Instead of a gas cylinder, we could could have a treat dispenser and a cat in a superposition of purring and non-purring states. Or we could just take a long delayed revenge and put Schrodinger in his own box. Ha, justice at last!
Thank you for creating these videos, Dr. Carroll, they are truly great! I hope many people tune in and watch them in order to have a better understanding of how science and the universe works, something that we desperately need to happen if we are going to successfully navigate these surreal times we are living in. Cheers!
My favorite nugget of information so far in this series occurs around the 15:00 mark where Sean reveals that “this is the origin of the Uncertainty Principle”... I feel like a big part of understanding concepts is knowing how they were first imagined... this was like finding gold to me. ❤️
Sean's explanation reminds me of Bach's music, - very intricate and pleasing, yet I have no idea of what is going on ! As to Hilbert and his Grand Hotel with an infinite number of rooms, no problem if a further infinite number of guests turn up. Plenty of room in the ballroom for the dancers to spin and entangle and a high probability of a good meal in the dining room. There is no charge for neutrons in the bar, but quantum tunnelling on the golf course is against the rules. Now I'm all puckered out and need to find my rest mass.
Is there anything interesting to make of the fact that in MW the absolute amplitudes of each branch must be astronomically small, because the universe has been splitting for billions of years, but from existing inside each branch we always experience the probabilities as summing up to 1?
Wow. The way you answered "what space is the wave function in" actually made me realise.. When you describe the wave function as a transformation on a vector space into another space, its easy to understand why the earliest attempt at formalising QM was called "Matrix Mechanics." If you described those spaces in a matrix, you're just doing some transformation on it.
I am so gripped by this series I am unashamedly binge-watching. Started July 29 and already at the entanglement Q and A. The Q and A sections are SO helpful and as if by magic I am intuitively grasping maths that I would have predicted beyond me. Some significant air-punching going on :) What a great teacher. Thank you so much.
Thanks for those great vides!. I'm not sure that the many worlds is the most economical understanding of QM. My (naive) understanding is that we have 2 things: 1. What might happen and 2. What "really" happens. The MW formulation affirms that 1 & 2 are in fact the same thing. But it can be also seen from another POV that the Copenhagen formulation is the most economical in that only one thing happens instead of all of them. BTW this seems a little oddly similar to the domain of computation: there we have also 1. Programs and 2. Processes. Program is the source code which describes what "should happen" for each possible branche in the program. Processes are what "happens" when you actually run the program. Running the program to some point collapses some branches and chooses only one branch to continue evaluation. In fact there is what we call "lazy evaluation" where a piece of code is not actually evaluated until necessary (when we need the value to figure out which branch to take). What's more? Some branches are finite (testing a Boolean value) while other branches are infinite (like which branch to take based on the value provided by the user). **EDIT** One more thing is that in computation we distinguish between "pure computations" and "computations with side effects". Pure computations seem similar to the Laplacian view: in a closed program we can predict deterministically the outcome before running the program. With side effects however it's not possible. One kind of side effects is "non determinism" where evaluating an expression could return multiple answers (there is even one version with probabilities"). The point is maybe the interpretation of the wave function is simply that the universe is non deterministic in nature: that may sound crazy because it implies that elementary particles have free will. Well that's not crazier than human having it according to the free will theorem en.m.wikipedia.org/wiki/Free_will_theorem
Very good writing! Maybe in this view, entanglement collapses by structure complexity. Instead of some fixed probabilities or linear amount of particles in objective collapse theories.
If a physical theory is fundamentally probabilistic ( non deterministic), that does not imply, of course, that elementary particles have " free will". Free will is a notion that has to do with the macroscopic world that emerges from fundamental physics. It's a " category error" to think about " free will " as if it was something like a " fifth fundamental interaction" that affects each " particle" individually or anything like that..
Watching this series through for the second time. It's good. Near the end of the video, Sean uses an example where the particles have spins with un-equally weighted probabilities: 1/root(3)*(up) + 2/root(3)*(down) Sean sorta "hand waived" when he set it up and said, "it's my experiment, I can do it how I want" which suggests that such a system is not really possible. However, if we could make a system like that that was also entangled, then we could do faster than light communication. e.g. If we imagine a system in this configuration (up and down here are with respect to Z): 1/root(3)*(aliceIsUp, bobIsUp) + 2/root(3)*(aliceIsDown, bobIsDown) Let's also imagine that spacetime is flat, so that having agreed beforehand on a predetermined "time" and "afterwards" to make the measurements might make sense. Then, we could make a big box of particles entangled in such a way and give one box to Bob and the other to Alice and move them far apart. At some predetermined "time", Alice could either a) not measure her particles, or she could b) measure all the particles in her box in the Y direction, which would give them a definite spin in that direction and a fully indefinite spin in the Z direction "Afterwards", Bob could measure all his particles in the Z direction. If Alice did "a", he would get 1/3u, 2/3d. If she did "b" he would get 1/2u, 1/2d. In this way, Alice could transfer a bit of information to Bob faster than light by changing the probability of his measurements. My assumption is that such a system can't be constructed for some reason or that I've made some kind of a mistake while constructing it.
I've watched every single TH-cam video with you Sean. But I don't understand the first thing about entanglement or the wave function. But I'm not giving up 👆 Keep the awsome content coming, much abliged
Love the content as always. I just noticed this is the 2nd or 3rd video that features a somewhat irritating ~120Hz hum in most parts. Especially obvious when it goes away e.g. at 8:38.
How big is a "world" when it branches? Is it just a local branching which then propagates from there (at the speed of light)? Or is it the size of the entire "parent" universe from the beginning? Neither?
Correct me if I am wrong: In the last part of the video, isn’t it cheating to represent the two subsequent experiments with separate wave functions, especially if we are talking in the context of the Many Worlds Theory? The moment we are putting a condition for doing the second experiment based on the outcome of the first one, needn’t the two to be treated entangled with each other within a single wave function? I think of it as prooving 1=2 from a mathematical equation by ignoring the initial assumptions or some fundamental rules. I am probably missing some point in this particular thought experiment, so I am looking for an explanation of why the above-mentioned assumptions do not apply here. I would be happy if you had time to bring a clarification.
I think this got me one baby step closer to understanding what "probability" means in Many Worlds. And for me, if I ever get there, it will be a big deal. Cool.
My understanding of the collapse wave function is that in the Many World Interpretation, this describes 100% outcome after the collapse with the entire system (branched); whereas, David Bohm Pilot Wave Theory is describing before the collapse there is hidden (from us) information what the actual outcome will be and thus we have this probability equation.
The probability problem was the thing I had the most trouble with regarding Many Worlds when I read Something Deeply Hidden. I don't understand how it explains that I could use statistics to predict, say, how many spin up vs spin down outcomes I'd get from repeating a prepared experiment, and get the distribution I expect. I guess the problem is that questions like "Which future branch of the wave function will I find myself on?" seem like they aren't really well defined questions at all, since I will find myself on all of them. It's more like, "after I do the experiment but before I learn the result, what credence will make sense at that point to assign to the different possibilities of self-location?" So confusing.
Is a superposition an interaction necessarily? that is; is it a physical event or just a state? (can a state not be a physical event, even?) I know that not ALL interactions are superpositions, but are ALL superpositions interactions?
Hello Sean, can you please explain what is the process that entangles particle, where why how. If particles get entangled at a point in time how do they get to the other side of the universe. I am looking for the applications of entanglement in the real world. Keep up the great work.
