[HN Gopher] How Bell's Theorem proved 'spooky action at a distan... ___________________________________________________________________ How Bell's Theorem proved 'spooky action at a distance' is real Author : theafh Score : 163 points Date : 2021-07-20 14:43 UTC (8 hours ago) (HTM) web link (www.quantamagazine.org) (TXT) w3m dump (www.quantamagazine.org) | willyg123 wrote: | What is the prevailing theory to explain quantum entanglement? | Must there be another dimension we cannot access or measure that | is not subject to the laws of relativity? (I understand the laws | of relativity break down at the quantum level but please ELI5) | benbayard wrote: | I'd probably start here: https://youtu.be/ZuvK-od647c | gpsx wrote: | I think people get confused when they think that each object | has a wave function. This is not correct. The universe has one | wave function. The wave function consists of a bunch of | possible states along with the coefficient for each state. You | can think of each state as being a distinct snapshot of what | the universe might look like - including for example the | position and spin of each particle. In the example of two | electrons shown here, the wave function has non-zero | coefficients only for states where the two electron spins are | in opposite directions. | | When we make a measurement, the state of the universe appears | to collapse, meaning any state that is not consistent with that | measurement disappears. This means the other electron is left | in the opposite spin state. (Important aside here, some people | believe the wave function collapses, "Copenhagen | interpretation" and some people believe the wave function | doesn't change but the the brain of the observer | correlates/entangles with the electron, "Many Worlds | Interpretation". Either way there is an operational collapse of | the wave function.) | | A special case for a wave function is when the coefficients are | arranged so that state of one particle, say particle 1 spin, is | symmetric no matter what the state of another particle, | particle 2, is. This special case is when particles are NOT | entangled. | | (Edit: added paragraph on measurement) | gpsx wrote: | I want to add to my above comment. Non-entanglement is a | special mathematical case, but it happens quite often. If the | two particles never interact in any way, then the special | condition will be true and they will not be entangled. There | is another case where the particles _appear_ not to be | entangled. This is when the wave function is so jumbled that | even though the particles are entangled you can't detect it. | This is called a decoherence. This also happens quite often | and is why macroscopic quantities don't exhibit entanglement | and hence quantum behavior. | martincmartin wrote: | Quantum entanglement falls out of the quantum mechanics, so in | some sense, the prevailing theory to explain quantum | entanglement is quantum mechanics. | | Of course, it's unintuitive and unsettling, so you could | generate other theories about other dimensions if you like. But | as far as predicting the results of any experiments we can do, | QM is all you need. | | Also, there are two very different theories of relativity, the | special and the general. Special relativity is taught in 1st | year undergraduate physics, you really only need high school | math & physics, plus an open mind, to understand it. This has E | = mc^2, twin paradox, length contraction, time dilation, speed | of light as a limit. It's actually a pretty small topic, it | usually doesn't have a separate course because it wouldn't fill | a one semester course. QM is fully consistent with Special | Relativity. | | The other is general relativity, which revises gravity in light | of special relativity. This is a much bigger topic and | typically taught in grad school, although there are some | undergrad texts now that don't require math as advanced as the | grad school ones. QM and GR are incompatible, and the search | for a "quantum theory of gravity" is a key plank in any "theory | of everything." | martincmartin wrote: | It's easy to explore QM and SR, because it's easy to | accelerate fundamental particles to near the speed of light. | Here's a video from 1962 where electrons were accelerated, | they measure the time between passing two points (to get | speed), and heat energy deposited on a target (to get kinetic | energy) to show how SR works. Nothing QM specific, but shows | how easy it is to get quantum particles moving that fast, so | you can do experiments on them: | https://www.youtube.com/watch?v=B0BOpiMQXQA | | Combining gravity, which needs great mass, with QM, which | needs small space scales, is "hard" to do in a lab. | lisper wrote: | There isn't really an "explanation" for quantum entanglement. | It is a fundamental property of the universe, arguably _the_ | fundamental property of the universe. But the Right Way to | think about it IMHO is this: the quantum wave function is not | defined over physical space, it is defined over _configuration | space_. A wave function defined over physical space is a | special case that pertains when you are dealing with a system | consisting of a single particle, in which case physical space | and configuration space are the same. But as soon as you add a | second particle, this physical intuition breaks down. | | You might also want to read this: | | https://flownet.com/ron/QM.pdf | nimih