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Say you put a red marble and a blue marble in two envelopes. You randomly post one envelope to Australia. One year later, you open the other envelope. You now
by andomar 6y ago
Say you put a red marble and a blue marble in two envelopes. You randomly post one envelope to Australia. One year later, you open the other envelope. You now know the color of the marble in Australia.
What's the difference between this and quantum entanglement?
- unkown 6y agoactually the marbles change colour every 1 second and you can take them really far apart, meaning one can go at a really high speed and distance trough universe, so the time would have dilated for it. when you open them both have same color
- andomar 6y agoThat sounds logical. Relativity theory allows you to age one object faster than another by changing their relative speed. Nobody would claim there was information travelling faster than light in your example. What makes people say information travels faster than light with quantum entanglement?
- throwaway_pdp09 6y agoIf the marbles were changing colour at random but still alwasy different colours, that would suggest info is doing so.
- andomar 6y agoIf they change color in sync then that is a known property of both marbles. Say you have a marble that is blue if the number of seconds is even and red otherwise. Knowing the color of one marble is enough to know the color of the other marble without information travelling between the marbles?
- throwaway_pdp09 6y agoNot my area. My understanding: colours sync exactly on measurement (when you look at them). > Knowing the color of one marble is enough to know the color of the other marble I guess so. > without information travelling between the marbles? The marble colours are in sync on measurement. Somehow that info has travelled instantaneously. You just can't use it to send information, at all.. above is just my understanding. I have no background in this. Just a programmer.
- pegasus 6y agoThey don't.
- mrmonkeyman 6y agoThe envelope is moving to Australia faster than light.
- Simon321 6y agoThis would be a 'local hidden variable' theory. According to wikipedia these have largely been ruled out: Most advocates of the hidden-variables idea believe that experiments have ruled out local hidden variables Source: https://en.wikipedia.org/wiki/Bell%27s_theorem#Bell_inequalities https://en.wikipedia.org/wiki/Bell%27s_theorem#Bell_inequali...
- goldenkey 6y agoIt seems that hidden variables have always been made to be simple hidden states. But we now know about RNGs and seeds and such. A shared RNG seed is essentially entanglement. This delves more into complex hidden variables, that normal analyses ignore: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC137470/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC137470/
- kgwgk 6y ago> A shared RNG seed is essentially entanglement. Classical entanglement, which is not good enough to explain quantum entanglement.
- aeternum 6y agoIt can explain quantum entanglement, seems to be a version of superdeterminism. In QM, experiments show us that entangled particle spin probabilities vary non-linearly with the angle between detectors (even if those detectors are far apart). This means that either: 1) locality is broken.. state is somehow transmitted faster than the speed of light between particles. 2) realism is broken.. god plays dice with the universe But there's also a 3rd, which is: the choice of detector angle is not an independent variable (a necessary assumption for Bell's inequalities to hold).. instead the state of the universe is pre-determined and the experimenter's choice of detector angle is known beforehand so there is no need for spooky action at a distance. This isn't a very popular explanation since it provides no reason as to why we don't see this weird lack of independence elsewhere.
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- throwaway_pdp09 6y agoApparently this common explanation is wrong. If you actually measure one, the other actually changes. Although you can't use that to send information, so einstein's faster-than-c restriction isn't violated. Maybe this will help https://html.duckduckgo.com/html?q=bell%27s%20inequality%20simply https://html.duckduckgo.com/html?q=bell%27s%20inequality%20s... I imagine the youtube links might be more comprehensible.
- yetihehe 6y agoIf the other changed, you could ue those changes to send information by varying time between changes (pulse width modulation). Instead when you measure one you go from "not knowing which one is red or blue" to "knowing color of both".
- throwaway_pdp09 6y agoYou can't.
- yetihehe 6y agoExactly. Because they don't change. If you detect one color, it stays the same.
- liminvorous 6y agoI think you can only tell if it’s changed by measuring the thing and comparing the results with the other person.
- yetihehe 6y agoAFAIK you don't need to compare. It's like random number generator, but you have two complementary generators. When one generates 1, the other generates 0. You don't know what you will get next, but you know what was last and you know that other person got opposite number.