Okay, so I'm not Sean, but here goes my attempt anyway. There are several ways to create entangled particles that follow two main themes: 1: Create a pair of particles with a conserved quantity from a heavier particle that lacks that property. So, for example, if you have a spin-0 particle like a Higgs boson, it must decay into two particles with opposite spins. Those spins must remain opposite in order for angular momentum to be conserved, thus they are entangled. The same can be done with a charge-0 particle like a Z boson or photon (or the Higgs), which must also decay into two particles with opposite electric charge. This is _not_ the method usually used for practical applications of entanglement in the real world because the easiest pair of entangled particles to create with this method is a pair of photons, which is basically useless for quantum computing since they're, y'know, always zipping along at the speed of light no matter what. The Higgs can decay into an electron-anti-electron pair with entangled spin, but the Higgs is extremely difficult to create, and you can't generally build a Large Hadron Collider for every quantum computer you want to make. 2: Bring two particles/atoms together so that they interact in such a way that you cannot know, even in principle, which particle did a thing. What kind of thing? Well, things like exciting them to a superposition of both particles emitting a photon each and not emitting a photon each (this is done with a carefully tuned laser). You then pass the resulting photons through a beam-splitter (half-silvered mirror) and then on to detectors. This sets up a situation where you can't, even in principle, know which detected photon came from which atom, so they are then entangled. (I realize I'm using extremely sloppy language here, but it's helpful; in truth, the words 'you' and 'know' are mushy and not really getting at the truth of what happens, which is exactly what created the confusion of the Copenhagen interpretation in the first place, so just keep in mind that there's a deeper truth that does not need a conscious observer or the particles to "know" things.) This method is much more useful because atoms are much easier to contain and manipulate. The primary application for entanglement in the real world is in quantum computing, in which a complex device sets up an array of entangled particles and then performs operations on them in such a way that the most likely way for them to behave solves problems in which superpositions are useful. How many particles determines how useful it is, with two particles being able to solve only very basic problems that are much easier and faster with an ordinary computer. But if you can get up to 10 particles, you're already pushing the boundary where using a normal computer is impractical, and 100 can solve problems that would take a normal computer longer than the age of the universe to solve. It's worth noting, however, that only certain very well-defined classes of problems, such as factoring large numbers are doable with a quantum computer. To date, it's simply impossible to create all types of logic gates with qubits, so you cannot create a Turing machine or anything like it. A quantum computer is thus really more akin to a magnificently superior calculator than a general computing device like what you're reading this comment on right now, though it is conceivable that in the (fairly distant) future, we'll be able to build hybrid computers that can use their quantum processor for calculations that need it, and a normal processor for things the quantum one can't do. I say distant future because right now, quantum computers are extraordinarily fragile things. Even a stray photon from the computer's own casing can decohere your carefully entangled system, so they have to be in a near-perfect vacuum and near absolute zero to even have a chance of lasting long enough to do a computation. Edit: I should also briefly mention another method that I'll call "1.5". In this method, you create two easy-to-make particles, like two photons with correlated (entangled) polarization, which are then absorbed by two atoms, which then become entangled since the photons were entangled. This is called "Second Generation Entanglement", and it's... less useful than it sounds. The problem is, controlling a pair of individual photons to be absorbed by a specific pair of individual atoms in such a way that you don't decohere either the photons or the atoms, is practically impossible. The result is that it basically comes down to luck whether you actually manage to create an entangled pair of atoms. That's why the other name for this method is "Entanglement By Accident".
I'll be reading 'Something Deeply Hidden' next week. I have many doubts about MWI, but between your book and this podcast (starting it now), I suspect they'll be alleviated.
@@mikkel715 the book is good (Something Deeply Hidden). It is devoted to the MWI - in my case I enjoyed the book even though I'm not a huge fan of MWI.
does the size of the system determine the amount of branches in the universe? If we take the universe as our system, is there only one branch? The wavefunction branches when two systems come into contact with each other?
Just asking.. let's say we replace the cat with an explosive that could go off at any time. Does observing it determine if it blows up or would it just blow up randomly?
26:00 so my summary of the problem of Spooky Action at a Distance, which Sean builds up to in the previous 26 mins, is that: Once Alice does a measurement of her own electron, she knows something real about the spin of Bob’s electron immediately (say, that its spin Up), regardless of distance. If the spin of Bob’s electron was truly random before Alice’s measurement, *_it seems like locality is violated by Alice’s knowledge_* . So for locality to not be violated, the spin of Bob’s electron mustn’t be truly random, and therefore must have always been spin Up, inspiring ideas of hidden variables that travel with the electron that determine its spin beforehand. The kicker is that spin *is* truly random, and so there’s a problem there It’s unlikely that my description above is completely accurate to Sean’s description, so you should probably rewatch the video instead of relying on that
34:40 Thanks for giving a clear and meaningful answer to this question. 37:54 So the Bohm pilot wave theory not working well in case of many particles.
Slightly off topic but maybe somebody can explain this please. The Centre of the Earth is younger (as time goes slower there ) than the Surface. So if the Earth is created from the centre to the outside then if you could go back in time, then the outside of the Earth would be older that the centre. Is this a Paradox. Even allowing for the matter changing, the space in the centre would have had to be created before something that is older than it ! Can you explain this ?If I created instantly(or close to, hypothetically) my own sphere/earth of uniform material from the centre to the outside. Would the same question exist. How could the older outside be built up on a younger centre ? Thanks.
Thank you for great answers! Finally got the EPR and Bell's through the uncertainty principle. So, position, momentum, spin do emerge from the complex amplitudes of wavefunctions right? Although we write in one direction as mapping from (RealSpace^3)^N to ComplexSpace, because wavefunction is one for the entire universe, intuitively it seems that the mapping should be in the opposite direction, from ComplexSpace to emergent variants in the "permutation space" (configuration space). Thanks again! :-)
Thanks Sean Carroll for this fantastic serie. This goes in better dept than many, and not too deep. Should I recommend something. Delete that cat, as you planned. Don't delete the double slit. But the cat is only confusing for layman. As layman you need to first understand superposition and entanglement by other examples, to understand that cat. Consider accepting Simulation Theory as a Quantum Mechanic Interpretation. The deep simulation of the simulation theories.
At 28:00 ish Sean answers my problems with ‘detecting’, ‘collapsing’, and ‘entangling’ in the DSE, and clears up the difference between Entangling vs Interacting, by seeming to say that the electrons fire and interact (are affected by) with a heavy wall (that’s states are not prone to being contingent on the superposition of the electron, and so interacts but doesn’t entangle) and then hit a detector (that is, and so it does entangle). This seems to skirt my understanding and doesn’t really seem to resolve my issues, so I’ll have to figure that out
For a single electron, maybe it's more efficient or takes less energy for it to simply propagate as a wave and go through both slits in the double slit experiment. I think the electrons are behaving in such a way to simple obey the laws of conservation.
Mr Carroll I have a question, not related to this video necessarily, I'm only asking here anyway cuz I can't find any answer anywhere else on the internet about it... My question has to do with how all those things look like, are they real? Quarks, atoms, protons neutrons etc? Or are they just mathematical models, nothing more than mathematics? For example, if we were to blow up an atom to the size of say... a basketball, ... what would it look like? Would it have like colors or even a surface? Would it have anything that we could see? (assuming we could see the entire spectrum of light and not just visible light). Could we touch it and if yes how would that even feel like? Or would it be invisible? Like a force sphere that you just can't see or feel in any way, but if you tried to pass through it - it would be standing in your way blocking it from you?
Dear Prof. Carroll, what is the best way to send you a question please ? (I do not have a twitter account.) Thanks. All the best from West Wales (UK), Paul C.
@@Psnym Hi Denis, yes I know - but is there just the one Patreon account for Sean, i.e. the Mindscape Podcast ? Or is there a different Patreon account for The Biggest Ideas channel ? Thanks. Paul C.
The question I have always wanted to ask is, in the next few hundred years with advances in Ai and computing, do you feel it may be possible to compute probabilities of macroscopic events such as, "should I take the job?" or "should I ask her to marry me?" My understanding of the 2 slit experiment and decoherence dictates that the only reason we see an interference pattern is we have not disturbed the waveform by entangling with it. I don't mean telling the future. I mean having a large enough database, fast enough computer and lot of supervised learning models. In this sense wouldn't we be in a sense reconnecting to another branch of the waveform? But on purpose. I feel like that's almost telling the future. Is this impossible and why?
How does the conservation of energy work with Many Worlds? Everytime we get a branch from the wavefunction, we get a new universe spanning off this branch? Where is this energy coming from? Doesn't make sense. Also, probabilities don't make sense in Many Worlds. For example, in the double slit experiment, you'll find a world where the interference pattern doesn't show up because it's extremely unlikely to happen but it is still going to happen due to the non-zero probability from the wavefunction.
In the awake/sleeping cat example, why for example (cat awake, seen sleeping) is not taken into account- isn‘t that just possible or do we as observer prejudge what makes sense or not - is there a hidden bias of the observer distracting the system (leading to decoherence)
Sean, I hope you’ve considered that when you see a different probable world (or particle), you’re also in a world that has a slightly different history ;) - time traveler :)
Just a quick note about your Stern-Gerlach descriptions. They CANNOT be done with electrons. Electrons are charged and experience Lorentz forces, which overwhelm the spin-dependent force. This is why the experiment was done with neutral silver atoms. This is a common error seen in many, but not all texts. Just letting you know so you can make a correction for the future.
First it was stated if a particle is measured in Z to be spin up then you measure it again for Z it will always be spin up. So in the Alice and Bob scenario if Alice measures Z to be spin up we know Bob is spin up. Ok now say Bob measures X and gets spin right. Now we cannot say if Bob Z is spin up due to uncertainty. NOW ALICE PERFORMS A SECOND CONSECUTIVE Z MEASUREMENT. Will it be spin up, due to the first Z being spin up or 50/50 due to Bob making the Z direction uncertain ?
It always was uncertain. It actually "collapses" when Alice and Bob reconcile their diverged versions of reality using classical signaling. What do you think versions are allowed to converge so energy, momentum, and spin do conserve? :-)
In my scenario Alice and bob don’t talk about anything. Alice measures Z spin ad it’s spin up. In this video Sean says if that same particle is measured again it will be still be up. Now Bob checks the X spin and gets spin left. Alice and bob don’t signal or reconcile. so now Alice checks the Z spin expecting up since it was already determined up and as far as she knows bob may or may not have done something. Or are They now not entangled since measurements were made on each and Alice will get spin up as that’s what state it was in when she observed it. Or is alices Z undetermined as bob took away the certainty from that direction
@@robertspiess9859 I think measuring an entangled property breaks the entanglement, so Alice's second measurement wouldn't depend on Bob's measurement.
