Yeah. And the best part is, these aren't even the densest videos on youtube, forget all lectures possible. There are some professors that are even better. I once took a break from my minor in physics and went back the next semester. I felt so strange after my first lecture back, I had forgotten what it was like to be challenged...
The subject itself is deep. A 20 minute presentation is bound to be incomplete no matter how dense, so it is partially due to this. Learn a little by osmosis and it'll help in the future. Here's a more advanced/complete link on quantum spin liquids which puts these ideas to the test (it is long and a 2 parter): th-cam.com/video/CUg-sGeuJA8/w-d-xo.html
this one is seriously mind blowing to me.. the more of these videos you watch, the better they get.. because over time you understand more and more and then you put those pieces together and it's like BLAM! and suddenly your concept of reality becomes so .... unreal
I’m a molecular biologist and I appreciate life at the molecular level. I’ve been searching for the deeper underpinnings of reality and life and have watched these for years. When he connected the quantum with the macro, it literally blew my mind and I visually saw all of the concepts covered through the years into one theory of the fabric of reality
The answers at the end of this episode just increased exponentially my interest in a full PBS SpaceTime episode about the Quantization of Space. I'd really like to know more about Loop Quantum Gravity's grid of abstract connections between points, and how is possible that Space emerges only on larger scales.
How does time dilation affect smaller scales? That is really the question. So, is the instantaneous momentum of particles caused by time dilation, like the idea that gravity is? As you approach the plank scale, what is dilating anymore...? Point space, and it's _"abstract"_ geometries are an attempt at describing the interactions that build up to things that can then dilate. What comes before that...🤷
I just want to thank you guys for all you do. I love learning about space and I have trouble sleeping. Listening to your videos before bed distracts and keeps my mind busy enough to not over think about life until i can fall asleep. Unsuccessful today since its 6:40am, but I don't know what I would have done without this for the past few years. I have listened to all your videos and been repeating them since they are amazing.
This takes me back to my dissertation - “Defining work in a quantum battery” where I utilised heavily Von Neumann Entropy and the concept of temperature at the quantum level. This was a great episode and made me miss my days in academia, thank you for another phenomenal episode Matt.
@@death_parade I have attempted to post a link but for some reason, TH-cam is removing the comment. I do have a link to my dissertation on my LinkedIn profile. If you were to add /jordanleeevans to LinkedIn URl you’d be able to find my profile along with my dissertation
Quantum Entangled Twisted Tubules: "A theory that you can't explain to a bartender is probably no damn good." Ernest Rutherford When we draw a sine wave on a blackboard, we are representing spatial curvature. Does a photon transfer spatial curvature from one location to another? Wrap a piece of wire around a pencil and it can produce a 3D coil of wire, much like a spring. When viewed from the side it can look like a two-dimensional sine wave. You could coil the wire with either a right-hand twist, or with a left-hand twist. Could Planck's Constant be proportional to the twist cycles. A photon with a higher frequency has more energy. (More spatial curvature). What if gluons are actually made up of these twisted tubes which become entangled with other tubes to produce quarks. (In the same way twisted electrical extension cords can become entangled.) Therefore, the gluons are actually a part of the quarks. Mesons are made up of two entangled tubes (Quarks/Gluons), while protons and neutrons would be made up of three entangled tubes. (Quarks/Gluons) The "Color Force" would be related to the XYZ coordinates (orientation) of entanglement. "Asymptotic Freedom", and "flux tubes" make sense based on this concept. Neutrinos would be made up of a twisted torus (like a twisted donut) within this model. Gravity is a result of a very small curvature imbalance within atoms. (This is why the force of gravity is so small.) Instead of attempting to explain matter as "particles", this concept attempts to explain matter more in the manner of our current understanding of the space-time curvature of gravity. If an electron has qualities of both a particle and a wave, it cannot be either one. It must be something else. Therefore, a "particle" is actually a structure which stores spatial curvature. Can an electron-positron pair (which are made up of opposite directions of twist) annihilate each other by unwinding into each other producing Gamma Ray photons. Does an electron travel through space like a threaded nut traveling down a threaded rod, with each twist cycle proportional to Planck’s Constant? Does it wind up on one end, while unwinding on the other end? Is this related to the Higgs field? Does this help explain the strange ½ spin of many subatomic particles? Does the 720 degree rotation of a 1/2 spin particle require at least one extra dimension? Alpha decay occurs when the two protons and two neutrons (which are bound together by entangled tubes), become un-entangled from the rest of the nucleons . Beta decay occurs when the tube of a down quark/gluon in a neutron becomes overtwisted and breaks producing a twisted torus (neutrino) and an up quark, and the ejected electron. The phenomenon of Supercoiling involving twist and writhe cycles may reveal how overtwisted quarks can produce these new particles. The conversion of twists into writhes, and vice-versa, is an interesting process. Gamma photons are produced when a tube unwinds producing electromagnetic waves.
I would love to see an experimental test of the notion that quantum entanglement is necessary for the property of entropy, in any average balloon containing hydrogen molecules or oxygen at room temperature. What makes me doubt: such molecules are large, temperatures are high, and it’s moist compared to conditions normally used to measure quantum entanglement.
I'm happy to hear your remark about von Neumann and how great he actually was: people often don't realize how much von Neumann was ahead of his time and what kind of genius he was.
How to go from superposition, to entangled quantum states to classical. This was possibly the most brilliant and insightful presentation ever! Thank you!
Wow. It took me a long to get through digesting it properly but eventually when you linked the quantum with the classical. So many different concepts and puzzle pieces just fell in together in the most beautiful harmonic mannerism. Reality truly is something else
nah, it would have to be the band name. And then everyone would always ask which one is Shannon, but of course there is no Shannon. It's just the name of the band.
12:16 "You've already become entangled with the coin and live in the slice of the wave function (the mixed state) where the coin is *either* heads *or* tails"
@@mechadense But it is either one or the other, not both at the same TIME. The wave function is an emergent property of time. This means that the coin is what it is, regardless of the wave function in any other segment of time. That's why it's heads (or tails) when it's revealed at a certain TIME. It already was/it already is/it already will be, but only at whichever time it's being measured. This is the time that exists, and no other, because any other expression of time has either already occurred, or has yet to occur.
@@toughenupfluffy7294 - Not sure what you mean with "The wave function is an emergent property of time". A well isolated and thus in its entirety accessible wave function describes an *undirected* temporal evolution of a system holistically in its entirety. A (pure state) wave function does not specify a direction-of-time aka an arrow-of-time. Backwards is indistinguishable from forwards (as it is in reversible computing). The arrow-of-time does not lead to the wave function. What does lead to an arrow-of-time are is the statistics of microstates in slices of incompletely known wave functions (mixed states) when the system is not in equilibrium, when it does not have maximal entropy. The wave function very much has the capacity do house truly counterfactual things (like an electric current flowing in counter-rotating directions at the same time). This is experimentally testable via the Bell test and has been repeatedly tested. - - - Well … Except if there are global hidden variables. Meaning we do *not* have access to the entire wave function then I guess. Global hidden variables have been pushed quite far out by now. Experimentally via cosmic bell test. But since we'll never be able to see infinitely far out in spacetime we'll thus never be able to definitively disproof global hidden variables with absolute certainty. - - - I know, there's time symmetry breaking in weak force beta decay. I won't go into that.
Forget about the wave function! It depends on differential equations and latter on infinitesimal calculus, which is not a proper mathematical tool to approach at quantic scales.@@toughenupfluffy7294
I love this episode. Everything quantum seems to make more sense now and is less daunting and unfamiliar. The visuals helped so much too. Looks and sounds like the entanglement of all particles weaving the fabric of space. Feels like a familiar warm comforting blanket rather than a feeling like being hopelessly lost driving an unfamiliar car on a super tangly spaghetti junction, in a blizzard or something. I just hope Schrodinger's cat doesn't tear apart the fabric of space time like my cat did my blankets. I mean I'd want revenge if my owner kept putting me in a box for extended periods just to contemplate weather I'm alive still or not.
My mind was in the superposition of both understood the episode or didn't, until i broke the uncertainty with a rewatch😂 Really excited for the upcoming episode.
Some More News Coverage of the current Work-Crisis affects us all, so excuse the RANDOMNESS but i want my fellow PBS-Space-Time-Fans (man, that's a long word, i should have shortened that, but whatever) to know such.
Loving him being honest about the updated information. Also thie fact he took a comment seriously enough to go back and dig to confirm the information.
Ooh information theory next. I love information theory! As a software engineer I think that information theory feeds into computer science in a way that is massively influential while barely anyone is even aware of it. You don't need it every day, but knowing about it really helps you understand certain things at a much more fundamental level.
Congratulations on the excellent explanations. PBS does an awesome job in this channel, really outstanding. I will yet be a little bit picky and address a conceptual disagreement about the second law being a statement about the von Neumann entropy of a system. Quantum thermodynamics is mainly concerned with energetic and, further, informational processes; not states. The second law is a statement about a quantum process and the quantity which entails the irreversibility of this process is the entropy production. One should bear in mind that the closed-system evolution in quantum mechanics is unitary and, thus, leaves the entropy of a quantum system untouched. As von Neumann brilliantly notes in his work, irreversibility stems from measurements and, as we understand today, from general quantum channels --- like open quantum systems. By no means I want to say you are wrong in the simplification made. I understand that all those subtleties would make the content very technical and, of course, not as accessible. But, as a young scientist from the quantum thermodynamics community, I thought it'd be nice to add my view on the subject.
Thank you, thank you, thank you for explaining these concepts. I am only an engineer, so I don’t always understand, but I can always feel my mind expand.
I have considered this for ages! Very glad this simple little detail is being presented in depth. I've heard this specifically only in lectures and only in passing, never in any books I've read.
Von Neumann entropy: Sabine Hossenfelder : "doubt" The difference between the pure quantum state with Von Neumann entropy=0 and the known state after measurement is the measurement problem. Hossenfelder says that we don't know enough details about how physics really works to know how there is a transition between the two - we don't have a way to describe that transition within quantum equations. The Copenhagen interpretation is to just say "our experiments work, quantum theory works - so lets just ignore the complicated part that happens during measurement and pretend it isn't a problem." The many worlds theory replaces one handwaving with another handwaving - because it posits a splitting of universes, part of the quantum state become inaccessible, but it has no idea when or how that happens. Just saying "it all happens within the laws of quantum physics and the wave function never pops" doesn't save you from the fact that you have no information about how we get from the unmeasured state to the measured one. If you say it's within the theory, then you have to be able to calculate it within the theory and they can't. So does decoherence solve the measurement problem? Hossenfelder says "no" but she hasn't gotten around to explaining why, at least not in her channel. I haven't finished her book, so I can't say whether she explains it there. But I have to say that the transition you described from entropy=0 to entropy>0 sounds like another one of those "ok, exactly when and how did that happen? Can you calculate it? No." situations.
How do we know that no way to calculate exists. If i use occlums razor i can just say it exists but we aren't able to measure it cause laws get too complex at that size. Like maybe if it's up or spin depends on a particle 20 km away and even a small change can change everything. Like in chaotic system. I am still in high-school about to go to college but it's still a valid question no one seems to answer. It just doesn't seem skeptical enough.