wrote: | The prevailing theory that explains quantum entanglement is | precisely the theory of quantum mechanics, OP. If you're | genuinely curious, I strongly encourage you to obtain an | undergraduate degree in physics, which will equip you with the | mathematical and theoretical background to see how the one | explains the other. | qwerty456127 wrote: | How long is it going to take until we can have a near-zero- | latency Internet connection on Mars (e.g. on a Mars rover) or | Moon? | void_mint wrote: | At the speed of light, it would take between 4 minutes and 14 | minutes to travel between Mars and Earth. A quick google says | fiber optic cable can transfer data at roughly 70% of that | speed. It may not be possible to get the latency you're | describing. Mars is far away. | uh_uh wrote: | You can not use QM for faster-than-light communication: | https://en.wikipedia.org/wiki/No-communication_theorem | qwerty456127 wrote: | U.S. Department of Energy unveils blueprint for the quantum | internet: https://news.fnal.gov/2020/07/u-s-department-of- | energy-unvei... | | Fermilab and partners achieve sustained, high-fidelity | quantum teleportation: | https://news.fnal.gov/2020/12/fermilab-and-partners- | achieve-... | Zamicol wrote: | If you "measure" the bits per character in the base 45 | alphanumeric encoding used in QR code, you'd get 5.5 bits per | character as 11 bits is used for two characters. | | How is it possible to have information less than a bit, a partial | bit? What is that ".5" part? Isn't a bit indivisible? | | Only in the context of a character doublet is all information | expressed. To know the "half bit" part, you cannot "look" at just | one character, you have to look at the total. The information is | shared between the two characters. Measuring the bits-per- | character is only useful when considering the whole system. The | "partial bits" is information smeared across the system. Changing | the middle bit may change one, or both, characters. | | Here's a 11 bit example, where the middle bit is changed and it | changes both characters: (11101001010 vs 11101101010, or '/L' vs | '%8' encoded) | | https://convert.zamicol.com/?in=11101001010&inAlpha=01&outAl... | | https://convert.zamicol.com/?in=11101101010&inAlpha=01&outAl... | | vs changing the last bit only changes the last character: (Using | the preceding example, 11101101010 vs 11101101011, or '%8' vs | '%9' encoded) | | https://convert.zamicol.com/?in=11101101011&inAlpha=01&outAl... | | The same principle applies to information theory and | cryptography. Security can be measured in "partial bits" because | it's measured across something larger. | jdb1729 wrote: | 5.5 bits is also the average information content of a single | run of the GHZ experiment. In this setup three parties | independently choose a binary detector setting and each observe | a binary outcome. The first two parties observe an independent | random bit regardless of their settings. If an odd number of | the parties have their setting "on", then the third party also | observes an independently random bit (6 bits total to record, 3 | for the settings and 3 for the observations). But if an even | number of of the three settings are "on", then the third | party's observation is completely determined by the other 5 | bits. When the settings are chosen randomly these two | possibilities are equally likely so on average it takes 5.5 | bits to record the results of the experiment. | dQw4w9WgXcQ wrote: | Or Superdeterminism is true: | https://en.wikipedia.org/wiki/Superdeterminism | moedersmooiste wrote: | I'm no expert but I also lean toward superdeterminism. It's | either that or the universe is not deterministic at all. | Believing that the universe is only partly deterministic is the | same as believing someone can be partly pregnant. | nobodyandproud wrote: | Those objections to super determinism seem weak, or more along | the lines of "I don't like the implications, so I won't | consider it." | | Genuine question: Would quantum computers work in any | deterministic framework? | themgt wrote: | I've quoted it before but I will again just because I hate | superdeterminism so much: | | _First, the logical flow: Bell's theorem proves that no | local, realistic theory can reproduce the predictions of | quantum mechanics. It does so by considering a very specific | situation of entangled particles being measured by spin | detectors set at different angles. Critically, the angles of | these spin detectors are assumed to be set independently from | one another. ..._ | | _Experimenters have tried to ensure independence for all | practical purposes with elaborate techniques: independent | quasi-random number generators running with different | algorithms on different computers are one very basic example. | On more advanced experiments, they use quantum sources of | randomness, and try to make sure that the choice is only made | once the particles are in flight._ | | _The trouble is that in principle, there will always be a | point in the past at which mechanism used for the angle | choice, and the mechanism used to produce the entangled | particles were in causal contact with one another. (If all | else fails, then the early universe will provide such a | point.) The super-determination thesis says that any past | causal contact can in principle provide correlation between | the settings of the two detectors (or the detectors and the | properties of the particles), and is the source of the | violation of Bell's inequality._ | | _Here's a deliberately ridiculous example. Once the | particles are in flight, I throw in the air a box of Newton's | notes on alchemy. I select the one that falls closest to my | feet. I roll two dice, and use them to select a random word | from that page. I match the word with its closest equivalent | in Caesar's commentary on the Gallic wars, or the Iliad, or | the complete works of Dickens, my choice of work depending on | the orientation of the Crab pulsar at the moment of | measurement. I use the word position in these works to select | a number in this book A Million Random Digits (take the time | to read the customer reviews). And I use this number to set | my detectors. I repeat this for my other measurement runs, | but I substitute in Dan Brown's Da Vinci Code for Dickens | every third go._ | | _Superdetermination advocates would tell me that there is in | principle a causal connection between my throwing the papers | in the air, Newton, Caesar, Dickens as they sat down to write | 300, 2000, and 150 years ago, the Crab pulsar and the RAND | corporation's random digit selection. And that it's possible | that these things have conspired (unknowingly) to make sure | that my detector settings and a particle's spin measurement | is correlated in a particular way in my lab in a law-like | way._ | | _I can only reply that yes, it's possible. I cannot prove it | wrong. But I can find it unreasonable. And I would be tempted | to call these people philosophically desperate._ | | https://www.quora.com/Why-do-some-crackpot-scientists-go- | aft... | dane-pgp wrote: | > I would be tempted to call these people philosophically | desperate. | | Wouldn't it be equally valid to say that the Quora | commenter is philosophically desperate to avoid the natural | conclusion that there is an entity that is able to | influence the actions of Newton and Caesar etc. and the | commenter themselves? | mnowicki wrote: | Is it reasonable to say the universe might be | superdeterministic, but in the example of choosing | measurements for an experiment(or almost any other example | imaginable), it might as well be truly random as the causal | links affecting the instruments isn't likely to be | 'conspiring' in some way to impact the results of the | experiment? | | e.g Anything could be predicted with absolute knowledge of | the starting state of the universe, and infinite computing | power, but in most practical cases the causal connections | between seemingly unrelated objects is irrelevant and as | good as random? | sebzim4500 wrote: | I think it stops being science at that point though. For | example, if someone made a quantum computer powerful | enough to factorise large numbers then that would appear | to disprove superdeterminism. However, proponents could | always argue that the computer only works because the | universe conspires to make the human entering in the | numbers to be factorized enter specific values which the | computer will then know the factors of. | | I'm not a physicist though, so I might have something | wrong here. | AnimalMuppet wrote: | > I can only reply that yes, it's possible. I cannot prove | it wrong. But I can find it unreasonable. And I would be | tempted to call these people philosophically desperate. | | I'd be tempted to call those people closet theists who are | in denial, but maybe you're more polite than I am. | | What I mean is that they have something in their system | that is playing a god-like role, but they're "scientific", | so it can't be God. | | By the way, I would say the same about the "universe is a | simulation" people. | naasking wrote: | > And that it's possible that these things have conspired | (unknowingly) to make sure that my detector settings and a | particle's spin measurement is correlated in a particular | way in my lab in a law-like way. | | Yes exactly, which is to say that your instrument | calibration dicated by that elaborate randomization | process, just ensures that the particle will arrive in a | specific configuration, which is a purely local, realistic | phenomenon. | | Sabine and Palmer recently explained how superdeterminism | can be understood easily as future input dependence: | | https://www.frontiersin.org/articles/10.3389/fphy.2020.0013 | 9... | | Edit: despite superdeterminism annoying you so much, I bet | you're perfectly fine with general relativity in which time | is just another space-like coordinate, and the correlation | you describe is a perfectly well-defined path along a | closed timelike curve. An interesting inconsistency if | true. | latenightcoding wrote: | Gerard 't Hooft believes we would still have quantum | computers faster than classical computers in a | superdeterministic universe. However, the speedups would be | more modest and factoring huge numbers in poly time would be | out of the question | moedersmooiste wrote: | Unless you could build a classical computer on the Planck | scale. | wyager wrote: | MWI allows you to have entanglement without "spooky action at a | distance". However, it requires exponential blowup in | representational complexity of the universe, which also feels | aesthetically displeasing. | choeger wrote: | Does the article do justice to the hidden variables hypothesis? | | In case of the hidden variables, the spin is a (3-dimensional?) | value that is identified by the