2022-12-08: How Are Quasiparticles Different From Particles?
- 05:43: But this seems a bit more like a sound wave than a particle.
- 05:47: In fact sound waves in solids do propagate exactly like this.
- 06:25: ... via these vibrations - so this makes the phonon a quantum of a sound wave, similar to how a photon is a quantum of light - of an electromagnetic ...
- 06:44: They travel at the speed of their wave-type - sound in this case.
- 13:28: ... appear in lattices of quantum spin, like are magnons - quanta of waves in that lattice, or skyrmions, which are localized, stable topological ...
2022-11-23: How To See Black Holes By Catching Neutrinos
- 00:30: There’s the James Webb Space Telescope and its infrared supervision and of course LIGO with its ability to see gravitational waves.
- 04:32: ... expanding EM waves created by the charged particle expand slower than the particle itself, ...
- 12:01: ... can also look for neutrino Cherenkov radiation at radio wavelengths, which allows us to scan vast tracks of the Antarctic glacier with ...
2022-11-09: What If Humanity Is Among The First Spacefaring Civilizations?
- 17:08: ... Tch and zomgthisisawesomelol point out that Einstein was referring to wavefunction collapse when he said "spooky action at a distance" not quantum ...
- 17:23: ... was referring to general wavefunction collapse, in which the wavefunction appears to change everywhere at the ...
- 17:37: ... and basically discovered quantum entanglement in an effort to disprove wavefunction collapse through a reductio ad ...
- 17:49: He showed that instant collapse of entangle wavefunctions led to crazy FTL-like effects, and so thought it couldn’t be real.
- 18:04: So, “spooky action at a distance” does refer to wavefunction collapse, including to the wavefunction collapse of entangled particles.
- 18:34: They imagined waves traveling from both cause to effect and from effect to cause.
- 18:50: ... with the time-reversed signals corresponding to negative frequency waves. ...
- 20:25: This branch of my wavefunction only remembers not going to any of them, but I assume the other guy had a really great time.
2022-10-26: Why Did Quantum Entanglement Win the Nobel Prize in Physics?
- 03:07: Quantum systems are described by a mathematical object called the wavefunction, which evolves according to the Schrodinger equation.
- 03:13: ... joint wavefunction of two entangled objects only contains information about the ...
- 03:22: They only gain specific values when observed and the wavefunction “collapses”.
- 03:28: For our quantum balls to know their own color the whole time, there would need to be extra information not contained in their wavefunction.
- 03:46: ... exist, while others like Neils Bohr insisted that the wavefunction was the complete description of a quantum ...
- 04:21: David Bohm got the worst of that with his pilot wave theory, which we talk about in another video.
- 12:04: But there could still be hidden variables that exist in the global wavefunction of the entangled particles.
2022-10-19: The Equation That Explains (Nearly) Everything!
- 01:33: ... example, if we insist that the phase of the quantum wavefunction is fundamentally unmeasurable, then we need to add a term to the ...
- 02:21: ... symmetries also come from the fact that the wavefunction can be distorted in different ways that have no effect on the laws of ...
- 04:36: ... it seems like it might be a good idea to figure out the Lagrangian for a wavefunction that has our symmetries of interest. And that is exactly what the ...
- 09:24: ... That’s what the second term in the Lagrangian represents. The psi is the wavefunction of the fermion fields. Strictly speaking there are 12 fields for the 12 ...
- 13:49: ... it works. Putting in your particle wavefunction and setting your indices right and including the correct masses, you can ...
2022-10-12: The REAL Possibility of Mapping Alien Planets!
- 01:25: ... is always better. When light passes into a telescope, its wave nature interacts with the edges of the aperture, causing ...
- 10:07: ... first cluster of craft was the first pearl. Even if that wave doesn’t get it quite right, its data will help the next ...
- 15:45: ... no - Hubble was most sensitive at visible and ultraviolet wavelengths, while JWST is an infrared scope. These are very ...
2022-09-28: Why Is 1/137 One of the Greatest Unsolved Problems In Physics?
- 01:43: ... in the light observed when we break it up into a spectrum of different wavelengths. ...
- 04:05: ... repulsive energy between two electrons is 137 smaller than a photon with wavelength equal to the distance between the ...
2022-09-21: Science of the James Webb Telescope Explained!
- 03:54: The choice of long wavelength light specializes JWST for a number of particular science goals.
- 04:40: ... stars, as well as peer through that dust which normally blocks shorter wavelength ...
- 05:16: ... with sensitivities from visible red light through the slightly longer wavelengths of near-infrared all the way to the much longer wavelength ...
2022-08-03: What Happens Inside a Proton?
- 00:45: ... are particles in the universe to store all the information in the wavefunction of a single large molecule. We also talked about the hack ...
2022-07-27: How Many States Of Matter Are There?
- 10:24: The frequent interactions between people cause liquid-like phenomena like currents and waves as individuals lose their autonomy of motion.
2022-07-20: 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.
- 02:20: ... quantum mechanics, the fundamental building block of reality is the wavefunction, which describes the evolving probability distribution of all possible ...
- 02:33: The results of your measurements are plucked from the wavefunction of whatever you’re observing.
- 02:39: We say that measurement “collapses” the wavefunction, obliterating all potential results in favor of one actual result.
- 02:45: A wavefunction can span multiple distinct, even contradictory states.
- 02:56: And a wavefunction can also span multiple particles, holding information about the relationships between those particles.
- 05:34: ... about its own physical state, in a way that was somehow hidden from the wavefunction of standard quantum ...
- 07:59: Things like pilot wave theory and objective collapse models try to do that.
2022-06-22: Is Interstellar Travel Impossible?
- 16:16: Yash Chaurasia asks whether asking an electron "are you a particle?" automatically answers "are you a wave?”.
- 16:24: ... refresh your memory, the wave-particle duality was explained in the context of informational quantum mechanics ...
- 16:34: But if there are only two possible answers - particle or wave - then asking one answers the other.
- 16:41: ... are the most elementary, and so we don’t know if a quantum system’s wave-particle nature has a binary ...
- 17:09: ... can either ask about the wave-like properties (for example the phase), or about the particle-like ...
2022-06-15: Can Wormholes Solve The Black Hole Information Paradox?
- 07:24: ... tidal wave of math in these papers pulls ideas from string theory, ...
2022-06-01: What If Physics IS NOT Describing Reality?
- 08:49: ... the limited knowledge that we can extract from a quantum wavefunction. For example, that the product of the measurement error ...
- 09:26: ... original and most mysterious features of quantum mechanics - wave-particle ...
- 10:02: ... experiment. This experiment causes a photon to behave like a wave or a particle depending on the question asked of it. And ...
- 10:33: ... uncertainty to the situation, the team said that the wavefunction contained only one answer to two complementary ...
- 11:24: ... In quantum mechanics, we tend to think of the quantum wavefunction as pretty fundamental. It describes the evolving distribution of ...
- 12:09: ... if the wavefunction is about the information content of a system, again, ...
2022-05-25: The Evolution of the Modern Milky Way Galaxy
- 03:22: ... disks, and their violent convulsions settled into the density waves that we see as spiral arms. The new spiral galaxies ...
- 05:11: ... from specific elements sucking up or producing light at specific wavelengths. Stars with similar metallicities could have come from the same merger ...
- 12:11: ... formation in about 2 billion years. The accompanying supernova waves may not be the best thing for life on Earth, but we do have 2 ...
2022-05-18: What If the Galactic Habitable Zone LIMITS Intelligent Life?
- 08:01: ... bulge. As the galactic bulge grew, it was wracked by further waves of supernovae. As Moiya mentioned, having excessive exploding ...
2022-05-04: Space DOES NOT Expand Everywhere
- 14:34: ... or “conscious awareness” as the causal event that collapses the wavefunction, or in this case manifests the universe. Rather than for example saying ...
- 16:38: ... “creates itself” by constructive interference - only electrons whose wavefunction peaks and valleys line up on each orbit can exist. Maybe the universal ...
2022-04-27: How the Higgs Mechanism Give Things Mass
- 02:31: ... an example of this. The exact phase of the quantum wavefunction from one point in space to the next - local phase - doesn’t ...
2022-04-20: Does the Universe Create Itself?
- 01:59: ... a real, physical universe could be interpreted in the behavior of the wavefunction, such as de Broglie-Bohm pilot wave theory or objective collapse ...
- 06:24: ... the combination of phase shifts in the beamsplitters causes the photons wavefunction to perfectly line up in detector 1 - constructive interference, and to ...
- 16:10: ... fields in a way that looks like thermal radiation. That radiation has a wavelength that’s on the scale of the event horizon. So the horizon radiation from ...
2022-03-08: Is the Proxima System Our Best Hope For Another Earth?
- 03:33: Proxima’s emissions lines seemed to shift back and forth from the wavelengths dictated by the laws of physics.
- 04:22: ... the wavelengths of all the star’s light are stretched as the star moves away from us and ...
- 16:39: ... on the last two episodes: the one on objective collapse theories, where wavefunction collapse is explained as a real, physical ...
- 16:52: ... the objective collapse episode we talked about some field “hitting” the wavefunction to cause it to collapse, and Kadag asks what exactly is doing the ...
- 17:04: It has to be a field that has a non-linear influence on the wavefunction.
- 17:13: But in general it means different branches of the wavefunction are able to influence each other, which is not the case in standard quantum mechanics.
- 17:27: ... one field that might be able to do this is gravity, in which case the wavefunction is being “hit” by the non-linearities across the wavefunction introduce ...
- 18:33: When those cosmic strings radiate gravitational waves, how is the Higgs field supposed to smooth itself out?
- 19:27: ... phase angle is fundamentally unmeasurable - just the the phase of the wavefunction - it’s a symmetry of the Higgs field and doesn’t affect the behavior of ...
2022-02-23: Are Cosmic Strings Cracks in the Universe?
- 10:09: ... in the kinks causes them to radiate gravitational waves. In this way cosmic strings shed energy, and so they slowly decay ...
- 12:19: ... “regular” cosmic strings in many ways - like the gravitational waves and the lensing. But there are differences. While cosmic ...
2022-02-16: Is The Wave Function The Building Block of Reality?
- 00:49: ... definite properties. Rather they are described by something called the wave function. In fact, a particle is its wave function: a fuzzy distribution ...
- 01:06: ... to be plucked from the wide range of possible values defined by the wave ...
- 01:16: We say that the wave function collapses - it appears to shrink to a window whose narrow width is defined by the precision of our measurement.
- 01:24: ... Prior to opening the box, from the scientist’s perspective the atom’s wave function exists in what we call a superposition of states. It is ...
- 02:24: ... idea of wave function collapse was first proposed by Werner Heisenberg, one of the ...
- 03:02: ... span all extremes. John von Neumann and Eugene Wigner thought that wave function collapse happens at the instant of subjective awareness - in ...
- 03:24: ... example in Hugh Everett’s Many Worlds interpretation, the wave function never collapses, rather lasts forever, splitting into parallel ...
- 03:52: We've discussed all of theses ideas in the past. But today we’re going to look at a different approach to collapsing the wave function.
- 03:59: ... that accepts the wave function as the fundamental building block of reality, unlike pilot wave ...
- 04:36: ... objective collapse theories, wave functions are real, physical entities that literally collapse when ...
- 05:00: The behavior of the wave function is described by the Schrodinger equation, which tracks its evolution through space and over time.
- 05:09: ... of what makes superpositions possible - it allows different parts of the wave function corresponding to different possible measurement results to ...
- 05:44: ... wave function collapse happens, different parts of the wave function interact ...
- 06:04: ... to model the effect of wave function collapse, Ghirardi, Rimini, and Weber added a non-linear term ...
- 06:22: ... of this non-linear action as a rare and random hit that the wave function takes at a particular location. That hit causes it to collapse ...
- 06:53: ... of them experiences collapse, and that single single event collapses the wave function of the entire system. Any attempt to measure an isolated ...
- 07:44: ... this value, a single particle wave function remains uncollapsed for around 100 million years. But if you ...
- 08:02: ... interaction with this fluctuating field would continuously collapse the wave function, in contrast to the discrete and violent hits of GRW ...
- 08:32: ... force. They thought nature already gave us a perfectly good source of wave function collapse: ...
- 09:25: ... introduces a nonlinear term in the Schrödinger equation, causing the wave function to rapidly and randomly choose to make the object appear either ...
- 11:09: ... signs of collapse models. For example, the models imply that a quantum wave function will be randomly tossed about and jostled by gravity or some ...
- 12:55: ... And one that we’ll be coming back to. What, in fact, is the quantum wave function? And how does this abstract system of shifting realities give ...
- 13:19: ... Level. Ben there are many uncertainties in the world of physics. Is the wave function objectively real? Or is it a statistical or subjective fiction? ...
- 14:52: ... BuzzBen asks what happens when gravitational waves pass through black holes. Is there gravitational lensing? Well that’s ...
2022-02-10: The Nature of Space and Time AMA
- 00:03: ... okay increases the difference between its peaks and increases its wavelength okay uh decreasing its energy but if we calculate what redshift would ...
2022-01-27: How Does Gravity Escape A Black Hole?
- 02:02: For example we have gravitational waves - ripples in spacetime caused by certain types of motion.
- 02:08: ... at the speed of light, and that’s been confirmed when gravitational waves from colliding neutron stars reach us at about the same time the ...
- 02:46: It would take 8 minutes for the Sun’s deep indentation in the fabric of space to smooth itself - in the wake of some pretty crazy gravitational waves.
- 13:06: ... method for simulating the insane amount of information in the quantum wavefunction with density functional theory, and then went from the tiny to the ...
- 13:42: ... interesting thought on the matter and I quote: "That a small part of the wavefunction can be used to "reconstruct" the whole wavefunction, or at least the ...
- 14:03: ... not that the information of the wavefunction can be compressed below it's "true" informational volume, it's that it ...
2022-01-19: How To Build The Universe in a Computer
- 00:30: ... spiral structure will be obliterated, gas will be compacted to produce waves of supernovae, and the giant Milkdromeda galaxy will have been ...
- 10:02: ... watch as galaxies form, with gas and dark matter interacting to produce waves of star formation and supernovae, settling into spiral structures - just ...
2022-01-12: How To Simulate The Universe With DFT
- 00:18: That’s how insanely information dense the quantum wavefunction really is.
- 01:28: In fact you need more particles than exist in the solar system to store the wavefunction of the electrons in a single iron atom.
- 01:48: ... describes how the wavefunction of a quantum particle - that’s this psi thing - changes over space, ...
- 02:19: ... can also solve the Schrodinger equation to find the wavefunction, and the square of that wavefunction gives the the probability ...
- 02:50: That’s nice because then the wavefunction is just a 1-D array of values.
- 02:55: ... array stores the wavefunction - the distribution of possible locations - it doesn’t store the actual ...
- 04:52: ... every time we add a particle we increase the dimensionality of the wavefunction. ...
- 05:25: So it seems like even for a single atom of iron, a fairly run of the mill element, we can’t even store the wavefunction let alone calculate it.
- 06:48: In quantum mechanics, we’re dealing with the wavefunction, and the wavefunction fills all of configuration space.
- 08:11: We need to know the wavefunction for every particle everywhere.
- 10:11: ... density - is just a tiny fragment of the information held in the total wavefunction of all of those ...
- 10:29: ... without having to go through the impossibly complex many-electron wavefunction. ...
- 12:22: ... main takeaway is that physicists realised that a tiny sliver of the full wavefunction - the density distribution - could be mapped to all sorts of useful ...
- 13:15: What does it mean that there exists a map between the low-information slice of the wavefunction and really all the information we want to get from it?
- 13:35: ... no doubt deeper truths to be found by understanding how the universal wavefunction with its insane hyper dimensionality is connected to the narrow sliver ...
- 14:25: Peter, the infinite dimensional universal wavefunction barely contains enough information to describe your generosity.
2021-12-29: How to Find ALIEN Dyson Spheres
- 03:05: ... spectrum - light generated by its 6000K surface is distributed at all wavelengths, but it peaks in the visible part of the ...
- 03:24: ... new thermal spectrum, now at 300 or so Kelvin, with its peak at infrared wavelengths. ...
- 07:31: Two pure thermal spectra would be stitched into one weird spectrum with too little light at visible wavelengths and too much at infrared wavelengths.
- 07:41: If we carefully broke up the star’s light with spectrographs spanning a huge wavelength range, we might be able to see two distinct thermal spectra.
- 08:12: In astronomy, color refers to the ratio of brightnesses at two different wavelengths.
- 09:20: At visible wavelengths a star’s color might not change much - it’ll just look dimmer.
- 09:31: But if we measure its colour using an infrared wavelength along with our visible light, we’d find too much of that IR.
2021-12-20: What Happens If A Black Hole Hits Earth?
- 09:03: ... seismic waves would reach all points on the Earth’s surface. Even at the lowest mass ...
- 17:55: ... string theory. There are simulations that suggest that the gravitational waves created when fuzzball merge should look almost exactly the same as those ...
- 18:16: ... may be that the so-called ring-down - the waves produced as the merged object settles back into a spheroid - lasts ...
2021-12-10: 2021 End of Year AMA!
- 00:02: ... it plenty but the idea is that every time you know a the evolving wave function in the quantum world sort of makes a decision uh uh in the ...
2021-11-10: What If Our Understanding of Gravity Is Wrong?
- 09:15: AQuaL also had the unfortunate prediction of faster-than-light waves in this added scalar field, which broke causality.
2021-11-02: Is ACTION The Most Fundamental Property in Physics?
- 08:39: ... not as a particle with a well-defined trajectory, but as a quantum wavefunction that represents all possible paths it could take. The wavefunction at ...
- 09:56: ... action existed that was related to the integrated time evolution of the wavefunction. And he realized that this quantity should result in destructive ...
- 11:12: ... of previous versions of quantum mechanics - for example, Schrodinger’s wave mechanics that talks about the evolution of a single wavefunction. This ...
