ... be used to eliminate many of the infinities that arise in quantum field theory for example, the infinite shielding of electric charge due to virtual ...
 10:51: That means the theory can't predict that particular property from scratch.
 11:01: Nonetheless, renormalization saved quantum field theory from this plague of infinities.
 11:26: ... 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.


20170707: Feynman's Infinite Quantum Paths
 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.
 02:53: But it led to the most elegant formulation of quantum mechanics ever devised and became a key to quantum field theory.
 08:16: That means it treats space and time symmetrically and so works very naturally with Einstein's theory of special relativity.
 08:42: But perhaps the greatest power of the path integral is that it very naturally converts into a true quantum field theory.
 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.
 15:16: String theory states that all particles are different vibrational modes in onedimensional objects called strings.
 15:30: ... stunning success and is the foundation of the standard model, string theory is untested and may have nothing to do with ...


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.
 00:55: 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: ... Field Theory, QFT, describes all elementary particles as vibrational modes in ...
 08:21: He named the resulting theory quantum electrodynamics.
 09:37: It is one of the most carefully tested theories in all of physics.
 10:10: No other theory in physics has done so well.
 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: ... between quantum mechanics and relativity, check out the course, The Theory of Everything, by Professor Don Lincoln from Fermi ...
 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: ... special and general relativistic corrections tend to introduce into the theory. ...


20170621: AntiMatter and Quantum Relativity
 00:16: Einstein's theory of special and general relativity had changed forever the way we think about motion, space, and time.
 00:31: Yet, this year, 1928, one brilliant insight would bring these theories together and unveil the quantum fabric of reality.
 05:27: Instead of having a twocomponent spinor, up and down, as in Pauli's theory, he needed four components.
 09:02: Now, quantum field theory is a very deep topic.
 11:03: ... was also a key step in the discovery of quantum field and quantum field theory and the development of the standard model of particle physics, which ...


20170607: Supervoids vs Colliding Universes!
 08:44: A popular version of inflation theory is that of eternal inflation.
 09:30: And it could happen frequently or rarely, depending on the completely unknown details of the string theory parameter space.


20170531: The Fate of the First Stars
 03:40: And this brings us to the leading theory as to the mysterious disappearance of population three.


20170426: Are You a Boltzmann Brain?
 00:40: His most incredible insight was the kinetic theory of gases.


20170202: The Geometry of Causality
 00:05: The special theory of relativity tells us that one person's past may be another's future.
 00:15: ... we peer deeper into Einstein's theory to find that the immutable ordering of cause and effect emerges when we ...
 01:04: First, let's recap a little bit of Einstein's special theory of relativity.
 12:07: ... the mathematical singularity at the center of black holes is with string theory, which proposes that particles that we see in regular 4D spacetime result ...
 12:47: Mathematician Georg Cantor invented set theory, the mathematics we use to study different types of infinity.


20170119: The Phantom Singularity
 03:20: But the reality of the black hole singularity may give reason to doubt the theory that predicts such a thing.
 03:29: ... physical singularity, and we've been forced to reject the corresponding theory. ...
 04:16: ... Newton's law gives the wrong answers, and we need Einstein's general theory of relativity, which is the far more complete theory of ...
 11:19: Actually, Einstein's theory and the Schwarzschild solution that is derived from it suggests it must exist.
 11:34: ... better understand why the central infinity is unavoidable in Einstein's theory, we have to go back to that coordinate shift at the event ...


20170111: The EM Drive: Fact or Fantasy?
 06:49: So the last part of the paper talks about a connection between the EmDrive and pilot wave theory.
 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.
 07:12: However, it's highly speculative and isn't necessarily even an obvious outcome of pilot wave theory.
 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.
 08:29: ... than described by the otherwise amazingly successful quantum field theory. ...


20170104: How to See Black Holes + Kugelblitz Challenge Answer
 00:07: We tend to be pretty theoretical in how we think of them, partly because the theory predicts some fun stuff that no human will likely ever experience.
 04:41: ... powerful tests of whether they behave as predicted by Einstein's general theory of relativity or whether there are tantalizing ...