@@pravinrao3669 I didn't say that no way to calculate it exists. It could just be complex enough that we haven't calculated it yet. Quantum physics is amazingly successful at describing systems with just a few particles. But measurement equipment isn't just a few particles. I'm not a physicist, but I guess she's saying that the interactions that make up a measurement device might be too complicated for us to calculate or maybe even they might depend on details that the theory left out. So if you can't point at sample calculation of a measurement, it's premature to claim that there is no problem with one. Also there's something incompatible with the description of a simple system and a measured state. In the pre-measured state, any linear combination of states is considered a valid outcome - and so you have probabilities. But in the measured state you have definite outcomes. But as Matt said when he described a combination of states as a known, 0 entropy state, it's not a matter of there being an unknown that you discover when you measure. It's that the measured state is a DIFFERENT state than the premeasured one. You need a level of suspension of disbelief to buy that - that, for instance, the photon didn't pick a spot on the film... And maybe it DID pick a spot because after it reaches the film it isn't just a few particles anymore - because the effects on the film cascade past the photon to many atoms etc. Is that measurement or decoherence? Well maybe... but then there are the quantum eraser experiments and the fact that the system seems to be able to change its mind based on things that happen later in time then the time when some of those mass effects would have taken place if a certain choice were made. So the things you think create a measurement or a decoherence can depend stuff the wave function (that isn't supposed to exist after a measurement) encounters AFTER the measurement could have taken place. Note, I made an edit describing the problem with the quantum eraser experiment.
What i got out of this episode is that the macro world appears classical because any particle affecting an object is entangled with other particles which the object cannot have information about, i'm assuming because of the finite speed of information. Since the object only has access to a small part of a bigger wavefunction, the particle appears statistical instead of superpositioned. From the sound of it, decoherence happens as soon as an interaction with a system only has limited access to the wavefunction of that system. That would happen naturally in any uncontrolled environment where particles fly around freely. I don't know what it means for carefully controlled experiments, though.
You make some valid points regarding the various interpretations of QM but to be fair, the founders of the so called "Copenhagen" interpretation were pretty clear from the beginning that quantum probabilities were observer dependent. It provoked a reaction from Einstein where he jokingly stated the following, "I like to think the moon is there when I'm not looking at it". In regards to decoherence, she's right, it doesn't explain away the measurement problem. It just describes how quantum systems represented as state vectors in a complex Hilbert space transition into statistical mixtures that can't be expressed in terms of state vectors when you average over multiple measurements. And it certainly doesn't explain how a system can go from a linear combination of basis states to a well defined state with probability equal to 1 after a measurement is made. The so called collapse of the wave function. The thing with QM is, quantum systems don't have well defined physical properties that exist independently of you measuring it. Prior to any measurement, it exists purely as a mathematical wave function. On the other hand, quantum entanglement is about states of knowledge where 2 or more systems share a common wave function or share information so by measuring 1 of the systems, you learn something about the other corresponding systems
Wow, I just was reading The Order of Time by Carlo Rovelli, about Quantum Gravity, and it covers this exact same thing! I almost feel like I am gaining partial understanding! Honestly, this is very cool, and thank you so much
I didn't realize the same von Neumann whose name pops up in computer science all the time (von Neumann architecture) was also involved in thermodynamics, but there you go!
I will just let you read the Wikipedia entry for the areas he contributed to. The first time I ran across something to do with von Neumann was the book "2001: A Space Odyssey" (A.C. Clarke wrote a book after the movie that was based on two of his stories). One of the black obelisks turns out to be a von Neumann machine, or self-replicating machine
I've been waiting for Quantum Information Theory to be covered for ages. Can't wait for next week's episode! To me QIT is the only satisfying resolution to the question of how quantum things "become macroscopic".
If the arrow of time arises from increasing entropy, meaning increasing quantum entanglement over time, does that imply that at the beginning of time (assumedly the instant before the big bang) there was no entangled quantum systems?
well, before the big bang it is assumed there were not particles in general. since nothing WAS at all before the big bang. so yes your assumption would theoretically be correct.
It only implies that at Bing Bang there was less entanglement, than at the instant just after it (roughly speaking). The previous sentence already reveals a problem of our understanding of time: is it continuous or quantized? How exactly you go from "no time" to "having time", from "no entanglement" to "first entanglement"? Is time even fundamental? We don't even know what time is, and without that knowledge, we can only speculate. It's hard to reason about nothing (no time, no space), since we haven't observed nothing anywhere, because it's impossible. As depressing as it sounds, we may never know.
If a particle's entanglements only "diffuse" in a sea of entanglements possibly with every other particle in the universe, but never really break, how can we ever produce fresh entangled pairs so isolated that we can use them in quantum computing?
You can force a qubit into a known state by measuring it and flipping it if the measurement came out wrong. This works even if you and the qubit are entangled with the rest of the world. Basically what's happening is that this process swaps the qubit's tainted state for a clean one that ultimately came from moving the entropy in the qubit into the surrounding environment (which needs to be not max entropy for this to work).
@@alextaunton3099 Right, as long as the larger system is in a low entropy state. Resetting a qubit is possible for the same reason that it's possible for a fridge to cool down its interior.
That's only true about mirrors because of silver. Judas betrayed Jesus for silver, and so all the wicked and demonic creatures of the world were cursed to be weak to it. This means that vampires would be invisible in old-fashioned silvered mirrors or on photographic film because the photoactive part of film is crystals of silver hallides, but would be perfectly visible on silicon-based CCD cameras and aluminium-based modern mirrors, including those of telescopes.
@@alexv3357 you raise some pertinent and important points - no doubt about that. Absolutely no doubt. We know that Jesus and at least 7 of his apostles were scientists
@@PetraKann Scientist apostles? Blessed are the peer-reviewers, for they shall obtain peer reviews. Blessed are the theorists, for they produce testable models. Blessed are the experimenters, for they improve our theories. Blessed are the mathematicians, who write the language of knowing....
So, this has me thinking about the relationship between entropy and gravity. If there are more interactions due to higher energy density/strong force kinematic energy, does that essentially slow the ‘clock’ of entropy as the interactions take more ‘time’ to sort out all the entanglements. Could this explain gravity as an emergent property of the speed of causality and the quantum interactions of the wavefunction?
0:00: 🔑 The Significance of Entropy and the 2nd Law of Thermodynamics 2:57: 🔗 Connection between entropy, information, and quantum entanglement explained through Boltzmann's recasting of entropy and Shannon's information theory. 5:50: 🔬 Von Neumann entropy reveals the connection between quantum particles, driving the 2nd law of thermodynamics and measuring entanglement in quantum systems. 8:42: 🔗 Quantum entanglement creates a unique connection between two entangled quantum coins, leading to a superposition of states and correlated results. 11:37: 🔗 The process of decoherence leads to the emergence of the classical world from quantum entanglement, driving entropy growth. 15:17: ⚛️ Exponential processes have scale invariance, with the location of rapid growth depending on axis choice. Space debris increase may reach a threshold. 17:36: 🔍 Exploring concepts of quantum uncertainty, grid of abstract connections, and momentum transfer in quantum measurement. Recap by Tammy AI
Entropy always made my head hurt. It's like, it's all-encompassing, but it's also a measurement of nothing, or of what's potentially there, or what it can do, or how long... It's just... Man, I'm glad there are smart people out there to do this thinking for me.
@@bobaldo2339 Bob - there are a class of chemical explosives that are entropy driven - so if entropy is a mathematical construct, it is a construct that can hurt a lot in the real world. There are also chemical reactions that are primarily entropy driven.
That’s because they’re all just different effects of the underlying phenomena - that being the complex network of entanglement between particles (which brings us back to structural complexity and unpredictability). Those other metrics are useful in their fields, and valid within their fields, but they are not what entropy “is”. This is the driving force behind them.
"Zombies that when you shoot them just turn into thousands of smaller zombies" This is my boomstick.. Shop smart... Shop S-Mart... Also I'm now horrified that this has moved from hilarious Bruce Campbell comedy to my personal zombie apocalypse model. Thanks PBS.
I spent half of the video staring at Matt's throat and thinking whether he had been bitten as there were two puncture marks close together like the classic vampire bite. Then he started talking of being bitten by zombies and I was like "Oh!".
Yes I agree when my headphones are in my messy pocket, it gets entangled so I think this is a good proof that entropy is related to quantum entanglement.
When Matt started talking about the classical coin being influenced by all of its constituent parts and everything they've ever come in contact with, it made me think of almost like subpixel values in Mario. The current behavior is a product of all of the previous interactions interacting to create some sum.
If entanglement networks are a measure of entropy, when we accelerate particles in accelerators are we temporarily detaching these particles from the planet's entanglement network? And when we measure the results from collisions, are we simply measuring the resultant particles as they enter our entanglement network?
I find it so surprisingly satisfying when they show that some of the questions and statements people comment are answered by the show's own viewers. People like us. Lets Go! PBS!
I aprecciate how correctly Matt pronounces peoples names, whether scientist's or commenter's. Have I just heard "Michal" with H and silent C? That't the correct polish pronounciation, sir! I'm impressed with your attention to details and being so thoughtful.
So if everything is entangled after observation does that mean that certain probabilistic mechanisms (i.e decay rates of particles, 'downward' electron transitions) can be explained by entanglement?
Great question! In short, yes due to the peculiar nature of quantum decoherence when a radioactive nuclei is "measured". Paradoxically, the radioactive nuclei tends to stop decaying altogether when "measured" by a local observer. This is called the Quantum Zeno Paradox. Entanglement can then be seen as the decoherence (or in this case, decay) of the radioactive nuclei.
Yes, but you are only describing an ideal state by thinking about them one atom at a time. That is not how the object exists in the world. If you could possibly map the complete wave function you could answer a lot of questions. But, what light cone do you pick???
I watched the video twice, it has something new to me. I was tired of the "multiverse" series, they just seemed sience fiction stories. This is an improvement. Thanks Matt.
Are quantum dice a thing? Is it possible to like make an object that is able to be in more then 2 states? like why does it have to be head or tails? why not 3 different options at the same time?
Loved this video - had to watch 3x lol... So if we assume more particle interactions over time, are you saying the Shannon entropy will always increase over time for a system while the Von Neumann entropy (when only looking at individual particles rather than the whole system) will always decrease for each particle it measures (as that particle's wavefunction collapses due to interaction)? If so, is the explanation for why we experience a "net" increase in entropy over time at macro scales because at quantum scales, the interactions between particles generate more entropy than the Von Neumann entropy "removes"? Separately, how would the existence of a quantum multiverse impact this - is Von Neumann entropy actually decreasing to zero (for each individual particle as its wavefunction collapses) in this scenario?
Show idea: how do loop quantum gravity, string theory and other theories that claim to successfully unite gravity and quantum mechanics describe what happened at the Big Bang and in black holes?
Shouldnt or unverse have a entangled universe partner so where is it -we exist - it dont , ours die it exist - Does they ever though of our universe to have a antiverse .I mean you are way to early to want one -wait 30-50 years
If information has mass, is it possible that “dark matter” could be a form of metadata about the full wave function of all quantum entangled particles in the universe and the fact that the arrow of time moves in one direction could account for the expansion of the universe needing more space for this exponentially growing information?
Erik Verline has already shown that the change of entanglement entropy in spacetime is equal to what we call acceleration. This retrieves general relativity but with a quantum correction that happens to be the same we measure and currently ascribe to dark matter. So dark matter doesn't exist. The discrepancy is a quantum correction, as should have been expected.
From what you describe, it seems like particles are getting more and more entengled due to decoherenve. As the entropy of an entangled system is zero (because you have all information with the wave function) then it would mean that the universe would reach an entropy of zero once all particles becomes entangled. I'm lost, please help.