2021-10-20: Will Constructor Theory REWRITE Physics?
- 12:30: ... in Fact do particles even travel at all or do their wave functions just randomly tunnel every which way so that their ...
- 14:00: ... the particle itself is ever “inside the barrier”, but its wavefunction certainly is inside the barrier, and its wavefunction does seem ...
- 14:48: ... emergent consequence of causality. If every particles wavefunction is really spread over all of space can anything really move ...
2021-10-13: New Results in Quantum Tunneling vs. The Speed of Light
- 02:41: We represent the location of, say, a proton in a nucleus as a wavefunction.
- 02:46: It’s an abstract wave that encodes the information of where the proton might be.
- 02:52: ... with another particle, the proton can end up anywhere within that wavefunction, with some locations more likely than ...
- 03:01: ... when a proton bounces around inside a nucleus, we need to see how its wavefunction evolves according the the Schrodinger equation - which is just the ...
- 03:13: This equation tells us that the wavefunction is mostly reflected or scattered back by the wall of the nucleus.
- 03:26: Due to the blurred-out nature of the wavefunction, a small part of it leaks out through to the other side.
- 03:37: Now the latter is very improbable - only as likely as the tiny fraction of the wavefunction that peaks through that barrier.
- 05:56: It seems natural to define those times as whenever the center of the wavefunction passes the start and end points.
- 06:01: But what if the wavefunction changes during the tunneling.
- 06:06: In a sense, the leading edge of the old wavefunction becomes the center of the new wavefunction.
- 06:45: It’s hard to measure the travel time of a quantum train OR a quantum wavefunction because it’s hard to define the start and end points.
- 07:01: Launch a particle through empty space with a well defined starting position, and it’s position wavefunction will spread out before the finish line.
- 07:08: ... center of that wavefunction can’t travel faster than the speed of light, but upon measurement, the ...
- 08:50: ... study also finds that the tunneling wave packet isn’t necessarily “reshaped” all that much - it’s not clear that ...
- 13:59: ... through solid bedrock so there’s a low probability that your quantum wavefunction will make it through - but if you do then the trip is instantaneous, and ...
2021-10-05: Why Magnetic Monopoles SHOULD Exist
- 04:37: ... are unaltered by changes in one simple property - the phase of the wavefunction. ...
- 06:52: In quantum mechanics, this works by shifting the phase of the particle’s wavefunction.
- 07:34: ... shift induced between the different sides of the string is exactly one wave cycle - which means no observable ...
2021-09-21: How Electron Spin Makes Matter Possible
- 02:59: ... in the recent episode - but for now just know that it’s just the type of wavefunction that fermions have, and has this property that it returns to its ...
- 05:59: ... in the classical sense. They’re quantum objects described by a quantum wavefunction. A wavefunction is this thing that holds information about the ...
- 06:49: ... spinor wavefunction of the electron can “wave” through space, but it includes another wavy ...
- 07:22: ... degree rotation shifts their phase by a half cycle and adds a -1 to the wavefunction. But we also know from the belt trick analogy that swapping two spinors ...
- 08:37: ... excited state. We can think of these two electrons as having a shared wavefunction - a two-particle wavefunction we’ll call Psi(A,B) - which has two ...
- 09:08: ... are fermions, which means that if we swap their locations the wavefunction gets multiplied by -1. Electron A goes into the first excited state and ...
- 09:45: ... be indistinguishable from each other. But it seems like the two-particle wavefunction changes if we swap the particles. Doesn’t that give us a way to ...
- 10:32: ... see that, we need to see what this two-particle wavefunction looks like in terms of the individual wavefunctions of our two ...
- 11:10: ... two-particle wavefunction needs to be a combination of f and g covering all the possibilities - in ...
- 11:21: ... it because it works. To prove it, let’s switch the particles and the wavefunction sign should flip. We want Psi(A,B) to become Psi(B,A). And Psi(B,A) is ...
- 12:04: ... swapping electrons flips the sign - so we’ve successfully discovered the wavefunction for a pair of ...
- 12:31: The two particle wavefunction would then look like this. The fs become gs.
- 13:03: ... saw from the belt-trick previously about spinors having anti-symmetric wavefunctions, is the pauli exclusion principle. That is, particles with half integer ...
- 13:25: ... rather more rigorous explanation of why spinors must have anti-symmetric wavefunctions that doesn’t involve pant-retention technology. It boils down to the ...
- 13:49: ... equation by itself doesn’t force you to use symmetric or anti-symmetric wavefunctions - but if you try to use the symmetric wavefunctions of the boson then ...
- 14:00: ... state of a particle forever. But if you use the correct anti-symmetric wavefunction then everything works just works out great. So it’s a proof by ...
2021-09-15: Neutron Stars: The Most Extreme Objects in the Universe
- 08:15: ... are outnumbered by neutrons 5 to 1. A given neutron’s wavefunction is so spread out that it becomes hard to even localize ...
- 10:06: ... get dragged in circles, making a very weak gravitational wave signal. These gravitational waves are much weaker than the ...
2021-09-07: First Detection of Light from Behind a Black Hole
- 02:41: A spectrum, by the way, is what you get when you split light into its component colors or wavelengths.
- 04:05: ... causing different parts of the disk to brighten - first the shorter wavelength which corresponds to the hot, inner disk, then to longer wavelengths of ...
- 05:15: In a normal spectrum we see the light from these electron transitions as sharp spikes at specific wavelengths - what we call emission lines.
- 05:22: But in a quasar, the gas is moving fast, and that motion shifts the wavelengths of the light as we see it.
- 05:29: ... we’ve all experienced this Doppler shift when the sound waves of an ambulance siren shift between higher and lower pitch as it passes ...
- 07:33: Its light is blue-shifted to shorter wavelengths.
- 07:41: Meanwhile the gas closer to us is actually moving away from us as it falls towards the black hole - it’s redshifted to longer wavelengths.
- 10:22: We see that iron because it shines at a specific X-ray wavelength - this is the iron K-alpha line.
2021-08-18: How Vacuum Decay Would Destroy The Universe
- 01:31: ... rings, and so it can transfer its oscillations, causing a wave to propagate through space. And there are other ways for ...
- 02:52: ... the field value is zero. For example, for an electromagnetic wave - a photon - the electric and magnetic fields rise and fall ...
2021-08-10: How to Communicate Across the Quantum Multiverse
- 00:23: ... your skull, that sound is nothing but an expanding series of density waves - air molecules mindlessly bumping and shoving each other, oblivious to ...
- 00:53: ... traffic. Each sound is its own configuration of overlapping sinusoidal waves. All these waves overlap to produce a fantastically complex bath of ...
- 01:29: ... called the superposition principle. This principle also applies to the wavefunction in quantum ...
- 01:46: ... the Many Worlds interpretation of quantum mechanics, the universal wavefunction is the reality, encompassing all possible histories and futures and all ...
- 02:29: ... For example there’s the Copenhagen Interpretation, which says that the wavefunction collapses at the point of measurement, leaving only one reality; or de ...
- 03:30: ... Schrodinger equation describes how the wavefunction of a quantum system changes over space and time - and so it should ...
- 04:30: ... understand all of this, let’s first go back to sound waves. As we discussed in that previous episode, this ability for waves to pass ...
- 05:54: ... to be treated independently. A linear restoring force leads to a linear wave equation - and a linear wave equation is what you need for the ...
- 06:09: ... by too much. Non-linearities creep in which can do things like damp the waves - cause them to lose ...
- 06:28: ... assumed that linearity and the superposition principle hold. Stack wavefunctions on top of each other and they behave as though the others aren’t there. ...
- 07:14: ... the Schrodinger equation would add extra non-linear observables to the wavefunction. The normal linear observables are things like position, momentum, spin - ...
- 09:57: ... that you choose to align the magnets. So your choice affects the quantum wavefunction. Polchinski lays out the steps very clearly: you send a spin half ...
- 11:05: First, you, but not other you, need to inject some information into the electron’s wavefunction.
- 11:11: ... perhaps impossible device that subjects both branches of the electron wavefunction to a non-linear field. That field sort of spreads the local information ...
- 12:00: ... that in a non-linear quantum mechanics, actions can influence the entire wavefunction - spanning different “worlds”. Perhaps real communication would be ...
2021-08-03: How An Extreme New Star Could Change All Cosmology
- 03:19: ... atom move between orbitals, they emit or absorb light with very specific wavelengths. That tells us what kind of atoms are in the object, but also a lot more. ...
- 09:18: ... with black holes and neutron stars when LIGO detected the gravitational waves from the last moment of those inspirals. But it should happen with white ...
2021-07-21: How Magnetism Shapes The Universe
- 07:15: When radio waves interact with those electrons, their polarizations are also affected.
- 15:58: For example, particle position wavefunction is typically a smooth distribution of possible locations - some more probable than others.
- 16:18: To get this sort of splitting, two parts of that wavefunction need to influence other particles in ways that are distinguishable from each other.
- 16:49: ... that mean for the different weights - probabilities of those different wavefunction ...
- 17:42: One thing that will influence the number of worlds is if there’s any degree of suppression of the wavefunction.
- 17:49: For example, do the weakest, less “probable” parts of the wavefunction get pruned?
- 18:08: So Barefoot asks what if there’s a damping function that suppresses the universal wavefunction?
- 18:33: And anyway, as many of you pointed out - we don’t really need wavefunction damping if we have the time variance authority pruning worlds for us.
2021-07-13: Where Are The Worlds In Many Worlds?
- 01:47: ... wave mechanics, this principle tells us that when two waves overlap, their ...
- 02:09: Each ripple moves as though it’s the only wave on the pond.
- 02:25: The weirdness of this is clearer if we watch two waves cross each other in one dimension.
- 02:30: ... at their collision seems to hold no record of the shapes of the incoming waves, and yet its motion perfectly regenerates those waves, which travel on as ...
- 02:46: If the amplitude of the waves is is too high, the principle can break down.
- 03:06: The main point is that this holds approximately for familiar waves, up to some amplitude.
- 03:13: But the superposition principle seems to always hold for the waves that drive quantum mechanics.
- 03:20: ... the ability for the quantum wavefunction to co-exist and overlap without being affected by that overlap is how ...
- 03:39: Quantum mechanics is a theory about waves.
- 03:42: It tells us that everything in the universe can be described by a wavefunction.
- 03:46: Where a pond ripple is an oscillation in surface height, the wavefunction is an oscillation in probability, or more accurately probability density.
- 04:04: ... appear to be randomly selected based on the current state of the wavefunction - more likely where the wavefunction is stronger, less where it’s ...
- 04:12: The wavefunction is what underlies our perceived reality.
- 04:16: We never see the wavefunction - we only see measurements - we pluck our reality from this fantastically complex structure.
- 04:23: ... array of possibilities, a sprinkling of the high points of the cosmic wavefunction. ...
- 04:32: The actual mechanics of quantum mechanics is all about determining the shape and evolution of the wavefunction.
- 04:38: To calculate this we use the Schrodinger equation, which tells us how the amplitude of the wavefunction changes over time and space.
- 04:46: Just as with our pond ripples, the wavefunction can overlap and either stack stack up or cancel out - constructive or destructive interference.
- 04:54: ... of this behavior is in the double-slit experiment, where the position wavefunction of an electron passes through two gaps in a screen and then interferes ...
- 05:06: ... on a detector screen, we find that we’re more likely to see it where the wavefunction is high - and so electron after electron we trace out these interference ...
- 05:22: ... of quantum mechanics - the Copenhagen Interpretation - tells us that the wavefunction “collapses” - it instantaneously shrinks from encompassing a huge range ...
- 05:53: It says that the wavefunction never collapses - it evolves forever by the Schrodinger equation.
- 05:59: The wavefunction of the electron joins the wavefunction of the detector screen at all points, rippling onwards.
- 06:09: What happens to the rest of its wavefunction?
- 06:11: ... understand that we have to remember that the electron’s wavefunction is only a tiny sliver of a great cosmic wavefunction that includes every ...
- 06:23: ... screen, what we’re really seeing is a cascade of ripples in the cosmic wavefunction, which encompasses the piece-wise wavefunctions of many particles as it ...
- 06:37: ... the wavefunction ripples through the detector, along wires, through computer circuitry, ...
- 06:54: The Copenhagen interpretation says that at some point in this process, most of the wavefunction vanishes.
- 07:00: ... paths to the electron's wavefuntion not corresponding to our observation of that spot cease to exist. Many ...
- 07:23: ... because the many, many interactions that these wavefunction branches experience on their way to your brain render them forever ...
- 07:51: But the key is that the wavefunction slice corresponding to those two worlds was still coherent.
- 07:57: ... still line up in a systematic way to produce high and low points in the wavefunction - meaningful blips in the probability ...
- 08:14: ... a perfectly reliable measurement without corrupting the phase of the wavefunction in a way that destroys coherence - destroys the relationship between ...
- 08:28: ... the detectors you still have two parts of the same electron’s wavefunction, but now the phase relationship, the correlation between peaks and ...
- 09:04: Once there’s no longer a recoverable phase relation between the branches of the wavefunction, the worlds have separated forever.
- 09:11: ... means the wavefunction of your brain also has branches - different internal states that ...
- 09:21: But those parts of your brain wavefunction are out of phase with each other.
- 10:05: After your visual cortex gets an image of the computer screen, a small slice of your brain's wavefunction splits in response to the possible results.
- 10:19: Ultimately your body’s position wavefunction splits - in one version you move left, in the other you move right.
- 11:02: Well, sort of - in the sense that the position wavefunctions of the two yous can be mapped to these spatial locations.
- 12:01: On a quantum scale, worlds - or wavefunction components - recombine all the time.
2021-07-07: Electrons DO NOT Spin
- 02:25: ... properties of electrons. That came from looking at the specific wavelengths of photons emitted when electrons jump between energy levels in ...
- 07:30: ... how quantum objects behave as evolving distributions of probability - as wavefunctions.It was proving amazingly successful at describing some aspects of the ...
- 09:59: ... brings it back to normal. To get a little more technical - the spinor wavefunction has a phase that changes with orientation angle - and a 360 ...
- 10:47: Meaning you can represent a particle wavefunction in terms of either of these properties.
2021-06-23: How Quantum Entanglement Creates Entropy
- 06:38: ... Quantum systems are described by what we call the wavefunction - that’s the distribution of probabilities of all the ...
- 06:56: ... an example, imagine you have a quantum coin. It has a wavefunction that just describes which side is up - heads or tails. ...
- 07:44: ... because its state is entirely defined by its superposition wavefunction - it is in a pure state of 50% heads 50% tails. This is ...
- 08:42: ... tails before you reveal it. That information of IS embedded in its wavefunction, it just isn’t known to you. So the regular coin's entropy - in this ...
- 09:22: ... - both possibilities exist simultaneously. The unrevealed wavefunction is like this, which means 50% heads tails and 50% tails heads. ...
- 11:00: ... that it soon becomes impossible to access the entire wavefunction. We call this process decoherence - it’s how the ordinary ...
- 11:50: ... become entangled with the coin and live in the slice of the wavefunction - the mixed state -where the coin is either heads OR ...
2021-06-16: Can Space Be Infinitely Divided?
- 03:14: ... you can only clock the instant of the return to within one wave-cycle of the electromagnetic wave. That gives a distance ...
- 03:47: ... Light carries energy and momentum - and the shorter the wavelength, the more it carries. If you bombard your object with a powerful ...
- 04:30: ... photon’s momentum is the Planck constant divided by its wavelength. So just replace photon momentum with the uncertainty momentum of ...
- 06:02: ... and who cares about momentum. We keep decreasing the wavelength of our measuring photon - ultraviolet - X-ray - ...
- 06:39: ... and the energy of a photon is Planck’s constant times c^2 over the wavelength. We have this thing that’s full of our wonderful fundamental ...
- 07:10: ... you pump up the energy of your photon, reducing its wavelength also reduces the regular Heisenberg uncertainty, but at the same ...
- 07:48: ... a one-Planck-length object. You need a photon with a wavelength smaller than one-Planck-length. But that photon has enough ...
2021-06-09: Are We Running Out of Space Above Earth?
- 00:00: ... of the Chinese Long March 5 rocket burning up on re-entry has made waves through the world- in some cases, quite literally, as the debris from ...
2021-05-25: What If (Tiny) Black Holes Are Everywhere?
- 02:52: ... the wavelength of the emitted particles are about the size of the whole event horizon, ...
- 03:08: ... such black holes the Hawking radiation is just photons - electromagnetic waves with kilometers-long wavelengths, so really, really low energy radio ...
- 03:25: But as the black hole shrinks in mass and in size, its Hawking radiation also decreases in wavelength - but it increases in energy.
- 05:13: In that motion they produce thermal radiation that includes every possible wavelength of light.
- 05:18: But if you zoom in on a single iron atom - it can’t emit every wavelength of light.
- 11:17: ... with the limits of the uncertainty principle in detecting gravitational waves. ...
- 13:36: ... can be gamed to improve measurements - in particular in gravitational wave ...
2021-05-19: Breaking The Heisenberg Uncertainty Principle
- 00:25: ... And also pretty recently we have the measurement of gravitational waves by ...
- 02:05: That version is called matrix mechanics, but we get the same uncertainty principle using the wave mechanics of Schrodinger.
- 02:13: ... you can watch our episode on how it comes about from thinking about waves. ...
- 03:31: ... example, how can a quantum object sometimes be a “wave” and some times be a “particle?” In a sense it is both, and in a sense it ...
- 05:01: ... Laser Interferometer Gravitational Wave Observatory measures ripples in the fabric of space caused by ...
- 05:19: For fainter gravitational waves we quickly run up against the Heisenberg limit.
- 05:36: ... paths and then later recombined in such a way that the electromagnetic waves of these laser beams destructively ...
- 05:46: By that I mean that the peaks of one wave lines up with the troughs of the other, canceling out perfectly.