measurement result. In case of | quantum theory we have have a probability distribution. How is | that probability distribution different from a hidden variables, | except that it's not a straight number but a function instead? | | Speaking as a programmer, is the difference between hidden | variables and quantum mechanics that the former postulate a real- | valued property whereas the latter speak of something like a | monad? | subroutine wrote: | I believe the QM interpretation is that probability | distributions are to be taken literally - a flipped coin under | a napkin is both heads and tails with P=.5 | | Hidden variables on the other hand acknowledges the | probability, but contends nevertheless that the coin is | actually in a specific but unknown state. | 6gvONxR4sf7o wrote: | Speaking as a lay person, I think the difference might be that | it's specifically about _local_ hidden variables. If two | particles are coupled, there 's no _per-particle_ hidden | variable? | 6gvONxR4sf7o wrote: | edit-too-late-to-edit: I remember I think it's actually more | complicated. | | If I write 0 and 1 on two different pieces of paper, then | flip a coin to decide which paper to give you, we have | "entangled" unknowns. When I reveal my paper, we instantly | know what's on yours. The joint distribution can't be | described per-particle, but we don't consider it spooky. So I | think there's something more to it. | blueplanet200 wrote: | I think Einstein would've considered nonlocal hidden variables | the same as spooky action at a distance. | | >How is that probability distribution different from a hidden | variables, except that it's not a straight number but a | function instead? | | Because for entangled particles (separated by a large distance! | but also any entangled particle) their PDFs will be correlated | in a way that is impossible to define for just a single | particle. This makes physicists uncomfortable because of | relativity and things happening faster than light. | nsxwolf wrote: | I'll never understand entanglement. Every explanation makes me | wonder why it can't be used to instantaneously send a message. I | never fully understand the explanations why it can't be used to | do so. I don't understand how you can be sure about the state of | the other particle, what if someone already measured it and then | did something to it? | snissn wrote: | Two balls are a box. Neither are spinning. The box gets "shaken | up" and the balls hit each other. We know that one ball is | spinning clockwise and the other is counter clockwise because | angular momentum spin is conserved. The balls launch far away | from each other. We know the spin is entangled in that one is | clock wise the other is counter clockwise but we don't know | which is which until we measure. How do we use that to | communicate? | ende wrote: | By constraining all your communications to a game of | interstellar rock paper scissors? | alisonkisk wrote: | that doesn't communicate across the distance. that | communicates from the common starting point | stevenjgarner wrote: | Or even better than instantaneously, let's get messages sent to | us from the future using a Ronald Lawrence Mallett time machine | based on a ring laser's properties, such that at sufficient | energies, the circulating laser might produce not just frame- | dragging but also closed timelike curves (CTC), allowing time | travel into the past. I cannot believe that Ronald Mallett's | biggest challenge is getting funding for a feasibility test. | Isn't it the greatest venture capital opportunity of all time? | PavleMiha wrote: | Can't say I have perfect intuition on it either, but the closes | I've gotten was by reading this book: | https://www.qisforquantum.org | codezero wrote: | It's easy to understand (I'm being a bit hyperbolic) if you can | believe that space and time are emergent properties of matter | and not required for the underlying physics. | wwarner wrote: | Not a physicist, but my answer to you is that usually | superliminal speeds is the price that physicists are willing to | pay to explain what is observed in experiment. I get your | objection to the rather convoluted argument that special | relativity still applies to message transfer, but I accept it. | John Preskill explains the information within entanglement with | an analogy to a book. Normally with a book, you can read one | page seperately from all the other pages. Further, if you | unbound the book, and randomly distributed the pages to your | friends, you could put your heads together and reconstruct the | entire book. With a "quantum book", the information is encoded | in the correlations between the observables, and you can only | see the information when all the pages of the book are together | and in the correct order. If you look at a single page of the | quantum book, it's purely random gibberish, and you can't | derive anything about the book by looking at a part of it. | simonh wrote: | It can't be used to send a message because all you can do is | measure your particle. Even if doing so changes the state of | the other particle far away (which isn't really what's | happening, but that doesn't matter), all the other person at | the end can do is measure their particle. | | Neither of you can choose what the state of either particle is. | You have no control, so there's no way to transmit information. | | What you can do is agree in advance that you will