It won't. the information of the properties of the entire combined wavefunction from the entangled partner is hidden and the more particles entangle the more the wavefunction grows so the hidden hiddeness of the information grows too with entropy
10:23 "When viewed with its entangled partner, the coin exhibits quantum weirdness like superposition that could be revealed [in bell test] but treated individually each separate entangled quantum coin behaves kind of like a regular classical coin. For example, it doesn't by itself exist in a pure superposition of states; that superposition of states only appears when you include its entangled partner. It's what we call a mixed state." This is the most critical section of the entire thesis that entanglement creates entropy and deserves more drill down. A mixed state is just the mathematical fact that the two particles are anticorrelated and have a definite relationship. (for type II SPDC specifically) The purity of superposition of an individual particle is dependent upon your knowledge that it is, in fact, entangled. You're getting into "consciousness causes collapse" territory here if you are presuming that the superposed nature of the particle depends on our knowledge of its entanglement state. You say "Head or tails, not heads and tails" What is the basis for this inference that entangled particle is equivalent to a fully collapsed wave function? ...you're describing many worlds. You're proselytizing a decoherence worldview and need to be more clear about this. What you've done here is hide faith behind circular reasoning: You believe a mixed state is not actually superposed because you believe in many worlds. You believe in many worlds because it gives a convenient logical escape from problems with decoherence, namely the problem of why one macro state of many is experienced. (why you believe a mixed state and entanglement are the process) It's fine that you like this route of reasoning but please be clear to point out your preference based assumptions so others can more easily pick out these dependency loops. You've tied in the fact that Von Neumann entropy is different for these two situations (mixed versus pure) but you've glazed over the very silly fact that there are "known unknowns" and "unknown unknowns" and you're tying an ontological state to our knowledge about it again, thus returning back to consciousness causes collapse. You're conflating states of knowledge with states of existence without acknowledging it. At 6:18 you say it's Von Neumann entropy tells us how much entanglement is in the system, but around 10:00 you explain that the entanglement hides part of the information thus granting it VN entropy. Obviously you'd have to know the amount of entanglement to determine the VN entropy. (we're in a loop again) Many worlds is your belief because interactions lead to shared wavefunction information that make up consensus networks that define a given macro world. All particles remain forever superposed at their scale and collapsed at the macro scale. There's just propagation of network decoherence through interaction/entanglement. Isolated systems are merely a time-frame based illusion of low interaction during a given period. That all sound right? There's still a problem of a sharp and well defined cut between worlds that should obviously be continuous. At what point is enough entanglement reached to obliterate all superposition? You've just said near the 10:00 mark that the mixed state is equivalent to collapsed so it seems to me that any particle exhibiting the slightest quantum behavior would have to be perfectly unentangled. How'd that happen exactly? I'm not asking about loss of access to a history in another network/world, I mean a loss of entanglement with the current macro network/world. Might you be simultaneously inferring no superposition existing anywhere and also espousing it existing everywhere at the same time but with enough complexification in your explanation that you don't notice the mutual exclusivity of the components of your worldview? I've seen lots of people do this with a lot of different kinds of worldview. Most of these problems with information entropy come from poor definitions of information being fundamentally based upon human symbolic representation and cognition. They come in the form of knowledge level versus fundamental existence. (which is questioned in Copenhagen, but not in many worlds) We can resolve this nonsense by better defining information through first exploring the process of symbolic representation and interaction between non-thinking entities via geometry mediated energy interactions, but I digress. I'd first have to get you to rethink bell tests under a different regime where photons have more degrees of freedom than assumed so you could discard faulty ideas of entanglement. Fat chance of that, right? "Einstein starts from the hypothesis that the laws will look the same to all observers in uniform motion. This permits a very concise and elegant formulation of the theory, as often happens when one big assumption can be made to cover several less big ones... But in my opinion there is also something to be said for taking students along the road made by FitzGerald, Larmor, Lorentz and Poincaré. The longer road sometimes gives more familiarity with the country." - J. Bell "That the guiding wave, in the general case, propagates not in ordinary three-space but in a multidimensional-configuration space is the origin of the notorious ‘nonlocality’ of quantum mechanics. It is a merit of the de Broglie-Bohm version to bring this out so explicitly that it cannot be ignored.” ~ John Bell 'Speakable and Unspeakable in Quantum Mechanics' page 115 “But in 1952 I saw the impossible done. It was in papers by David Bohm. Bohm showed explicitly how parameters could indeed be introduced, into nonrelativistic wave mechanics, with the help of which the indeterministic description could be transformed into a deterministic one. More importantly, in my opinion, the subjectivity of the orthodox version, the necessary reference to the ‘observer,’ could be eliminated… But why then had Bohm not told me of this ‘pilot wave’?... Why did von Neumann not consider it? More extraordinarily, why did people go on producing “impossibility” proofs, after 1952, and as recently as 1978?... Why is the pilot wave picture ignored in textbooks? Should it not be taught, not as the only way, but as an antidote to the prevailing complacency? To show us that vagueness, subjectivity, and indeterminism, are not forced on us by experimental facts, but by deliberate theoretical choice?” - J.S. Bell, On the Impossible Pilot Wave. 1982
I suppose one could give you more detail about the stuff in the room if there’s matter in there, as opposed to it being empty. You cannot order the void in many ways.
I may be wrong but I think it's something like this: imagine all particles have x/y coordinates. If the max x is 10 and the max y is 10, a particle may be at x=10 and y=10 if it's in a corner. But there are only so many positions particles can be in. In a bigger room, a particle could be in more possible positions, like x=23,y=51. In that way, a description of all the positions in a larger room is more information because there are more possibilities.
Yes, that section made me pause to think too. (To be fair, that happens a lot in these videos). It helped me to think about a chessboard with a few pieces on itt. How many arrangements can you make with all the pieces in the 4x4 corner section. How many arrangements using the full 8x8 board. (And how many bits would it take to convey those different arrangements) You would need more bits of info, just because of the greater possibility space.
@@alvarorodriguez1592 yes but he is talking about information not possibilities... The only explanation i can think is the unsertenty principle... but even there i think the waveform would be more complex because of it... Isn't that more information?
@@some-say-gregms Yes there are less possible positions but still every particle has one position so their x, y coordinates information sould stay the same.
I have in the past referred to this idea as Quantum Causal Democracy. Basically, as quantum entanglement propagates, each entangled partner "votes" on the weighting of various outcomes of the wave function. The weight of the "votes" that each quantum entangled partner gets is proportional to how causally connected an outcome would be to that particle's own quantum information. The idea behind this is that causality is always preserved, even at the expense of normally invariant factors (on the quantum level) of space and time. The wave function conveys information instantaneously regardless of distance, but it can only propagate at the speed of light (the speed of information). This also provides a resolution for the Quantum Eraser experiment. Variants in which a photon would appear to go through a single slit and not interfere based on their distribution on the screen would be strongly voted against by the particles in detectors C and D because such particles are highly causally connected to information about the position of the particle at particular times. No information travels backwards in time at all, even in theory. Instead, the weighting of the photon's causal connection would depend on its level of entanglement with various other particles and how causally influenced they are by a particular outcome. But I dunno, I don't really understand Quantum Mechanics. I feel like what I described could be formalized into some set of useful equations if I was educated enough, but I'm not. C'est la vie.
Love this description, don't sell yourself short, this is a perfectly coherent interpretation of quantum mechanics as understood and extrapolated from VonNeuman entropy. What I find interesting is considering how this may relate back to the mind. If consciousness exists on the quantum scale, and the reality of quantum states are determined by their democratized entanglement with quantum systems, then internal consciousness may influence external reality insofar as those internal pointer states are preferentially entangled with elements of the external world. In simpler terms, this may suggest, in an extremely limited sense, that our perception influences the composition of the external world by biasing the results of its entangled states. Decoherence makes this so that we dont have absolute control over this democratization, or even significant control in most circumstances, however, I do wonder if our internal intentionality (which could be seen as the internal pointer state) may have some not-insiginificant influence on external events in the cases where it is extremely limited in scope. Food for thought anyways.
@@liamlieblein6375 You know on second thought I should name it something else, since QCD is Quantum Chromodynamics. The way I think about it, and this is a "theory" or "interpretation" of QM I've had internally for years, is that future states are determined according to wave function propagation. So for quantum objects, the only "direction" of time is expanding entanglement. I'll look at a particular example to examine how what I'm talking about is different from the Copenhagen Interpretation or from Quantum Darwinism. We conduct the traditional double-slit experiment with a detector to see if the electron passes through one of the slits. When the electron's wave function passes the detector, it becomes entangled in the way that one would expect: |Right Slit|Detector Activates> + |Left Slit|Detector Silent>. This in particular entangles the *position* of the electron causally with the detector very strongly. This strong causal entanglement (which I distinguish from plain old entanglement) forces certainty into the position and out of the momentum, since the entangled particles in the detector have a very strong "vote" about the position value. However, they have no causal relationship with other values, and these values remain undetermined. Once the electron reaches the screen, the position once again becomes entangled with the particles composing the screen that also have a very strong "vote" due to their causal correlation with the position value. However, they may only vote for values which remain consistent with the entanglement of previous strong votes on position values. In this way, causality is preserved above all other principles, even though QM fundamentally isn't deterministic. If you set up the quantum eraser experiment instead, the screen gets first vote, and then the detector does. It's not that the act of scrambling the information using the third and fourth detectors reintroduces interference patterns, it's that those detectors are allowed to vote, or have valid voting power on the position value, only for particles which remain causally consistent and connected. The wave function propagates through reality, and the whole wave function is always "aware" of all other participants in the wave function as its entanglement expands without being restricted by the speed of light. But, it can only share information about the wave function itself. This lets behaviors like "time reversed" behavior such as in the quantum eraser remain consistent and respect the speed of light. The speed of light becomes instead the speed at which entanglement can propagate. Thus, in order for you to compare the detector results and the screen results, you must entangle your particles with both, but the propagation necessary for you to entangle fully with the quantum states of both can only happen at the speed of light. I have this vague idea too of mass being expressed as a value which slows or hampers quantum propagation. There would be three steps in the process: encountering a new wave function, becoming entangled with that new wave function, and then propagating that entanglement to nearby particles. Mass would then be a resistance at step 3. But this is all that crackpot stuff that physicists hate getting emails about so I've just never told anyone. I figure, if I'm even remotely correct in this interpretation, someone who actually knows the math will eventually think of it on their own.
@@jordanledoux197 All that seems pretty consistent to me, and a farcry from the crackpot conspiracies that quantum mechanics have spawned. I'm also of the opinion that what's primarily causing the current impasse in physics is a lack of serious consideration of alternatives to the current dogma. I understand that they are probably tired of armchair quantum physicists, but they also seem tired of the speculations of actual quantum physicists. At root, all fields of knowledge were spawned from philosophy, and the beginning of philosophy is wonder. If scientists fail to wonder outside of the current systems, they will forever be constrained by them. Some attempts have been made, to be sure, and each has a piece to the puzzle. But until the scientific community writ large begins seriously working on these non-dogmatic theories/interpretations, we will not figure out the TOE. In short, I appreciate your speculative contribution, and wish it were more common place among actual scientists.
Yeah, I rewatched it once or twice but the easiest way to grasp it in my mind is by imagining a mosaic. You have this image made up of countless, tiny pieces, and each piece has properties like size, shape, color, etc. As those pieces align into the final shape of the mosaic, they form connections with other pieces they interact with. Not all of those links are visible, but if you flip one piece for instance, another will flip the opposite way. Now, zoom out from the individual pieces and they start to lose their individual details. Zoom out enough and you start seeing the details of the whole mosaic's image. The mosaic is less complex than the parts it's made up of, and that "lost" detail is von Neumann entropy. Zooming back in reveals those "lost" details of the individual pieces, thus lowering entropy. Zooming out in that example is the quantum decoherence that emerges from numerous quantum entanglements, and zooming in is performing precise measurements. Hope that helps, though I'm sure someone smarter may fix my analogy to be more accurate :P
It's indeed the hardest to wrap your head around. But I think it leads to quantum gravity (or gravitationalized quantum mechanics to be politically correct)
This perspective on entropy should be added to all undergrad thermodynamics courses. A 15 minute description linking entropy to quantum entanglement has done more to help me understand why the second law is inescapable than all of the engineering courses combined. Well maybe that has more to do with engineers not caring about "why".