- 05:51: But if a gravitational wave passes through the interferometer, the relative lengths of the two paths change in a very particular way.
- 06:05: This measurement is incredibly sensitive to the path lengths - but that means it’s also sensitive to the phase of the light waves.
- 06:11: Phase refers to the relative positions of the peaks and troughs of the waves.
- 06:39: And that noise will obscure faint gravitational wave signals.
- 06:44: ... are larger than the change in the arm lengths due to a gravitational wave, then we’ll never see those ...
- 07:07: To improve our ability to detect faint gravitational waves we need to reduce the uncertainty in the phase of the laser beams.
- 07:15: That would enable us to line up those waves more perfectly to reduce quantum fluctuations.
- 09:05: Less flickering due to random phase shifts means that we can see real signals due to much weaker gravitational waves.
- 09:13: ... the next upgrade will allow them to detect up to 50% more gravitational wave events - events from further away, and involving lower-mass mergers of ...
- 09:43: But that noise is less of a problem than the phase uncertainty, at least for the higher frequency gravitational waves.
2021-04-21: The NEW Warp Drive Possibilities
- 09:33: We can think of the warp field as a special type of isolated wave moving through space - what we call a soliton.
- 09:39: In previous work, this wave only waved in the direction of motion.
- 10:01: ... found that by including components of the wave motion that were perpendicular to the direction of motion he could build ...
- 12:47: And possibly also building a starship, to propel humanity into the galaxy on waves of warped space time.
2021-03-23: Zeno's Paradox & The Quantum Zeno Effect
- 02:52: In the language of the Copenhagen interpretation of quantum mechanics, we say that the “wavefunction collapses” on observation.
- 02:58: ... as just the distribution of probability amplitudes of its position; its wavefunction is spread between the start and end of the ...
- 03:58: ... if there’s no observation the wavefunction evolves - less and less amplitude at the starting state and more and ...
- 04:15: ... your eyes for a second, which is your mistake - it allows the arrow’s wavefunction to evolve smoothly into the state of quantum ...
- 04:28: Every observation you make of the arrow collapses its wavefunction into one of its possible positions - start or end.
- 04:41: ... observation resets the trajectory to the start, at which point the wavefunction has to start evolving from scratch - but you keep observing it and keep ...
- 06:53: ... to the wavefunction collapse picture, it has to make a choice - the superposition must ...
- 07:23: In theory, if these “measurements” are fast enough they should stop the wavefunction from evolving.
- 08:43: ... what exactly do we mean by a “measurement” and what do we mean by wavefunction ...
- 09:55: ... idea is that measurement causes wavefunction collapse because it scrambles the delicate information connecting ...
- 10:04: Superposition only exists if the different parts of the wavefunction are connected or correlated with each other.
- 10:09: We would say that the wavefunction for different electron states or quantum arrow positions are in phase with each other, or “coherent”.
- 10:25: Decoherence occurs, and the different parts of the wavefunction, representing possible realities, can no longer interact.
- 10:38: ... to perfectly measure it, and that means decoherence - or the illusion of wavefunction ...
- 10:49: So on to wavefunction collapse.
- 10:52: In the Copenhagen interpretation, only the part of the wavefunction corresponding to the measurement outcome survives.
- 10:57: But in the Many Worlds interpretation, the entire wavefunction survives and splits and you split with it.
- 11:18: But in this case, you’re not forcing the wavefunction to collapse back to its starting position through the power of observation.
- 11:24: Your interaction with the wavefunction causes it to decohere - which means two things - you perturb the system in a non-subtle way.
- 12:15: And what is wavefunction collapse?
- 14:45: Max Graham asks how gravitational waves encode the distance that they've traveled.
- 15:08: But it's different with gravitational waves from merging black holes.
- 15:11: The intensity or amplitude of those waves drops off with distance, not distance squared.
- 15:16: But the important thing is that the amplitude of the wave is directly encoded in the frequency of the wave.
- 15:32: But that chirp mass also determines the power that was radiated in gravitational waves during the inspiral.
- 15:48: So then the amplitude of the wave as we see it at Earth tells us how much distance the wave must have traveled.
2021-03-16: The NEW Crisis in Cosmology
- 01:16: ... us through the expanding universe it gets stretched out - its wavelength increases. If we also know how far that light traveled ...
- 10:08: ... “baryon acoustic oscillations” are the fossils of ancient sound waves that reverberated through the hot, dense plasma of the early ...
- 11:57: ... before too long we may even be able to use gravitational waves from merging black holes to measure the Hubble constant. ...
- 15:19: ... you can figure out the interference pattern by thinking of circular waves originating from the slits, and calculating how these ripples add ...
2021-03-09: How Does Gravity Affect Light?
- 02:58: See, light is a wave.
- 03:00: The distance between the peaks of that wave is its wavelength.
- 03:18: Wavelength increases, which means frequency and energy drop.
- 04:10: These are the ticks of a clock, and the frequency dictates the frequency and the wavelength of the photon produced by that motion.
- 04:27: ... light emerging from it can be sapped of ALL energy - redshifted so the wavelength is effectively ...
- 07:31: Huygens’ wave theory of light advanced the field of optics enormously.
- 07:40: The idea is that any wave can be described as an infinite number of point-like oscillations, each of which produces new waves.
- 07:49: The sum of all those waves perfectly describes the future evolution of the original wave.
- 07:58: At any point in time, the expanding ripple can be thought of as an infinite number of sources of new circular ripples, or wavelets.
- 08:07: Those wavelets also expand outwards, but they cancel each other out everywhere except in the outward direction of the original ripple.
- 08:23: A plane wave of light is just an infinite number of new sources of light that generate the next step in the plane wave.
- 08:41: Our plane wave reaches the boundary to a new medium with a slower speed of light.
- 08:47: ... it arrives at some angle, then the next set of wavelets forming at that boundary will be more closely packed - the fronts of ...
- 09:00: So now if we connect the wavelets to reconstruct the overall wavefront, we see that the path of the light has bent.
- 09:17: ... - first that light acts like a very classical, 17th-century style plane wave so you can use Huygens' ...
- 10:54: At each location perpendicular to a gravitational field, the wavefront of light can be thought of as a vertical column of new wavelets.
- 11:11: So those lower wavelets become bunched up from your perspective.
- 11:15: If you track the path of the wavefront by connecting the ripples, you see it bends.
- 11:59: Light isn’t really a simple plane wave - it’s a much weirder quantum wave-particle thing.
- 12:32: Light is a wave and a particle; time slows or space flows in gravitational fields.
2021-02-24: Does Time Cause Gravity?
- 08:39: Last time we talked about the gravitational wave background - the ambient buzz of gravitational waves from the distant and ancient universe.
- 09:10: ... I mentioned in reference to a potential component of the gravitational wave ...
- 10:04: ... the big bang, and gravitational Kinkusnacht asks whether gravitational waves can be used to test ideas in quantum ...
- 10:21: The most well known prospect is by detecting the signatures of primordial gravitational waves - waves from the inflationary epoch.
- 10:28: These could be found in the gravitational wave background, but also indirectly through their effect on the cosmic microwave background.
- 10:35: ... of those waves with matter right after inflation may have caused characteristic ...
2021-02-17: Gravitational Wave Background Discovered?
- 00:00: ... impressive when we built this giant machine that spotted gravitational waves from colliding black holes well we've just taken it to the next level ...
2021-02-10: How Does Gravity Warp the Flow of Time?
- 08:13: Now the worldline is.a sine wave.
2021-01-19: Can We Break the Universe?
- 00:02: Black holes, gravitational waves, he was even the first to realize that friggin lasers could be a thing.
- 14:15: ... "true" is like asking if light is made up of particles or if light is a wave? ...
2021-01-12: What Happens During a Quantum Jump?
- 02:55: ... says that “measurement collapses the wavefunction”, which these days is more often taken to mean that interaction with the ...
- 03:07: But one guy was not impressed by this idea - the inventor of the wavefunction himself, Erwin Schrödinger.
- 04:45: He believed it all came down to waves—and that nothing was particularly special about these waves compared to any other kind of classical wave.
- 10:54: ... the act of measuring a system will, in Copenhagen terms, collapse the wavefunction, which drastically changes how the system behaves - for example, trapping ...
- 11:50: ... and Heisenberg in Copenhagen, or ride the continuous and deterministic wave of Schrodinger and ...
2020-12-15: The Supernova At The End of Time
- 14:24: And WE observers ride the wave of time in a particular direction.
- 14:28: If correlations grew in the opposite direction - the wave flowed backwards, our definition of future and past would flip.
- 15:25: ... after the measurement of particle position is made, the state of the wavefunction before that measurement is ...
- 15:38: ... the many worlds interpretation the wavefunction persists, so reversing time means reversing all outcomes of the ...
2020-12-08: Why Do You Remember The Past But Not The Future?
- 13:26: Yossi Sirote asks essentially the same question - doesn't the collapse of the wave function break time symmetry.
- 13:33: ... is that yes, IF quantum mechanics is fundamentally random, and IF the wavefunction collapse is a random rather than deterministic event, then time-reversal ...
- 13:47: ... and at any rate invoking random collapse doesn’t tell you why the wavefunction collapses in one direction and not the ...
2020-11-11: Can Free Will be Saved in a Deterministic Universe?
- 05:52: The quantum information in the state of the wave function before collapse is destroyed, but information is also created.
- 06:04: Information threads both end and begin at every wave function collapse.
2020-11-04: Electroweak Theory and the Origin of the Fundamental Forces
- 04:50: ... try an example: In quantum mechanics, the wavefunction determines the probabilities of certain outcomes being measured for ...
- 05:01: Quantum mechanical equations of motion like the Schrodinger equation describe how the wavefunction evolves through space and time.
- 05:07: Like all waves, the wavefunction has a phase - the current position of the peaks and troughs.
- 05:42: So there we go - we insisted on a symmetry - that the Schrodinger equation is invariant to changes in the local phase of the wavefunction.
- 06:05: ... shouldn’t change when we shift both the real and complex parts of the wavefunction by some amount, we shift the phase, a process which leaves the ...
- 06:20: ... not stretch or shrink: the length of the vector is the magnitude of the wavefunction, and the rotation amount is our local phase ...
- 06:57: ... can be completely represented by just one function, like our single wavefunction from the Schrodinger ...
2020-10-27: How The Penrose Singularity Theorem Predicts The End of Space Time
- 13:38: ... with the other worlds. - AKA branches of the wavefunction. That’s exactly what a quantum interference experiment is seeing - ...
2020-10-20: Is The Future Predetermined By Quantum Mechanics?
- 02:46: According to quantum mechanics, physical systems, parts of the universe evolve as wave functions.
- 03:04: The wave function can be thought of as a state in which all physically possible realities intermingle.
- 03:21: The wave function is real.
- 04:03: At which point, the wave function collapses into a defined state.
- 04:23: ... wave function evolves in a precise way, perfectly defined by the equations of ...
- 04:36: The dice are thrown when the wave function collapses.
- 04:45: Another popular interpretation of quantum mechanics is the Many-Worlds Interpretation, which simply states that the wave function never collapses.
- 05:13: The wave function never collapses, it evolves deterministically forever.
- 05:17: The illusion of randomness is that we find ourselves in the one branch of the wave function, corresponding to the reality we perceive.
- 05:41: It's tempting to equate everything outside our past light cone with the unobserved wave function.
- 05:48: You can imagine that light cone sort of just plowing through the undefined universal wave function, collapsing it as it goes.
- 05:56: Or at least the parts of that wave function for which signals actually reach our awareness.
- 06:09: But now let's say we believe that other observers in the universe can also collapse the same universal wave function with their observations.
- 06:58: ... past, and if we believe in other observers there's no way to keep the wave function of your future from being collapsed before you get ...
- 07:12: Now, there are subtleties in this wave function collapse idea.
- 07:36: In that case, un-collapsed wave functions tend to exist only in microscopic pockets or in very special circumstances.
- 07:46: ... the only totally coherent way for a non-deterministic wave function collapse interpretation like Copenhagen, to give you an ...
- 08:08: Your light cone sweeps through the global wave function but it doesn't collapse that wave function, rather it selects from it.
- 10:14: The evolution of the wave function is deterministic.
- 10:18: ... means all future branching of the wave function of your present, by which I mean the entanglement network that ...
- 10:50: It's that part of the global wave function that you are connected to via entanglement and that shares your timestamp of now.
- 11:10: ... should make an honorable mention de Broglie-Bohm pilot wave theory, This is an entirely deterministic interpretation that doesn't ...
- 11:27: ... universe of pilot wave theory is really a block universe but unfortunately, no one has ...
2020-10-13: Do the Past and Future Exist?
- 03:56: Our awareness of the universe rides this forward-moving wave of the present.
- 09:23: Imagine that the future is created as the wave of the present sweeping out the block universe.
- 09:29: But where is that wave?
2020-10-05: Venus May Have Life!
- 02:22: ... of Venus appear to absorb the Sun’s light in a weird way - more short wavelength visible and UV light is sucked up than expected, leading to the yellow ...
- 03:58: This can be done at far infrared and submillimeter radio wavelengths where the star’s own glare doesn’t kill the signal.
- 04:07: One possible biosignature in this range is phosphine, which absorbs photons of around 1.1mm wavelength.
2020-09-28: Solving Quantum Cryptography
- 06:59: ... different computers, you’re processing in different parts of the quantum wavefunction - or in different parallel realities if you’re into the Many Worlds ...
- 07:51: But now the entire superposition - all elements of the wavefunction are related by the period of their repetition.
- 08:00: ... the correct one - essentially, you cause those incorrect parts of the wavefunction to destructively interfere, leaving the correct period ...
2020-09-21: Could Life Evolve Inside Stars?
- 14:01: ... any continuous, periodic function can be represented as a sum of sine waves of different ...
- 14:11: But then motion in a circle can be represented by 2 separate sine waves for displacement in the x-y directions.
- 14:19: ... arbitrarily complex orbital motion can be represented with enough sine wave pairs in a fourier series - which can also look like a series of ...
2020-09-08: The Truth About Beauty in Physics
- 04:17: ... in time, space, angle, or something more abstract like the phase of the wavefunction. ...
- 07:49: He sought to develop a quantum mechanical wave equation that agreed with Einstein’s special relativity.
- 09:30: And Maxwell’s equations, which parsimoniously unite electricity and magnetism but also predict the existence of electromagnetic waves - of light.
- 09:42: ... mirrors - but the resulting theory predicts black holes, gravitational waves, and even the big ...
- 11:30: His idea of introducing a new symmetry to space was translated to adding a new symmetry to the wavefunction in quantum mechanics.
- 13:50: Basically, why do we see specific wavelengths missing from starlight due to electrons absorbing those wavelengths in atoms?
- 13:58: Shouldn't those same electrons then drop back down in energy level, emitting the same wavelengths they absorbed?
- 14:04: ... absolutely do - and in some cases you see extra light at those special wavelengths - what we call emission lines, in some cases less light - absorption ...
- 14:22: ... in question are between us and a source of light that's bright at all wavelengths, then we see absorption - that's because although those atoms to reemit ...
2020-08-17: How Stars Destroy Each Other
- 02:45: But it can be found if you look a little off center for a spot of light that flares erratically from visible to X-ray wavelengths.
- 06:16: ... pulses - most brightly in radio light, but potentially at all wavelengths. ...
- 07:38: He observed these objects using visible wavelength of light - and found one object was indeed pulsing.
- 10:43: ... to our episode on this strange new observation by LIGO: gravitational waves from the merger of a black hole with ... something ...
- 12:44: ... then the universe should be very faintly humming with a gravitational wave background from the countless mergers than happened in the earlier ...
- 13:15: That's an easy one - in order to generate detectible gravitational waves, both objects need to be extremely compact.
- 13:22: The waves get generated when extreme masses spiral together at very small distances.
- 13:32: They are ripped apart before getting close enough to generate gravitational waves.
2020-08-10: Theory of Everything Controversies: Livestream
- 00:00: ... have in the case of a photon you have the c in which the photon is a wave if you will and then you have the wave itself and you can say well i ...
2020-07-28: What is a Theory of Everything: Livestream
- 00:00: ... of this theory from 100 years ago was this notion of gravitational waves and these were only verified experimentally just a few years ago so ...
2020-07-20: The Boundary Between Black Holes & Neutron Stars
- 00:00: When we detected the very first gravitational wave, a new window was opened to the mysteries of the universe.
- 00:23: By now we’re becoming used to announcements that a new gravitational wave event has been detected.
- 00:38: ... the LIGO and VIRGO gravitational wave observatories spot event after event, the excitement is shifting from ...
- 01:04: ... the shape of the gravitational waveform, and based on calculations using Einstein’s general theory of relativity, ...
- 01:53: We’ve done gravitational wave astronomy before, but this event is so mysterious we had to cover it.
- 02:18: ... passage of a gravitational wave causes extremely tiny changes in these arm lengths, which in turn causes ...
- 02:30: ... August 14 2019, a gravitational wave hit the LIGO and VIRGO observatories one after the other in close ...
- 02:44: ... the shape of the detected waveform, the masses of the merging objects were figured figured out as 23.2 and ...
- 11:01: With new gravitational wave events coming every week or two, we’re sure to see more of these sorts of mergers.
2020-06-30: Dissolving an Event Horizon
- 08:55: ... any rate, our observations of gravitational waves from colliding black holes and various other methods for estimate black ...
- 15:14: ... mentioned that in conformal cyclic cosmology, photons and gravitational waves can pass the boundary from universe end to new big bang, and so there ...
2020-06-22: Building Black Holes in a Lab
- 00:16: ... into tiny spaces in quasars or X-ray binary systems. Gravitational waves that perfectly match our theoretical prediction for black hole mergers. ...
- 02:12: ... So what happens if another fish goes over the waterfall? Since sound waves are just vibrations propagating through a medium, if the medium is ...
- 04:45: ... of water decreases, the current accelerates while the speed of surface waves slows ...