Yes. Photosynthesis actually makes extensive use of quantum tunneling. AFAIK, that's the only biological system that we've confirmed to use quantum effects, but it's a pretty important one. ;)
Hey Sean thank you for this very informative as always! Has anyone ever postulated or written any theories about the possibility of the big bang creating a "big expanding black hole" that we're basically living in? I've day dreamed about the largest explosion ever presumed (the big bang) creating a big expanding "black hole" that we exist within. Could explain weird dark matter and acceleration possibly? Or is this maybe just a good way to dream about what we are as a universe but it isn't necessarily a "black hole".
Yes, that's a common place for one's mind to wander once one learns a sufficient amount about the Big Bang, and about black holes. It's not a bad line of thought necessarily, and can be fun to think about. Sadly, this is almost certainly not the case, because our universe is nowhere remotely near the level of density required to create a black hole. There is, however, a horizon surrounding our visible universe; an expansion horizon. However, this is only an apparent horizon. The entire universe is somewhere between 250 times the size of the visible universe and infinite in size, to the best of our current measurements, and in the prevailing theory, it isn't expanding "into" _anything_. (A black hole expands into pre-existent spacetime.) Such a theory would also do a poor job of explaining Dark Matter and Dark Energy, I'm afraid. Dark Matter has very specific properties that are relatively well-understood (discounting less popular theories that attempt to account for the data using modified gravity of some sort), including discrete and detectable densities that vary quite a lot throughout the universe, clustered especially around large collections of ordinary matter. And Dark Energy, well... there have been some experimental results lately that are calling that into question altogether, or at least its strength, and are instead suggesting that while the universe does seem to be accelerating in its expansion, it is not doing so homogeneously. Rather, there is some indication (still awaiting peer review, so take it with a hefty grain of salt) that the visible universe has a dipole flow away from some kind of "great repeller" and/or toward some kind of "great attractor" beyond the horizon of the visible universe. The first experiments that won the Nobel Prize, that discovered the apparently homogeneous expansion and acceleration just happened, through bad luck, to be pointing in opposite directions approximately along what would be this theoretical polarized universe's 'ecliptic', hence the sameness of the measurements.
@@barefootalien Wow thank you for that thorough and very well thought out response. We don't really know how chaotic or calm the inside of a black hole is necessarily, that's why i thought it might be an interesting way to think about it. Maybe a kind of large weak black hole style expansion.. The cold vacuum, and empty, yet filled with micro particle "space" our galaxy exists in, has always been fascinating for me to daydream about.
@@hollowthere3850 There is a similar thought I forgot to mention: the possibility that the universe is a _white_ hole, which is basically a time-reversed black hole on the bottom of a Kruskal-Szekeres diagram. In this concept, whenever a black hole forms, it forms a new universe which spews out all the matter and spacetime the black hole accreted. Thus our universe could potentially be a _supermassive_ white hole. A paper arguing this via the holographic principle can be found here: www.researchgate.net/publication/256459927_Out_of_the_White_Hole_A_Holographic_Origin_for_the_Big_Bang
Based on what you said, the impression I get of the "measurement" is it signifies "entanglement." So, os the universe. from the perspective of a detector (i.e., observer) a collection of entangled objects and non-entangled wave functions, with respect to the detector?
If you have two entangled particles, and one falls into a black hole, when you measure the (say) spin of the particle outside of the BH, do you now know the spin of the particle in the BH? Is there some other case when two entangled particles are outside of one another's light-cone, yet may effect a change upon the other?
It was bad enough when all these half-existent dead cats started showing up all over the apartment, but now there is spectral copy of Sean Carroll observing each one of them and half of those are demanding tea and biscuits. The other half want coffee and croissants. I can't afford this quantum mechanics stuff. Help!
When the electron is falling into gravitational field, its entangled gravitationally, that is why its falling i.e. behaving in a certain way rather than wandering randomly. Plss explain.
Does the problem with locality arise if you take the frequentist view of probabilities? Say, Alice measured up and left, so Bob is "forced" to measure down and right. But why isn't he allowed to measure "right", given psi = (right/sqrt(2) + left/sqrt(2))? That equation does not prevent this particular measurement from going any particular way. And if we take a series of experiments, Bob's frequencies are determined by Alice's frequencies, which will comply with amplitudes of outcomes.
I think the Born rule is circular, without using the L2 norm, you won't get the absolute square. There is no explanation why absolute value can't be the probability instead of absolute square.
I don't understand what the branch probabilities mean in many worlds. As Sean points out it's not the credence meaning of probability. And it can't be the frequency meaning because all branches happen with the same probability (p=1). What meaning is left? It seems for many worlds to work it needs to make some extra postulate about probability even if such isn't called a postulate.
So in the first MWI probability example (two spins equal prob.), you'll end up with the upperbranch given amplitude = √1/2, and the other two branches with an amplitude √1/4....?
Awesome and sad 76ers point in the video. No one in the world would have thought there would not be a 2020 championship series. Maybe we will see a no fan playoff bracket. Then you’ll still be right.
@@rage9715 You could also try watching "Your Daily Equation" with Prof. Brian Greene. They are very good, and he does a Livestream Q & A once a week. All the best, Paul C.
Are these the biggest ideas in the universe? It occurred to me that there are much larger ideas in mathematics, like the Enormous Theorem. But then, are they really in the universe?
So if Bob measures his spin first he knows x light years before Alice what her spin is. Could you say that Bob can tell the future wrt to Alice? And what if we were once all entangled our lives might be playing out in a fatalistic way that was already known at the big bang? Somebody or something (call it the Universe) might already know our destiny- now that's spooky. And if our brains are quantum measuring devices we might be able to 'sense' things not immediately in front of us?
At the "Big bang point" there were no time and space as concepts. Hilbert space is real. Spacetime is a projection. Bob can tell whatever his _local_ consistent future he can happen to be in, but global universe will keep reconciling branches which yet to be converged in a very distant future for both Alice and Bob. See arxiv.org/abs/1902.05080 for more detail how exactly that works.
THANK YOU DR.SEAN CARROLL...!!! What, a continuous learner like me understand is that according to SCIENCE : Every thing in the living and non living world happens because of the wave - particle properties of the light : The Electromagnetism and spin properties of the electrons and electron oscillations to be in pair all the time in the configurational space of large and small molecules of the macro world and atoms of the micro world...of stability and instability...!!! Then the probability is due to the spin state of electrons and structure of the atoms or molecules( charges + or -) ...we interpret as HALF LIFE ( not exactly...but you know it better) ...!!! THE EQUILIBRIUM IS NOT 50 - 50 mathematically ...!!! It is a constant budgeting and adjustments with pluses and minuses...!!! ( additions , deletions, division or multiplications)...!!! PHILOSOPHY: NOTHING IN THIS WORLD IS ABSOLUTE ...whether there is one world or multiple world ...we all are unique ... Our world is the world we make out of the UNCERTAINTIES to be IN BEAUTY , BALANCE AND IN PEACE & ORDER...WITHOUT BREAKING THE BALANCE OF THE OTHER WORLDS ...TO HAVE ALL IN EQUILIBRIUM...!!! BECAUSE WE ALL ARE IN THE FIELD OF ENTANGLEMENTS...!!! SO , LET EACH OF US MAKE THE BEST OUT OF THE WORLD, with what WE HAVE AROUND, WITHOUT RELIGIOUS POLITICS...!!! After all SCIENCE IS WHAT IT MATTERS ...SCIENCE IS ABOUT CONSTANT CHANGE TO CORRECT , REPAIR , REBUILD AND RENEW...THE CYCLE HAVE TO GO ON... FOR THE WORLD TO EXIST...HAPPILY & HEALTHY AND THAT IS EQUILIBRIUM ...!!! THANKS AGAIN DR. CARROLL...!!!
53:15 This reminds me of the independence of irrelevant alternatives (IIA) axiom in decision theory. Assigning equal credence or probability to all branches is like assuming IIA holds. The example of deciding to do another measurement in one branch and not measuring anything in the other branch is like the "red bus blue bus" example, which shows that IIA can lead to nonsensical conclusions. Edit: Never mind, I kept watching and Sean did indeed mention decision theory at 57:45, so I guess I was on to something in connecting the two.
Planet-A is many l.y. away from Planet-B; Bob will misure speen-Z every 20 seconds so Alice can send istantant-fast message to Bob; how? spin-z-up=1 and spin-z-down=0; A want to send a 1 to Bob, A mesures spin-Z=down=0 (wrong), so A mesure spin-X and ignores the result, then re-mesures spin-Z=down=0=wrong, then she re-mesures spin-x (just to "reset" the superposition of the Z-spin) and she re-mesures spin-Z and so on until she mesures the spin-Z=up=1=ok! (hopefully in 20 seconds, or you can add an error code). !?!?!?!? What's wrong?