20161208: What Happens at the Event Horizon?
 01:07: ... hole rotational growth, the simplest black hole of Einstein's general theory of relativity purely gravitational, static, and eternal is a subtle ...
 13:47: Onto the comments from last week's episode on De BroglieBohm theory.
 14:02: Now, a lot of you wondered why I never mentioned the EM drive when talking about pilot wave theory.
 14:14: ... produced by their EM drive and then go on to talk about how pilot wave theory might explain the apparent conservation of momentumbreaking ...
 14:30: I might get into the details in an upcoming episode, but for the sake of explaining pilot wave theory this paper isn't relevant.
 14:38: ... is extremely speculative, and honestly I wondered whether pilot wave theory was chosen partly because the internet happens to love it at the ...
 14:50: ... asks how it can be that pilot wave theory predicts different particle trajectories, given that the particles ...
 15:11: ... pilot wave theory states that the particle riding the wave does have a definite position ...
 15:51: More generally, it allows pilot wave theory to agree with Heisenberg's uncertainty principle.
 16:05: ... BroglieBohm pilot wave theory states that this uncertainty just arises from our imperfect knowledge ...
 17:15: ... entirely accurate when I said that De Broglie, the founder of pilot wave theory, remained convinced by Niels Bohr and his Copenhagen camp, even after ...
 18:08: ... version of what was to be a much more intricate double solution theory in which the socalled particle was actually a matter wave itself ...
 18:34: ... Broglie never completed his full double solution theory, but did work on it intermittently throughout his life and was inspired ...
 18:57: ... De BroglieBohm pilot wave theory is a great example of how a deterministic theory can at least go some ...
 19:17: I like the idea of a deterministic theory, but the universe has often demonstrated that it couldn't care less about our pet theories.
 19:36: We'll figure this out, and until then it's OK to like one theory over another but belief should wait on the evidence.


20161130: Pilot Wave Theory and Quantum Realism
 00:16: It's the de BroglieBohm pilotwave theory.
 00:19: And despite its alluringly intuitive nature, for some reason it remains a fringe theory.
 00:26: ... hooha and unfounded mystical storytelling of any scientific theory. ...
 01:26: That's de BroglieBohm pilotwave theory.
 01:30: ... theory, also known as Bohmian mechanics, stands in striking contrast to the much ...
 01:47: Pilotwave theory is perhaps the most solidly physical, even mundane, of the complete and selfconsistent interpretations of quantum mechanics.
 02:16: ... quantum theory was coming together in the '20s, they were fervent about the need to ...
 03:11: ... to counter Bohr and Heisenberg there needed to be a full theory that described how a quantum object could show both wave and ...
 03:25: ... theory came from Louis de Broglie, the guy who originally proposed the idea ...
 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.
 03:51: This is pilotwave theory.
 04:05: Importantly, the wave function in pilotwave theory evolves exactly according to the Schrodinger equation.
 04:21: This means that pilotwave theory makes the same basic predictions as any other breed of quantum mechanics.
 05:18: When de Broglie presented his stillincomplete theory at the famous Solvay Conference of 1927, it didn't go down so well.
 05:56: Bohm took up where de Broglie left off and completed the theory.
 06:00: The result was Bohmian mechanics, also known as de BroglieBohm pilotwave theory.
 06:21: See, although pilotwave theory makes all of the usual predictions of quantum mechanics, it has some really fundamental differences.
 06:54: So what uncomfortable thinking does pilotwave theory require?
 07:51: According to pilotwave theory, the wave function just describes the possible distribution of those variables given our lack of perfect knowledge.
 08:18: That proclamation contributed to the long shelving of pilotwave theory.
 08:57: This helped the resuscitation of pilotwave theory, because Bohmian mechanics doesn't use local hidden variables its hidden variables are global.
 10:40: I should probably also add that de BroglieBohm pilotwave theory is certainly wrong.
 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.
 11:13: Pilotwave theory postulates that the particle really takes a single actual trajectory, the Bohm trajectory.
 11:21: This is not consistent with quantum field theory, and so there isn't a complete relativistic formulation of Bohmian mechanics yet.
 11:41: Also, we can't ignore the fact that the initial motivation behind pilotwave theory was to preserve the idea of real particles.
 11:55: ... that said, pilotwave theory does do something remarkable it shows us that it's possible to have a ...