both take | certain actions based on the measured state of the particles. | There's no way to be sure the person at the other end actually | does so though. | ende wrote: | I now have to imagine that Quantum Game Theory is a thing | that exists. | ethn wrote: | Look up how entanglement is done experimentally. It will always | involve a technology which can be used to classically transmit | information at a distance. | | What happens in entanglement is that the two entangled objects | receive say an entangled photon, it is at this point where the | two objects are entangled. | | Entanglement is a dance of the statistical limits and position | of a particle/object given a specific space/energy | configuration (initial condition). From this we know the | probability of where it can be, what states it can assume, and | the limits of both--given the energy it takes to traverse space | and assume those states at once. | | They are entangled because once information of the states of | one of the entangled objects is measured (mainly by analyzing | the exiting photon), we can apodictically discern the state of | the other. | 725686 wrote: | Funny, I never understood how you could possibly send a message | using entanglement. Try to explain how would you do it, and | either you will understand why it can't be done... or earn a | Nobel prize. Win-Win. | guyomes wrote: | I find that this article [0] from Conway and Kochen is helpful. | The authors do not really explain the paradoxes of quantum | mechanics. Instead they reduce them to minimal fundamental | axioms that have been tested and observed experimentally, even | though they are arguably highly counter-intuitive (notably SPIN | and TWIN). Based on those axioms, the authors show that you | cannot send a message through entanglement. More precisely, | they show that a particle has a free will, in the sense that | the result of a measurement on it "is not a function of | properties of that part of the universe that is earlier than | this response". | | [0]: https://www.ams.org/notices/200902/rtx090200226p.pdf | superposeur wrote: | > how you can be sure about the state of the other particle, | what if someone already measured it and then did something to | it? | | Indeed, you are only sure about the state of the other particle | in the instant just after they measured it. Whoever measures | first instantly destroys the entanglement link, so if they | chose to manipulate the particle after measurement, you will | have no knowledge of these manipulations. | | More generally, note that in quantum mechanics "reading" the | state of a particle (i.e. performing a measurement) is | drastically different than "writing" information by | manipulating a particle. Most entanglement-related weirdness | hinges on this fundamental asymmetry between "read" and "write" | operations for quantum information. | naasking wrote: | > I'll never understand entanglement. Every explanation makes | me wonder why it can't be used to instantaneously send a | message. | | Say you and Bob share a bunch of entangled particles. Bob wants | to send you a message using those particles, so he takes one | particle at a time and encodes his information. How would you | know he did so? At the very least, Bob would still have to send | you a classical signal to say he did something. | | There are more subtle arguments why this doesn't work even at | the particle level, but that at least should give you an idea | why superluminal communication won't work. | axelf4 wrote: | Maybe this video by Veritasium could help: | https://www.youtube.com/watch?v=kTXTPe3wahc | sergiotapia wrote: | Reminds me of the in-lore comms system in Mass Effect. I think | the comms in the ship were two atoms that were entangled, | allowing instant messages no matter how many lightyears away | the ship was from Earth. | [deleted] | blueplanet200 wrote: | You can measure a particle's spin to be up or down. But you | can't choose to measure it to be up. It's random and up to | nature. This is exactly why it can't be used to send | information. | abetusk wrote: | Let's say particles have a 'direction angle' that we can | measure with a detector that only gives 'up' or 'down' relative | to a direction angle measurement. We can change this direction | angle measurement with a knob to set what the measured 'up' and | 'down' answers are relative to the detector's direction angle. | Further let's say particles can be quantum entangled so that | when when two detectors are placed very far apart, many light | years apart, say, and measure a quantum entangled pair of | particles. | | When the two detectors are set to the same, but arbitrary, | angle, the detectors give the same answer. This is normal | correlation. Quantum correlation says that as one dial moves | away from the other reference point, the correlation falls off | as a sine wave, not a linear decrease as would be expected by | classic probability. | | To see how bonkers this is, do the following experiment: | | Set detector X to be at angle 0 and detector Y to give a 1% | error rate. Call that 1% angle 'a'. So a sample experiment run | might be: X(0): 0001000101001110...111010 | Y(a): 0011000101001110...111010 | | In the above, 1 could be an 'up' and 0 could be a 'down' | detection, say. For concreteness, let's just say A and B ran | 100 detections and there was one difference between them | (giving 1% error), represented by the third