- 6y ago
- cbkeller 6y agoThis is fairly far from my field, but as I understand it, that would be a hidden variable interpretation of QM [1], and specifically in that analogy a local hidden variable theory. That's what Einstein himself wanted. There is a famous test, Bell's inequality [2], that specifically rules out local hidden variable interpretations of QM. Nonlocal hidden variable interpretations, such as De Broglie - Bohm theory [3], are potentially still on the table, however. It is somewhat ironic that Bell's theorem is sometimes presented in popular media as a general disproof of all hidden variable theories, in a context where locality is taken for granted -- because Bell himself seems to have been partial to nonlocal hidden variable theories. An article by the same Mermin mentioned in the OP is worth a read, on this subject [4]. [1] https://en.wikipedia.org/wiki/Hidden_variable_theory https://en.wikipedia.org/wiki/Hidden_variable_theory [2] https://en.wikipedia.org/wiki/Bell%27s_theorem https://en.wikipedia.org/wiki/Bell%27s_theorem [3] https://en.wikipedia.org/wiki/De_Broglie%E2%80%93Bohm_theory https://en.wikipedia.org/wiki/De_Broglie%E2%80%93Bohm_theory [4] https://cqi.inf.usi.ch/qic/Mermin1993.pdf https://cqi.inf.usi.ch/qic/Mermin1993.pdf
- flubert 6y agoAnyone know if anyone has followed up on Caroline Thompson's work after she passed away? "The Chaotic Ball: An Intuitive Analogy for EPR Experiments" https://arxiv.org/abs/quant-ph/9611037 https://arxiv.org/abs/quant-ph/9611037
- cbkeller 6y agoHaven't found anything yet myself, but would love to know -- that looks quite interesting!
- comedowntous 6y agoWikipedia's Simple English page on Bell's inequality actually has a nice overview of a simplified way of thinking about quantum entanglement: https://simple.wikipedia.org/wiki/Bell%27s_theorem https://simple.wikipedia.org/wiki/Bell%27s_theorem
- Toutouxc 6y agoThe way I understand it, this is exactly the simplified (and incorrect) explanation. Say SOMEONE ELSE puts the marbles in two envelopes and sends them to you and your friend in Australia. (it's someone else because we don't actually create the entangled particles, we just "get" them) The marbles being red and blue (or both red or both blue, depending on what you're measuring) from the beginning would be a LOCAL hidden variable. It's local because it's been predetermined at the moment of creation and the marbles carry the property on themselves and it's hidden because you don't know how/why the person putting the marbles in those envelopes decided those colors and you can't see them until you open the envelope (measure the particle). This way if you don't open your envelope, your friend's envelope contains a marble that's 50/50 red or blue and the color will be the predetermined one no matter what you do with your marble at home. So whatever decides the marble's color has nothing to do with your marble, it's local to the friend's one. The actual measurements work differently. It's been experimentally proven many times that at the moment you look at your marble, the other marble's 50/50 probability of being red and blue shifts substantially to, for example 75/25. And that's without it having any way of knowing that you've seen your marble. So there are hidden variables that we don't understand, but they're not local. They somehow affect both marbles. In real life there aren't only two colors and the probabilities aren't those nice numbers, but you get the principle.
- nojokes 6y agoCan you explain how is this shift in probability measured?
- GoblinSlayer 6y agoThe experiment is repeated many times, statistics is computed over results, and gives probabilities and correlation.
- tsian2 6y agoHow much work has been put into ensuring that the observed samples aren't biased?
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- ikken 6y agoIt's not my field, but I remember reading that your example doesn't represent entanglement because when put into envelopes, one marble is already red and another blue. In quantum entanglement they are both truly and really random until you measure one. And it's not random in a sense that you closed your eyes when putting them into envelope. They actually both don't have a "selected" color. They "snap into one of two colors" when you measure (look at) one. And the "unbelievable" thing is that when you measure one, the other one immediately snaps into opposite color, no matter how far it is.
- Koshkin 6y agoI don’t think this is correct. The two particle system is prepared in a perfectly known state (e.g. both spins up). There’s nothing random about it. Randomness only occurs at the measuring device, if it not aligned with the direction of the spin of the incoming particle.
- zkmon 6y agoNope. They don't "have" their own state until one of them is measured. But they do have a correlated state which exists before measurement, which says they have opposite/same states. The individual states arise only after measurement. I'm not a physicist, but wrote a Quantum Simulator.
- Tomminn 6y agoRoughly speaking: if you can see your marble through a purple filter, the one in Australia will turn out to be perfectly green.
- kgwgk 6y agoYou could have something similar to quantum entanglement if these were some strange kind of marbles which cannot have a well defined color and size at the same time and are magically linked. If you look at the marble you got and it's red (or blue) the size becomes indeterminate. Focusing now on the size you will find it's large or small, but the color becomes indeterminate. It could be red the next time you look at it. When you take your entangled marble, look at the color and see it's red you know the other marble is in the "blue" state (and the entanglement is broken). If someone looks at the color of that marble you know they will find it's blue. But if they look at the size before looking at the color it could be large or small (and looking now at the size of your marble will tell you nothing about it) and if they look at the color later it could be red or blue. In the classical case, if there is a large red marble in one envelope and a small blue marble in the other it doesn't matter in what order you look at the color and the size. You will always know what the other person found. In the quantum case, if both look at color first they will find complementary colors. If they both look at size first they will find complementary sizes. But the second measurement will be uncorrelated. And if they make the measurements in a different order, everything will be uncorrelated.