What happens if Bz is rotated 90 degrees whilst measuring spin, say through a rotating cylinder ? Is our current form of measurement too discrete to get anything substantial?
My understanding is that in such a situation, the initial determination of spin would be 50/50. After that, as the electron continues through the rotating magnetic field, it's essentially a smooth evolution from the Z axis to the X axis, so a counter-clockwise rotating cylinder would either see it deflect up-and-left or down-and-right. That way of phrasing it is a classical intuition, of course, but to put it in quantum mechanical terms, it still works out. There is no magical point at which the electron has deflected "enough" to suddenly flip a switch and determine its spin; it's already determined as it enters the magnetic field, with amplitude 1/√2 (↑) + 1/√2 (↓). From there, we proceed by chunking up space along the electron's path in shrinking intervals (taking the limit as the interval goes to zero, i.e. integrating, but I'll just do a numerical illustration here). So say the electron is spin up, and we use intervals such that the probability in the new interval is 1/√0.9 (↑) + 1/√0.1 (↓), which repeats N times until we have a very large probability (~99.999%) that the electron is spin-left at the end, and a small (but non-zero) probability (~0.001%) that it is spin right. Then let us shrink the intervals in our calculation. Now the probability in each new interval is 1/√0.99 (↑) + 1/√0.01 (↓), which repeats 10N times until we have an enormously large probability that the electron is spin-left at the end, and a very small (but non-zero) probability that it is spin-right. (Even at this interval the probabilities are too absurd to write here, with left being 99.99999999... well... about 98 9's after the decimal point.) Repeat this until each interval is arbitrarily as small as you like, increasing the number of intervals such that they are sufficient to complete a 90° rotation, and as you approach a smooth translation through the rotating magnetic field, you'll (very quickly) approach a probability of 1 that it comes out spin-left and 0 that it comes out spin-right. Of course, it could just as easily have started out spin-down with a 50/50 probability, in which case the same procedure would end up with probably 0 that it's spin-left and 1 that it's spin-right, so all told, you have a 50/50 chance that it will deflect upward then left, or that it will deflect downward and right; nothing else can happen. This can be made rigorous with calculus, of course, but I'm not going to try that in a TH-cam comment. ;)
it would be great, if for each of ideas were told its origin author and Your own ideas or meaning would be clarified. And showing experimental results and mathematical interpretation. As one can read out, only after Bells unequation became known we can tell about an "experimental proove". But then it means, that before that wihtout such proove the Copenhagens interpratation was decided by Bohr group to be true, just using mathematics. And EPR paradox was also a mathematical one to show the "instant far interaction" with infinite big speed. The answer was, yes, thats true. Even the authority of Einstein wasnt enough, to overwhelme Bohrs decision. Double split probably was the only one known QM experiment before Bells unequation? Which QM experiments did made Bohrs group so sure?
It's a good question. Did see an article about two particles' in superposition of their individual relativistic time dilation. They used particles that decay within a certain time. One path had more time dilation.
I liked this video and agreed with you in this universe, and in the other universe, my other self disliked this video and disagreed with you regarding Many Worlds.
Could the bertlemann’s sock example be improved by saying not only does bertlemann always wear different colored socks but he only puts on a second sock when someone sees his first sock and also bertlemann is blind?
I am a British citizen who has been to Cambridge university to teach about stupidity and I now have to watch the entire life of the man who is clearly from a place I don't think anyone else has ever tried to explain. Did anyone watch him tear into Neil DeGrasse Tyson and get it right??? I can't find it he's absolutely everywhere. He's exhausted and he hasn't stopped reading information. Only one name is correct about a real person in history but he said a reason that blew my mind. He thinks he's God, called bullshit on the big bang theory and said the Greeks measuring reality by reading men and women's teeth in motion is how we can calculate Newtonian quantum elementary gravitational wave function collapse and put the cat in a forest as a tree before saying that the cat is opening the draw and that probably means he expects him to be alive. A trust him never to kill that cat. Mainly because his quTumn entangled moon dust computer shouldn't be dangerous. Because he is looking away from it when his own cat exists. I'm busy but this is my new life. He's never going to stop he's not coping. I've not been able to laugh at this kind of thing before. He's offering forgiveness and saying Von broun was a Hindu from china who has a ying and yang with interdictional function and decided in was wrong. Terdictional? And wtf???😅🎉
No, actually. That's kind of the thing that makes them separate worlds in the first place. They decohere (which means they break entanglement with each other) never to communicate (become entangled) again. Well... in the simplest interpretation of Many Worlds. I think the truth is quite a lot more complicated than that, but I can't back it up with math.
I have chosen to go a step farther from "Many Worlds" to a many blurred universes. A string universe, a probability universe and a many worlds universe are the first three. To be continued...
The arrows represent complex wavefunction amplitudes and would usually be enclosed in “kets” | > notation, and the 1/2s would be square roots. Then the magnitude squared of the entire expression is the probability of finding spin up.
The non bolsmann copy of me seems problematic as you need a copy of the "infinite" universe, to create a copy of me. You are either going to need a radically different universe, where you can't spit without hitting life, that every solar system has life and a large potion of it has some intelligence, because you need to create an infinite number of not me's in order to create one me. Even an infinite universe can't just have ME, Me2 and nothing else, it must have an infinite number of not me's, in order to have a chance of creating just one ME and an even higher number in order to create a ME2.
That's correct, but it's not actually a problem. If the universe is truly infinite (and homogeneous, which is kind of doubtful, but is part of the underlying assumptions of that part of the video), then it has an infinite number of everything. It gets way more mind-blowing than just an extra copy of you... it has an _infinite_ number of copies of you. Not only that, it has an infinite number of precise, atom-by-atom replicas of our entire visible universe (although you'd have to travel a _whole lot further_ to encounter another one of those, than to encounter just another copy of you). At least, that's how the reasoning goes of the single infinite universe. I, personally, don't believe that the universe is infinite, but even if it were, it wouldn't actually matter. The distances involved before you start encountering such repetitions are so inconceivably vast that there's zero chance of the two copies ever interacting in any way, so really it's as if they are separate worlds.
There's something wonderful about how important it is to Sean that we don't kill the cat, even in a thought experiment. Loving these lectures.
Instead of a gas cylinder, we could could have a treat dispenser and a cat in a superposition of purring and non-purring states. Or we could just take a long delayed revenge and put Schrodinger in his own box. Ha, justice at last!
there is something important about all people who are kind to animals :)
I thought the same thing. So adorable. Who doesn’t appreciate an animal lover? 💕
This cat should be deleted from all quantum mechanics documentaries and books!
Beautiful and astute comment 👏🏾
Top notch, plus like alot of other viewers, I too think you have a lovely speaking voice ♥
It's soothing and nice to fall asleep to
unintentional ASMR...except I stay awake because its interesting unfortunately
Thank you for creating these videos, Dr. Carroll, they are truly great! I hope many people tune in and watch them in order to have a better understanding of how science and the universe works, something that we desperately need to happen if we are going to successfully navigate these surreal times we are living in. Cheers!
I love these talks. Most of it is too complicated for me, but the little bit I do follow is fascinating.
Same here
A little more understanding each time makes for a pleasurable journey
My favorite nugget of information so far in this series occurs around the 15:00 mark where Sean reveals that “this is the origin of the Uncertainty Principle”... I feel like a big part of understanding concepts is knowing how they were first imagined... this was like finding gold to me. ❤️
Sean, I wish I could upvote your videos more than once.
You can. Just set up a different TH-cam channel under a different name and off you go!
@@Twobarpsi this comment makes me glad i do not really know what reddit is
Same
Sean's explanation reminds me of Bach's music, - very intricate and pleasing, yet I have no idea of what is going on ! As to Hilbert and his Grand Hotel with an infinite number of rooms, no problem if a further infinite number of guests turn up. Plenty of room in the ballroom for the dancers to spin and entangle and a high probability of a good meal in the dining room. There is no charge for neutrons in the bar, but quantum tunnelling on the golf course is against the rules. Now I'm all puckered out and need to find my rest mass.
You'd think Hilbert's Hotel would have a lot of Yelp reviews.
Is there anything interesting to make of the fact that in MW the absolute amplitudes of each branch must be astronomically small, because the universe has been splitting for billions of years, but from existing inside each branch we always experience the probabilities as summing up to 1?
I'm a layperson and I got u. U explain things so well! U r such a gift!
I could listen to Sean Carroll and Brian Greene for hours on end. Oh wait, I already do!
Wow. The way you answered "what space is the wave function in" actually made me realise.. When you describe the wave function as a transformation on a vector space into another space, its easy to understand why the earliest attempt at formalising QM was called "Matrix Mechanics." If you described those spaces in a matrix, you're just doing some transformation on it.