- 04:55: At some point the flow is faster than the waves - and that’s your analog event horizon.
- 05:01: ... the flow is in the opposite direction to the waves this is actually an analog white hole. Other experiments use a ...
- 05:25: ... hole scattering the vibrational modes of the quantum fields that have wavelengths similar to the black hole’s event ...
- 08:04: ... black holes can donate some of their rotational energy to particles or waves that pass close by. This is the Penrose process, and when the particle ...
- 08:58: ... captures all the action to great precision. On one side of the tank, a wave generator propagates waves across the surface where they pass across the ...
- 09:09: These waves are analogous to incoming particles. The waves are only 1 millimeter high, but superradiance can increase their height by as much as 10%.
2020-06-15: What Happens After the Universe Ends?
- 14:02: It turns out that, as well as photons, gravitational waves should be able to pass between aeons.
2020-05-27: Does Gravity Require Extra Dimensions?
- 04:32: ... fact we saw in a previous episode how a particular gravitational wave detection from LIGO seemed to rule out the possibility of extra spatial ...
2020-05-11: How Luminiferous Aether Led to Relativity
- 02:33: ... the fluid dynamics of the aether. But Huygens is most famous for his wave theory of light. By thinking of light as a wave, he was able to build a ...
- 03:25: ... a wave on a string: each string segment moves up and down only, tugging on ...
- 04:06: ... of Huygens’ aetheric gravity. And Newton also opposed this whole wave theory for light business. Now Newton’s case is complicated - some of ...
- 05:08: ... versus Newton. Light as a wave versus a particle. Most accepted Newton - as most always did. This was ...
- 05:53: ... light experiences refraction and interference like a wave. Add to that the fact that in the 1860s, Maxwell’s equations predicted ...
- 06:48: ... classical waves travel at a constant speed relative to their medium. For example, sound ...
- 07:00: But hop in a jet plane and you can chase your own sound waves so they appear to stand still.
- 07:06: ... apparent velocity of an object - or a wave - depends in a simple way on the velocity and direction of motion of the ...
- 07:19: ... wanna hope Galilean relativity is right OK, so if light is a classical wave in some medium then we should see changes in the apparent speed of light ...
- 09:02: ... in different places. Changes in length quite a bit smaller than a single wavelength of light would produce observable shifts in the fringe pattern. And this ...
- 09:26: ... the relative speed of light along the two arms. That would cause the wave pattern in one arm to lag behind the other, leading to a similar shift ...
- 11:04: ... aether - at least, not one that resembled a classical medium for wave propagation. The speed of light appeared to be independent of the motion ...
2020-05-04: How We Know The Universe is Ancient
- 01:35: ... incredible speeds, based on their Doppler shift - the lengthening of the wavelengths of their light due to their motion. Then Edwin Hubble figured out the ...
- 16:59: ... multiverse and how there are way more treats in other branches of the wavefunction. ...
2020-04-28: Space Time Livestream: Ask Matt Anything
- 00:00: ... of photons that are redshifted okay and the restrict of gravitational waves what happens to their energy well so the answer is there are a couple ...
2020-04-14: Was the Milky Way a Quasar?
- 07:25: ... shock waves created by the supernovae from a starburst in the Milky Way could ...
2020-03-24: How Black Holes Spin Space Time
- 01:01: ... told us that black holes are very real. We’ve seen the gravitational waves caused by their mergers, we’ve witnessed the havoc they wreak on their ...
2020-03-16: How Do Quantum States Manifest In The Classical World?
- 00:44: ... mechanics tells us that the atom’s wavefunction can be in a superposition of states - simultaneously decayed or not ...
- 05:32: ... how entanglement is connected to measurement and the collapse of the wavefunction. ...
- 08:44: ... electron and positron. The measurement hasn't actually happened yet. The wave function hasn't collapsed. Here’s more evidence, even with the ...
- 09:56: ... so our atomic measurement device doesn’t “collapse the wavefunction.” It doesn't settle measurement basis. So where does that happen? In order ...
- 16:29: ... may be how our big bang happened. If so, then the never-ending global wavefunction of the Many worlds interpretation could indeed be a big-bang machine. On ...
- 17:40: ... world interpretation handles the probabilistic interpretation of the wave function. And then goes on to correctly answer their own question - to ...
2020-03-03: Does Quantum Immortality Save Schrödinger's Cat?
- 01:11: It only explains why separate branches of the wavefunction - separate “alternate histories” - stop being able to interact with each other.
- 01:29: ... example the Copenhagen interpretation, which says that the wavefunction branches that we don’t observe somehow vanish at the moment of ...
- 02:33: ... radioactive decay over a certain period of time - that means the quantum wavefunction of the atom splits equally - the atom is simultaneously decayed and not ...
- 02:49: So then surely the cat’s wavefunction splits too - into dead and alive.
- 02:55: According to Copenhagen, one of these results becomes “real” when the physicist opens the box, while the other branch of the wavefunction vanishes.
- 03:03: But in Many Worlds both branches continue forever - and the physicist’s wavefunction also splits into two - I guess into guilty and relieved.
- 03:13: ... no way for them to confirm the existence of the other branch of the wavefunction. ...
- 04:50: According to Copenhagen, all branches of the wavefunction besides “definitely dead” get cut off with ruthless efficiency almost all the time.
- 04:59: But that’s not true in Many Worlds - according to which all branches of the wavefunction persist.
- 05:04: ... even after trying this experiment even once, there’ll be a branch of the wavefunction where the physicist opens the box and crawls out, to the amazement of ...
- 05:31: Many Worlds, on the other hand, guarantees their survival in at least one branch of the quantum wavefunction.
- 06:57: ... even if some insanely rare branches of your wavefunction keep you alive beyond your years, I’d advise you to quit smoking and do ...
- 10:55: And to all of you - thanks for joining me on this wavefunction branch.
- 12:19: Well, Vampyricon answers this partically, saying that each observer will be on one decohered branch of the wavefunction.
- 12:46: ... make consistent observations, and who are unaware of observers on other wavefunction branches who make different ...
- 15:33: Some of you may recall that this is also the official salute to identify yourself as someone capable of seeing the wavefunction.
2020-02-24: How Decoherence Splits The Quantum Multiverse
- 00:35: ... measurement problem - the question of why and where the blurry quantum wavefunction collapses into well-defined measurement ...
- 00:48: We focused on a simple question: does conscious observation of a quantum system cause the wavefunction to collapse?
- 01:03: The upshot is that more and more physicists think that consciousness - and even measurement - don’t directly cause wavefunction collapse.
- 01:16: The collapse itself may be an illusion, and the alternate histories that the wavefunction represents may continue forever.
- 01:41: ... to dip our toes and cover one aspect of it, by thinking in terms of the wavefunction. ...
- 01:52: ... quantum systems are described by this wavefunction thing - it’s the mathematical object that defines the distribution of ...
- 02:04: Wavefunctions evolve over time according to the Schrodinger equation, and that evolution tracks how the system’s properties might change.
- 02:13: Another way to think about it is that the time-dependent wavefunction maps all possible histories for the object.
- 02:50: But this only works if those alternate histories - those branches of the wavefunction - remain “coherent”.
- 03:11: ... general wave mechanics, we say that a set of waves are coherent if they match in ...
- 03:29: Laser light is an example of a coherent wave.
- 03:38: ... particle seems to pass through two slits simultaneously as a probability wave that ultimately “collapses” to leave it as a single position on a ...
- 04:22: We can think of those paths as slices of the wavefunction that represent possible trajectories.
- 04:36: In this case that mostly means these two paths - these wavefunction slices, which we can represent with simple sine waves.
- 04:44: ... the path lengths are the same, the peaks of one wave line up with the peaks of the other - the two waves are perfectly in ...
- 04:57: Because the wavefunction is amplified at that spot, there’s a high probability of the particle landing there.
- 05:16: Here the peaks of one wave line up with the troughs of the other and the wavefunction completely cancels out.
- 05:32: Here the path lengths differ by exactly one full wavecycle.
- 05:36: And so on - so we ultimately see this series of bands - lots of particles where the wavefunction is amplified, few where it’s canceled.
- 05:44: In general we can see an interference pattern if there is coherence between different parts of the photon wavefunction.
- 05:59: In this case, the phases match perfectly when the wavefunction leaves the slits - peaks and troughs come out at the same time.
- 06:21: So we have two parts of the wavefunction - two branches or alternate histories - that have a consistent phase relation between them.
- 06:28: In principle we can bring those parts of the wavefunction back together to cause interference.
- 07:25: - but only as long as the wave function defining those histories remains coherent.
- 07:30: ... both slits AND it reaches both points on the screen - as long the wavefunctions defining those outcomes remain ...
- 07:58: The part of the wavefunction - corresponding to a possible path of the photon - is now disturbed by those particles.
- 08:05: ... can think of that wavefunction slice as the “possible photon” being absorbed and reemitted by those ...
- 08:18: ... that emerging wavefunction can still interfere with itself - the random phase offset would just ...
- 08:58: From our perspective the wavefunction has lost coherence - decoherence has occurred.
- 09:11: Any measurement device must introduce some level of decoherence to the wavefunction before it reaches the screen.
- 09:18: ... decoherence hypothesis, it’s not really some magical effect whereby the wavefunction “knows” that it has been observed and so ...
- 09:35: Let’s now leave the slits alone and let the coherent photon wavefunction reach the screen again.
- 09:54: We can think about the photon wavefunction becoming mixed with the wavefunctions of the quantum particles along this chain.
- 10:16: But by now that wavefunction is getting pretty messy.
- 10:27: Phase differences get introduced between the different branches of the increasingly complex wavefunction.
- 10:38: Two branches of the wavefunction will represent histories where the photon landed in different locations.
- 11:07: ... that phase offset becomes less and less knowable the further the wavefunction advances, and the chaotic nature of the system also ensures that the ...
- 11:21: Without a consistent wave offset it’s not possible to map an interference pattern.
- 11:35: Ultimately, that expanding wavefunction includes the circuitry of the computer, and then the circuitry of your brain.
- 11:41: ... multiple alternate histories propagating from the original double slit wavefunction, but by now each of those wavefunction branches corresponds to a specific ...
- 11:57: ... result in the conscious awareness consistent with that one branch of the wavefunction - corresponding to a single location for the double-slit ...
- 12:10: At this point, as far as you’re concerned, the wavefunction has collapsed - decoherence has occurred.
- 12:16: ... actually, the original double-slit wavefunction may well continue to expand and complexify as it mixes with the ...
- 12:31: So you shouldn’t think of yourself as this gods-eye observer, capable of seeing the whole wavefunction and causing it to collapse.
- 12:39: Rather you are embedded within the wavefunction and see only a slice of it - a slice corresponding to a single history.
- 12:46: ... still interact with each other due to the coherence of that part of the wavefunction. ...
- 12:59: ... order to do quantum experiments we need to isolate a slice of the global wavefunction and maintain its coherence - we need to have information about the ...
- 13:26: And by environment I mean anything that isn’t as perfectly controlled as your tiny, isolated wavefunction slice.
- 14:12: Nor is it accepted that decoherence fully explains the measurement problem and wavefunction collapse.
- 14:19: ... Many Worlds interpretation of quantum mechanics, in which there is no wavefunction collapses at ...
- 14:33: The multiple branches of the wavefunction as it interacts on macroscopic scales.
- 14:38: ... visible to us, stranded as we are on a single branch of the universal wavefunction that itself contains so much more than our little, decohered slice of ...
2020-02-18: Does Consciousness Influence Quantum Mechanics?
- 02:17: That’s the same pattern that would be produced by a wave passing through both slits - a so-called interference pattern.
- 02:31: Each solitary electron must know the entire wave pattern - which means it must, in some sense, travel through both slits.
- 02:40: ... saying that the electron does NOT travel as a particle or as a physical wave along one of these ...
- 02:51: Instead it travels as an abstract “probability wave” - something we call a wavefunction.
- 02:58: That probability wave defines the location of the electron at any point IF you try to measure it.
- 03:16: Prior to measurement, it IS its wavefunction.
- 03:20: ... tells us that when we make that measurement the wavefunction “collapses” - it goes from a cloud of possible final destinations for ...
- 03:34: ... Wavefunction collapse seems essential because our large-scale, classical world isn’t ...
- 03:56: ... electron wavefunction passes through both slits, reaches the electronic detector, and there it ...
- 04:46: ... wrote that wavefunction collapse must happen somewhere between the measuring apparatus and the ...
- 04:56: Probably not as soon as our electron wavefunction reaches the detector.
- 05:05: That means the traveling electron’s wavefunction will just become mixed with the wavefunctions of all electrons that it could possibly excite.
- 05:14: ... should get what we call a superposition of states: a wavefunction in which an electron at every location on the detector screen is ...
- 05:27: So perhaps the wavefunction transition happens somewhere in the circuitry, or in the computer, or in the retina.
- 05:42: With no clear boundary between the quantum and the classical, where does the collapse of the wavefunction happen?
- 05:53: John von Neumann believed that wavefunction collapse must happen at the moment of conscious awareness of the result of an experiment.
- 06:12: ... idea that consciousness collapses the wavefunction is now called the von Neumann-Wigner interpretation, and it’s sort of a ...
- 07:26: They think you’re crazy - they tell you the wavefunction collapsed as soon as the physical experiment was completed.
- 07:38: So there’s the conflict - different observers say the wavefunction collapses at different times.
- 07:55: Therefore he concluded that conscious experience must itself must play a role in generating wavefunction collapse.
- 09:16: ... - like that you can influence reality by acts of will - collapse the wavefunction in your favour to force the location of a spot on a screen, or influence ...
- 10:41: ... Heisenberg’s later writing he states that the wavefunction collapse must be a continuous process between the measurement device and ...
- 11:24: You talk to each other and agree that you observed the same result - the wavefunction collapses in the same way for both of you.
- 11:30: So what ... maybe one of you is forcing their preferred wave function collapse on everyone else?
- 12:00: ... you could talk about a global consciousness collapsing a universal wavefunction - but that’s not going to give you any powers of quantum ...
- 12:19: In fact there are some very precise explanations for why the wavefunction appears to collapse.
- 12:32: ... what happens to these multiple alternate histories after the electron wavefunction reaches the detector - and why these histories stop communicating with ...
- 12:49: ... now, one thing I can say with certainty is that your own future wavefunction includes a deeper dive into the quantum-classical divide, on an upcoming ...
2020-01-27: Hacking the Nature of Reality
- 01:08: ... representations of quantum mechanics soon followed - for example, the wave mechanics driven by the Schrodinger equation and Paul Dirac’s notation ...
- 14:50: Adam Wulg asks whether gas surrounding a pair of merging black holes might significantly affect the gravitational wave signature.
- 14:57: Well, the answer is that those waves would be affected - but not by much.
- 15:01: ... to merge faster, so that should increase the frequency of the those waves and to a lesser extend the actual shape of the ...
2020-01-13: How To Capture Black Holes
- 00:24: ... September 2015 the laser interferometer gravitational wave observatory - LIGO - detected its first gravitational wave from the ...
- 00:59: ... not so surprising. Einstein’s general relativity predicted gravitational waves and astrophysics predicted black hole mergers. When two very massive ...
- 08:50: ... could lead to a bright burst of light to accompany the gravitational waves. ...
- 09:53: ... the release of gravitational waves delivers a kick to the final black hole - a bit like the recoil of a ...
- 10:18: ... of the two LIGO and the VIRGO observatories locates a gravitational wave source to a pretty large blob on the sky, which will typically contain ...
- 10:40: ... we now have advanced follow-up systems in place. As soon as a candidate wave is detected, multiple telescopes scan that region of the sky to search ...
- 11:32: ... like I said: gravitational wave astronomy will reveal many cosmic mysteries and strange phenomena. Now ...
2019-12-02: Is The Universe Finite?
- 01:25: ... episode how that speckled pattern is the frozen imprint of sound waves that reverberated through the first few hundred thousand years after the ...
2019-11-04: Why We Might Be Alone in the Universe
- 13:37: ... to test Loop Quantum Gravity So LQG predicts that light of different wavelengths travels at very slightly different ...
- 14:00: ... if space is quantized on tiny scales, then we expect the very shortest wavelengths of light to be slightly perturbed by these quantum cells of space - sort ...
- 14:15: Wavelengths longer than this quantum scale can ignore this fragmentation and so travel at normal speed.
2019-10-15: Loop Quantum Gravity Explained
- 01:58: Like actors on a stage, where the actors are particles and wavefunctions and fields and the stage is the coordinates of space and time.
- 04:00: Absent measurement, they exist in a fuzzy space of possibilities called a wavefunction.
- 04:06: In the first formulations of quantum mechanics, that wavefunction describes the distribution of possible positions and momenta of, say, a particle.
- 04:16: These can then be resolved into concrete, measured values by acting on the wavefunction with so-called position and momentum operators.
- 04:25: The wavefunction and operators are fundamentally tied to the coordinate system.
- 04:51: In quantum mechanics, time is treated completely separately to other variables - there is no “time wavefunction” or “time operator”.
- 12:41: ... high-energy gamma rays travelling a wee bit slower than low energy radio waves due to the way they propagate through the graininess of a loop quantum ...
- 14:15: David Bennack likes the idea of gravitational lensing of gravitational waves. Well so do I, David.
- 14:38: ... is that it was just one black hole merger, but the gravitational wave from it was deflected by a galaxy or something on its way to us - it was ...
- 15:03: Gravitational waves should be lensed in the same way as light, so it's a plausible explanation.
- 15:22: Still, we'll probably see a lensed gravitational wave at some point.
- 16:16: ... if the fabric of space and time can be stretched and if can have waves, that means it must have a sort of elasticity and resistance to ...
2019-10-07: Black Hole Harmonics
- 00:14: And the rich harmonics of those vibrations, seen through gravitational waves, could hold the secrets to the nature of the fabric of spacetime itself.
- 01:08: ... to detect with the miraculous work of the LIGO and VIRGO gravitational wave ...