- haxiomic 6y agoSabine Hossenfelder gives the best explanation to address this that I've found https://www.youtube.com/watch?v=j6Mw3_tOcNI&ab_channel=SabineHossenfelder https://www.youtube.com/watch?v=j6Mw3_tOcNI&ab_channel=Sabin...
- rssoconnor 6y agoWelcome to Bell's Casino. You and your partner will be playing our famous two-coin game today. We have hidden two coins under these two opaque cups. You and your partner are to guess the orientation, heads or tails, of both of the coins. Guess correctly and win $1. Guess incorrectly and lose your $1 bet. In order to help you out, after you two have made your guess we are going to give you two a chance to back out and lose nothing. After your prediction we are going to reveal one coin to you and another coin to your partner. Together you and your partner will have an opportunity to back out, but the catch is that you two are not allowed to communicate! Instead of communicating, you can raise either a red flag or a green flag after seeing your coin. Similarly, your partner can raise either their red flag or their green flag after seeing their coin. If you both raise the same colour flag, the game keeps going and we see if you win or lose. If you both raise different colour flags, the game stops and you lose nothing. To ensure you don't cheat, we've separated you and your partner by 200 million kilometers and you have one minute to raise one of your flags after seeing your coin, otherwise you lose the game. (Alternatively you are your partner are separated by 400 meters and you have 100 nanoseconds to raise one of your flags.) Good luck. --- The above casino game cannot be beaten using envelopes of marbles, but it can be beaten (i.e. positive expected value) using envelopes of entangled particles. See quantum pseudo-telepathy.
- opaque 6y agoThis argument is called "Bertlmann's Socks" https://en.wikipedia.org/wiki/Reinhold_Bertlmann#Bertlmann%E2%80%99s_socks https://en.wikipedia.org/wiki/Reinhold_Bertlmann#Bertlmann%E... The other replies explain why it's wrong, but here's a link to Bell's refutation for good measure http://cds.cern.ch/record/142461/files/198009299.pdf http://cds.cern.ch/record/142461/files/198009299.pdf
- _8091149529 6y agoWhat seems to be missing from the replies posted so far is the notion of coherence, and the choice of measurement basis. What separates a coherent "quantum" superposition, say, |0> + |1>, from a probabilistic "non-quantum" 50:50 mixture is that I can choose a measurement basis in which the coherent state always yields a definite result, say "1", whereas measuring the mixed state always yields a 50:50 mixture of "0"s and "1"s. A continuous sweep of the angle of the measurement basis generally results in an interference pattern, the amplitude of which can be used to assess the fidelity of the quantum state. (I get paid to work on quantum communication and related experiments.)
- tim333 6y agoIf you do the experient with an entangled source and two Stern Gerlach detectors oriented the same way it's not so interesting a bit like the marbles in envelopes - either they both red of green. The interesting bit is if you rotate them a bit the correlation varies like cos(the angle) between them. So correlation 1 at 0 degrees, 0 at 90 degrees, -1 at 180 degrees and about 0.98 at 10 degrees. But how does nature or whatever know the angle between them when they are far apart? In most 'hidden variables' scenarios the correlation at 10 degrees is more like 0.89 or a linear change and that is basically the essence of Bell's theorem and experiments - you can't get the correlations without the particle at one end kind of knowing the set up at the other, or 'non locality' as Bell called it.
- kubanczyk 6y agoSo many confusing answers in this thread, but yours is clear and enlightening (and factually correct, afaik).
- stillsut 6y agoYour answer seems to focus on the key un-addressed subtlety. Why is the difference in orientation of the detector necessarily linear? What is the control aspect of this experiment where classical-system shows this linear pattern? Or can the argument be made more fundamentally?
- tim333 6y agoYou can think of an example where things are classical, the particles start with some definite orientation randomly determined at the start and if they are within say 45 degrees of the angle of the detector they go one way, over 45 the other and it's not so hard to figure in that case it will vary linearly. As to how to prove the general case I don't know. Try Bell's paper?
- tim333 6y agoAs an aside I don't think the classical 'hidden variables' situation has a prefered orientation which contradicts the premise of the featured article that you get the odd entanglement effects so as to not have a prefered orientation.
- wwarner 6y agoThe phenomenon is statistical. In your example (which is a bit too simple but still), the analogous surprise would be something like each party guesses what's in the envelope before they open it, and the accuracy of their guess is too high to explain by chance.