20161116: Strange Stars
 00:55: Einstein's general theory of relativity tells us that the core of a dead star must collapse under its own incredible weight.
 01:02: What happens to the resulting ultradense material depends on quantum theory.
 12:50: A lot of you asked for a video on De BrogileBohm pilot wave theory.
 13:09: ... the black hole information paradox, Hawking radiation, some string theory, the holographic principle, other ...


20161026: The Many Worlds of the Quantum Multiverse
 06:00: ... was proposed by Hugh Everett in his 1957 PhD thesis entitled "The Theory of the Universal Wave Function." It's come to be known as the many ...


20160929: Life on Europa?
 09:57: ... observable difference between the predictions of a local hidden variable theory versus pure quantum mechanics is if you measure the spins of both ...
 10:17: ... the local hidden variable theory, you'd expect to sometimes measure spins in the same direction, depending ...


20160921: Quantum Entanglement and the Great BohrEinstein Debate
 09:40: That sounds blasphemous to anyone who accepts Einstein's theory of relativity.
 10:53: Also, the De BroglieBohm Pilot Wave Theory works by assuming real and nonlocal hidden variables.


20160810: How the Quantum Eraser Rewrites the Past
 08:27: ... interpretation of the wave function, like the De BroglieBohm Pilot Wave Theory, requires an underlying physicality, a set of defined properties that ...


20160727: The Quantum Experiment that Broke Reality
 09:36: ... theory of quantum mechanics produces stunningly accurate predictions of reality ...
 09:54: ... know that light is a wave in the electromagnetic field and quantum field theory tells us that all fundamental particles are waves in their own ...


20160720: The Future of Gravitational Waves
 04:07: Beyond the detection of gravitational waves, this is another awesome validation of the theory.


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.


20160615: The Strange Universe of Gravitational Lensing
 01:27: ... general theory of relativity describes the real universe as a flexible, dynamic ...
 02:33: The deflection angle was exactly what Einstein's theory predicted.
 12:02: ... de BroglieBohm pilot wave theory, the manyworlds interpretation, and others, allow a deterministic ...


20160601: Is Quantum Tunneling Faster than Light?
 00:12: [THEME MUSIC] Quantum mechanics is a spectacularly weird theory.
 01:26: This is one of the early realizations in the development of quantum theory.
 10:15: Throw in some string theory and black holes and a really unique writing style and it's a very insightful Pop Sci book.


20160518: Antigravity and the True Nature of Dark Energy
 00:19: ... you to take a wild ride with me into the heart of Einstein's general theory of relativity and its description of the vaster of scales of our ...


20160427: What Does Dark Energy Really Do?
 00:16: ... how the fate of the universe can be described using Einstein's general theory of relativity via the Friedmann ...
 11:45: ... when the theory general relativity, in this case is so thoroughly verified in so many ...


20160420: Why the Universe Needs Dark Energy
 00:08: ... strange influence called "dark energy." [THEME MUSIC] Einstein's general theory of relativity allows us to describe the behavior of the cosmos on the ...
 00:35: ... attempts to constrain the predictions of this theory with real astronomical observations tell us that the fate of the ...


20160413: Will the Universe Expand Forever?
 00:12: Yet the fact that Einstein's theory allows us to learn the answer to this question is incredible.
 00:19: ... MUSIC] Soon after Albert Einstein proposed his general theory of relativity, industrious physicists and, in particular, a brilliant ...


20160323: How Cosmic Inflation Flattened the Universe
 00:15: [MUSIC PLAYING] The Big Bang theory describes the earliest epochs of our universe amazingly well.
 06:57: ... the field equations of his general theory of relativity, he added this as a way to allow his theory to describe a ...
 09:13: With inflation, the Big Bang theory takes on new meaning.