I am so gripped by this series I am unashamedly binge-watching. Started July 29 and already at the entanglement Q and A. The Q and A sections are SO helpful and as if by magic I am intuitively grasping maths that I would have predicted beyond me. Some significant air-punching going on :) What a great teacher. Thank you so much.
Thanks for those great vides!. I'm not sure that the many worlds is the most economical understanding of QM. My (naive) understanding is that we have 2 things: 1. What might happen and 2. What "really" happens. The MW formulation affirms that 1 & 2 are in fact the same thing. But it can be also seen from another POV that the Copenhagen formulation is the most economical in that only one thing happens instead of all of them.
BTW this seems a little oddly similar to the domain of computation: there we have also 1. Programs and 2. Processes. Program is the source code which describes what "should happen" for each possible branche in the program. Processes are what "happens" when you actually run the program. Running the program to some point collapses some branches and chooses only one branch to continue evaluation.
In fact there is what we call "lazy evaluation" where a piece of code is not actually evaluated until necessary (when we need the value to figure out which branch to take). What's more? Some branches are finite (testing a Boolean value) while other branches are infinite (like which branch to take based on the value provided by the user).
**EDIT** One more thing is that in computation we distinguish between "pure computations" and "computations with side effects". Pure computations seem similar to the Laplacian view: in a closed program we can predict deterministically the outcome before running the program. With side effects however it's not possible. One kind of side effects is "non determinism" where evaluating an expression could return multiple answers (there is even one version with probabilities"). The point is maybe the interpretation of the wave function is simply that the universe is non deterministic in nature: that may sound crazy because it implies that elementary particles have free will. Well that's not crazier than human having it according to the free will theorem
en.m.wikipedia.org/wiki/Free_will_theorem
Very good writing!
Maybe in this view, entanglement collapses by structure complexity.
Instead of some fixed probabilities or linear amount of particles in objective collapse theories.
If a physical theory is fundamentally probabilistic ( non deterministic), that does not imply, of course, that elementary particles have " free will".
Free will is a notion that has to do with the macroscopic world that emerges from fundamental physics.
It's a " category error" to think about " free will " as if it was something like a " fifth fundamental interaction" that affects each " particle" individually or anything like that..
I cracked up at the 28:00 mark.
Cats are great, I've had many over the decades, and I love how you changed Schrödinger's terminology!
Watching this series through for the second time. It's good.
Near the end of the video, Sean uses an example where the particles have spins with un-equally weighted probabilities:
1/root(3)*(up) + 2/root(3)*(down)
Sean sorta "hand waived" when he set it up and said, "it's my experiment, I can do it how I want" which suggests that such a system is not really possible. However, if we could make a system like that that was also entangled, then we could do faster than light communication.
e.g. If we imagine a system in this configuration (up and down here are with respect to Z):
1/root(3)*(aliceIsUp, bobIsUp) + 2/root(3)*(aliceIsDown, bobIsDown)
Let's also imagine that spacetime is flat, so that having agreed beforehand on a predetermined "time" and "afterwards" to make the measurements might make sense.
Then, we could make a big box of particles entangled in such a way and give one box to Bob and the other to Alice and move them far apart. At some predetermined "time", Alice could either
a) not measure her particles, or she could
b) measure all the particles in her box in the Y direction, which would give them a definite spin in that direction and a fully indefinite spin in the Z direction
"Afterwards", Bob could measure all his particles in the Z direction. If Alice did "a", he would get 1/3u, 2/3d. If she did "b" he would get 1/2u, 1/2d. In this way, Alice could transfer a bit of information to Bob faster than light by changing the probability of his measurements.
My assumption is that such a system can't be constructed for some reason or that I've made some kind of a mistake while constructing it.
I've watched every single TH-cam video with you Sean. But I don't understand the first thing about entanglement or the wave function.
But I'm not giving up 👆
Keep the awsome content coming, much abliged
Customer : This cat is dead!
Sean : It's only sleeping.
It's pining for the fjords!
Love the content as always. I just noticed this is the 2nd or 3rd video that features a somewhat irritating ~120Hz hum in most parts. Especially obvious when it goes away e.g. at 8:38.
@@Twobarpsi mine don't. advantage, cheap headphones!
How big is a "world" when it branches? Is it just a local branching which then propagates from there (at the speed of light)? Or is it the size of the entire "parent" universe from the beginning? Neither?
Correct me if I am wrong: In the last part of the video, isn’t it cheating to represent the two subsequent experiments with separate wave functions, especially if we are talking in the context of the Many Worlds Theory? The moment we are putting a condition for doing the second experiment based on the outcome of the first one, needn’t the two to be treated entangled with each other within a single wave function? I think of it as prooving 1=2 from a mathematical equation by ignoring the initial assumptions or some fundamental rules. I am probably missing some point in this particular thought experiment, so I am looking for an explanation of why the above-mentioned assumptions do not apply here. I would be happy if you had time to bring a clarification.
I think this got me one baby step closer to understanding what "probability" means in Many Worlds. And for me, if I ever get there, it will be a big deal. Cool.
I have a hypothesis. Sean decided to do these videos because he is in love with this new writing gadget he's using !
R
My understanding of the collapse wave function is that in the Many World Interpretation, this describes 100% outcome after the collapse with the entire system (branched); whereas, David Bohm Pilot Wave Theory is describing before the collapse there is hidden (from us) information what the actual outcome will be and thus we have this probability equation.
But in Many Worlds, there is no collapse. That's its entire point.
@@barefootalien Dear Barefoot - are you an alias for someone more well-known ?
Just wondering. Best regards, Paul C.
The probability problem was the thing I had the most trouble with regarding Many Worlds when I read Something Deeply Hidden. I don't understand how it explains that I could use statistics to predict, say, how many spin up vs spin down outcomes I'd get from repeating a prepared experiment, and get the distribution I expect. I guess the problem is that questions like "Which future branch of the wave function will I find myself on?" seem like they aren't really well defined questions at all, since I will find myself on all of them. It's more like, "after I do the experiment but before I learn the result, what credence will make sense at that point to assign to the different possibilities of self-location?" So confusing.
Is a superposition an interaction necessarily? that is; is it a physical event or just a state? (can a state not be a physical event, even?) I know that not ALL interactions are superpositions, but are ALL superpositions interactions?
Hello Sean, can you please explain what is the process that entangles particle, where why how. If particles get entangled at a point in time how do they get to the other side of the universe. I am looking for the applications of entanglement in the real world. Keep up the great work.
Okay, so I'm not Sean, but here goes my attempt anyway. There are several ways to create entangled particles that follow two main themes:
1: Create a pair of particles with a conserved quantity from a heavier particle that lacks that property. So, for example, if you have a spin-0 particle like a Higgs boson, it must decay into two particles with opposite spins. Those spins must remain opposite in order for angular momentum to be conserved, thus they are entangled. The same can be done with a charge-0 particle like a Z boson or photon (or the Higgs), which must also decay into two particles with opposite electric charge. This is _not_ the method usually used for practical applications of entanglement in the real world because the easiest pair of entangled particles to create with this method is a pair of photons, which is basically useless for quantum computing since they're, y'know, always zipping along at the speed of light no matter what. The Higgs can decay into an electron-anti-electron pair with entangled spin, but the Higgs is extremely difficult to create, and you can't generally build a Large Hadron Collider for every quantum computer you want to make.
2: Bring two particles/atoms together so that they interact in such a way that you cannot know, even in principle, which particle did a thing. What kind of thing? Well, things like exciting them to a superposition of both particles emitting a photon each and not emitting a photon each (this is done with a carefully tuned laser). You then pass the resulting photons through a beam-splitter (half-silvered mirror) and then on to detectors. This sets up a situation where you can't, even in principle, know which detected photon came from which atom, so they are then entangled. (I realize I'm using extremely sloppy language here, but it's helpful; in truth, the words 'you' and 'know' are mushy and not really getting at the truth of what happens, which is exactly what created the confusion of the Copenhagen interpretation in the first place, so just keep in mind that there's a deeper truth that does not need a conscious observer or the particles to "know" things.) This method is much more useful because atoms are much easier to contain and manipulate.
The primary application for entanglement in the real world is in quantum computing, in which a complex device sets up an array of entangled particles and then performs operations on them in such a way that the most likely way for them to behave solves problems in which superpositions are useful. How many particles determines how useful it is, with two particles being able to solve only very basic problems that are much easier and faster with an ordinary computer. But if you can get up to 10 particles, you're already pushing the boundary where using a normal computer is impractical, and 100 can solve problems that would take a normal computer longer than the age of the universe to solve.