You guys should put a number on the episodes so it's easier to find what episode you're referring to when you do the cliff hangers at the end saying what you'll be covering in the next episode
Thank you for finally explaining decoherence in a way that at least gives me hope I understand it somewhat. The fact that entanglement is a fundamental part of the difference between the macro world is... it fits the puzzle in my head so well. And I guess, puzzle is a good word in that case. Fundamental particles are like the jigsaw puzzle piece that has all possible shapes and choosing/changing that shape when interacting with other pieces. The more pieces are uniting in one system, the more defined the shape becomes due to interaction with other pieces. We can never know which specific shape the piece was before it fit the puzzle, because it was all shapes. But the big puzzle is always defined.
So say you somehow are able to get ahold of every piece of information of every single particle in the universe, can you now perfectly predict the future or is there still some quantum randomness involved?
Hi Matt. I very much like your videos, they do a great job of explaining difficult concepts. I was wondering if you could do an episode on double copy, which appears to be a possible link between QCD and GR/quantum gravity. Thanks!
Cool story: Even the beginner levels of quantum computing use almost all of these concepts and theories. IBM has a pretty neat beginner's guide to quantum theory and even explain some relevant theories AND they give you a cute little playground to mess around in.
Mind blown I love the viewpoint that our classical reality just emerges as a point of view deeply buried in the cosmic web of entanglement. But my human mind is also afraid because this is already getting too close to many worlds! :D
@@TheDummbob Well, the square of the amplitude of the wavefunction represents the probability of finding a quantum system in a given state (whether said quantum system is something as simple as an electron or perhaps as complex as a cat in a box). Whether the reality of these probabilities is a product of wavefunction collapse, Many Worlds or Bohmian mechanics is a conundrum that is unresolved, although my personal theory is that Classical reality is an emergent property of quantum probability, and not the other way around.
@@Vasharan Ok I think I get your point, but I still have trouble pinning it down in the case of the wavefunction of the whole universe (which is highly hypothetical): Does it mean, if i were to "measure the whole universe, the probability of finding it in "our" reality would be less then one? It seems to make sense, but then, i think it doesn't, there is no wa to "measure" the whole, this will happen always by an outside system. If we say the probality less than 1 just says: If we would take one random reality of all the realities contained in the wavefunktion, then of course we can assign a prob.
eh...he kind of but it's not "relative". What he's talking about is what's called "Hidden variables." These variables are things you simply can't keep track of because there are so many of them. Your measuring aparatus is also made up of things, and therefor is also a variable, that you need to keep track of. How can you do a measurment on something and also make a measurment on your measuring apparatus to account for all the variables? It's an infinite regress and it leads to the fact that you can never know the state of a system without knowing about all it's components...which means you need infinite amount of information to do such a task. Entanglement, which is the interaction created by two particles, and maintained at great distances, means that when you do a measurement on a system, that system is now entangled with your measuring apparatus...again in order to account for that information you need to now measure your measuring apparatus...and measure the measuring apparatus of your measuring apparatus...and measure your measuring apparatus of your measuring apparatus of your measuring apparatus and so on in infinite regress. Because of Entanglement, your system might be entangled with particles on the other side of the universe and you wouldn't be able to know. So in essence, as a system becomes more and more entangled with it's environment, the more information is required to understand the system, and this is dependent on the size of the environment. The environment includes the measuring apparatus. The best way to think about Entropy, is how it's known classicly...which is a system moving from a homogenous state which is a state of complete uniformity, to a state of complete heterogeneity known as equilibrium. Both states are essentially equivalent, with the exception that the previous state is "more" uniform then the resultant state being "less" uniform. A perfect example, is by thinking about coins. You have a system of three sided coins that can be in either Heads Tails or Snouts. The system begins in a state of all Heads, all Tails or All Snouts, so for example the system can evolve like this : (TTT/SSS/HHH)--->HHT->HTT->TSS->-TTS->SHH->SSH->HTS. In the above there are 3 perfectly homogenous states and there are also 27 possible heterogenous states, 6 of which are unique, and the 7th is a very special state...a state of equilibrium. This state of equilibrium HTS is considered maximally heterogenous...But you notice that it's also uniform...and this is why it's called equilibrium, because it's essentially the same as a homogenous state...but it's "less" uniform then a state of all heads or all tails or all snouts. You realize that if you were to expand this example to an arbitrarily large number of coins, then a system in equilibrium is a completely random system, and would take the appearance of white noise. In terms of information, how would you describe a system that is completly random? You need to go through every single pixel explain what it's color is because there is no algortythm or shortcut you can use to describe the system. This is what entropy of information is...it's when a system approaches thermodynamic equilibrium, which is essentially randomness and to describe that randomness in terms of information, requires a brute force method which makes such systems hard to describe in terms of information.
@h4ck573r sorry I'm confused...doctors degree defense? Veratasium has the best explanation for Entropy online in his video "What is NOT Random", and the example with the coins is basically derived from that explanation of it. Small incendental anecdote, but he makes a statement at the end where he says that Quantum Mechanics might be fundamentally random...but I actually disagree with that. I actually think the world is completely deterministic and that quantum mechanics exhibits emergent randomness because of previously stated hidden variables.
@@NightmareCourtPictures Veratasium, like me, may wish that there is fundamental randomness, because pure determinism feels wrong / bad. I don't know that we have enough data to really decide one way or the other, but I think the data we do have lean in your direction, not mine. :/
17:41 what's the difference between a grid of space and a grid of abstract connection between points? isn't space just abstract connections between points anyway?
I had an explanation of quantum entanglement change my perception on it recently. We think of the two “coins” in this case scenario as two separate “coins” that have a “spooky” interaction with each other, but the reality is that because of the interaction between the “coins” their wave probabilities become one single wave, meaning it’s essentially one “coin” that has two representations of its wave function.
these videos are so dense. if i get distracted for a minute i need to go back 5
Yeah. And the best part is, these aren't even the densest videos on youtube, forget all lectures possible. There are some professors that are even better.
I once took a break from my minor in physics and went back the next semester. I felt so strange after my first lecture back, I had forgotten what it was like to be challenged...
Think about it this way... what does that tell you about other random video's?
i watched it twice and still understand little. guess i'm also just as dense
so true, this was was specially challenging, Gonna have to watch a couple of times....
The subject itself is deep. A 20 minute presentation is bound to be incomplete no matter how dense, so it is partially due to this. Learn a little by osmosis and it'll help in the future.
Here's a more advanced/complete link on quantum spin liquids which puts these ideas to the test (it is long and a 2 parter): th-cam.com/video/CUg-sGeuJA8/w-d-xo.html
this one is seriously mind blowing to me.. the more of these videos you watch, the better they get.. because over time you understand more and more and then you put those pieces together and it's like BLAM! and suddenly your concept of reality becomes so .... unreal
I’ve been “blamming” for years watching these videos
I’m a molecular biologist and I appreciate life at the molecular level. I’ve been searching for the deeper underpinnings of reality and life and have watched these for years. When he connected the quantum with the macro, it literally blew my mind and I visually saw all of the concepts covered through the years into one theory of the fabric of reality
Reality is mental, bro. Once you get - you get the pieces together.
@@olegc.7877 I'm thinking a la Sean Carroll that there is no mind! it's an emergent property...
@@birdthompson it is matter which is an emergent property of mind
The answers at the end of this episode just increased exponentially my interest in a full PBS SpaceTime episode about the Quantization of Space. I'd really like to know more about Loop Quantum Gravity's grid of abstract connections between points, and how is possible that Space emerges only on larger scales.
Well you're in luck, there already is one. Use the search on the channel page.
See th-cam.com/video/L2suMPiuog4/w-d-xo.html
It’s hard to wrap my head around “larger scales” without space being a given. But emerging from abstract connections between points huh? … interesting
How does time dilation affect smaller scales? That is really the question. So, is the instantaneous momentum of particles caused by time dilation, like the idea that gravity is? As you approach the plank scale, what is dilating anymore...? Point space, and it's _"abstract"_ geometries are an attempt at describing the interactions that build up to things that can then dilate. What comes before that...🤷
I wish PBS Spacetime would do an episode on Quantum Holonomy Theory. Since Arvin Ash's video on it, I can't stop thinking about it.
I am positive that Matt just loves to say 'Von Neumann'.
I’m negative - electron
@@jameslacey01 good one.
@@Hyszy Are you saying you don't like to say that?
Yeah I have noticed it too. And the way he says the name sounds a bit kinky😉😂😂.
@@abrahamlincoln9758 never said that I dislike him saying it nor me saying it. It's fun name.
I just want to thank you guys for all you do. I love learning about space and I have trouble sleeping. Listening to your videos before bed distracts and keeps my mind busy enough to not over think about life until i can fall asleep. Unsuccessful today since its 6:40am, but I don't know what I would have done without this for the past few years. I have listened to all your videos and been repeating them since they are amazing.
This takes me back to my dissertation - “Defining work in a quantum battery” where I utilised heavily Von Neumann Entropy and the concept of temperature at the quantum level. This was a great episode and made me miss my days in academia, thank you for another phenomenal episode Matt.
Sounds interesting. Can you please post a link to your dissertation. I'd like to read it if possible. Thanks.
@@death_parade I have attempted to post a link but for some reason, TH-cam is removing the comment. I do have a link to my dissertation on my LinkedIn profile. If you were to add /jordanleeevans to LinkedIn URl you’d be able to find my profile along with my dissertation
Quantum Entangled Twisted Tubules: "A theory that you can't explain to a bartender is probably no damn good." Ernest Rutherford
When we draw a sine wave on a blackboard, we are representing spatial curvature. Does a photon transfer spatial curvature from one location to another? Wrap a piece of wire around a pencil and it can produce a 3D coil of wire, much like a spring. When viewed from the side it can look like a two-dimensional sine wave. You could coil the wire with either a right-hand twist, or with a left-hand twist. Could Planck's Constant be proportional to the twist cycles. A photon with a higher frequency has more energy. (More spatial curvature). What if gluons are actually made up of these twisted tubes which become entangled with other tubes to produce quarks. (In the same way twisted electrical extension cords can become entangled.) Therefore, the gluons are actually a part of the quarks. Mesons are made up of two entangled tubes (Quarks/Gluons), while protons and neutrons would be made up of three entangled tubes. (Quarks/Gluons) The "Color Force" would be related to the XYZ coordinates (orientation) of entanglement. "Asymptotic Freedom", and "flux tubes" make sense based on this concept. Neutrinos would be made up of a twisted torus (like a twisted donut) within this model. Gravity is a result of a very small curvature imbalance within atoms. (This is why the force of gravity is so small.) Instead of attempting to explain matter as "particles", this concept attempts to explain matter more in the manner of our current understanding of the space-time curvature of gravity. If an electron has qualities of both a particle and a wave, it cannot be either one. It must be something else. Therefore, a "particle" is actually a structure which stores spatial curvature. Can an electron-positron pair (which are made up of opposite directions of twist) annihilate each other by unwinding into each other producing Gamma Ray photons.
Does an electron travel through space like a threaded nut traveling down a threaded rod, with each twist cycle proportional to Planck’s Constant? Does it wind up on one end, while unwinding on the other end? Is this related to the Higgs field? Does this help explain the strange ½ spin of many subatomic particles? Does the 720 degree rotation of a 1/2 spin particle require at least one extra dimension?