20160316: Why is the Earth Round and the Milky Way Flat?
 11:04: In our recent episode, we talked about some of the outstanding issues in the Big Bang Theory.


20160309: Cosmic Microwave Background Challenge
 00:05: ... been talking about the Big Bang theory a lot recently, and the most important piece of evidence for this theory ...


20160302: What’s Wrong With the Big Bang Theory?
 00:10: The Big Bang Theory suggests that once the entire universe was compacted into an infinitely small speck at the beginning of time.
 00:22: What parts of this theory are still under serious question?
 00:26: [MUSIC PLAYING] In the last episode, I showed you why the Big Bang Theory is right, or at least, what parts of it pretty much definitely happened.
 01:06: ... of physics, and in particular running the math of Einstein's general theory of relativity ...
 02:46: Our theories look really good to that point.
 03:11: ... we call these grand unified theories, except they aren't theories in the same sense as relativity or evolution ...
 04:26: And we need a theory of quantum gravity, a socalled theory of everything, to go further.
 04:31: ... can talk about why these theories don't play nice together and what some of the resolutions might be ...
 07:47: The theory that describes this pow is called inflation.
 08:31: ... fact, inflation solves a number of vexing problems with the Big Bang Theory so well, in fact that most cosmologists accept that something like this ...
 08:56: ... this sense, it may be more accurate to think of the Big Bang Theory not as a theory of the origin of the universe, but instead as a theory ...
 09:09: Aspects of this theory have such hard evidence that we know that the basic picture is right.
 09:15: However, as with every really wellestablished theory, there are boundaries to what the Big Bang Theory currently explains.
 09:28: Perhaps the theory will eventually encompass a true origin for this universe.
 12:16: So it's unfortunate that this statement is used to deride the Big Bang Theory.
 12:36: Perhaps our understanding of this state will eventually lead to a theory of the origin of the universe.
 12:42: But the Big Bang Theory as it stands does not claim to explain such an origin.


20160224: Why the Big Bang Definitely Happened
 00:11: ... PLAYING] The Big Bang theory was pretty contentious when it was first proposed, as is any picture of ...
 00:27: ... these days, there's really no doubt that at some level, the Big Bang theory gives an accurate description of the earliest epochs of this ...
 00:43: Today, we're going to talk about the evidence that gives us so much certainty for parts of the theory.
 00:55: I'm not going to spend a lot of time describing the theory.
 01:04: ... Big Bang theory is a set of descriptions detailing the expansion of the universe from a ...
 01:28: Some of these experiments have verified certain parts of the theory beyond reasonable doubt, while other parts remain untested.
 01:50: ... the context of Einstein's theory of general relativity, the only sensible interpretation for this fact is ...
 04:49: So at least that far back in time, the Big Bang theory is right.
 06:29: ... the Big Bang theory is right, then those ripples should have been frozen into the ...
 07:15: ... Big Bang theory tells us how long these elements were baked and at what temperature, and ...
 07:31: The Big Bang theory has powerful, direct evidence, almost down to the first second.
 08:55: Brendon Binns asks, given this detection, is the "theory" of general relativity still just a theory?
 09:02: Well, actually, it's even more solidly a theory than ever.
 09:06: In science, when we say theory, we mean a description of reality that has stood up to many, many experiments.
 09:15: We only call it a theory if we're pretty much certain that the basic picture is correct.
 09:21: Theories actually contain laws, and those laws are often the most wellestablished parts of a theory.
 09:28: A theory may still have parts that aren't so well established, but such uncertainties don't invalidate the overall picture.
 09:38: If they did, then we wouldn't be calling it a theory.


20160211: LIGO's First Detection of Gravitational Waves!
 00:17: ... existence of these waves is the last major prediction of Einstein's theory of general relativity to be directly verified a century after the theory ...
 04:57: See, gravitational waves are inevitable if the theory is correct.
 05:22: ... significantly from the expected signal, then it may be a clue that the theory is incomplete, or even point to a new, deeper ...
 05:37: However, physicists will be all over this data, looking for holes in the theory for some time.