differing bit in | the above. | | Now let let's change both X and Y by the same angle so the | relative error rate between them is still 1%, this might give | something like: X(a): | 0011000001001110...111010 Y(2a): | 0011000101001110...111010 | | X and Y still have one difference in the above, but now with | the 8th position changed. So far this is nothing unexpected | from classical probability. | | Now, we know that from X(0) to Y(a) there's one change, from | X(a) to Y(2a) there's one change. Classic probability says that | there can be at most two flipped bits from X(0) to Y(2a). | Quantum mechanics predicts three. | | To convince yourself, try making a list of bits such that | there's one difference between X(0) and Y(a), one difference | between X(a) and Y(2a) but _three_ differences from X(0) to | Y(2a). It 's impossible and this is the heart of Bell's | theorem. | | Bell's theorem is a classical probability statement, | generalized from my above statement that if |X(0)-Y(a)|=1, | |X(a)-Y(2a)|=1 then |X(0)-Y(2a)|<=2. Quantum entanglement | violates Bell's inequality. | | The 0 reference point has to be arbitrary (in the above it | should really be X(ref_angle + a), Y(ref_angle + 2a), etc.) and | you have to assume no faster than light communication (that is, | independence) to get the contradiction. There are some further | subtleties with the above argument but hopefully that's | intuitive enough to follow why quantum entanglement is so | counter intuitive. | | EDIT: corrected X(a) bit string | abetusk wrote: | I see, I actually answered the wrong question, sorry about | that. | | I'm also a bit confused by why it can't be used to send | information but here's a try: | | In the above scenario, if the particle (pair) has completely | random spin, one that can only be observed by detection and | not by some sort of construction, then each observer sees a | completely random bit, regardless of whether it gets | "flipped" by the "non-local" observation/communication of the | other particle. They'll only be able to discover the | correlation after the fact, if they compare notes and thus | have to meet up, destroying any non-local benefit. | | Put another way, if you have a bit with probability p of | being 1 ((1-p) of being 0) that you're communicating over the | wire but the wire is so noisy as to flip it with probability | 1/2, then you won't be able to recover what the transmitted | information was. | | You'll be able to discover the correlation between the bits | if you compare notes after the fact but since the "wire" acts | as a completely noisy channel, you can't recover the | transmitted bit. | mmaroti wrote: | I think you need more assumptions. This satisfies your | requirements: | | X(0) = 0000, Y(a) = 0001, X(a) = 0011, Y(2a)= 0111. | abetusk wrote: | |X(0) - X(a)| = 2, not 1 and X(a) != Y(a) | | The subtler issue is that it's a counterfactual question. | What would have happened if I had measured or been able to | measure all three angles 0, a, 2a? In this case the bit | string is the same except for the 1% difference. In other | words, X(t) = Y(t), for all t. | | The argument is essentially trying to construct a "hidden | variable" model and showing that it can't work. | misiti3780 wrote: | This book elucidates the concepts well: | | https://en.wikipedia.org/wiki/Something_Deeply_Hidden | hintymad wrote: | It's as if the universe is a simulation in a gigantic computer. | We get entanglement because particles are aliases of the same | pointer. | | edit: I didn't mean it as an explanation of entanglement. Just | thought it was a convenient joke. | drcode wrote: | Imagine you have a pouch with a red and a blue marble in it, | then take out a marble without looking at it and hand the pouch | to a friend. Later, if you look at your marble, you instantly | have information about the other marble at a speed greater than | the speed of light... but you couldn't use that fact to send a | message. | | The only difference in quantum physics is that there are | actually two parallel universes: One in which you took out the | red marble & one in which you took the blue one. You don't know | what universe you're in until you look at the marble, but still | it doesn't help you to transmit a message to your friend. | | (This is assuming the "multiple universes" interpretation- In | the other interpretations there is "spooky action at a | distance", but this action happens in EXACTLY THE RIGHT WAY to | prevent you from transmitting a message to your friend) | zby wrote: | This marble setup is a 'hidden variable' theory - the article | is how quantum is different from that. | joe_the_user wrote: | Your discussion is inherently within the classical realm and | so it doesn't explain the uniqueness of quantum phenomena. | You easily have "classical many worlds" where unknown | information makes a model "split" and gaining the information | decides which split you get. That's still not quantum in | particular. | abetusk wrote: | This is incorrect. What you've described is classical | correlation, not quantum correlation. | dkersten wrote: | Would this be correct: | | You take a marble out of the bag without looking and give | the bag to your friend. Your friend also take a marble out | of the bag without looking. Both you and your friend now | look at your marbles and they will both be the same colour | every time. | | You can't send information this way because you don't know | the colour until your friend has already taken a marble | too. You cannot do anything with the fact that they are | both the same colour unless you can control or know the | colour in advance, which you can't. When you look at your | marble and see that its red, your friend looks at their | marble and sees that its red, all you know is you both have | red marbles. | | The only way to send information would be if you took | multiple marbles, looked at them until you found one that's | blue (say, the third) and then told your friend to look at | the third marble. But since you can't tell your friend to | do that without using traditional information sending, you | may as well just tell them that the third marble is blue | and forego the marbles altogether, you're not sending | faster than light information anymore anyway. | abetusk wrote: | This is, as stated, again classical correlation. Where | have you used the fact that the observation of one marble | affects the observation of the other? | | Your above experiment could be done with just a simple | bag and two marbles without the need to contort yourself | around looking or not looking. | | Here's an attempt to fix your example: | | You and your friend each take a marble out of the bag, go | very far away from each other and make an agreement to | look at the marble at a given time in the future and not | before or after. If you look at the marble before or | after the agreed upon time, the result will be random. If | you both look at it at the exact same time, the marbles | will be equal. | | Maybe you have many bags of marbles so you can do this | experiment many times over. You decide to fudge some | results by looking at some marbles before or after the | agreed up time. You and your friend will see the same | marble color for all marbles seen at the agreed upon time | and potentially different marble colors for ones that | were opened at different times. | | How do you tell if your friend fudged the result? How | does your friend tell if you fudged the result? The | marbles have a 50-50 distribution of being red and blue, | and the extra probability of it flipping to one color or | no if it's fudged is lost in that noise. | | If you then reconvene and compare notes on what you | observed, you can see a very clear correlation of which | experiments were fudged and which weren't but now you've | done the work of getting in close proximity and destroyed | any chance of faster than light communication. | | I'm not a physicist and I don't have a deep knowledge of | this stuff. This is a toy example and may or may not be a | valid reduction of quantum entanglement. The above | explanation is my current understanding, which could be | wrong. | gpsx wrote: | I think your analogy works for both many worlds and | Copenhagen. You can view each universe in your analogy as | states in the wave function. The two interpretations diverge | only when the "observation" occurs. In the Copanhagen | interpretation the other universe disappears. In the many | worlds interpretation they both remain. | TheOtherHobbes wrote: | The only difference is that in QM the marbles don't really | exist until you look at them. | | Somehow they still manage to align themselves so if one | person sees red the other sees blue. | | Although it's even more accurate to say that if one person | sees [colour] the other person sees [opposite colour]. | | The colours are random, but the relationship between them is | fixed. | | Very crudely (and rather misleadingly but never mind) this is | why you can't communicate at FTL. | | _You need the other marble_ to know whether you had [colour] | or [opposite colour]. And that info can 't travel faster than | the speed of light. | | It's even more accurate to say there are no marbles anywhere | - only interaction events between marble objects and people- | looking-at-marble objects, and the API does not allow you to | look inside either to see state. | | (The state has to exist _somewhere_ otherwise none of this | would work. But Bell proves it 's not inside the marbles. So | it's "non-local" which is code for "we have no idea where it | is".) | morpheos137 wrote: | >we have no idea where it is. | | It is probably encoded in the cosmic horizon a la Green's | Theorem. | AnimalMuppet wrote: | You're giving "probably" quite a workout there. | | For it to be encoded at the cosmic horizon, it has to | communicate with the cosmic horizon. It's hard to see it | doing so, within the time frame of the experiments, | without superluminal communication. | tinus_hn wrote: | Also you could look up some other, related quality instead | and the result on the other side would still be the reverse. | This cannot be explained using some hidden variable in the | particles (like the color of your marbles), so it requires an | action to happen in the distant particle dependent on which | quality you chose to look up in the local particle. | danbruc wrote: | _The only difference in quantum physics is that there are | actually two parallel universes: One in which you took out | the red marble & one in which you took the blue one. You | don't know what universe you're in until you look at the | marble, but still it doesn't help you to transmit a message | to your friend._ | | I don't think it is helpful to talk about multiple universes, | that makes a strong implication towards a many world | interpretation. It is better to say that