- 02:14: ... inspiralling black holes make powerful spacetime ripples – gravitational waves – which intensify as the black holes approach merger, only becoming ...
- 02:48: As those vibrations give up their energy – in this case to sound waves – the vibrations fade. The bell rings down.
- 03:12: In the latter cases we can describe a vibrating string as a series of standing sine waves of different frequencies, all happening at the same time.
- 03:56: In the case of the event horizon, or any spherical-ish surface, we break down the oscillations not into sine waves but into spherical harmonics.
- 04:05: ... are a set of functions pretty analogous to 2-D sine wave on the surface of a sphere, and each spherical harmonic can represent a ...
- 04:24: For a black hole, another way to think of its quasinormal modes is as a set of gravitational waves trapped in orbit around the black hole.
- 06:34: ... the waveform was nicely simulated by spherical harmonic oscillations right from the ...
- 07:22: ... with much greater precision than if they’d just used the gravitational wave signal from the lead-up to the ...
- 07:41: So this sort of frequency analysis of gravitational waves is being called gravitational wave spectroscopy.
- 08:22: ... team analyzed the harmonics in the gravitational wave ring-down from this event and claim a likely detection of at least one ...
- 09:13: ... with the estimate that was previously obtained by analyzing the entire waveform but ignoring the ...
- 11:42: LIGO has a publicly available alert system so that astronomers can follow up gravitational wave detections with other telescopes.
- 12:41: So, long story short – the initial promise of LIGO and the first detection of gravitational waves really seems to be panning out.
- 12:49: Gravitational wave astronomy is now really a thing.
- 12:59: ... with the new subfield of gravitational wave spectroscopy, we can now listen to the harmonics of ringing black holes, ...
2019-09-30: How Many Universes Are There?
- 10:12: But consider the wave of universes that formed one second after our own.
2019-06-20: The Quasar from The Beginning of Time
- 03:22: Light is a wave and the wavelength of that wave determines the properties of light.
- 03:27: For example, visible light – the wavelength range that our eyes are sensitive to – spans only a tiny fraction of the spectrum.
- 03:34: That's why we create telescopes – the universe looks very, very different at different wavelengths.
- 04:01: ... distant light somewhat. Turbulence in the atmosphere causes incoming wavefronts of light to be warped, and it blurs our ...
- 04:53: ... spectrograph takes incoming light and breaks it into its component wavelengths, similar to a prism, and it records how much energy is received at each ...
- 05:12: ... traveling through the expanding universe sapped energy and stretched the wavelength of that light so that it was infrared by the time it reached the earth ...
- 06:24: ... same signature wavelengths used to measure redshift are also broadened due to the extreme speeds of ...
- 07:43: Look out for Physics Girl's exploration of gravitational waves at LIGO.
2019-06-17: How Black Holes Kill Galaxies
- 14:07: or in the detailed shape of the gravitational wave signal before collision.
2019-06-06: The Alchemy of Neutron Star Collisions
- 02:47: ... shot to prominence last year when the LIGO and Virgo gravitational wave Observatories spotted the space-time ripples from the merger of a pair ...
- 13:02: ... cosmic background radiation wasn't yet stretched to invisible microwave wavelengths?" - actually most of the dark ages would have actually been dark at least ...
2019-05-16: The Cosmic Dark Ages
- 05:45: ... its spin direction it either absorbs or emits a radio photon with a wavelength of 21cm. When the first stars ignited they heated the surrounding gas, ...
- 08:11: ... the second photon of interest. It’s the Lyman-alpha photon – one with a wavelength of exactly 121.57 nanometers. That’s a hard ultraviolet photon that can ...
- 08:36: ... has expanded slightly. Photons that were once at the Lyman-alpha wavelength have been redshifted to longer wavelength and are no longer threatened ...
- 09:21: ... light continues on its way towards us, but the universe keeps expanding. Wavelength by wavelength, photons get absorbed as they are shifted into the danger ...
- 10:10: ... or being blasted back out again. This is the redshifted Lyman-alpha wavelength – once hard-ultraviolet, but now infrared. Everything to the left of ...
2019-05-09: Why Quantum Computing Requires Quantum Cryptography
- 04:52: Another example is the polarization of a photon, a quantum of electromagnetic wave.
- 04:58: Polarization defines the direction that its electric and magnetic fields … wave.
2019-05-01: The Real Science of the EHT Black Hole
- 01:53: We can think of light from a very distant point as coming in a series or plane waves.
- 01:58: A given wavefront will reach one telescope slightly before the other.
- 02:03: So they arrive at a different part of their wave cycle – there’s a phase difference between them.
- 02:27: It resolves between two points on the sky if the separation between those points results in a relative phase shift of around one wavecycle.
- 02:36: ... other words, the extra distance the wavefronts have to travel to reach the second telescope should be different for the ...
- 02:51: ... separated by an angle that is the same as the ratio between the observed wavelength and the separation of the telescopes – also called the ...
- 03:03: The longer the baseline and the shorter the wavelength, the better the resolution.
- 03:08: ... ratio between wavelength and baseline is the same as the ratio between the size of the object ...
- 03:19: ... resolution of any telescope – it’s the diffraction limit – the observed wavelength divided by the diameter of the ...
- 03:50: ... you build an interferometer that spans the planet Earth the wavelength you need in order to get this resolution is around 1mm, which is around ...
- 04:34: ... as an interferometer by literally matching the identical mm-separated wavefronts that reach these telescopes separated by thousands of ...
- 07:43: Remember that the EHT observes radio light with a wavelength of around a millimeter.
- 07:52: That wavelength should be dominated by synchrotron radiation, not from the thermal radiation of the accretion disk.
- 10:17: ... cool fact is that, just like those gravitational wave signals from a couple of years ago, the black hole looks just like we ...
2019-04-10: The Holographic Universe Explained
- 08:23: ... weird thing is that when you write the quantum wave equation for the gluon strand with length expressed as a separate ...
2019-02-20: Secrets of the Cosmic Microwave Background
- 01:34: ... of matter right after the big bang which evolved as colossal sound waves reverberated through the first few hundred thousand years of the ...
- 02:05: ... of pressure Collapsing baryons rebounded producing an expanding sound wave That expanding shell was eventually frozen in place 380,000 years later ...
2019-02-07: Sound Waves from the Beginning of Time
- 01:22: They are the fossils of the first sound waves in the universe, imprinted on the distribution of galaxies on the sky.
- 02:09: Unbound electrons present a huge target to scatter any wavelength of light.
- 02:54: Second: Light was able to exert an enormous pressure on this plasma, as we'll see that it'd lead to the production of colossal sound waves.
- 03:04: And third: Those sound waves travelled fast.
- 04:35: This resulted in an acoustic wave, a true sound wave in the form of an expanding shell of increased density.
- 05:49: As the wave of plasma and photons decoupled, light began to stream freely through the universe as the cosmic background radiation.
- 06:07: The wave of plasma-turned-gas essentially froze in its current state.
- 06:46: ... the expanding wave froze, both dark matter and baryons flowed together and consolidated the ...
- 07:40: In reality, the density waves sloshed inwards and outwards.
- 11:35: So, we know how far the acoustic wave should have travelled before being frozen by recombination.
- 12:39: I mean think about it. There are rings in the sky inscribed in galaxies, frozen echoes of the very first sound waves to reverberate across space-time.
2019-01-24: The Crisis in Cosmology
- 03:05: This is the lengthening of the wavelength of light from that galaxy,...
- 08:16: ...really vast sound waves that rippled across the universe.
- 12:37: Independent methods, like using gravitational lensing, or gravitational waves,...
2019-01-16: Our Antimatter, Mirrored, Time-Reversed Universe
- 03:02: ... the other type KL is long-lived and has an odd CV state it's wave function gets multiplied by -1 on a CP transformation and that means ...
2019-01-09: Are Dark Matter And Dark Energy The Same?
- 09:31: ... fact that sinusoidal solution is only valid for the bit of the sine wave where the universe is expanding from zero time – the big bang - slowing ...
2018-12-20: Why String Theory is Wrong
- 08:17: These strings are vibrating with standing waves like guitar strings, and their energy also depends on the frequency of that vibration.
- 08:25: That frequency depends on the density of wave cycles on the string.
- 08:30: ... just the number of wave cycles around each coil, or the mode number divided by the radius. So, ...
2018-12-12: Quantum Physics in a Mirror Universe
- 00:02: ... shifts in space-time and even the rather abstract phase of the wave function in quantum mechanics so it might be surprising to learn that ...
2018-11-14: Supersymmetric Particle Found?
- 14:54: Some of you recalled a recent episode in which we talked about a study of gravitational waves that appears to refute the idea of extra dimensions.
2018-11-07: Why String Theory is Right
- 00:59: ... string theory are literal strands and loops that vibrate with standing waves simply by changing the vibrational mode and you get different particles ...
- 06:05: ... equations of motion and follow a standard recipe to turn them into wave equations with various quantum weirdness added in like the uncertainty ...
- 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.
- 10:41: ... smooth out that surface mathematically and write a nice, simple quantum wave equation from the equations of motion, but only for 1D strings making a ...
2018-10-25: Will We Ever Find Alien Life?
- 04:26: ... observations revealed that the wavelength dependence of the dips is consistent with dust, so likely natural space ...
2018-10-18: What are the Strings in String Theory?
- 05:35: The key is that strings can carry waves.
- 05:38: And if the string has ends or is tied in a loop, then a wave will end up overlapping with itself.
- 05:45: In that case, you get a standing wave.
- 05:48: Roughly speaking, when these traveling waves overlap each other, they can either stack up or cancel out, constructive or destructive interference.
- 05:57: Constructive interference only happens if the wavelength of the wave fits a neat number of times along the length of the string.
- 06:04: Then the phases of the overlapping wave match in the right way, and that wavelength/frequency of the wave is enhanced.
- 06:22: These resonant frequencies depend on the length of the string, also its tension, which defines wave velocity and so relates frequency to wavelength.
- 06:48: Niels Bohr came up with the first quantum model for electron orbits by thinking of them as ring-like standing waves around the hydrogen atom.
- 08:00: By the way, those vibrations, the standing waves, are not some abstract internal wave.
- 08:05: The strings are real physical strands, and the waves are wiggles in actual space.
2018-10-10: Computing a Universe Simulation
- 12:07: ... week, we looked at an amazing new result in which gravitational waves were used to search for and rule out the existence of an extra spatial ...
- 12:21: Glenn Stern asks about the fact that the gravitational waves from this neutron star merger arrived two seconds before the light from the merger.
- 12:31: How then can we say that the gravitational waves and the light traveled at the same speed?
- 12:40: Those gravitational waves and that light traveled a crazy long distance, 40 megaparsecs or around 150 million light years.
- 13:10: That led to the radio emission arriving hours after the gravitational waves.
- 13:30: ... from the neutron star merger started slightly after the gravitational wave ...
- 13:41: The gravitational waves start to get strong before the neutron stars even make contact.
2018-10-03: How to Detect Extra Dimensions
- 00:10: Fortunately, with the discovery of gravitational waves, we're now living in a science fiction future.
- 00:18: ... We may have mentioned once or twice that the new era of gravitational wave astronomy is going to open new windows to the universe and unlock many ...
- 00:59: The key to this breakthrough was the gravitational wave event observed in August of 2017, GW170817.
- 01:17: And the LIGO and Virgo gravitational wave observatories detected the resulting ripples.
- 01:29: The resulting kilonova is first observed in gravitational waves and then as a gamma ray burst.
- 01:35: In GW170817, the flash of gamma radiation arrived 1.7 seconds after the gravitational waves.
- 01:50: Among other things, this optical identification gave a completely independent measurement of the distance traveled by the gravitational waves.
- 08:37: Well, here's where we finally get back to our gravitational waves.
- 08:41: ... into this hypothetical extra spatial dimension, then gravitational waves should lose energy to that extra dimension as they travel through ...
- 09:02: In regular 3D space, gravitational waves drop in intensity proportional to just distance, not distance squared.
- 09:11: If space has four or more dimensions, then gravitational waves should drop off in intensity faster than you'd expect in three dimensions.
- 09:22: Just observe a gravitational wave and figure out how much its intensity dropped off over the distance traveled.
- 09:41: All you need is a billion-dollar network of gravitational wave detectors and a way to independently measure the distance the wave traveled.
- 09:58: ... us to measure its distance completely independently to the gravitational wave signal, something that's impossible with black hole ...
- 10:10: ... in order to determine how much intensity was lost by the gravitational wave, we need to know how intense it was when it started its ...
- 10:20: ... super convenient property of gravitational waves is that you can figure this out by looking at other properties of the ...
- 10:42: The gravitational wave lost the right amount of intensity for a 3-plus-1-dimensional space-time.
- 11:06: ... the way, comparison of the electromagnetic and gravitational wave arrival times also allowed us to verify that gravity really does travel ...
2018-09-20: Quantum Gravity and the Hardest Problem in Physics
- 02:25: It describes particles as waves of infinite possibility whose observed properties are intrinsically uncertain.
- 02:41: That math started with the Schrodinger equation, which tracks these probability waves through space and time.
- 02:58: We already talked about how Paul Dirac fixed part of the problem with a relativistic wave equation for the electron.
- 07:01: ... know that for a particle to have a highly defined location, its position wave function needs to be constructed from a wide range of momentum wave ...
- 13:30: When two black holes merge, a lot of energy is pumped into gravitational waves.
2018-09-05: The Black Hole Entropy Enigma
- 00:53: Also, we've seen them in their gravitational effects on their surrounding space and in the gravitational waves caused when they merge.
- 06:22: If you merge two black holes, some of their mass gets converted to the energy radiated away in gravitational waves.
2018-08-30: Is There Life on Mars?
- 11:51: This is the same way we map the ocean, by analyzing radio waves reflected from layers below the surface.
2018-08-23: How Will the Universe End?
- 15:43: All they have is their quantum wave function, which tells the probability of the particle's location, momentum, spin, direction, et cetera.
- 15:50: Now, we can think of a quantum wave function as having a size because it can be spread out over space.
- 16:03: If we know with 100% certainty the position of an electron, then the size of its quantum wave function becomes zero.
- 17:40: As for the little financial firm, yeah, I heard they were doing pretty well under the wave of banking deregulation of the '80s and '90s.
2018-08-15: Quantum Theory's Most Incredible Prediction
- 15:13: Another possible mechanism is through turbulence in waves generated by the rapid motion of magnetic fields.
2018-08-01: How Close To The Sun Can Humanity Get?
- 04:08: Finally, it will detect radio waves from processes responsible for the acceleration of particles in the solar wind.
2018-07-11: Quantum Invariance & The Origin of The Standard Model
- 02:35: ... describes the evolution of the wave function, which is the mathematical object that contains all the ...
- 02:44: We can never see the underlying wave function of, say, a particle.
- 02:54: The wave function can represent different observables and it determines the distribution of possible results of measurement of those observables.
- 03:02: In this episode, we'll be talking about the position wave function.
- 03:11: The square of the magnitude of this wave function tells us the probability distribution of a particle's position.
- 03:24: This step of squaring the wave function is called the Born rule.
- 03:36: Let's see what happens when we square the wave function.
- 03:47: It's no simple wave.
- 04:03: Phase is just the wave's current state in its up-down oscillation.
- 04:07: When we apply the Born rule, what we're doing is squaring these two waves and adding them together.
- 04:40: In fact, as long as you make the same shift across the entire wave function, all the observables are unchanged.
- 05:21: We'll try this because, well, we already know that the magnitude squared of the wave function should still stay the same under local phase shifts.
- 05:38: ... here, only that location changes, as if it were part of the shifted wave, making a discontinuous ...
- 05:50: If you allow this sort of local phase shift, you can change each point in a different way and really mess up the wave function.
- 06:15: See, momentum is related to the average steepness of the wave function.
- 06:19: Change the shape of that wave function with local phase shifts and you actually break conservation of momentum.
- 06:57: ... that's specially designed to undo any mess we make to the phase of the wave ...
2018-06-13: What Survives Inside A Black Hole?
- 13:06: ... wave function prescribes the probability of observing a given value for a ...
- 13:22: In the Copenhagen interpretation, the wave function collapses and unitarity is not preserved.
- 13:30: More likely is that the observer and the observation are a small part of a global wave function that continues to evolve in a unitary manner.
2018-05-23: Why Quantum Information is Never Destroyed
- 04:51: The time dependent Schrodinger equation describes the time evolution of this thing called the wave function.
- 04:58: The wave function of a system fully describes all of its properties.
- 05:02: ... of all of its properties, which you can get by taking the square of the wave ...
- 05:10: ... example, the wave function of a particle encapsulates the probability that it will be ...
- 05:19: ... perfectly predicts both the past and future evolution of a given wave function in any given environment, or in quantum speak, in any given ...
- 05:36: ... principle, a given wave function in a given potential could mean the wave function of an ...
- 06:10: Remember that the wave function encapsulates the distribution of probabilities for a given property.
- 06:42: If this is true, and it must be, we say that the time evolution of the wave function is unitary.
- 08:12: That value seems to be chosen randomly based on the probability distribution encoded in the wave function.
- 08:29: Quantum information refers to the full information content of the wave function, not just what we measure.
- 08:35: And in principle, make enough measurements and you can extract all of the information from a wave function.
- 08:41: ... worth mentioning that the collapse of the wave function in the Copenhagen interpretation of quantum mechanics actually ...
- 08:50: ... that interpretation, the active measurement actually alters the entire wave function causing it to shrink down to the narrow range of possible ...
- 09:02: But that measured wave function can't then be tracked backwards to recover the past wave function.
- 09:14: ... for example, Everett's many-worlds or the de Broglie-Bohm pilot wave theory preserve this time ...
- 09:22: In the case of many-worlds, the entire wave function continues to exist even after measurement.
- 09:35: And in the case of pilot wave theory, the wave function contains hidden information that is carried with the final measured particle.