It's worth noting, however, that only certain very well-defined classes of problems, such as factoring large numbers are doable with a quantum computer. To date, it's simply impossible to create all types of logic gates with qubits, so you cannot create a Turing machine or anything like it. A quantum computer is thus really more akin to a magnificently superior calculator than a general computing device like what you're reading this comment on right now, though it is conceivable that in the (fairly distant) future, we'll be able to build hybrid computers that can use their quantum processor for calculations that need it, and a normal processor for things the quantum one can't do. I say distant future because right now, quantum computers are extraordinarily fragile things. Even a stray photon from the computer's own casing can decohere your carefully entangled system, so they have to be in a near-perfect vacuum and near absolute zero to even have a chance of lasting long enough to do a computation.
Edit: I should also briefly mention another method that I'll call "1.5". In this method, you create two easy-to-make particles, like two photons with correlated (entangled) polarization, which are then absorbed by two atoms, which then become entangled since the photons were entangled. This is called "Second Generation Entanglement", and it's... less useful than it sounds. The problem is, controlling a pair of individual photons to be absorbed by a specific pair of individual atoms in such a way that you don't decohere either the photons or the atoms, is practically impossible. The result is that it basically comes down to luck whether you actually manage to create an entangled pair of atoms. That's why the other name for this method is "Entanglement By Accident".
Your "Why" entangle, is a good question...
I'll be reading 'Something Deeply Hidden' next week. I have many doubts about MWI, but between your book and this podcast (starting it now), I suspect they'll be alleviated.
Are the books worth it?
Or too much about MWI?
@@mikkel715 the book is good (Something Deeply Hidden). It is devoted to the MWI - in my case I enjoyed the book even though I'm not a huge fan of MWI.
@@johnbach3144 Thanks.
Many cornerstones in QM anyway?
does the size of the system determine the amount of branches in the universe? If we take the universe as our system, is there only one branch? The wavefunction branches when two systems come into contact with each other?
Just asking.. let's say we replace the cat with an explosive that could go off at any time. Does observing it determine if it blows up or would it just blow up randomly?
Randomly
that lapsus at the end is gold
Hello doctor Sean! Thanks for the great video! It was awesome! =)
26:00 so my summary of the problem of Spooky Action at a Distance, which Sean builds up to in the previous 26 mins, is that:
Once Alice does a measurement of her own electron, she knows something real about the spin of Bob’s electron immediately (say, that its spin Up), regardless of distance. If the spin of Bob’s electron was truly random before Alice’s measurement, *_it seems like locality is violated by Alice’s knowledge_* . So for locality to not be violated, the spin of Bob’s electron mustn’t be truly random, and therefore must have always been spin Up, inspiring ideas of hidden variables that travel with the electron that determine its spin beforehand.
The kicker is that spin *is* truly random, and so there’s a problem there
It’s unlikely that my description above is completely accurate to Sean’s description, so you should probably rewatch the video instead of relying on that
The first rule of entanglement is we do not talk about entanglement.
This is the way
Wow... I now finally really get what the fuss is about with quantum mechanics. Hurray~
By the way R,S are the unitary operators for measuring the first and 2nd spins.
the universe... what a concept! :D
34:40 Thanks for giving a clear and meaningful answer to this question.
37:54 So the Bohm pilot wave theory not working well in case of many particles.
Slightly off topic but maybe somebody can explain this please.
The Centre of the Earth is younger (as time goes slower there ) than the Surface. So if the Earth is created from the centre to the outside then if you could go back in time, then the outside of the Earth would be older that the centre. Is this a Paradox. Even allowing for the matter changing, the space in the centre would have had to be created before something that is older than it ! Can you explain this ?If I created instantly(or close to, hypothetically) my own sphere/earth of uniform material from the centre to the outside. Would the same question exist. How could the older outside be built up on a younger centre ? Thanks.
I love Sean’s t-shirt 🤟
Thank you for great answers! Finally got the EPR and Bell's through the uncertainty principle. So, position, momentum, spin do emerge from the complex amplitudes of wavefunctions right? Although we write in one direction as mapping from (RealSpace^3)^N to ComplexSpace, because wavefunction is one for the entire universe, intuitively it seems that the mapping should be in the opposite direction, from ComplexSpace to emergent variants in the "permutation space" (configuration space).
Thanks again! :-)
Thanks Sean Carroll for this fantastic serie. This goes in better dept than many, and not too deep.
Should I recommend something. Delete that cat, as you planned. Don't delete the double slit. But the cat is only confusing for layman.
As layman you need to first understand superposition and entanglement by other examples, to understand that cat.
Consider accepting Simulation Theory as a Quantum Mechanic Interpretation.
The deep simulation of the simulation theories.
When the alert sound went off I wasted a minute trying to find the tab that made it...
At 28:00 ish Sean answers my problems with ‘detecting’, ‘collapsing’, and ‘entangling’ in the DSE, and clears up the difference between Entangling vs Interacting, by seeming to say that the electrons fire and interact (are affected by) with a heavy wall (that’s states are not prone to being contingent on the superposition of the electron, and so interacts but doesn’t entangle) and then hit a detector (that is, and so it does entangle).
This seems to skirt my understanding and doesn’t really seem to resolve my issues, so I’ll have to figure that out
For a single electron, maybe it's more efficient or takes less energy for it to simply propagate as a wave and go through both slits in the double slit experiment. I think the electrons are behaving in such a way to simple obey the laws of conservation.
Mr Carroll I have a question, not related to this video necessarily, I'm only asking here anyway cuz I can't find any answer anywhere else on the internet about it...
My question has to do with how all those things look like, are they real? Quarks, atoms, protons neutrons etc? Or are they just mathematical models, nothing more than mathematics? For example, if we were to blow up an atom to the size of say... a basketball, ... what would it look like? Would it have like colors or even a surface? Would it have anything that we could see? (assuming we could see the entire spectrum of light and not just visible light). Could we touch it and if yes how would that even feel like? Or would it be invisible? Like a force sphere that you just can't see or feel in any way, but if you tried to pass through it - it would be standing in your way blocking it from you?
Dear Prof. Carroll,
what is the best way to send you a question please ? (I do not have a twitter account.) Thanks.
All the best from West Wales (UK), Paul C.
Patreons get a monthly AMA
@@Psnym Hi Denis, yes I know - but is there just the one Patreon account for Sean, i.e. the Mindscape Podcast ? Or is there a different Patreon account for The Biggest Ideas channel ? Thanks. Paul C.
I'm invested in figuring out the correct interpretation of QM, but with 95% certainty it's probably an Everettian model.
The question I have always wanted to ask is, in the next few hundred years with advances in Ai and computing, do you feel it may be possible to compute probabilities of macroscopic events such as, "should I take the job?" or "should I ask her to marry me?" My understanding of the 2 slit experiment and decoherence dictates that the only reason we see an interference pattern is we have not disturbed the waveform by entangling with it. I don't mean telling the future. I mean having a large enough database, fast enough computer and lot of supervised learning models. In this sense wouldn't we be in a sense reconnecting to another branch of the waveform? But on purpose. I feel like that's almost telling the future. Is this impossible and why?
How does the conservation of energy work with Many Worlds? Everytime we get a branch from the wavefunction, we get a new universe spanning off this branch? Where is this energy coming from? Doesn't make sense. Also, probabilities don't make sense in Many Worlds. For example, in the double slit experiment, you'll find a world where the interference pattern doesn't show up because it's extremely unlikely to happen but it is still going to happen due to the non-zero probability from the wavefunction.
In the awake/sleeping cat example, why for example (cat awake, seen sleeping) is not taken into account- isn‘t that just possible or do we as observer prejudge what makes sense or not - is there a hidden bias of the observer distracting the system (leading to decoherence)
This means, no one really understood how QM works. Everyone has their own interpretations, and each of them has certain limitations.
You got it. For about 100 years.
Time to look towards Simulation Hypothesis (Simulation Theory)
Sean, I hope you’ve considered that when you see a different probable world (or particle), you’re also in a world that has a slightly different history ;) - time traveler :)
Just a quick note about your Stern-Gerlach descriptions. They CANNOT be done with electrons. Electrons are charged and experience Lorentz forces, which overwhelm the spin-dependent force. This is why the experiment was done with neutral silver atoms. This is a common error seen in many, but not all texts. Just letting you know so you can make a correction for the future.
First it was stated if a particle is measured in Z to be spin up then you measure it again for Z it will always be spin up. So in the Alice and Bob scenario if Alice measures Z to be spin up we know Bob is spin up. Ok now say Bob measures X and gets spin right. Now we cannot say if Bob Z is spin up due to uncertainty. NOW ALICE PERFORMS A SECOND CONSECUTIVE Z MEASUREMENT. Will it be spin up, due to the first Z being spin up or 50/50 due to Bob making the Z direction uncertain ?
It always was uncertain. It actually "collapses" when Alice and Bob reconcile their diverged versions of reality using classical signaling. What do you think versions are allowed to converge so energy, momentum, and spin do conserve? :-)
In my scenario Alice and bob don’t talk about anything. Alice measures Z spin ad it’s spin up. In this video Sean says if that same particle is measured again it will be still be up. Now Bob checks the X spin and gets spin left. Alice and bob don’t signal or reconcile. so now Alice checks the Z spin expecting up since it was already determined up and as far as she knows bob may or may not have done something. Or are They now not entangled since measurements were made on each and Alice will get spin up as that’s what state it was in when she observed it. Or is alices Z
undetermined as bob took away the certainty from that direction
@@robertspiess9859 I think measuring an entangled property breaks the entanglement, so Alice's second measurement wouldn't depend on Bob's measurement.