Alpha decay occurs when the two protons and two neutrons (which are bound together by entangled tubes), become un-entangled from the rest of the nucleons
. Beta decay occurs when the tube of a down quark/gluon in a neutron becomes overtwisted and breaks producing a twisted torus (neutrino) and an up quark, and the ejected electron. The phenomenon of Supercoiling involving twist and writhe cycles may reveal how overtwisted quarks can produce these new particles. The conversion of twists into writhes, and vice-versa, is an interesting process.
Gamma photons are produced when a tube unwinds producing electromagnetic waves.
Wow ... so like.. you went to ... college and stuff...kewl.
I would love to see an experimental test of the notion that quantum entanglement is necessary for the property of entropy, in any average balloon containing hydrogen molecules or oxygen at room temperature. What makes me doubt: such molecules are large, temperatures are high, and it’s moist compared to conditions normally used to measure quantum entanglement.
I'm happy to hear your remark about von Neumann and how great he actually was: people often don't realize how much von Neumann was ahead of his time and what kind of genius he was.
How to go from superposition, to entangled quantum states to classical. This was possibly the most brilliant and insightful presentation ever! Thank you!
Its so unbelievably refreshing to see the topics/titles for spacetime vids to not be click baity, ALL CAPS, or a hook! Well done team 👍
Whew, definitely going to have to re-watch this one again a few times to actually grok it. Love episodes that really shift my understanding!
Lol grok is such a great word
It's hard to grok a nonsensical gibberish. Although constant inserts of word quantum makes it sound cool
@@M4R0Zzz are you suggesting this is nonsensical gibberish?
Love finding random uses of 'grok' in the wild.
dude it’s basically 3 am and i totally felt this, looking forward to tomorrow at 3 am again!!
“How quantum entanglement creates entropy”
Me: I know some of these words.
“How” and “creates”?
@@viliamvacula8111 you should both apologise
Me: maybe if I watch this while I'm drinking, I'll get smarter by diffusion
@@PetraKann
You are undeserving of apologies. Many magical girls died fighting equilibrium.
◕‿◕
@@Aereto The Equilibrium religious cult is an illusion of reversibility and neurotic obedience to Cartesian reductionism.
Is the Universe reversible?
6:55: This guys is so into Quantum Mechanics, even his hair changes when you try to measure it.
lmao I just noticed
@@nene_san Anyone wants to check out some yet-unkown-to-him/her science-youtuber?
@@nene_san I personally legit think 'we science-fans' dont recommend each other enough;
arguably even hindering 'us'.
After 3 viewings, I'm still entangled with confusion. More please.
Wow. It took me a long to get through digesting it properly but eventually when you linked the quantum with the classical. So many different concepts and puzzle pieces just fell in together in the most beautiful harmonic mannerism. Reality truly is something else
This is the best (short and clear) explanation for Entropy I ever heard. Thank you for the great presentation.
Neumann was truly a genius.
Watch an even shorter video from Arvin Ash. Then that will be the shortest. It’s from 2 weeks ago.
"Shannon Entropy" sounds like the name of a Bassist in an all girl metal band.
She started out super quiet and shy, now she is always loud and dancing...
@@Robert_McGarry_Poems 😂
Nahhhh that's totally a roller derby name.
nah, it would have to be the band name. And then everyone would always ask which one is Shannon, but of course there is no Shannon. It's just the name of the band.
At the same time Entropy Shannon would be a great name for an violinist in an Irish dance band.
The movie Tenet needs to provide a link to this video in the credits.
I laughed at this comment but also dear god no. Tenet should have an apology to PBS Spacetime in its credits.
@@jogandsp Tenet really got it *backwards*
Chris Nolan forgot to put this product placement in his movie? How dare he.
Tenet should be forgotten.
You sort of compressed about four episodes into this one.
Yeah, I think I need to rewatch this one.
Maybe it's a joke? The connection between entropy and file compression?
Well, they were all called out as links to actual episodes...
11:12 - Best part:
"Our capacity to observe quantum effects like superposition depends on being able to access the entire wave function."
12:16 "You've already become entangled with the coin and live in the slice of the wave function (the mixed state) where the coin is *either* heads *or* tails"
@@mechadense But it is either one or the other, not both at the same TIME. The wave function is an emergent property of time. This means that the coin is what it is, regardless of the wave function in any other segment of time. That's why it's heads (or tails) when it's revealed at a certain TIME. It already was/it already is/it already will be, but only at whichever time it's being measured. This is the time that exists, and no other, because any other expression of time has either already occurred, or has yet to occur.
@@toughenupfluffy7294 - Not sure what you mean with "The wave function is an emergent property of time".
A well isolated and thus in its entirety accessible wave function describes an *undirected* temporal evolution of a system holistically in its entirety. A (pure state) wave function does not specify a direction-of-time aka an arrow-of-time. Backwards is indistinguishable from forwards (as it is in reversible computing). The arrow-of-time does not lead to the wave function. What does lead to an arrow-of-time are is the statistics of microstates in slices of incompletely known wave functions (mixed states) when the system is not in equilibrium, when it does not have maximal entropy.
The wave function very much has the capacity do house truly counterfactual things (like an electric current flowing in counter-rotating directions at the same time). This is experimentally testable via the Bell test and has been repeatedly tested.
- - -
Well … Except if there are global hidden variables. Meaning we do *not* have access to the entire wave function then I guess.
Global hidden variables have been pushed quite far out by now. Experimentally via cosmic bell test.
But since we'll never be able to see infinitely far out in spacetime we'll thus never be able to definitively disproof global hidden variables with absolute certainty.
- - -
I know, there's time symmetry breaking in weak force beta decay. I won't go into that.
Forget about the wave function! It depends on differential equations and latter on infinitesimal calculus, which is not a proper mathematical tool to approach at quantic scales.@@toughenupfluffy7294
I love this episode. Everything quantum seems to make more sense now and is less daunting and unfamiliar. The visuals helped so much too. Looks and sounds like the entanglement of all particles weaving the fabric of space. Feels like a familiar warm comforting blanket rather than a feeling like being hopelessly lost driving an unfamiliar car on a super tangly spaghetti junction, in a blizzard or something. I just hope Schrodinger's cat doesn't tear apart the fabric of space time like my cat did my blankets. I mean I'd want revenge if my owner kept putting me in a box for extended periods just to contemplate weather I'm alive still or not.
Blog post?
:(
My mind was in the superposition of both understood the episode or didn't, until i broke the uncertainty with a rewatch😂
Really excited for the upcoming episode.
Matt O'Dowd and the crew on this show are some of the greatest science communicators of our time.
Some More News Coverage of the current Work-Crisis affects us all,
so excuse the RANDOMNESS but i want my fellow PBS-Space-Time-Fans (man, that's a long word, i should have shortened that, but whatever) to know such.
@@slevinchannel7589 heyyy Iove that channel too
@@LabGoats :)
listening to you talk about entropy makes me think about relationships with people and the information we get from each other.
I love this gentleman's knowledge and the way of his video presented without annoying background music. Thanks.
Loving him being honest about the updated information. Also thie fact he took a comment seriously enough to go back and dig to confirm the information.
Ooh information theory next. I love information theory! As a software engineer I think that information theory feeds into computer science in a way that is massively influential while barely anyone is even aware of it. You don't need it every day, but knowing about it really helps you understand certain things at a much more fundamental level.
So, you want to create Universal Programing i.e Magic? I'm down for that
@@benjaminconnor6980 I personally legit think 'we science-fans' dont recommend each other enough;
arguably even hindering 'us'.
Congratulations on the excellent explanations. PBS does an awesome job in this channel, really outstanding.
I will yet be a little bit picky and address a conceptual disagreement about the second law being a statement about the von Neumann entropy of a system. Quantum thermodynamics is mainly concerned with energetic and, further, informational processes; not states. The second law is a statement about a quantum process and the quantity which entails the irreversibility of this process is the entropy production.
One should bear in mind that the closed-system evolution in quantum mechanics is unitary and, thus, leaves the entropy of a quantum system untouched. As von Neumann brilliantly notes in his work, irreversibility stems from measurements and, as we understand today, from general quantum channels --- like open quantum systems.
By no means I want to say you are wrong in the simplification made. I understand that all those subtleties would make the content very technical and, of course, not as accessible. But, as a young scientist from the quantum thermodynamics community, I thought it'd be nice to add my view on the subject.
Thank you, thank you, thank you for explaining these concepts. I am only an engineer, so I don’t always understand, but I can always feel my mind expand.
As an engineer I object to "only an engineer"
I have considered this for ages! Very glad this simple little detail is being presented in depth. I've heard this specifically only in lectures and only in passing, never in any books I've read.
Von Neumann entropy:
Sabine Hossenfelder : "doubt"
The difference between the pure quantum state with Von Neumann entropy=0 and the known state after measurement is the measurement problem.
Hossenfelder says that we don't know enough details about how physics really works to know how there is a transition between the two - we don't have a way to describe that transition within quantum equations.
The Copenhagen interpretation is to just say "our experiments work, quantum theory works - so lets just ignore the complicated part that happens during measurement and pretend it isn't a problem."
The many worlds theory replaces one handwaving with another handwaving - because it posits a splitting of universes, part of the quantum state become inaccessible, but it has no idea when or how that happens. Just saying "it all happens within the laws of quantum physics and the wave function never pops" doesn't save you from the fact that you have no information about how we get from the unmeasured state to the measured one. If you say it's within the theory, then you have to be able to calculate it within the theory and they can't.
So does decoherence solve the measurement problem? Hossenfelder says "no" but she hasn't gotten around to explaining why, at least not in her channel. I haven't finished her book, so I can't say whether she explains it there.
But I have to say that the transition you described from entropy=0 to entropy>0 sounds like another one of those "ok, exactly when and how did that happen? Can you calculate it? No." situations.
How do we know that no way to calculate exists. If i use occlums razor i can just say it exists but we aren't able to measure it cause laws get too complex at that size.
Like maybe if it's up or spin depends on a particle 20 km away and even a small change can change everything. Like in chaotic system.
I am still in high-school about to go to college but it's still a valid question no one seems to answer.
It just doesn't seem skeptical enough.
@@pravinrao3669 I didn't say that no way to calculate it exists. It could just be complex enough that we haven't calculated it yet. Quantum physics is amazingly successful at describing systems with just a few particles. But measurement equipment isn't just a few particles. I'm not a physicist, but I guess she's saying that the interactions that make up a measurement device might be too complicated for us to calculate or maybe even they might depend on details that the theory left out.
So if you can't point at sample calculation of a measurement, it's premature to claim that there is no problem with one.
Also there's something incompatible with the description of a simple system and a measured state. In the pre-measured state, any linear combination of states is considered a valid outcome - and so you have probabilities. But in the measured state you have definite outcomes. But as Matt said when he described a combination of states as a known, 0 entropy state, it's not a matter of there being an unknown that you discover when you measure. It's that the measured state is a DIFFERENT state than the premeasured one.
You need a level of suspension of disbelief to buy that - that, for instance, the photon didn't pick a spot on the film... And maybe it DID pick a spot because after it reaches the film it isn't just a few particles anymore - because the effects on the film cascade past the photon to many atoms etc. Is that measurement or decoherence? Well maybe... but then there are the quantum eraser experiments and the fact that the system seems to be able to change its mind based on things that happen later in time then the time when some of those mass effects would have taken place if a certain choice were made. So the things you think create a measurement or a decoherence can depend stuff the wave function (that isn't supposed to exist after a measurement) encounters AFTER the measurement could have taken place.