2018-05-16: Noether's Theorem and The Symmetries of Reality
- 01:22: Its wavelength increases.
2018-05-09: How Gaia Changed Astronomy Forever
- 04:49: ... shows the tiny Doppler shift-- the stretching or compression of the wavelength of starlight due to the motion towards or away from ...
- 08:02: Gaia even helps us with the pulsar timing array, a galactic scale gravitational wave observatory which we spoke about recently.
2018-05-02: The Star at the End of Time
- 05:23: The black-body spectrum of a hot object emits relatively more photons at short energetic wavelengths than a cooler object.
- 05:31: For most of its life, the spectrum of a red dwarf peaks at infrared wavelengths.
2018-04-25: Black Hole Swarms
- 02:26: ... at between five and 15 solid amasses, although, the recent gravitational wave signals detected by LIGO, suggest they may be even more ...
- 07:48: Besides being very cool and kind of freaky, this result is especially important for the new field of gravitational wave astronomy.
- 07:57: Now, we keep seeing these gravitational wave signals from black hole merges, and as I've discussed previously, they're kind of confusing.
- 08:05: ... know that, if we want to understand the source of these gravitational waves. ...
- 09:17: Last week, we talked about some of the incredible ways for detecting gravitational waves beyond LIGO.
- 09:26: Majestic potato asked, whether a supernova can produce gravitational waves detectable from Earth?
- 09:40: Gravitational waves are produced when the quadrupole moment of a mass distribution changes.
- 09:52: So if the explosion of a supernova is concentrated, say, more on one side, then LIGO could potentially see the resulting gravitational waves.
- 10:00: Juxtaposed stars asks whether, theoretically, you could build an engine to extract power from gravitational waves via the sticky bead method?
- 10:29: A couple of you asked whether the gravitational waves interfere with each other?
- 10:38: Two gravitational waves crossing paths will add together at any one point in space and time.
- 10:55: You'd need a material capable of blocking gravitational waves.
- 11:16: ... rogue wolf notes, that stellar gravitational wave detectors, like pulsar timing arrays, are a bit like using the rustling ...
2018-04-18: Using Stars to See Gravitational Waves
- 00:07: Now that gravitational waves are definitely a thing, it's time to think about some of the crazy things we can figure out with them.
- 00:14: In some cases, we're going to need a gravitational wave observatory the size of a galaxy.
- 00:23: [MUSIC PLAYING] We are at the cusp of a golden age of gravitational wave astronomy.
- 00:31: We've already talked about the Laser Interferometer Gravitational-Wave Observatory, LIGO, and the first discovery of gravitational waves here.
- 02:00: Yet, everyone wants in on the gravitational wave game.
- 02:09: Perhaps these gravitational waves signals were amplified by another phenomenon predicted by Einstein's general relativity, gravitational lensing.
- 02:19: ... paths of gravitational waves should also be warped by intervening gravitational fields which can ...
- 02:45: For the first time, the event behind a gravitational wave signal was also seen in light.
- 02:59: ... like this should allow us to figure out where the gravitational wave signals are often also gravitationally ...
- 03:10: ... the Italian-based gravitational wave observatory, was online for the neutron star merger, and was extremely ...
- 03:49: ... that live in the centers of galaxies, we need to observe gravitational waves in the 0.1 million hertz to 0.1 hertz ...
- 05:00: ... expect a faint gravitational wave background buzz from an earlier epoch of the universe in which binary ...
- 05:23: But much of this gravitational wave background will have wavelengths as long as many light years.
- 05:28: That's beyond any gravitational wave interferometer that we could ever physically construct.
- 05:51: We're already using these to study the gravitational wave background at the 1 to 100 nanohertz range.
- 06:17: ... pulsar array volume due to the passage of impossibly vast gravitational waves. ...
- 06:27: This galaxy scale observatory is already in operation and has placed valuable limits on the amplitude of the gravitational wave background.
- 06:44: Some scientists are even trying to see how gravitational waves should interact with stars.
- 06:58: He came up with a thought experiment of a simple gravitational wave detector, a rod with two sliding beads.
- 07:05: ... a gravitational wave passes by, the beads are free to follow the expansion and contraction of ...
- 07:18: That heat energy comes from the gravitational wave.
- 07:21: ... but it demonstrates that in the right circumstances gravitational waves should be able to dump some of their energy into matter, for example, ...
- 07:38: If a gravitation wave frequency matches the natural resonant frequency of a star, oscillations can be set up inside the star.
- 07:52: ... binary supermassive black holes that are generating gravitational waves. ...
- 08:19: Gravitational wave astronomy is currently in a gold rush.
- 08:40: ... theory of relativity, which predicted the existence of gravitational waves, he had to master it precursor, Newtonian ...
2018-04-11: The Physics of Life (ft. It's Okay to be Smart & PBS Eons!)
- 09:32: Waves and vortices have their own complex and regular structures, but they ultimately serve to dissipate the flow.
- 12:59: ... horizon should produce a type of Hawking radiation, but its wavelength would be comparable to the distance to that horizon, so it's completely ...
2018-04-04: The Unruh Effect
- 09:46: ... even in classical systems, like this really cool study with water waves. ...
2018-03-28: The Andromeda-Milky Way Collision
- 06:20: When those black holes are around a light year apart, they'll start losing orbital energy to gravitational waves.
2018-03-21: Scientists Have Detected the First Stars
- 00:23: Not everything wows, like gravitational waves or space-faring sports cars.
- 01:42: That photon has a wavelength of 21 centimeters, which is radio light.
- 03:08: Absorption at 21 centimeters would now look like absorption at a much longer wavelength.
- 03:14: In fact, there should be this broad dip at a range of wavelengths, representing the epoch of the universe in which this absorption was occurring.
- 03:55: The wavelength range of the dip corresponds to the epoch between 180 to 270 million years after the Big Bang.
2018-03-15: Hawking Radiation
- 07:18: Black holes tend to scatter modes with wavelengths similar to their own sizes.
- 07:23: The quantum field that emerges is distorted in the same wavelength range.
- 07:27: And so it produces wave packets.
- 07:29: It produces particles that also have wavelengths about as large as the event horizon.
- 07:34: So the more massive the black hole, the longer the wavelength of its radiation.
- 08:51: Remember that Hawking radiation has wavelengths the size of the event horizon, the size of the entire black hole.
- 08:57: Well, these are the de Broglie wavelengths of created particles.
2018-03-07: Should Space be Privatized?
- 04:28: Asteroid mining seems likely to drive the next wave of private enterprise, because the potential profits are astronomical.
2018-01-24: The End of the Habitable Zone
- 08:03: ... the initial extinction wave from the loss of much of Earth's plant life, other complex multicellular ...
2018-01-17: Horizon Radiation
- 05:19: As we saw in our recent episode on Fourier transforms, it's possible to describe any vibration or wave in two ways.
- 05:28: Sound waves can be described in terms of variation over time or variation over frequency.
- 05:35: Quantum wave functions and quantum fields can be described in terms of variation with position or variations with momentum.
- 07:51: They behave like simple harmonic oscillators, so their value over time is like a simple sine wave.
2018-01-10: What Do Stars Sound Like?
- 00:14: Believe it or not, we can now map the interiors of stars by listening to their harmonies as they vibrate with seismic waves.
- 01:13: Well, we may not see light from beneath the stellar surface, but another type of wave travels freely through stars.
- 01:21: I'm talking about seismic waves.
- 01:33: ... waves reflect around the stellar interior, setting up global oscillations, ...
- 02:34: ... earth, seismic waves are generated by earthquakes and can travel around the planet as ...
- 02:49: And these are true sound waves that echo around their interiors.
- 02:53: Because stars are fluid rather than solid, they don't support shear waves.
- 02:57: However, they do support two types of gravity waves.
- 03:01: Now, these are not gravitational waves.
- 03:04: Gravity waves result from the restoration of gravitational equilibrium.
- 03:14: In stars, these waves occur below the surface, g-waves, and on the surface, f-waves.
- 03:20: The latter are closely analogous to ocean surface waves on the earth.
- 03:24: However, it's the pressure waves-- the p-waves-- that really dominate in stars like the sun.
- 03:30: ... acoustic waves are generated by turbulence just below the surface of a star, just as ...
- 03:41: They start as traveling waves that can move throughout the stars in a structure.
- 03:45: ... just as a single tap can set an entire bell ringing, a single traveling wave feeds its energy into standing pressure waves that cause the entire star ...
- 08:12: ... helioseismic holography, the visible wave field-- so the distribution of Doppler velocities across the visible ...
2017-12-06: Understanding the Uncertainty Principle with Quantum Fourier Series
- 00:16: ... the humble sound wave is going to open the door to really understanding Heisenberg's ...
- 02:24: See, quantum mechanics is a type of wave mechanics.
- 02:29: However, it turns out that something like the uncertainty principle arises in any wave mechanics.
- 02:35: So let's choose a type of wave that's a little more intuitive, sound waves.
- 02:41: You can describe a sound wave just as the intensity of the wave as it passes by.
- 02:51: That shape determines what the wave sounds like to our ears.
- 02:55: The sound wave for a simple pure tone, like a middle C, is a sinusoidal wave, with the frequency determining the pitch of the tone.
- 03:03: ... sound wave from, say, an orchestra is extremely complex, but amazingly, it can ...
- 03:23: ... states that any complex sound wave can be decomposed into a number of sine waves of different frequencies, ...
- 03:36: ... fact, instead of representing a sound wave in terms of intensity changing with time, you can also represent it in ...
- 04:02: In the physics of sound, time and frequency have a special relationship because any sound wave can be represented in terms of one or the other.
- 04:18: So we can make any shape sound wave with a series of sine waves of different frequencies.
- 04:24: ... example, you can build a wave packet by adding frequency components with the right phases to ...
- 04:35: The tighter you want to make that time window for the wave packet, the more frequency components you need to use.
- 04:41: ... fact, to get those steep edges of the wave packet, you need to add higher and higher frequencies, because the high ...
- 04:52: So what if you try to compress the wave packet to a single spike?
- 05:01: Is it even possible to make an instantaneous spike at one point in time out of a bunch of sine waves that themselves extend infinitely through time?
- 05:12: ... point in time, you need to use infinitely many different frequency sine waves, each of which exists at all points in ...
- 05:30: ... the same time, a sound wave with a perfectly known frequency is a simple traveling sine wave that ...
- 05:41: That sounds an awful lot like a frequency-time uncertainty principle for sound waves.
- 05:47: ... it's not really a statement about the fundamental knowability of a sound wave, as is Heisenberg's uncertainty principle, it's more a statement about ...
- 06:04: Well, before we get back to quantum fields, let's think about the wave function.
- 06:15: Like the sound wave, it oscillates through space at a particular frequency.
- 06:20: To keep things simple, we're just going to consider a wave function that doesn't vary in time.
- 06:27: This is more like a standing sound wave inside an organ pipe rather than the traveling sound wave familiar.
- 06:43: See, momentum is sort of the generalization of frequency for what we call a matter wave.
- 06:49: In the early days of quantum mechanics, it was realized that photons are electromagnetic wave packets whose momentum is given by their frequency.
- 06:58: ... generalizes the relationship between frequency and momentum of a matter wave. ...
- 07:08: ... now call matter waves wave functions, and we can describe them in terms of position or ...
- 07:21: So any particle, any wave function, can be represented as a combination of many locations in space, with accompanying intensities.
- 07:41: And of course, this means that position and momentum have the same kind of uncertainty relation that time and frequency had in the sound wave.
- 07:50: But what does it even mean for a particle to be comprised of waves of many different positions or momenta?
- 07:57: To answer this, we need one more bit of physics; the interpretation of the wave function itself, known as the Born rule.
- 08:06: The magnitude of the wave function squared is the probability distribution for the particle.
- 08:12: ... we're expressing the wave function in terms of position, then applying the Born rule tells us how ...
- 08:38: So if we measure a particle's position, then from our point of view, it's wave function is highly localized in space.
- 08:48: ... resulting particle wave packet, now constrained in position, can only be described as a ...
- 09:00: The result is a very fat momentum wave function that gives a wide range of possible momenta.
- 09:06: ... precisely we try to measure position, the narrower we make its position wave function, and so the less certain we become about its momentum, as that ...
- 09:50: It's an unavoidable outcome of describing particles as the superposition of waves.
- 09:55: Waves that can be represented in terms of either position or momentum.
- 09:59: The fact that both can't be known simultaneously with perfect precision is a property of the nature of the wave function itself.
2017-11-29: Citizen Science + Zero-Point Challenge Answer
- 03:53: ... example, spotting supernovae or looking for gravitational wave signals in LIGO and finding planets forming in the debris disks of new ...
- 05:15: But there's also Einstein at Home, which searches for LIGO gravitational wave data for signals produced by rotating neutron stars.
- 08:22: That corresponds to a photon wavelength of a tenth of a millimeter, which is in the far infrared part of the spectrum.
- 08:42: ... with wavelengths shorter than 0.1 millimeters definitely exist, and we see particle ...
- 09:06: That proves the existence of virtual photons with wavelengths smaller than the plate separation.
2017-10-25: The Missing Mass Mystery
- 04:28: ... like sound waves rippling outwards from high density regions, these baryonic acoustic ...
- 06:33: This cool gas then absorbs signature wavelengths from light that passes through it.
- 12:37: TS1336 was expecting last week's episode to be about the discovery of gravitational waves from merging neutron stars.
2017-10-19: The Nature of Nothing
- 08:51: ... organ pipe or a guitar string of a particular length only resonates with waves of certain frequencies, any non-resonant virtual photon would be ...
2017-10-11: Absolute Cold
- 02:53: Once nearly all particles occupy that one quantum state, they share a single, coherent wave function.
- 08:38: ... binary to spiral together from losing angular momentum to gravitational waves. ...
2017-10-04: When Quasars Collide STJC
- 03:59: ... sides of the planet, and phase differences in the incoming radio waves are used to find the origin of each wave with incredible ...
- 06:14: Spiraling electrons produce radio waves a lots of frequencies all the way down to very low energies.
- 06:21: ... we think the matter should be so dense that the lowest energy radio waves have trouble escaping the ...
- 06:30: Now, this is a process called synchrotron self-absorbtion, and it causes the base of AGN jets to be much fainter at long wavelengths.
- 08:32: A lot of you are probably thinking, what about gravitational waves?
- 08:45: And can LIGO see those waves?
- 08:52: ... this system is definitely producing gravitational waves, but it's going to take many billions of years to lose enough angular ...
- 09:01: And while those waves may be powerful, they have an incredibly low frequency-- something like 1 ten trillionth of a hertz.
- 09:10: LIGO is sensitive to gravitational waves from 10 to 10,000 hertz.
- 09:19: ... of a supermassive black hole binary with a galaxy-sized gravitational wave observatory called a pulsar timing ...
- 09:48: And this galaxy is so dusty that it's hard to peer into the core at other wavelengths of light.
2017-09-28: Are the Fundamental Constants Changing?
- 04:48: We see this effect in the sharp spikes or dips in light at specific wavelengths when we observe the spectrum of a gas.
- 06:09: The result is a very small difference in the wavelengths of the spectral lines produced by those transitions.
- 06:20: Well, the magnitude of this wavelength split depends very strongly on the fine structure constant.
- 08:26: ... distant quasars and gas clouds are massively redshifted-- their wavelengths stretched out due to the expansion of the ...
- 13:58: But that's because the distance between atoms is similar to x-ray wavelengths.
2017-09-20: The Future of Space Telescopes
- 02:12: The wave nature of light causes it to bend or diffract around the edges of a coronagraph back towards the central optical axis.
- 03:27: The number and length of pedals optimizes each starshade for a particular wavelength of light.
- 04:50: ... save money as its beneficiary telescope will require no coronagraphs or wavefront correctors or other high-contrast ...
- 06:16: Light diffracts around the disk, coming to focus on the optical axis where the light's wavefronts line up in constructive interference.
- 08:00: X-rays have such short wavelengths that telescope mirrors have to be astoundingly smooth to reflect them cleanly.
- 11:00: ... tantalizing rumor that the LIGO Observatory had detected gravitational waves from the merger of a pair of neutron ...
- 11:33: Nicholas Martino asks whether gravitational waves are redshifted by the expansion of the universe.
- 11:40: They have to travel along the same space-time fabric as light waves, after all.
- 11:45: I mean, there are waves in that fabric.
- 11:48: So stretch out the fabric and you stretch out its waves.
2017-09-13: Neutron Stars Collide in New LIGO Signal?
- 00:06: Last year, LIGO announced the detection of gravitational waves from the merger of two black holes.
- 00:15: ... rumor emerged, that LIGO had for the first time spotted gravitational waves from the collision of a pair of neutron ...
- 00:37: ... the Laser Interferometer Gravitational Wave Observatory, LIGO, detected gravitational waves from a pair of merging ...
- 02:55: In fact, the first real evidence of the existence of gravitational waves came from a pulsar.
- 03:09: This binary pair stirs up spacetime in its vicinity, creating ripples that travel outwards as gravitational waves.
- 04:46: Smaller mass means weaker gravitational waves.
- 05:37: ... second before merger, while neutron stars ring at audible gravitational wave frequencies for at least several ...
- 06:07: "Optical counterpart" means that there's a source of visible light associated with the gravitational wave.
- 06:12: And in this case, it's from the suspected galaxy that the wave came from.
- 06:25: ... there's also the rumor that the Italian Gravitational Wave Observatory, VIRGO, also spotted the signal, which helps triangulate the ...
- 07:32: And the particular observing program that was triggered is one specifically intended for following up on gravitational wave detections.
- 07:47: Someone in the know decided that this gamma ray burst was very likely associated with a gravitational wave.
- 09:32: Seeing a gravitational wave signal from merging neutron stars would allow us to determine pretty exactly how much mass is lost in the merger.
- 09:59: Black hole mergers are dark, so we have to infer almost everything from the gravitational waves alone.