Ben Marolt I figure so because otherwise I see how information could travel FTL
PLEASE Sean, answer me this question, please, Can quantum mechanics principles apply on biological systems?
Yes. Photosynthesis actually makes extensive use of quantum tunneling. AFAIK, that's the only biological system that we've confirmed to use quantum effects, but it's a pretty important one. ;)
Watch Jim Al-khalili video. He's working on quantum biology
@@sandrasandra7593 I have seen his videos, but I want more evidences for that, i am fond of this emerging new science of quantum biology.
Hey Sean thank you for this very informative as always!
Has anyone ever postulated or written any theories about the possibility of the big bang creating a "big expanding black hole" that we're basically living in? I've day dreamed about the largest explosion ever presumed (the big bang) creating a big expanding "black hole" that we exist within. Could explain weird dark matter and acceleration possibly? Or is this maybe just a good way to dream about what we are as a universe but it isn't necessarily a "black hole".
Yes, that's a common place for one's mind to wander once one learns a sufficient amount about the Big Bang, and about black holes. It's not a bad line of thought necessarily, and can be fun to think about.
Sadly, this is almost certainly not the case, because our universe is nowhere remotely near the level of density required to create a black hole. There is, however, a horizon surrounding our visible universe; an expansion horizon. However, this is only an apparent horizon. The entire universe is somewhere between 250 times the size of the visible universe and infinite in size, to the best of our current measurements, and in the prevailing theory, it isn't expanding "into" _anything_. (A black hole expands into pre-existent spacetime.)
Such a theory would also do a poor job of explaining Dark Matter and Dark Energy, I'm afraid. Dark Matter has very specific properties that are relatively well-understood (discounting less popular theories that attempt to account for the data using modified gravity of some sort), including discrete and detectable densities that vary quite a lot throughout the universe, clustered especially around large collections of ordinary matter.
And Dark Energy, well... there have been some experimental results lately that are calling that into question altogether, or at least its strength, and are instead suggesting that while the universe does seem to be accelerating in its expansion, it is not doing so homogeneously. Rather, there is some indication (still awaiting peer review, so take it with a hefty grain of salt) that the visible universe has a dipole flow away from some kind of "great repeller" and/or toward some kind of "great attractor" beyond the horizon of the visible universe. The first experiments that won the Nobel Prize, that discovered the apparently homogeneous expansion and acceleration just happened, through bad luck, to be pointing in opposite directions approximately along what would be this theoretical polarized universe's 'ecliptic', hence the sameness of the measurements.
@@barefootalien Wow thank you for that thorough and very well thought out response. We don't really know how chaotic or calm the inside of a black hole is necessarily, that's why i thought it might be an interesting way to think about it. Maybe a kind of large weak black hole style expansion.. The cold vacuum, and empty, yet filled with micro particle "space" our galaxy exists in, has always been fascinating for me to daydream about.
@@hollowthere3850 There is a similar thought I forgot to mention: the possibility that the universe is a _white_ hole, which is basically a time-reversed black hole on the bottom of a Kruskal-Szekeres diagram. In this concept, whenever a black hole forms, it forms a new universe which spews out all the matter and spacetime the black hole accreted. Thus our universe could potentially be a _supermassive_ white hole. A paper arguing this via the holographic principle can be found here: www.researchgate.net/publication/256459927_Out_of_the_White_Hole_A_Holographic_Origin_for_the_Big_Bang
Based on what you said, the impression I get of the "measurement" is it signifies "entanglement." So, os the universe. from the perspective of a detector (i.e., observer) a collection of entangled objects and non-entangled wave functions, with respect to the detector?
If you have two entangled particles, and one falls into a black hole, when you measure the (say) spin of the particle outside of the BH, do you now know the spin of the particle in the BH? Is there some other case when two entangled particles are outside of one another's light-cone, yet may effect a change upon the other?
It was bad enough when all these half-existent dead cats started showing up all over the apartment, but now there is spectral copy of Sean Carroll observing each one of them and half of those are demanding tea and biscuits. The other half want coffee and croissants. I can't afford this quantum mechanics stuff. Help!
When the electron is falling into gravitational field, its entangled gravitationally, that is why its falling i.e. behaving in a certain way rather than wandering randomly. Plss explain.
Does the problem with locality arise if you take the frequentist view of probabilities? Say, Alice measured up and left, so Bob is "forced" to measure down and right. But why isn't he allowed to measure "right", given psi = (right/sqrt(2) + left/sqrt(2))? That equation does not prevent this particular measurement from going any particular way. And if we take a series of experiments, Bob's frequencies are determined by Alice's frequencies, which will comply with amplitudes of outcomes.
No these won't comply. The reconciliation only happens between COMPATIBLE universes. arxiv.org/abs/1902.05080
I think the Born rule is circular, without using the L2 norm, you won't get the absolute square. There is no explanation why absolute value can't be the probability instead of absolute square.
I don't understand what the branch probabilities mean in many worlds. As Sean points out it's not the credence meaning of probability. And it can't be the frequency meaning because all branches happen with the same probability (p=1). What meaning is left? It seems for many worlds to work it needs to make some extra postulate about probability even if such isn't called a postulate.
So in the first MWI probability example (two spins equal prob.), you'll end up with the upperbranch given amplitude = √1/2, and the other two branches with an amplitude √1/4....?
Thanks, Sean!
Awesome and sad 76ers point in the video. No one in the world would have thought there would not be a 2020 championship series. Maybe we will see a no fan playoff bracket. Then you’ll still be right.
I'm assuming that the spin of a photon is related to it's polarization?
Do live streams!😂
Bits at a time🤔🙌
Better than all the other shit on youtube right now. Breath of fresh air to hear someone not mention the virus for 12+ videos.
@@rage9715 You could also try watching "Your Daily Equation" with Prof. Brian Greene. They are very good, and he does a Livestream Q & A once a week. All the best, Paul C.
@@rage9715 Indirect mention this time, though.
Are these the biggest ideas in the universe? It occurred to me that there are much larger ideas in mathematics, like the Enormous Theorem. But then, are they really in the universe?
“ ‘in’ is not a technical term”
LaTeX is starting to look nervous
Sean is starting to look like me in this quarantine. .. hungover. Lol
The last lecture kind of lost me, will have to try watch it again
i am on take 4, but i am pretty slow
In another world, Sean can draw a good cat.
"444 likes, 4 dislikes" -- Looks like 4 got entangled.
Actually, those dislikes are just in a state of superposition; |+like> + |-(dis)like>
Bra + Ket = Bracket..... I'm an engineer; that shouldn't have blown my mind >.
So if Bob measures his spin first he knows x light years before Alice what her spin is. Could you say that Bob can tell the future wrt to Alice? And what if we were once all entangled our lives might be playing out in a fatalistic way that was already known at the big bang? Somebody or something (call it the Universe) might already know our destiny- now that's spooky. And if our brains are quantum measuring devices we might be able to 'sense' things not immediately in front of us?
At the "Big bang point" there were no time and space as concepts. Hilbert space is real. Spacetime is a projection.
Bob can tell whatever his _local_ consistent future he can happen to be in, but global universe will keep reconciling branches which yet to be converged in a very distant future for both Alice and Bob. See arxiv.org/abs/1902.05080 for more detail how exactly that works.
He's _really_ careful not to kill these fictional cats isn't he?
How any two things -- particles, photons, other -- become entangled? The process that creates entanglement...
Sir explain the concept of time dilition
It sounds like people say 'superposition' just because we don't understand how to measure things accurately
THANK YOU DR.SEAN CARROLL...!!!
What, a continuous learner like me understand is that according to
SCIENCE :
Every thing in the living and non living world happens because of the wave - particle properties of the light :
The Electromagnetism and spin properties of the electrons and electron oscillations to be in pair all the time in the configurational space of large and small molecules of the macro world and atoms of the micro world...of stability and instability...!!!
Then the probability is due to the spin state of electrons and structure of the atoms or molecules( charges + or -) ...we interpret as HALF LIFE ( not exactly...but you know it better) ...!!!
THE EQUILIBRIUM IS NOT 50 - 50 mathematically ...!!!
It is a constant budgeting and adjustments with pluses and minuses...!!!
( additions , deletions, division or multiplications)...!!!
PHILOSOPHY:
NOTHING IN THIS WORLD IS ABSOLUTE ...whether there is one world or multiple world ...we all are unique ... Our world is the world we make out of the UNCERTAINTIES to be
IN BEAUTY , BALANCE AND IN PEACE & ORDER...WITHOUT BREAKING THE BALANCE OF THE OTHER WORLDS ...TO HAVE ALL IN EQUILIBRIUM...!!!