Note, I made an edit describing the problem with the quantum eraser experiment.
What i got out of this episode is that the macro world appears classical because any particle affecting an object is entangled with other particles which the object cannot have information about, i'm assuming because of the finite speed of information. Since the object only has access to a small part of a bigger wavefunction, the particle appears statistical instead of superpositioned.
From the sound of it, decoherence happens as soon as an interaction with a system only has limited access to the wavefunction of that system. That would happen naturally in any uncontrolled environment where particles fly around freely. I don't know what it means for carefully controlled experiments, though.
@@volbla It means they can build a working Quantum computer.
You make some valid points regarding the various interpretations of QM but to be fair, the founders of the so called "Copenhagen" interpretation were pretty clear from the beginning that quantum probabilities were observer dependent.
It provoked a reaction from Einstein where he jokingly stated the following, "I like to think the moon is there when I'm not looking at it".
In regards to decoherence, she's right, it doesn't explain away the measurement problem. It just describes how quantum systems represented as state vectors in a complex Hilbert space transition into statistical mixtures that can't be expressed in terms of state vectors when you average over multiple measurements.
And it certainly doesn't explain how a system can go from a linear combination of basis states to a well defined state with probability equal to 1 after a measurement is made. The so called collapse of the wave function.
The thing with QM is, quantum systems don't have well defined physical properties that exist independently of you measuring it. Prior to any measurement, it exists purely as a mathematical wave function.
On the other hand, quantum entanglement is about states of knowledge where 2 or more systems share a common wave function or share information so by measuring 1 of the systems, you learn something about the other corresponding systems
This video changed my perspective on the nature of the universe. Several times in a row.
Wow, I just was reading The Order of Time by Carlo Rovelli, about Quantum Gravity, and it covers this exact same thing! I almost feel like I am gaining partial understanding! Honestly, this is very cool, and thank you so much
I didn't realize the same von Neumann whose name pops up in computer science all the time (von Neumann architecture) was also involved in thermodynamics, but there you go!
Also von Neumann probes.
He was a busy boy.
I will just let you read the Wikipedia entry for the areas he contributed to. The first time I ran across something to do with von Neumann was the book "2001: A Space Odyssey" (A.C. Clarke wrote a book after the movie that was based on two of his stories). One of the black obelisks turns out to be a von Neumann machine, or self-replicating machine
One of the smartest humans of all time, contributed to so many different fields
Thank you for this video. As always the explanations are clear even for those who don't study physics.
I've been waiting for Quantum Information Theory to be covered for ages. Can't wait for next week's episode!
To me QIT is the only satisfying resolution to the question of how quantum things "become macroscopic".
If the arrow of time arises from increasing entropy, meaning increasing quantum entanglement over time, does that imply that at the beginning of time (assumedly the instant before the big bang) there was no entangled quantum systems?
After plank time all physics breaks down, so there is no answer to this question until we figure out what happens inside a black hole.
well, before the big bang it is assumed there were not particles in general. since nothing WAS at all before the big bang. so yes your assumption would theoretically be correct.
of course we dont actually know this because of our limited knowledge. but with the current understanding you are in fact not wrong atleast
It only implies that at Bing Bang there was less entanglement, than at the instant just after it (roughly speaking). The previous sentence already reveals a problem of our understanding of time: is it continuous or quantized? How exactly you go from "no time" to "having time", from "no entanglement" to "first entanglement"? Is time even fundamental? We don't even know what time is, and without that knowledge, we can only speculate. It's hard to reason about nothing (no time, no space), since we haven't observed nothing anywhere, because it's impossible. As depressing as it sounds, we may never know.
basically for the reasons already stated the correctness of your assumption exists within a quantum state of being right & being wrong
So we just detangle the Quantums and therefore reverse Entropy, problem solved.
Classicalize quantum physics?
Egad!
Just start unobserving things and eventually it will happen
@@hansenchrisw Then I suggest Project DODO for a good read, does exactly that and then time travel happens
Quantum detanglement, it's so simple
If a particle's entanglements only "diffuse" in a sea of entanglements possibly with every other particle in the universe, but never really break, how can we ever produce fresh entangled pairs so isolated that we can use them in quantum computing?
You can force a qubit into a known state by measuring it and flipping it if the measurement came out wrong. This works even if you and the qubit are entangled with the rest of the world. Basically what's happening is that this process swaps the qubit's tainted state for a clean one that ultimately came from moving the entropy in the qubit into the surrounding environment (which needs to be not max entropy for this to work).
Or, TL;DR its related to how entropy can be reduced to almost nothing in a smaller subset of a larger closed system
@@alextaunton3099 Right, as long as the larger system is in a low entropy state. Resetting a qubit is possible for the same reason that it's possible for a fridge to cool down its interior.
@@CraigGidney I had the same question so thanks for clearing that up!
@@CraigGidney and in fact that’s exactly why they need to be so cold! So that’s another nice tie-in with the fridge thing.
37 YEARS OUT OF SCHOOL YOU GIVE FAST REVIEW AND NEW INSIGHTS THANKS
1 video that takes a minimum of 4 times watching it to catch everything and half way kind of understand! Well done
Why worry about space zombies? As xkcd pointed out, our reliance on reflector telescopes means that space vampires are completely undetectable!
That's only true about mirrors because of silver. Judas betrayed Jesus for silver, and so all the wicked and demonic creatures of the world were cursed to be weak to it. This means that vampires would be invisible in old-fashioned silvered mirrors or on photographic film because the photoactive part of film is crystals of silver hallides, but would be perfectly visible on silicon-based CCD cameras and aluminium-based modern mirrors, including those of telescopes.
@@alexv3357 How about those proposed mirrors made of spinning pools of mercury? After all, mercury is also known as quicksilver...
@@alexv3357 vampire admiring itself just after Judas betrayed Jesus: OH WTF where did my reflection go?!?!
@@alexv3357 you raise some pertinent and important points - no doubt about that. Absolutely no doubt.
We know that Jesus and at least 7 of his apostles were scientists
@@PetraKann Scientist apostles? Blessed are the peer-reviewers, for they shall obtain peer reviews.
Blessed are the theorists, for they produce testable models.
Blessed are the experimenters, for they improve our theories.
Blessed are the mathematicians, who write the language of knowing....
So, this has me thinking about the relationship between entropy and gravity. If there are more interactions due to higher energy density/strong force kinematic energy, does that essentially slow the ‘clock’ of entropy as the interactions take more ‘time’ to sort out all the entanglements. Could this explain gravity as an emergent property of the speed of causality and the quantum interactions of the wavefunction?
Information theory is so interesting! Would love to hear more
This format makes concepts so easy to understand. Really great video!
0:00: 🔑 The Significance of Entropy and the 2nd Law of Thermodynamics
2:57: 🔗 Connection between entropy, information, and quantum entanglement explained through Boltzmann's recasting of entropy and Shannon's information theory.
5:50: 🔬 Von Neumann entropy reveals the connection between quantum particles, driving the 2nd law of thermodynamics and measuring entanglement in quantum systems.
8:42: 🔗 Quantum entanglement creates a unique connection between two entangled quantum coins, leading to a superposition of states and correlated results.
11:37: 🔗 The process of decoherence leads to the emergence of the classical world from quantum entanglement, driving entropy growth.
15:17: ⚛️ Exponential processes have scale invariance, with the location of rapid growth depending on axis choice. Space debris increase may reach a threshold.
17:36: 🔍 Exploring concepts of quantum uncertainty, grid of abstract connections, and momentum transfer in quantum measurement.
Recap by Tammy AI
Entropy always made my head hurt. It's like, it's all-encompassing, but it's also a measurement of nothing, or of what's potentially there, or what it can do, or how long... It's just... Man, I'm glad there are smart people out there to do this thinking for me.
I think entropy is just a mathematical construct.
@@bobaldo2339 Bob - there are a class of chemical explosives that are entropy driven - so if entropy is a mathematical construct, it is a construct that can hurt a lot in the real world. There are also chemical reactions that are primarily entropy driven.
That’s because they’re all just different effects of the underlying phenomena - that being the complex network of entanglement between particles (which brings us back to structural complexity and unpredictability). Those other metrics are useful in their fields, and valid within their fields, but they are not what entropy “is”. This is the driving force behind them.
"Zombies that when you shoot them just turn into thousands of smaller zombies" This is my boomstick.. Shop smart... Shop S-Mart...
Also I'm now horrified that this has moved from hilarious Bruce Campbell comedy to my personal zombie apocalypse model. Thanks PBS.
Bruce Campbell or Brisco County jr maybe, or Sam Axe??
that's the only sentence i understood...
@@thomasstone7207 Don't mess around with the orb.
I spent half of the video staring at Matt's throat and thinking whether he had been bitten as there were two puncture marks close together like the classic vampire bite. Then he started talking of being bitten by zombies and I was like "Oh!".
Yes I agree when my headphones are in my messy pocket, it gets entangled so I think this is a good proof that entropy is related to quantum entanglement.
When Matt started talking about the classical coin being influenced by all of its constituent parts and everything they've ever come in contact with, it made me think of almost like subpixel values in Mario. The current behavior is a product of all of the previous interactions interacting to create some sum.
Spacetime is the main reason I check my subscription tab. You guys are doing such an incredible job! Every episode is killer!
If entanglement networks are a measure of entropy, when we accelerate particles in accelerators are we temporarily detaching these particles from the planet's entanglement network?
And when we measure the results from collisions, are we simply measuring the resultant particles as they enter our entanglement network?
1. No, and 2. Yes, technically.
No such thing as an error free experiment, and entanglement is part of the reason why. It's pretty rude.
I find it so surprisingly satisfying when they show that some of the questions and statements people comment are answered by the show's own viewers. People like us. Lets Go! PBS!
Has he gone 100% Wood Elf? My Granny told me, "You never go 100% Wood Elf!"
I aprecciate how correctly Matt pronounces peoples names, whether scientist's or commenter's. Have I just heard "Michal" with H and silent C? That't the correct polish pronounciation, sir! I'm impressed with your attention to details and being so thoughtful.
It's been almost 4 years since I've been following this channel, and I love it !!!!!
I'm just going to sit here and act like I understood everything that was presented to me. Yep.
So if everything is entangled after observation does that mean that certain probabilistic mechanisms (i.e decay rates of particles, 'downward' electron transitions) can be explained by entanglement?
Great question! In short, yes due to the peculiar nature of quantum decoherence when a radioactive nuclei is "measured". Paradoxically, the radioactive nuclei tends to stop decaying altogether when "measured" by a local observer. This is called the Quantum Zeno Paradox. Entanglement can then be seen as the decoherence (or in this case, decay) of the radioactive nuclei.
quantum Mechanic theory is incorrect, I don't know why scientist worship QMT
Yes, but you are only describing an ideal state by thinking about them one atom at a time. That is not how the object exists in the world. If you could possibly map the complete wave function you could answer a lot of questions. But, what light cone do you pick???
@@theunknown1426 we don't worship, we research.
I've always thought Shannon's information theory would be fundamental to a ToE.
I watched the video twice, it has something new to me. I was tired of the "multiverse" series, they just seemed sience fiction stories. This is an improvement. Thanks Matt.
Wow. Just mind blown by this video. Brilliant script, performance and video editing. Thank you so much!
See, Gina? I'm not 'letting myself go'... I'm just following a basic law of nature!
Yeah, that's a good way to get un-entangled.
💀 🗿 you two oml
Are quantum dice a thing? Is it possible to like make an object that is able to be in more then 2 states? like why does it have to be head or tails? why not 3 different options at the same time?
That's what quantum computers seek to be.