- 10:11: Comparing the EM and gravitational wave signatures will teach us a lot.
- 11:42: As it happens, Curiosity Stream has a really excellent overview of LIGO and gravitational waves.
- 11:49: "Gravitational Waves-- Rewinding Time" includes some fascinating behind-the-scenes footage at the observatories.
2017-08-24: First Detection of Life
- 01:47: ... dips that result from molecules in Earth's atmosphere absorbing specific wavelengths of light from what would otherwise be the smooth heat glow of the ...
- 02:24: Going to longer wavelengths we see carbon dioxide, nitrous oxide, methane, ozone, and, well, more water.
2017-08-10: The One-Electron Universe
- 08:23: We now think of electrons as oscillations, as waves, in the more fundamental electron field.
2017-08-02: Dark Flow
- 01:49: In all directions, it appears to be the same temperature-- around 2.7 Kelvin-- and hence, the same microwave wavelength.
- 02:13: That motion causes the CMB to be Doppler shifted, its wavelengths a little stretched out behind and a little more compacted ahead.
2017-07-19: The Real Star Wars
- 04:56: Then, by passing electromagnetic radiation at a wavelength tuned to an energy level transition in that substance, stimulated emission can occur.
2017-07-07: Feynman's Infinite Quantum Paths
- 01:27: ... if each of them travels through both slits, not as a particle but as a wave that fills the intervening space interacts with itself and defines the ...
- 01:52: ... particles on the screen can be calculated by adding the amplitude of a wave passing through one slit to the amplitude of a wave passing through the ...
- 02:10: The professor replied, obviously, you have to add together the amplitudes of waves passing through all three slits.
- 05:58: Schrodinger's wave function and Feynman's path integral describe this probability amplitude thing.
- 07:01: This is equivalent to the wave function along those paths being perfectly out of phase when they reach the destination.
- 13:12: ... in the late 19th century as the medium for the propagation of light waves. ...
- 13:22: It was imagined to be very closely analogous to air as the medium for propagation of sound waves.
2017-06-28: The First Quantum Field Theory
- 03:09: For example, in a 3D room full of air, sound waves are oscillations in air density.
- 03:16: ... is just the average density, but at every point in the room, a sound wave can cause air density to oscillate to higher and lower ...
- 04:16: Light is a wave in the electromagnetic field.
- 08:56: All it can do is move particles around via their evolving wave functions.
2017-06-21: Anti-Matter and Quantum Relativity
- 00:50: By the late 1920s, Einstein and Planck had already shown that light is a particle, as well as a wave.
- 00:56: And Louis de Broglie had shown that all matter has this dual wave-particle nature.
- 01:21: ... describes how these matter waves, represented as wave functions, change over time, and allowed physicists ...
- 01:56: ... the Schrodinger equation tracks the evolution of a particle's wave function according to one and only one clock, typically the clock in the ...
- 02:21: ... with the Schrodinger equation is that it describes particles as simple wave functions, distributions of possible positions and momenta that have no ...
- 04:16: We now call these two component wave functions, spinors.
2017-06-07: Supervoids vs Colliding Universes!
- 01:59: ... billion years of cosmic expansion later, and it stretched to microwave wavelengths, and to a temperature very close to 2.725 Kelvin all across the ...
- 05:46: ... layman's terms, they split the light from those galaxies into component wavelengths and determined the shift in the wavelengths of those spectra due to the ...
- 12:48: ... into a spectrum and look for emission lines, light at the signature wavelengths of heavier ...
2017-05-31: The Fate of the First Stars
- 06:29: Those electrons then lose that energy by emitting light at specific wavelengths-- signature photons that are different for every element or molecule.
- 08:03: ... environment of the old universe, we expect that there were violent waves of star formation followed by cascades of supernova explosions, ripping ...
- 10:21: They radiate intense light, with a signature ultraviolet wavelength of hydrogen.
2017-04-26: Are You a Boltzmann Brain?
- 02:54: ... bunched together in one corner or, I don't know, produce a density wave playing "The Ballad of Serenity" over and ...
2017-04-19: The Oh My God Particle
- 06:18: When a star explodes, the expanding shock wave carries a strong magnetic field.
2017-04-05: Telescopes on the Moon
- 01:51: ... but its biggest advantage is that it can see into near ultraviolet wavelengths and in the visible range observable within our ...
2017-03-15: Time Crystals!
- 00:18: [MUSIC PLAYING] In "Space Time Journal Club," we review new scientific papers that are making waves.
- 04:36: A laser is just a very well-ordered electromagnetic wave with a known period or frequency.
2017-03-01: The Treasures of Trappist-1
- 04:12: Wein's law tells us that the 2,500 Kelvin TRAPPIST-1 star shines brightest at infrared wavelengths.
2017-02-15: Telescopes of Tomorrow
- 01:34: These cameras see mostly at infrared wavelengths of light, unlike Hubble's, which are optimized for visible and ultraviolet light.
- 01:57: Longer wavelengths of light scatter less easily than shorter wavelengths, and so have an easier time escaping these dust-packed stellar nurseries.
- 02:06: Compare two shots from Hubble-- this taken in visible wavelengths, this in infrared.
- 02:11: Webb will see even longer wavelength infrared light and so will bore even deeper.
- 03:11: But it can also be deflected by the edges of our telescope, like a wave, in a process called diffraction.
- 03:29: The finest detail any telescope can observe is given by the diffraction limit, which increases with wavelength.
- 03:59: The biggest challenge in observing infrared wavelengths is heat.
- 04:31: But without sensitivity to visible or ultraviolet wavelengths, it will not replace Hubble.
- 05:18: Observing in infrared wavelengths is hard.
- 05:21: But GMT is built to explore visible wavelengths, just like Hubble.
- 05:40: We can think of light from a very distant point-like object-- say a star-- as reaching us as a series of wavefronts.
- 05:47: Our eyes and our telescopes can focus those wavefronts back into a point.
- 05:58: But turbulence in the atmosphere warps those wavefronts.
- 06:43: Its secondary mirrors will be flexible, deformable at high speed by thousands of computer-controlled actuators to correct the warped wavefronts.
2017-02-02: The Geometry of Causality
- 10:50: Janna Levin's "Black Hole Blues" is a wonderful take on the new window that gravitational waves are opening on our universe.
2017-01-25: Why Quasars are so Awesome
- 03:05: For one thing, its spectrum was redshifted, the wavelength of its light stretched out as those photons traveled through the expanding universe.
- 07:54: Waves of star formation, followed by waves of supernovae.
- 09:45: ... their supermassive black holes merge, the violence will deliver one last wave of fuel to the combined galactic core, and a new quasar will shine ...
2017-01-11: The EM Drive: Fact or Fantasy?
- 00:59: Most often, they turn out to be in error, like Opera's faster than light neutrinos and the BICEP2 primordial gravitational waves.
- 01:44: A resonant radiation field is induced inside, so microwave standing waves reflecting between the ends.
- 06:49: So the last part of the paper talks about a connection between the EmDrive and pilot wave theory.
- 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.
- 07:59: Instead, they invoke pilot wave theory to justify treating the quantum vacuum as a deformable medium.
- 12:28: Speaking of not using radio, Richy Rich and Gareth Dean had a nice discussion on whether aliens would use radio waves.
2017-01-04: How to See Black Holes + Kugelblitz Challenge Answer
- 02:33: ... recent observations of gravitational waves from a pair of merging black holes by LIGO could be considered our first ...
- 03:06: They use very long baseline interferometry, VLBI, to synthesize observations at millimeter and submillimeter wavelengths.
- 04:09: At visible wavelengths, this should look like a brightening of the star, an effect called microlensing.
- 04:28: ... and microlensing studies, and of course, more LIGO gravitational waves observations, over the next few years, we'll have mapped the space ...
2016-12-21: Have They Seen Us?
- 07:40: That emission, produced at 21 centimeters wavelength, or 1420 megahertz frequency, is, by definition, one of the boundaries of the waterhole.
- 07:49: But if such radio waves travel to us from the earliest of times, then they become stretched out as they travel through an expanding universe.
2016-12-14: Escape The Kugelblitz Challenge
- 06:46: Maybe the outgoing light wave will destroy the alien ships.
2016-12-08: What Happens at the Event Horizon?
- 14:02: Now, a lot of you wondered why I never mentioned the EM drive when talking about pilot wave theory.
- 14:14: ... thrust produced by their EM drive and then go on to talk about how pilot wave theory might explain the apparent conservation of momentum-breaking ...
- 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 ...
- 15:11: ... pilot wave theory states that the particle riding the wave does have a definite ...
- 15:22: So if you know the position perfectly and you know the wave function, you can perfectly predict future locations.
- 15:51: More generally, it allows pilot wave theory to agree with Heisenberg's uncertainty principle.
- 16:05: ... Broglie-Bohm pilot wave theory states that this uncertainty just arises from our imperfect ...
- 16:26: That velocity information is in the guiding wave.
- 16:29: ... extremely interesting papers that detail certain failings of the pilot wave ...
- 16:38: I'll link those and a couple of others that take different sides in the description of this video, as well as in the pilot wave episode.
- 16:47: ... really heated and fascinating discussion both for and against the pilot wave interpretation and some of it was from people who know a good deal more ...
- 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 ...
- 17:42: ... De Broglie from his 1956 book, he, Bohm, assumes that the [INAUDIBLE] wave is a physical reality, even the [INAUDIBLE] wave in configuration ...
- 18:01: In fact, De Broglie was never a huge fan even of his own simplistic particle carried by a wave idea.
- 18:08: ... solution theory in which the so-called particle was actually a matter wave itself embedded in and carried by the sine wave, represented by the wave ...
- 18:57: ... De Broglie-Bohm pilot wave theory is a great example of how a deterministic theory can at least go ...
- 19:07: Personally, I'm agnostic towards the relative truth behind the Copenhagen, many-worlds, pilot wave, or the other interpretations of quantum mechanics.
2016-11-30: Pilot Wave Theory and Quantum Realism
- 00:55: ... explanations claim stuff like things are both waves and particles at the same time, the act of observation defines reality, ...
- 02:27: One aspect of that radical thinking was that the wave function is not a wave in anything physical but an abstract distribution of probabilities.
- 02:36: ... the properties of, say, the particle that would emerge from its wave ...
- 02:59: This required an almost mystical duality between the wave and particle-like nature of matter.
- 03:11: ... to be a full theory that described how a quantum object could show both wave and particle-like behavior at the same time without being fundamentally ...
- 03:25: ... guy who originally proposed the idea that matter could be described as waves right at the beginning of the quantum ...
- 03:36: De Broglie's theory reasoned that there was no need for quantum objects to transition in a mystical way between non-real waves and real particles.
- 03:46: Why not just have real waves that push around real particles?
- 03:54: In it, the wave function describes a real wave of some stuff.
- 03:59: This wave guides the motion of a real point-like particle that has a definite location at all times.
- 04:05: Importantly, the wave function in pilot-wave theory evolves exactly according to the Schrodinger equation.
- 04:13: That's the equation at the heart of all quantum mechanics that tells the wave function how to change across space and time.
- 04:28: For example, this guiding wave does all the usual wavy stuff, like form an interference pattern when it passes through a pair of slits.
- 04:37: Because particles follow the paths etched out by the wave, it'll end up landing according to that pattern.
- 04:45: The wave defines a set of possible trajectories and the particle takes one of those trajectories.
- 07:05: ... well as the Schrodinger equation that tells the wave function how to change, it also has a guiding equation that tells the ...
- 07:24: However, the guiding equation is derived directly from the wave function, so some would argue that it was there all along.
- 07:32: A more troubling requirement of Bohmian mechanics is that it does contain real complexity that is not encoded in the wave function.
- 07:44: Bohmian mechanics has so-called hidden variables, details about the state of the particle that are not described by the wave function.
- 07:51: According to pilot-wave theory, the wave function just describes the possible distribution of those variables given our lack of perfect knowledge.
- 08:05: ... published a proof showing that hidden variable explanations for the wave function just couldn't ...
- 08:34: So there can't be extra information about a specific region of the wave function that the rest of the wave function doesn't know.
- 09:07: The entire wave function knows the location, velocity, and spin of each particle.
- 09:18: Not only does the entire wave function know the properties of the particle, but the entire wave function can be effected instantaneously.
- 09:25: So a measurement at one point in the wave function will affect its shape elsewhere.
- 09:30: This can therefore affect the trajectories and properties of particles carried by that wave, potentially very far away.
2016-11-16: Strange Stars
- 12:50: A lot of you asked for a video on De Brogile-Bohm pilot wave theory.
2016-11-09: Did Dark Energy Just Disappear?
- 14:40: ... interference bands when the distance between the slits is similar to the wavelength of the light, and with slit widths significantly narrower than that ...
2016-10-26: The Many Worlds of the Quantum Multiverse
- 00:53: Mathematically, this is encapsulated in the wave function of a quantum particle or system of particles.
- 01:17: These particles arrive at the screen distributed like the interference pattern you would expect from a simple wave.
- 02:16: It collapses the wave function.
- 03:17: But why can't the cat collapse its own wave function?
- 03:55: ... the wave functions describing quantum systems overlap sufficiently-- in other ...
- 05:12: What if the wave function never collapses?
- 06:00: ... Everett in his 1957 PhD thesis entitled "The Theory of the Universal Wave Function." It's come to be known as the many worlds ...
- 07:31: It seems extravagant to propose uncountable eternally-branching universes just to get out of collapsing a wave function.
- 07:57: It's just that Copenhagen merges them into a single timeline with its wave function collapsed.
- 08:04: ... worlds can be thought of as overlayed histories, slices of a universal wave function that diverge from each other as the universe evolves, but none ...
- 08:18: ... because there's nothing in that math that requires the collapse of the wave ...
- 10:02: ... happening when these neighboring coherent histories interact or why the wave function translates to probabilities the way it ...
2016-10-12: Black Holes from the Dawn of Time
- 00:25: LIGO's recent observation of gravitational waves from merging black holes is a stunning confirmation of this fact.
2016-09-21: Quantum Entanglement and the Great Bohr-Einstein Debate
- 02:00: In between observations, the wave function describing this superposition is a complete description of reality.
- 02:29: He insisted that the wave function, and by extension quantum mechanics, is incomplete.
- 03:36: ... requires that we describe the particle pair with a single combined wave function that encompasses all possible states of both ...
- 03:49: ... measurement of one particle automatically collapses the entire entangled wave function, and so affects the results of measurements of the other ...
- 05:00: Their wave functions are therefore entangled.
- 06:35: What if between creation and measurement, the electron and positron only exist as a wave function of all possible states.
- 06:43: In that case, measurement of one particle spin should cause the entire wave function to collapse, to take on defined values.
- 08:41: ... confirmed that the Bell inequalities are violated, suggesting that the wave function cannot have local hidden ...
- 10:53: Also, the De Broglie-Bohm Pilot Wave Theory works by assuming real and non-local hidden variables.
2016-09-07: Is There a Fifth Fundamental Force? + Quantum Eraser Answer
- 07:19: If either detectors A or B are triggered, then there's an asymmetry in the global wave function, passing through one slit versus the other.
- 07:32: Admittedly, this decoherence appears to affect the wave function at times before the apparent cause of the decoherence.
- 07:50: ... without inventing mystical interpretations that somehow give us psychic wave function collapsing powers, as much as we'd all like to believe we have ...
2016-08-24: Should We Build a Dyson Sphere?
- 00:53: ... only as strange points of infrared lights but otherwise black at visible wavelengths. ...
- 14:04: It's like adding a sign in a cosine wave.
2016-08-10: How the Quantum Eraser Rewrites the Past
- 01:08: The Copenhagen interpretation would tell us that in this space, a particle is only its wave function, a distribution of possible properties.
- 01:19: It's a probability wave that does all the usual wave-like stuff like making interference patterns, until something happens to collapse it.
- 01:29: At that point, the Copenhagen interpretation tells us that a true transition happens between wave and particle.
- 01:52: ... to believe that observation by a physicist is better at collapsing wave functions then observation by an electronic ...
- 02:12: But it's still pretty interesting to see what happens if we try to observe the wave function at different points in the double slit experiment.
- 02:19: The great mystery of the experiment is that very particle-like things appear to traverse both slits simultaneously, like you might expect of a wave.
- 03:01: ... even true if you place detectors on the far side of the slits after the wave particle thing should have already been interfering with itself, just ...
- 03:26: It's impossible to make these measurements without messing up the wave.
- 03:31: ... interference pattern happens because the waves emerging from each slit are what we call coherent, which is a fancy way ...
- 03:41: So the locations of peaks and valleys is predictable and stays consistent as the waves move forward.
- 03:49: This coherence is what allows the waves to produce the interference pattern in the first place.
- 03:54: But when you place some device in the path of either wave, you mess with this coherence, and so affect the pattern that reaches the screen.
- 05:33: As though any knowledge of which way the original photon traveled stops it from acting like a wave during its passage through the slits.
- 05:49: So a photon lands on the screen according to the pattern defined by its wave function.
- 07:29: ... interpretation that observation of the path causes the collapse of the wave function, and that the wave function can collapse all the way back to ...
- 08:01: ... when a spread out wave function resolves itself into a set of known properties, say, the ...
- 08:18: But if these wave functions are physical, as the Copenhagen Interpretation would tell us, then there is no real instantaneous physical interaction.
- 08:27: ... contrast, a physical interpretation of the wave function, like the De Broglie-Bohm Pilot Wave Theory, requires an ...
- 08:57: Now the delayed choice quantum eraser double slit experiment doesn't tell us whether the wave function is physical or not.
- 09:04: ... us that the Copenhagen, or any other metaphysical interpretation of the wave function, is no less well, crazy-sounding than a physical ...
2016-08-03: Can We Survive the Destruction of the Earth? ft. Neal Stephenson
- 11:15: ... suggests that the wave function is nothing more than a distribution of probabilities, and that ...