BECAUSE WE ALL ARE IN THE FIELD OF ENTANGLEMENTS...!!!
SO , LET EACH OF US MAKE THE BEST OUT OF THE WORLD, with what WE HAVE AROUND, WITHOUT RELIGIOUS POLITICS...!!!
After all SCIENCE IS WHAT IT MATTERS ...SCIENCE IS ABOUT CONSTANT CHANGE TO CORRECT , REPAIR , REBUILD AND RENEW...THE CYCLE HAVE TO GO ON... FOR THE WORLD TO EXIST...HAPPILY & HEALTHY AND THAT IS EQUILIBRIUM ...!!!
THANKS AGAIN DR. CARROLL...!!!
Where did you get that 1 over the square root of 2?
Your shirt is amazing 🤣🤣
53:15 This reminds me of the independence of irrelevant alternatives
(IIA) axiom in decision theory. Assigning equal credence or probability to all branches is like assuming IIA holds. The example of deciding to do another measurement in one branch and not measuring anything in the other branch is like the "red bus blue bus" example, which shows that IIA can lead to nonsensical conclusions.
Edit: Never mind, I kept watching and Sean did indeed mention decision theory at 57:45, so I guess I was on to something in connecting the two.
Wonder what Seans view is on the possible existence of a"Higgs Force?"
holy shit i think i legit heard a lightbulb go off in my head at 49:32
I wish I'd had Pete at CalTech but MWI is wrong.
Planet-A is many l.y. away from Planet-B; Bob will misure speen-Z every 20 seconds so Alice can send istantant-fast message to Bob; how? spin-z-up=1 and spin-z-down=0; A want to send a 1 to Bob, A mesures spin-Z=down=0 (wrong), so A mesure spin-X and ignores the result, then re-mesures spin-Z=down=0=wrong, then she re-mesures spin-x (just to "reset" the superposition of the Z-spin) and she re-mesures spin-Z and so on until she mesures the spin-Z=up=1=ok! (hopefully in 20 seconds, or you can add an error code). !?!?!?!? What's wrong?
What happens if Bz is rotated 90 degrees whilst measuring spin, say through a rotating cylinder ? Is our current form of measurement too discrete to get anything substantial?
My understanding is that in such a situation, the initial determination of spin would be 50/50. After that, as the electron continues through the rotating magnetic field, it's essentially a smooth evolution from the Z axis to the X axis, so a counter-clockwise rotating cylinder would either see it deflect up-and-left or down-and-right.
That way of phrasing it is a classical intuition, of course, but to put it in quantum mechanical terms, it still works out. There is no magical point at which the electron has deflected "enough" to suddenly flip a switch and determine its spin; it's already determined as it enters the magnetic field, with amplitude 1/√2 (↑) + 1/√2 (↓). From there, we proceed by chunking up space along the electron's path in shrinking intervals (taking the limit as the interval goes to zero, i.e. integrating, but I'll just do a numerical illustration here).
So say the electron is spin up, and we use intervals such that the probability in the new interval is 1/√0.9 (↑) + 1/√0.1 (↓), which repeats N times until we have a very large probability (~99.999%) that the electron is spin-left at the end, and a small (but non-zero) probability (~0.001%) that it is spin right.
Then let us shrink the intervals in our calculation. Now the probability in each new interval is 1/√0.99 (↑) + 1/√0.01 (↓), which repeats 10N times until we have an enormously large probability that the electron is spin-left at the end, and a very small (but non-zero) probability that it is spin-right. (Even at this interval the probabilities are too absurd to write here, with left being 99.99999999... well... about 98 9's after the decimal point.)
Repeat this until each interval is arbitrarily as small as you like, increasing the number of intervals such that they are sufficient to complete a 90° rotation, and as you approach a smooth translation through the rotating magnetic field, you'll (very quickly) approach a probability of 1 that it comes out spin-left and 0 that it comes out spin-right.
Of course, it could just as easily have started out spin-down with a 50/50 probability, in which case the same procedure would end up with probably 0 that it's spin-left and 1 that it's spin-right, so all told, you have a 50/50 chance that it will deflect upward then left, or that it will deflect downward and right; nothing else can happen.
This can be made rigorous with calculus, of course, but I'm not going to try that in a TH-cam comment. ;)
Heisenberg's uncertainty happens.
it would be great, if for each of ideas were told its origin author and Your own ideas or meaning would be clarified. And showing experimental results and mathematical interpretation. As one can read out, only after Bells unequation became known we can tell about an "experimental proove". But then it means, that before that wihtout such proove the Copenhagens interpratation was decided by Bohr group to be true, just using mathematics. And EPR paradox was also a mathematical one to show the "instant far interaction" with infinite big speed. The answer was, yes, thats true. Even the authority of Einstein wasnt enough, to overwhelme Bohrs decision.
Double split probably was the only one known QM experiment before Bells unequation? Which QM experiments did made Bohrs group so sure?
Could reference frames be entangled at the quantum level?
@@michaelsommers2356 I know but what I was asking, I guess I wasn't very clear, could the space within the reference frames be entangled.
It's a good question. Did see an article about two particles' in superposition of their individual relativistic time dilation.
They used particles that decay within a certain time. One path had more time dilation.
I liked this video and agreed with you in this universe, and in the other universe, my other self disliked this video and disagreed with you regarding Many Worlds.
Could the bertlemann’s sock example be improved by saying not only does bertlemann always wear different colored socks but he only puts on a second sock when someone sees his first sock and also bertlemann is blind?
I am a British citizen who has been to Cambridge university to teach about stupidity and I now have to watch the entire life of the man who is clearly from a place I don't think anyone else has ever tried to explain. Did anyone watch him tear into Neil DeGrasse Tyson and get it right??? I can't find it he's absolutely everywhere. He's exhausted and he hasn't stopped reading information. Only one name is correct about a real person in history but he said a reason that blew my mind. He thinks he's God, called bullshit on the big bang theory and said the Greeks measuring reality by reading men and women's teeth in motion is how we can calculate Newtonian quantum elementary gravitational wave function collapse and put the cat in a forest as a tree before saying that the cat is opening the draw and that probably means he expects him to be alive. A trust him never to kill that cat. Mainly because his quTumn entangled moon dust computer shouldn't be dangerous. Because he is looking away from it when his own cat exists. I'm busy but this is my new life. He's never going to stop he's not coping. I've not been able to laugh at this kind of thing before. He's offering forgiveness and saying Von broun was a Hindu from china who has a ying and yang with interdictional function and decided in was wrong. Terdictional? And wtf???😅🎉
If "many worlds" exist, are they entangled?
No, actually. That's kind of the thing that makes them separate worlds in the first place. They decohere (which means they break entanglement with each other) never to communicate (become entangled) again. Well... in the simplest interpretation of Many Worlds. I think the truth is quite a lot more complicated than that, but I can't back it up with math.
If Schrodinger’s cat is no longer alive or dead but is rather awake or sleeping, then it’s not in a box - it’s in a safe space.
I have chosen to go a step farther from "Many Worlds" to a many blurred universes. A string universe, a probability universe and a many worlds universe are the first three. To be continued...
And why are all the universes blurry? It's because pi is blurry!
Isn't ↑ = ½ → + ½ ← (no square roots)?
The arrows represent complex wavefunction amplitudes and would usually be enclosed in “kets” | > notation, and the 1/2s would be square roots.
Then the magnitude squared of the entire expression is the probability of finding spin up.
I drink and I watch things
Lol
What a waste
I pick things up then put them down.
@@alvarorodriguez1592 you are aware he was referencing the Tyrion Lannister " I drink and I know things" of Game of thrones?
@@thebendu33 i thought he was referencing Rick..., but i have never seen GoT
The non bolsmann copy of me seems problematic as you need a copy of the "infinite" universe, to create a copy of me. You are either going to need a radically different universe, where you can't spit without hitting life, that every solar system has life and a large potion of it has some intelligence, because you need to create an infinite number of not me's in order to create one me.
Even an infinite universe can't just have ME, Me2 and nothing else, it must have an infinite number of not me's, in order to have a chance of creating just one ME and an even higher number in order to create a ME2.
That's correct, but it's not actually a problem. If the universe is truly infinite (and homogeneous, which is kind of doubtful, but is part of the underlying assumptions of that part of the video), then it has an infinite number of everything. It gets way more mind-blowing than just an extra copy of you... it has an _infinite_ number of copies of you. Not only that, it has an infinite number of precise, atom-by-atom replicas of our entire visible universe (although you'd have to travel a _whole lot further_ to encounter another one of those, than to encounter just another copy of you).
At least, that's how the reasoning goes of the single infinite universe. I, personally, don't believe that the universe is infinite, but even if it were, it wouldn't actually matter. The distances involved before you start encountering such repetitions are so inconceivably vast that there's zero chance of the two copies ever interacting in any way, so really it's as if they are separate worlds.