Loved this video - had to watch 3x lol... So if we assume more particle interactions over time, are you saying the Shannon entropy will always increase over time for a system while the Von Neumann entropy (when only looking at individual particles rather than the whole system) will always decrease for each particle it measures (as that particle's wavefunction collapses due to interaction)? If so, is the explanation for why we experience a "net" increase in entropy over time at macro scales because at quantum scales, the interactions between particles generate more entropy than the Von Neumann entropy "removes"? Separately, how would the existence of a quantum multiverse impact this - is Von Neumann entropy actually decreasing to zero (for each individual particle as its wavefunction collapses) in this scenario?
It is so brilliantly explained indeed. Thank you PBS for your much valuable work.
This channel is a thick modern physics book that doesn’t miss a thing..
Show idea: how do loop quantum gravity, string theory and other theories that claim to successfully unite gravity and quantum mechanics describe what happened at the Big Bang and in black holes?
Shouldnt or unverse have a entangled universe partner so where is it -we exist - it dont , ours die it exist - Does they ever though of our universe to have a antiverse .I mean you are way to early to want one -wait 30-50 years
ryan kroph
That would be an excellent idea for a PBS spacetime episode.
If information has mass, is it possible that “dark matter” could be a form of metadata about the full wave function of all quantum entangled particles in the universe and the fact that the arrow of time moves in one direction could account for the expansion of the universe needing more space for this exponentially growing information?
Very interesting thought
It could also be the information being "clumped" together to form black holes effectively "loosing" the information in a large decoherence network.
Erik Verline has already shown that the change of entanglement entropy in spacetime is equal to what we call acceleration. This retrieves general relativity but with a quantum correction that happens to be the same we measure and currently ascribe to dark matter. So dark matter doesn't exist. The discrepancy is a quantum correction, as should have been expected.
@@realmetatron So, gravity is an attribute of entropy that's interest. I say this because gravity is more or less an acceleration.
@@KRYMauL Yes, all forces of nature are actually various processes of how entropy in the universe increases.
From what you describe, it seems like particles are getting more and more entengled due to decoherenve. As the entropy of an entangled system is zero (because you have all information with the wave function) then it would mean that the universe would reach an entropy of zero once all particles becomes entangled. I'm lost, please help.
It won't. the information of the properties of the entire combined wavefunction from the entangled partner is hidden and the more particles entangle the more the wavefunction grows so the hidden hiddeness of the information grows too with entropy
10:23 "When viewed with its entangled partner, the coin exhibits quantum weirdness like superposition that could be revealed [in bell test] but treated individually each separate entangled quantum coin behaves kind of like a regular classical coin. For example, it doesn't by itself exist in a pure superposition of states; that superposition of states only appears when you include its entangled partner. It's what we call a mixed state."
This is the most critical section of the entire thesis that entanglement creates entropy and deserves more drill down. A mixed state is just the mathematical fact that the two particles are anticorrelated and have a definite relationship. (for type II SPDC specifically) The purity of superposition of an individual particle is dependent upon your knowledge that it is, in fact, entangled. You're getting into "consciousness causes collapse" territory here if you are presuming that the superposed nature of the particle depends on our knowledge of its entanglement state.
You say "Head or tails, not heads and tails"
What is the basis for this inference that entangled particle is equivalent to a fully collapsed wave function? ...you're describing many worlds.
You're proselytizing a decoherence worldview and need to be more clear about this. What you've done here is hide faith behind circular reasoning: You believe a mixed state is not actually superposed because you believe in many worlds. You believe in many worlds because it gives a convenient logical escape from problems with decoherence, namely the problem of why one macro state of many is experienced. (why you believe a mixed state and entanglement are the process) It's fine that you like this route of reasoning but please be clear to point out your preference based assumptions so others can more easily pick out these dependency loops.
You've tied in the fact that Von Neumann entropy is different for these two situations (mixed versus pure) but you've glazed over the very silly fact that there are "known unknowns" and "unknown unknowns" and you're tying an ontological state to our knowledge about it again, thus returning back to consciousness causes collapse. You're conflating states of knowledge with states of existence without acknowledging it. At 6:18 you say it's Von Neumann entropy tells us how much entanglement is in the system, but around 10:00 you explain that the entanglement hides part of the information thus granting it VN entropy. Obviously you'd have to know the amount of entanglement to determine the VN entropy. (we're in a loop again)
Many worlds is your belief because interactions lead to shared wavefunction information that make up consensus networks that define a given macro world. All particles remain forever superposed at their scale and collapsed at the macro scale. There's just propagation of network decoherence through interaction/entanglement. Isolated systems are merely a time-frame based illusion of low interaction during a given period. That all sound right?
There's still a problem of a sharp and well defined cut between worlds that should obviously be continuous. At what point is enough entanglement reached to obliterate all superposition? You've just said near the 10:00 mark that the mixed state is equivalent to collapsed so it seems to me that any particle exhibiting the slightest quantum behavior would have to be perfectly unentangled. How'd that happen exactly? I'm not asking about loss of access to a history in another network/world, I mean a loss of entanglement with the current macro network/world.
Might you be simultaneously inferring no superposition existing anywhere and also espousing it existing everywhere at the same time but with enough complexification in your explanation that you don't notice the mutual exclusivity of the components of your worldview? I've seen lots of people do this with a lot of different kinds of worldview.
Most of these problems with information entropy come from poor definitions of information being fundamentally based upon human symbolic representation and cognition. They come in the form of knowledge level versus fundamental existence. (which is questioned in Copenhagen, but not in many worlds) We can resolve this nonsense by better defining information through first exploring the process of symbolic representation and interaction between non-thinking entities via geometry mediated energy interactions, but I digress.
I'd first have to get you to rethink bell tests under a different regime where photons have more degrees of freedom than assumed so you could discard faulty ideas of entanglement. Fat chance of that, right?
"Einstein starts from the hypothesis that the laws will look the same to all observers in uniform motion. This permits a very concise and elegant formulation of the theory, as often happens when one big assumption can be made to cover several less big ones... But in my opinion there is also something to be said for taking students along the road made by FitzGerald, Larmor, Lorentz and Poincaré. The longer road sometimes gives more familiarity with the country." - J. Bell
"That the guiding wave, in the general case, propagates not in ordinary three-space but in a multidimensional-configuration space is the origin of the notorious ‘nonlocality’ of quantum mechanics. It is a merit of the de Broglie-Bohm version to bring this out so explicitly that it cannot be ignored.” ~ John Bell 'Speakable and Unspeakable in Quantum Mechanics' page 115
“But in 1952 I saw the impossible done. It was in papers by David Bohm. Bohm showed explicitly how parameters could indeed be introduced, into nonrelativistic wave mechanics, with the help of which the indeterministic description could be transformed into a deterministic one. More importantly, in my opinion, the subjectivity of the orthodox version, the necessary reference to the ‘observer,’ could be eliminated…
But why then had Bohm not told me of this ‘pilot wave’?... Why did von Neumann not consider it? More extraordinarily, why did people go on producing “impossibility” proofs, after 1952, and as recently as 1978?... Why is the pilot wave picture ignored in textbooks? Should it not be taught, not as the only way, but as an antidote to the prevailing complacency? To show us that vagueness, subjectivity, and indeterminism, are not forced on us by experimental facts, but by deliberate theoretical choice?” - J.S. Bell, On the Impossible Pilot Wave. 1982
So glad you are here to guide me through these concepts! ❤️
In the example with the room. Can please someone explain to me why when the hole room is filed we have more information??
I suppose one could give you more detail about the stuff in the room if there’s matter in there, as opposed to it being empty. You cannot order the void in many ways.
I may be wrong but I think it's something like this: imagine all particles have x/y coordinates. If the max x is 10 and the max y is 10, a particle may be at x=10 and y=10 if it's in a corner. But there are only so many positions particles can be in. In a bigger room, a particle could be in more possible positions, like x=23,y=51. In that way, a description of all the positions in a larger room is more information because there are more possibilities.
Yes, that section made me pause to think too. (To be fair, that happens a lot in these videos).
It helped me to think about a chessboard with a few pieces on itt. How many arrangements can you make with all the pieces in the 4x4 corner section. How many arrangements using the full 8x8 board. (And how many bits would it take to convey those different arrangements)
You would need more bits of info, just because of the greater possibility space.
@@alvarorodriguez1592 yes but he is talking about information not possibilities... The only explanation i can think is the unsertenty principle... but even there i think the waveform would be more complex because of it... Isn't that more information?
@@some-say-gregms Yes there are less possible positions but still every particle has one position so their x, y coordinates information sould stay the same.
I have in the past referred to this idea as Quantum Causal Democracy. Basically, as quantum entanglement propagates, each entangled partner "votes" on the weighting of various outcomes of the wave function. The weight of the "votes" that each quantum entangled partner gets is proportional to how causally connected an outcome would be to that particle's own quantum information. The idea behind this is that causality is always preserved, even at the expense of normally invariant factors (on the quantum level) of space and time. The wave function conveys information instantaneously regardless of distance, but it can only propagate at the speed of light (the speed of information). This also provides a resolution for the Quantum Eraser experiment.
Variants in which a photon would appear to go through a single slit and not interfere based on their distribution on the screen would be strongly voted against by the particles in detectors C and D because such particles are highly causally connected to information about the position of the particle at particular times. No information travels backwards in time at all, even in theory. Instead, the weighting of the photon's causal connection would depend on its level of entanglement with various other particles and how causally influenced they are by a particular outcome.
But I dunno, I don't really understand Quantum Mechanics. I feel like what I described could be formalized into some set of useful equations if I was educated enough, but I'm not. C'est la vie.
Love this description, don't sell yourself short, this is a perfectly coherent interpretation of quantum mechanics as understood and extrapolated from VonNeuman entropy. What I find interesting is considering how this may relate back to the mind. If consciousness exists on the quantum scale, and the reality of quantum states are determined by their democratized entanglement with quantum systems, then internal consciousness may influence external reality insofar as those internal pointer states are preferentially entangled with elements of the external world. In simpler terms, this may suggest, in an extremely limited sense, that our perception influences the composition of the external world by biasing the results of its entangled states. Decoherence makes this so that we dont have absolute control over this democratization, or even significant control in most circumstances, however, I do wonder if our internal intentionality (which could be seen as the internal pointer state) may have some not-insiginificant influence on external events in the cases where it is extremely limited in scope. Food for thought anyways.
@@liamlieblein6375 You know on second thought I should name it something else, since QCD is Quantum Chromodynamics.
The way I think about it, and this is a "theory" or "interpretation" of QM I've had internally for years, is that future states are determined according to wave function propagation. So for quantum objects, the only "direction" of time is expanding entanglement. I'll look at a particular example to examine how what I'm talking about is different from the Copenhagen Interpretation or from Quantum Darwinism.
We conduct the traditional double-slit experiment with a detector to see if the electron passes through one of the slits. When the electron's wave function passes the detector, it becomes entangled in the way that one would expect: |Right Slit|Detector Activates> + |Left Slit|Detector Silent>. This in particular entangles the *position* of the electron causally with the detector very strongly. This strong causal entanglement (which I distinguish from plain old entanglement) forces certainty into the position and out of the momentum, since the entangled particles in the detector have a very strong "vote" about the position value. However, they have no causal relationship with other values, and these values remain undetermined. Once the electron reaches the screen, the position once again becomes entangled with the particles composing the screen that also have a very strong "vote" due to their causal correlation with the position value. However, they may only vote for values which remain consistent with the entanglement of previous strong votes on position values.