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
 00:00: [MUSIC PLAYING] Einstein's theory of special relativity has shown us mass and time are not the concrete things we imagine them to be.


20160120: The Photon Clock Challenge
 00:35: And the resulting slowing of clock ticks due to motion is the time dilation of Einstein's theory of special relativity.


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.
 01:54: Now, this is a very simplistic explanation of a theory that has produced an astoundingly accurate description of the subatomic universe.
 02:02: ... its incredible success, it was strange that quantum field theory, as it stood in the 1950s, gave a perfect description of the electron, ...
 06:04: Well, something like this must be true, because all of the rest of quantum field theory hangs together too well.
 06:11: We conclude that QFT is essentially correct, but it's an incomplete theory without a massgiving field.


20151209: How to Build a Black Hole
 03:15: ... 6D quantum phase space depends on two important principles of quantum theory, the Pauli exclusion principle and the Heisenberg uncertainty ...
 10:34: Of course, a real black hole is not the static creature that we sometimes describe in theory.


20151125: 100 Years of Relativity + Challenge Winners!
 00:24: ... this day in 1915, Albert Einstein first presented his complete theory of general relativity to the Prussian Academy of Sciences in Berlin, ...
 00:36: ... we cover a lot of material on this show, but Einstein's beautiful theory is an essential part of what inspires us here at "Space Time." General ...
 01:01: The elegance of this theory has inspired so many students of physics to follow in Einstein's path exploring the mysteries of the universe.


20151118: 5 Ways to Stop a Killer Asteroid
 10:19: Well first let me note that Panspermia is far from being an accepted theory.


20151028: Is The Alcubierre Warp Drive Possible?
 00:45: ... constructed a warp field in the mathematical language of Einstein's theory of general relativity, a real solution to the equations of GR that would ...
 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.
 08:36: ... doubt that Max Planck and Schrodinger and Bohr imagined that this crazy theory would lead to the invention of the transistor, a quantum mechanical ...


20151022: Have Gravitational Waves Been Discovered?!?
 00:03: Gravitational waves are the last prediction of Einstein's Theory of General Relativity.
 00:22: It has a lot to do with his revolutionary Theory of General Relativity, in which he showed us that the force of gravity is an illusion.


20151007: The Speed of Light is NOT About Light
 02:11: By the late 1800s, we have Maxwell's equations, Newton's mechanics, various other awesome theories.
 09:19: ... of the meaning of the Lorentz transformation gives us the special theory of relativity time dilation, length contraction, and, of course, mass ...


20150930: What Happens At The Edge Of The Universe?
 07:07: In addition, although general relativity is pretty cool, it's not a theory of everything.
 07:36: ... and others ask whether it's contradictory or circular to use Einstein's theory of general relativity to prove ...
 07:47: Well, the only way to test a theory is to use it.
 07:54: A model has to make multiple independent and accurate predictions to be accepted as a theory.
 07:58: And there are few theories with as many independent and accurate predictions as general relativity.


20150923: Does Dark Matter BREAK Physics?
 04:21: Any replacement theory has to reproduce all, and I mean all, of the verified predictions of Einstein's theory and be able to explain dark matter.
 06:46: ... in short, versions of this theory predict the existence of a set of counterparts to the familiar standard ...
 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 particle like ...
 10:44: ... can quantize any classical theory, as long as you are restricting yourself to looking at macroscopic ...
 10:53: ... or very high energies, that a lot of infinities start popping up in the theory that you can't get rid of, which is what we don't have a fully ...
 11:07: But from the philosophical perspective of quantum field theory, you should be able to quantize anything.
 11:26: You can look up something called KaluzaKlein theory, which is a way of trying to get a geometric version of electromagnetism plus general relativity.
 11:41: ... the other is to try to take field classical field theory versions of something and then add to them the machinery of quantum ...


20150729: General Relativity & Curved Spacetime Explained!
 08:32: ... even when people are referring to relativity or string theory or whatever, it's just a lot easier to say the word gravity than say ...


20150603: Is Gravity An Illusion?
 09:19: It makes several predictions that Newton's theory of gravity does not, and so far, it has passed all its experimental tests.