- 11:35: ... deterministic interpretation requires that the wave function conceal what we call hidden variables, that may change over ...
- 11:50: ... ideas is that they require instantaneous communication across the wave function, or between entangled particle pairs, in order to satisfy ...
- 12:14: vhsjpdfg inquires after the wave functions and interference patterns for massive objects.
- 12:21: Well, wave functions for macroscopic objects are incredibly complicated because they're comprised of countless quantum particles.
- 12:30: You can define a theoretical wavelength of a macroscopic object's wave function-- it's the de Broglie wavelength, and it's very, very small.
- 12:39: ... do so you'd need slits whose separation is similar to their de Broglie wavelength. ...
2016-07-27: The Quantum Experiment that Broke Reality
- 00:45: Some distance away, those waves encounter a barrier with two gaps cut in it.
- 00:51: Most of the wave is blocked but ripples pass through the gaps.
- 01:16: ... call this "constructive interference." But when the peak from one wave encounters the trough from another, they cancel out, leaving nothing, ...
- 01:34: Any type of wave should make an interference pattern like this, for example, water waves and sound waves but also light waves.
- 02:01: Of course, we now know that light is a wave in the electromagnetic field thanks to the work of James Clerk Maxwell a century later.
- 02:33: So each photon is a little bundle of waves, waves of electromagnetic field, and each bundle can't be broken into smaller parts.
- 03:56: This pattern has nothing to do with how each photon's energy gets spread out, as was the case with the water wave.
- 04:31: It knows the interference pattern of a pure wave that passed through both slits equally and it chooses its landing point based on that.
- 05:14: We have to conclude that each individual photon, electron, or buckyball travels through both slits as some sort of wave.
- 05:23: ... wave then interacts with itself to produce an interference pattern, except ...
- 05:37: It looks like a wave of possible undefined positions that at some point, for some reason, resolves itself into a single certain position.
- 06:00: ... call the mathematical description of this wave-like distribution of properties a "wave function." Describing the behavior of ...
- 06:12: But what does the wave function represent?
- 06:14: What are these waves of or waves in?
- 06:36: So the particle seems to be more particle-like at either end but wave-like in between.
- 06:44: ... wave holds the information about all the possible final positions of the ...
- 06:55: In fact, the wave must map out all possible paths that the particle could take.
- 07:02: ... could-be trajectories from start to finish and for some reason, when the wave reaches the screen, it chooses a final location and that implies ...
- 07:18: So what causes this transition between a wave of many possibilities and a well-defined thing at a particular spot?
- 07:39: We still couldn't figure out what the wave is made of.
- 07:59: The Copenhagen interpretation says that the wave function doesn't have a physical nature.
- 08:09: ... that a particle traversing the double-slit experiment exists only as a wave of possible locations that ultimately encompasses all possible ...
- 08:27: ... a possibility space to a defined set of properties "the collapse of the wave function." It tells us that prior to the collapse, it's meaningless to ...
- 09:25: ... the universe is fundamentally random within the constraints of the final wave ...
- 09:49: There are interpretations that give the wave function a physical reality.
- 09:54: ... we know that light is a wave in the electromagnetic field and quantum field theory tells us that all ...
- 10:06: This may give us a more physical medium that drives these waves of possibility.
2016-07-20: The Future of Gravitational Waves
- 00:00: On June 15, the LIGO team announced their second detection of a gravitational wave.
- 00:14: ... September 14, 2015, the Laser Interferometer Gravitational Wave Observatory, LIGO, detected the gravitational waves from the merger of ...
- 00:31: ... in the path lengths of the LIGO interferometer arms as the gravitational wave stretched and compressed the fabric of space as it passed ...
- 00:54: This incredibly important observation was hailed at the time as representing the dawn of gravitational wave astronomy.
- 01:02: However, that's only true if we ever detect another gravitational wave.
- 01:30: ... waveform looked just like what the researchers were expecting from theoretical ...
- 03:20: ... about the December signal when they announced the first gravitational wave detection back in ...
- 03:38: ... actual fact, LIGO probably saw a third gravitational wave back in October but it wasn't quite strong enough to satisfy the team's ...
- 04:07: Beyond the detection of gravitational waves, this is another awesome validation of the theory.
- 05:10: ... LIGO isn't particularly good at figuring out the direction that the wave came from, which is determined by the time difference in the signal ...
- 05:25: When European Virgo comes online later this year, we expect a massive improvement in our ability to locate the source of the waves.
- 05:33: Then we can turn all of our telescopes to that spot as soon as a wave is detected.
2016-06-29: Nuclear Physics Challenge
- 00:19: But here's TL;DR. Particles of matter have wave-like properties.
- 00:24: These matter waves don't have perfectly-defined positions, but rather, occupy a range of possible positions.
2016-06-22: Planck's Constant and The Origin of Quantum Mechanics
- 01:31: We talked about this recently when we discussed the de Broglie wavelength.
- 02:12: ... Heisenberg uncertainty principle and the de Broglie wavelength, but also the Schrodinger equation, the energy levels of electron orbits, ...
- 09:52: ... clue Einstein needed to hypothesize the existence of the photon-- part wave, part particle, carrying a quantum of energy equal to the now familiar ...
- 14:34: That's exactly the same type of swirliness that primordial gravitational waves should produce.
- 14:45: Ed Eggermont wonders if gravitational waves are also subject to gravitational lensing.
- 14:52: Gravitational waves are ripples in the fabric of space time, so they have to go where the space time goes.
2016-06-15: The Strange Universe of Gravitational Lensing
- 10:05: ... tunnel, you need to spontaneously find yourself at a point in your wave function that has an equal or lower energy state than your starting ...
- 10:24: An exponentially decaying part of its wave function is actually inside that wall.
- 10:29: The particle could find itself located anywhere that its wave function is non-zero.
- 10:54: ... Mayo asks whether my interpretation of the de Broglie wavelength as a range of possible locations is only true for the Copenhagen ...
- 11:07: So some of the language I used to describe the collapse of the wave function and possible positions did echo the Copenhagen interpretation.
- 11:37: Prior to that, it exists only as its wave function, which is a distribution of probabilities of these properties.
- 11:45: ... works, but it's also not deterministic in that in order for the wave function to become a set of physical properties, there needs to be a ...
- 12:02: ... de Broglie-Bohm pilot wave theory, the many-worlds interpretation, and others, allow a ...
- 12:16: The wave function that we calculate defines the probability that we will observe a particular set of physical properties.
- 12:39: ... a quantum system means doing something to it that collapses its wave function into the classical physical properties like position and ...
- 12:58: ... is another way of saying that a particle's wave function gets so hopelessly mixed with those of other particles that its ...
- 13:09: However, one view that's not really favored is the idea that a conscious observer is needed to collapse a wave function.
2016-06-01: Is Quantum Tunneling Faster than Light?
- 00:57: That distribution, and the way it changes over time, is coded in the object's wave function.
- 01:04: The reduction of a fuzzy possibility space into a specific measurable property is sometimes referred to as the collapse of the wave function.
- 01:30: French mathematician and physicist Louis de Broglie figured out that any material object is really a matter wave.
- 01:39: It can be described as a wave packet of positioned probability.
- 01:43: And that wave packet has a wavelength.
- 01:46: This de Broglie Wavelength defines how well determined an object's position is.
- 01:52: A large wavelength means a highly uncertain position.
- 01:57: A small wavelength means a well-defined position.
- 02:16: Observe me and you'll collapse my wave function and probably find me pretty much exactly where you expect to.
- 02:23: See an object's de Broglie wavelength depends on its momentum, so mass times velocity.
- 02:31: Higher momentum means a smaller wavelength.
- 02:37: ... tens of kilograms of thermal moving particles and have de Broglie wavelengths a couple of orders of magnitude smaller than the Planck ...
- 03:39: As an alpha particle approaches the force barrier of the nucleus, its wave packet is reflected backwards, usually.
- 03:48: See, that wave packet describes a range of possible locations for the approaching particle.
- 05:38: Remember the LEGO interferometer that discovered gravitational waves?
- 05:46: The photon wave packets interact with each other and produce an interference pattern that is incredibly sensitive to differences in path lengths.
- 06:18: ... like with the alpha particle, as the photon approaches the barrier the wave packet defining its possible location extends weakly beyond the ...
- 06:51: That will be apparent when their wave packets don't line up perfectly at the other end.
- 08:20: A particle resolves its location anywhere within the vicinity of its de Broglie wavelength.
- 08:39: ... could arrive at the earlier time of the tunneling photon, because its wave packet includes that in its range of possible ...
- 08:49: When you add the barrier, all you're really doing is reshaping the wave packet, selecting only the possibility space of early arrival.
- 08:59: This can look like an increase in the speed of light, but only within the uncertainty range defined by the de Broglie wavelength.
- 09:07: ... which is perhaps the deeper principle from which the de Broglie wavelength ...
2016-04-27: What Does Dark Energy Really Do?
- 01:33: During that expansion, it increases the wavelength of these electromagnetic waves, resulting in what we see as redshift, cosmological redshift.
2016-04-06: We Are Star Stuff
- 09:27: ... spiral in as they radiate away their orbital energy in gravitational waves. ...
2016-03-23: How Cosmic Inflation Flattened the Universe
- 02:26: They're defined by how fast sound waves could have traveled by the time the CMB was created.
2016-03-09: Cosmic Microwave Background Challenge
- 04:18: This coming Monday, March, 14th, I'll be participating in a public seminar on the new LIGO discovery of gravitational waves.
- 04:29: If you're in the area and would like to attend, please RSVP to email@example.com with the subject line NYC Gravitational Waves.
- 04:42: You'll learn way more about gravitational waves than on any YouTube show.
2016-02-24: Why the Big Bang Definitely Happened
- 01:42: Light from distant galaxies is red shifted, stretched to longer wavelengths.
- 06:16: We see ripples of sound waves in the pattern of those fluctuations.
- 08:40: ... ago, the LIGO team announced the very first detection of gravitational waves. ...
- 09:41: ... that Advanced LIGO was turned on just in time to catch the gravitational waves from the merger of black ...
- 11:39: ... quote Lawrence Stanley, "OK, but until the discovery of gravitational waves can lower my mortgage and reduce the price of gas at the pump, it ...
2016-02-17: Planet X Discovered?? + Challenge Winners!
- 03:37: The relativistic Doppler effect classically changes the wavelengths of light, blue-shifting approaching material and red-shifting receding material.
2016-02-11: LIGO's First Detection of Gravitational Waves!
- 00:05: Gravitational waves have been directly detected for the very first time.
- 00:17: ... existence of these waves is the last major prediction of Einstein's theory of general relativity ...
- 00:49: ... predicted that it should certainly detect the passage of gravitational waves, of ripples in the fabric of spacetime caused by extreme gravitational ...
- 01:19: ... the detection, we put together a video explaining what gravitational waves are, how they're formed, and exactly how advanced LIGO detects ...
- 01:53: Any orbiting pair of massive objects generates gravitational waves.
- 01:57: ... through orbiting extremely close together, produce gravitational waves strong enough for us to detect, at the ...
- 02:30: But gravitational waves carry energy, which is sapped from the orbital energy of the system.
- 02:51: And so this was a very convincing but indirect verification of gravitational waves.
- 02:57: ... the waves produced when these stellar cores are still distant from each other are ...
- 04:26: Spacetime is stretched and squeezed as the wave passes by.
- 04:57: See, gravitational waves are inevitable if the theory is correct.
- 06:13: ... LIGO is sensitive to gravitational waves at frequencies produced by merging black holes and neutron stars, as ...
- 07:03: This is a really, really big deal, and it marks the beginning of the era of gravitational wave astronomy.
2016-01-06: The True Nature of Matter and Mass
- 04:03: And then a pressure wave communications the force to the front until the whole spring is moving.
- 04:36: Photons in the photon box, but even in the spring, the density wave is ultimately communicated by electromagnetic interactions between the atoms.
- 04:46: That itself is a speed of light interaction, even if the resulting density wave isn't.
2015-12-16: The Higgs Mechanism Explained
- 07:55: ... falls to the horizon, the light it emits is red shifted such long wavelengths that it effectively becomes ...
- 08:49: Gareth Dean asks about this whole thing about using gravitational waves to turn up the core temperature of a star.
- 08:55: ... so gravitational waves carry a lot of energy, and some of it can get dumped into a star by ...
2015-12-09: How to Build a Black Hole
- 01:20: If you get impatient, you can turn up the core temperature by bombarding it with gravitational waves.
- 05:25: Certain numerical properties that you can assign to a particle exist in a wave of varying degrees of maybe.
2015-10-28: Is The Alcubierre Warp Drive Possible?
- 06:23: ... like a mini version of the one being used to detect gravitational waves, To measure the tiny changes in path length created by a warp ...
- 07:09: ... next episode of "Space Time." Last week, we talked about gravitational waves, and whether the advanced LIGO Observatory has maybe seen ...
- 07:31: It'll be an orbiting gravitational wave observatory designed to detect much higher frequency gravitational waves than advanced LIGO.
- 08:01: ... this was the much hyped gravitational wave detection based on polarization anisotropies in the cosmic microwave ...
- 08:12: So now, the money is on the signal actually being due to dust, not G waves.
- 08:24: Now, MrSh1pman wants to know, if we find these G waves, will it change anything?
2015-10-22: Have Gravitational Waves Been Discovered?!?
- 00:03: Gravitational waves are the last prediction of Einstein's Theory of General Relativity.
- 01:03: However, there's one last, incredible prediction that has never been directly observed-- gravitational waves.
- 01:19: However, the analogy can give us a sense of what a gravitational wave really is.
- 01:37: Same deal with gravitational waves.
- 02:00: So a rotating sphere or a cylinder doesn't make waves.
- 02:08: ... a certain speed determined by the stiffness of the rubber, gravitational waves-- and indeed, gravity itself-- propagate according to the stiffness of ...
- 02:49: ... ripples on a pond or even electromagnetic waves-- which are all simple, up-down, longitudinal waves-- gravitational waves ...
- 03:11: Well, let's first think about all the sorts of things that might produce detectable gravitational waves.
- 03:42: And this change is for the most powerful waves that have likely ever passed through you.
- 04:07: And so it's no wonder that gravitational waves remain the only major prediction of GR without a direct measurement.
- 04:20: Gravitational waves carry energy.
- 05:21: ... paths just right, we can make the peaks of one of those electromagnetic waves line up with the valleys of the other, causing them to completely cancel ...
- 05:33: ... signal is seen, but if a gravitational wave passes by, it will shrink one of those paths and lengthen the other, and ...
- 06:12: So how do we tell that it's a gravitational wave?
- 06:22: It's even possible to get a direction for the wave by measuring the relative path lengths.
- 06:37: So how many g-m waves did LIGO find?
- 06:40: Well, between 2002 and 2010 when it ran, it found zero-- no gravitational waves at all.
- 07:58: Even if they spotted a wave, they'd keep it super-secret until they quadruple-checked results, which could take months.
2015-10-15: 5 REAL Possibilities for Interstellar Travel
- 12:26: Ed Stephan asks why we're even talking about gravitational waves when none have ever been observed.
- 12:32: ... in the meantime, in pointing out the indirect detection of gravitational waves, Garreth Dean delivers the amazing quote, "So we haven't seen a duck, but ...
2015-10-07: The Speed of Light is NOT About Light
- 04:17: This transformation thing, it's like a mathy magic wand that you wave at your description of spacetime or your physical laws.
- 08:29: ... limit also happens to define the speed of propagation of electromagnetic waves-- the speed of ...
- 08:57: So lights or photons, also gravitational waves and gluons all have no mass.
2015-09-23: Does Dark Matter BREAK Physics?
- 09:36: In fact, in the vicinity of the black hole, this radiation is poorly localized, having a wavelength of all of the Schwarzschild radius.
2015-08-05: What Physics Teachers Get Wrong About Tides!
- 08:47: ... how Miller's planet in the movie "Interstellar" could've had such a huge waves without the astronauts themselves being stretched or ...
2015-06-24: The Calendar, Australia & White Christmas
- 06:16: ... McLean asked, "if aliens can't pick up our radio waves, then why are we trying to listen for alien radio waves with SETI?" Well, ...
2015-05-27: Habitable Exoplanets Debunked!
- 03:54: ... from that of its star and see how bright that light is at different wavelengths. ...
- 04:01: That graph of brightness versus wavelength is called an object's spectrum.
- 04:05: Since different atoms and molecules emit or absorb particular wavelengths of light only, the spectrum tells you a lot about atmospheric composition.
2015-03-25: Cosmic Microwave Background Explained
- 01:46: It's emitting electromagnetic waves of all wavelengths.
- 01:49: Moreover, the intensity at different wavelength is in very specific proportions that trace out a graph very close to this.
- 02:04: Now, everything has a temperature, so everything has a thermal spectrum, and it emits all electromagnetic wavelengths.
- 02:21: ... to 2.7 degrees above absolute zero, the peak shifts way into microwave wavelengths and, lo and behold, exactly matches the CNB, and I mean ...
- 03:16: And just like toasters, people and tacos, it was emitting a thermal distribution of electromagnetic waves.
- 04:28: ... a prior episode that you can revisit here, expanding space stretches the wavelength of free streaming light through a process called cosmological ...
- 04:37: ... orangey thermal spectrum of light was redshifted to longer and longer wavelengths, becoming toaster read and eventually infra-red, so that to human eyes, ...
2015-02-25: How Do You Measure the Size of the Universe?
- 00:55: That's the part that we, in principle, can see with light or gravitational waves.
- 03:02: Light has a color determined by its wavelength.
- 03:04: Longer wavelength light is redder, shorter bluer.
- 03:14: But because space is expanding, the wavelength of light gets stretched as it travels to us, making the blue light red; hence, the term redshift.
- 03:22: In more extreme cases, the wavelength can be stretched out of the visible spectrum altogether, into microwaves or radio waves.
- 03:42: And thus, it has its wavelength stretched more.
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