In this way, causality is preserved above all other principles, even though QM fundamentally isn't deterministic. If you set up the quantum eraser experiment instead, the screen gets first vote, and then the detector does. It's not that the act of scrambling the information using the third and fourth detectors reintroduces interference patterns, it's that those detectors are allowed to vote, or have valid voting power on the position value, only for particles which remain causally consistent and connected. The wave function propagates through reality, and the whole wave function is always "aware" of all other participants in the wave function as its entanglement expands without being restricted by the speed of light. But, it can only share information about the wave function itself. This lets behaviors like "time reversed" behavior such as in the quantum eraser remain consistent and respect the speed of light.
The speed of light becomes instead the speed at which entanglement can propagate. Thus, in order for you to compare the detector results and the screen results, you must entangle your particles with both, but the propagation necessary for you to entangle fully with the quantum states of both can only happen at the speed of light. I have this vague idea too of mass being expressed as a value which slows or hampers quantum propagation. There would be three steps in the process: encountering a new wave function, becoming entangled with that new wave function, and then propagating that entanglement to nearby particles. Mass would then be a resistance at step 3.
But this is all that crackpot stuff that physicists hate getting emails about so I've just never told anyone. I figure, if I'm even remotely correct in this interpretation, someone who actually knows the math will eventually think of it on their own.
@@jordanledoux197 All that seems pretty consistent to me, and a farcry from the crackpot conspiracies that quantum mechanics have spawned. I'm also of the opinion that what's primarily causing the current impasse in physics is a lack of serious consideration of alternatives to the current dogma. I understand that they are probably tired of armchair quantum physicists, but they also seem tired of the speculations of actual quantum physicists. At root, all fields of knowledge were spawned from philosophy, and the beginning of philosophy is wonder. If scientists fail to wonder outside of the current systems, they will forever be constrained by them. Some attempts have been made, to be sure, and each has a piece to the puzzle. But until the scientific community writ large begins seriously working on these non-dogmatic theories/interpretations, we will not figure out the TOE.
In short, I appreciate your speculative contribution, and wish it were more common place among actual scientists.
This episode is the hardest so far, at least for me.
Yeah, I rewatched it once or twice but the easiest way to grasp it in my mind is by imagining a mosaic.
You have this image made up of countless, tiny pieces, and each piece has properties like size, shape, color, etc. As those pieces align into the final shape of the mosaic, they form connections with other pieces they interact with. Not all of those links are visible, but if you flip one piece for instance, another will flip the opposite way.
Now, zoom out from the individual pieces and they start to lose their individual details. Zoom out enough and you start seeing the details of the whole mosaic's image. The mosaic is less complex than the parts it's made up of, and that "lost" detail is von Neumann entropy. Zooming back in reveals those "lost" details of the individual pieces, thus lowering entropy.
Zooming out in that example is the quantum decoherence that emerges from numerous quantum entanglements, and zooming in is performing precise measurements.
Hope that helps, though I'm sure someone smarter may fix my analogy to be more accurate :P
@UCylxY_LLOrfpUJPYvbexgFQ thank you! It's actually helpful!
I definitely need the videos..
It's indeed the hardest to wrap your head around. But I think it leads to quantum gravity (or gravitationalized quantum mechanics to be politically correct)
This perspective on entropy should be added to all undergrad thermodynamics courses. A 15 minute description linking entropy to quantum entanglement has done more to help me understand why the second law is inescapable than all of the engineering courses combined. Well maybe that has more to do with engineers not caring about "why".
Best description of the concept of decoherance I've ever heard
*coin lands on side instead of heads or tails*
*the big rip starts*
the big oof
Spacetime breaks and the whole fabric starts collapsing.
Backup will be restored and paradox fixed with next Universe upgrade.
You guys should put a number on the episodes so it's easier to find what episode you're referring to when you do the cliff hangers at the end saying what you'll be covering in the next episode
That's what Sabaton History did, and they've only been around two years.
"Small fast zombies", is that like baby zombies in Minecraft? Those are indeed scary and dangerous!
Thank you for finally explaining decoherence in a way that at least gives me hope I understand it somewhat. The fact that entanglement is a fundamental part of the difference between the macro world is... it fits the puzzle in my head so well. And I guess, puzzle is a good word in that case. Fundamental particles are like the jigsaw puzzle piece that has all possible shapes and choosing/changing that shape when interacting with other pieces. The more pieces are uniting in one system, the more defined the shape becomes due to interaction with other pieces. We can never know which specific shape the piece was before it fit the puzzle, because it was all shapes. But the big puzzle is always defined.
So say you somehow are able to get ahold of every piece of information of every single particle in the universe, can you now perfectly predict the future or is there still some quantum randomness involved?
Since Decoherence and Von Neumann entropy rely on the density matrix, any chance we'll see that discussed in an upcoming episode?
PBS Spacetime: Spells entropy with a capital sigma
Me: notices the use of rho first than sees sigma.
I noticed that too, but I do not know the significance of it.
@@dianagibbs3550 -- I think it's just a "sciency" style to write it in, but it just looks like SNTRORY to me.
So, in summary,
O what an entangled web we weave,
And hence we suffer entropy.
You are such an amazing teacher, you make everything sound easy. Thank you so much!
Hi Matt. I very much like your videos, they do a great job of explaining difficult concepts. I was wondering if you could do an episode on double copy, which appears to be a possible link between QCD and GR/quantum gravity. Thanks!
Cool story: Even the beginner levels of quantum computing use almost all of these concepts and theories.
IBM has a pretty neat beginner's guide to quantum theory and even explain some relevant theories AND they give you a cute little playground to mess around in.
qxq student?
Mind blown
I love the viewpoint that our classical reality just emerges as a point of view deeply buried in the cosmic web of entanglement.
But my human mind is also afraid because this is already getting too close to many worlds! :D
Replace Many Worlds with Any Worlds. At any point in time, the slice of reality you inhabit has a probability of less than 1.
@@Vasharan what does that mean that a slice of reality has probability less then 1?
what does this probability measure?
@@TheDummbob Well, the square of the amplitude of the wavefunction represents the probability of finding a quantum system in a given state (whether said quantum system is something as simple as an electron or perhaps as complex as a cat in a box). Whether the reality of these probabilities is a product of wavefunction collapse, Many Worlds or Bohmian mechanics is a conundrum that is unresolved, although my personal theory is that Classical reality is an emergent property of quantum probability, and not the other way around.
@@Vasharan Ok I think I get your point, but I still have trouble pinning it down in the case of the wavefunction of the whole universe (which is highly hypothetical):
Does it mean, if i were to "measure the whole universe, the probability of finding it in "our" reality would be less then one?
It seems to make sense, but then, i think it doesn't, there is no wa to "measure" the whole, this will happen always by an outside system.
If we say the probality less than 1 just says: If we would take one random reality of all the realities contained in the wavefunktion, then of course we can assign a prob.
Aliens 7: In space, no one can hear exploding alien zombies scream. Coming this Christmas to a theater near you.
This is really one-of-a-kind... Awesome and inspirational!
Every time I watch this channel they tell me exactly what I didn't know that I really needed to hear until I heard them tell me kind of thing.
So are you telling me that entropy is relative to the observer, and every increase in entropy is an entanglement the observer didn't keep track of?
eh...he kind of but it's not "relative". What he's talking about is what's called "Hidden variables." These variables are things you simply can't keep track of because there are so many of them. Your measuring aparatus is also made up of things, and therefor is also a variable, that you need to keep track of. How can you do a measurment on something and also make a measurment on your measuring apparatus to account for all the variables? It's an infinite regress and it leads to the fact that you can never know the state of a system without knowing about all it's components...which means you need infinite amount of information to do such a task.
Entanglement, which is the interaction created by two particles, and maintained at great distances, means that when you do a measurement on a system, that system is now entangled with your measuring apparatus...again in order to account for that information you need to now measure your measuring apparatus...and measure the measuring apparatus of your measuring apparatus...and measure your measuring apparatus of your measuring apparatus of your measuring apparatus and so on in infinite regress. Because of Entanglement, your system might be entangled with particles on the other side of the universe and you wouldn't be able to know.
So in essence, as a system becomes more and more entangled with it's environment, the more information is required to understand the system, and this is dependent on the size of the environment. The environment includes the measuring apparatus.
The best way to think about Entropy, is how it's known classicly...which is a system moving from a homogenous state which is a state of complete uniformity, to a state of complete heterogeneity known as equilibrium. Both states are essentially equivalent, with the exception that the previous state is "more" uniform then the resultant state being "less" uniform. A perfect example, is by thinking about coins. You have a system of three sided coins that can be in either Heads Tails or Snouts. The system begins in a state of all Heads, all Tails or All Snouts, so for example the system can evolve like this : (TTT/SSS/HHH)--->HHT->HTT->TSS->-TTS->SHH->SSH->HTS.
In the above there are 3 perfectly homogenous states and there are also 27 possible heterogenous states, 6 of which are unique, and the 7th is a very special state...a state of equilibrium. This state of equilibrium HTS is considered maximally heterogenous...But you notice that it's also uniform...and this is why it's called equilibrium, because it's essentially the same as a homogenous state...but it's "less" uniform then a state of all heads or all tails or all snouts. You realize that if you were to expand this example to an arbitrarily large number of coins, then a system in equilibrium is a completely random system, and would take the appearance of white noise. In terms of information, how would you describe a system that is completly random? You need to go through every single pixel explain what it's color is because there is no algortythm or shortcut you can use to describe the system. This is what entropy of information is...it's when a system approaches thermodynamic equilibrium, which is essentially randomness and to describe that randomness in terms of information, requires a brute force method which makes such systems hard to describe in terms of information.
@h4ck573r sorry I'm confused...doctors degree defense?
Veratasium has the best explanation for Entropy online in his video "What is NOT Random", and the example with the coins is basically derived from that explanation of it.
Small incendental anecdote, but he makes a statement at the end where he says that Quantum Mechanics might be fundamentally random...but I actually disagree with that. I actually think the world is completely deterministic and that quantum mechanics exhibits emergent randomness because of previously stated hidden variables.
@@NightmareCourtPictures Veratasium, like me, may wish that there is fundamental randomness, because pure determinism feels wrong / bad. I don't know that we have enough data to really decide one way or the other, but I think the data we do have lean in your direction, not mine. :/
@@dianagibbs3550 Why would it feel wrong? And what does feelings have to do with science? 🤔
@@Ebani exactly my point. It feels bad but that doesn't change the facts, and the facts lean towards determinism, in my opinion.
I... Didn't get a single thing in this episode xD
It's been a while since that happened. Entropy do be like that ig
He's not nearly as good at explaining this stuff as he thinks.
@@alkh3myst Easy for you to say huh.
I know y'all wanna be big brained, but how many even remember the name of last weeks episode?
@Fluffy Maximus he's joking.
I think it is a good joke.
I don't even remember what I ate for lunch....
@@pursuitsoflife.6119 I think he removed his comment. Lol
You're silly. I like you. 🙂
Ngl, I had a complete mindblown moment around 12:00 when you made me realize how increasing entanglement was creating entropy.
17:41 what's the difference between a grid of space and a grid of abstract connection between points? isn't space just abstract connections between points anyway?
The audio is well compressed
Space is a tree, with the ends of the branches forming physical objects, and higher nodes representing more abstract concepts.
I knew every words but understand nothing.
😂 dude its just a simulation dont take it lierally
At least you read my mind
I've learned so much from this channel oh my gawd.
I had an explanation of quantum entanglement change my perception on it recently. We think of the two “coins” in this case scenario as two separate “coins” that have a “spooky” interaction with each other, but the reality is that because of the interaction between the “coins” their wave probabilities become one single wave, meaning it’s essentially one “coin” that has two representations of its wave function.
That’s very interesting.
One of my favorite biology professors said that a chicken is an egg’s way of making another egg.