the difference is | that in the classical case the decision who gets which marble | happens when one of the marbles is taken out of the pouch | while in the case of entanglement we do not really know when | the decision happens but it does provably work differently | than in the classical case. It might be that the decision is | never truly made, that both outcomes happen in two parallel | worlds, it might be that the decision is only made when one | party inspects their marble, it might be that it happens at | the same time as in the classical example, ...we don't know. | fnord77 wrote: | in this example, what evidence is there that it works | differently than in the classical case? | ammon wrote: | That's exactly what the article we're all commenting on | is about! | joe_the_user wrote: | _I don 't think it is helpful to talk about multiple | universes, that makes a strong implication towards a many | world interpretation._ | | You're correct but the point is "many worlds" or Copenhagen | interpretation _having no implications_ , they each | describe the same mathematical/experimental results. | They're just "ways to think about the results". They matter | as much as whether you label the axes of a graph x and y or | A and B. So any theory that "requires" many worlds is | inherently not looking using the standard interpretation of | many worlds and quantum mechanics. | danbruc wrote: | Even if they have no observable differences, they still | make different metaphysical claims. If I see | Schrodinger's cat alive, many world claims that there | actually also exists a dead cat while Copenhagen claims | that there is only one alive cat. You may argue that the | differences are irrelevant for all practical purposes but | you don't get to claim that there are no differences | between different interpretations. | joe_the_user wrote: | _You may argue that the differences are irrelevant for | all practical purposes but you don 't get to claim that | there are no differences between different | interpretations._ | | It depends what one considers "significant differences". | If I go from caring about the practical implications of | an interpretation to some other implications, I could | make all sorts of distinctions. Explanation X might be | written in French and explanation Y might be written in | Spanish. Even if one is a translation of the other, you | could say they're different in various ways. Or maybe one | explanation contains swear words and makes the reader | feel bad and so the reader might not "like" that | explanation. | | But my point above is more specific. Since the two | interpretations have the same practical implications, a | practical prediction can't really "need" one | interpretation - the other _interpretation_ gives you the | result. This is the point about all the hidden objects | /states explanations have classical analogues. | | And if we're getting metaphysical, Copenhagen doesn't say | live cat or dead cat but says superimposed state. | danbruc wrote: | If you are only worried about analyzing a specific | quantum system, then yes, for most part the | interpretation does probably not matter. But I think in | general the differences are very important, especially as | we do not understand quantum mechanics and different | interpretations will direct future research in different | directions. If you believe in Copenhagen, you will try to | figure out how to reconcile unitary evolution with wave | function collapse. If you believe in Bohmian mechanics, | you will think about the quantum equilibrium hypothesis. | If you believe in many worlds, you might be thinking | about energy conservation. | tbabb wrote: | > that makes a strong implication towards a many world | interpretation | | You say that like it's a shortcoming. :) | | There are many who take the (very reasonable) position that | the many worlds interpretation is the most | epistemologically parsimonious one. Contrary to some | misunderstandings of it, it doesn't "add" extra worlds; it | _removes_ the concept of "wave function collapse", and | leaves all the other known laws of quantum mechanics | completely unchanged. The "worlds" arise naturally as more | and more particles in the environment become entangled with | the measured system, and "wave function collapse" turns out | to be the predicted observation of an observer who is | themselves made out of quantum states. | | The _only_ difference between many worlds and the | "standard" Copenhagen interpretation is that Copenhagen | _adds_ that, at some point, the entanglement process stops, | and a bunch of states in the wave function disappear. And | it doesn 't specify how, or why, or how to calculate when | it will happen. Those that advocate for many worlds would | point out that this extra epistemological burden is | questionable, given that the correct prediction is made | without it. | feoren wrote: | My understanding is that "Wave function collapse" is an | artifact of _one_ of the many possible ways of describing | quantum mechanics mathematically. There 's really nothing | to remove, is there? | dragonwriter wrote: | > My understanding is that "Wave function collapse" is an | artifact of one of the many possible ways of describing | quantum mechanics mathematically. | | The contention seems to be that the Copenhagen | interpretation elevates wave function collapse from | mathematical artifact to real phenomenon. | feoren wrote: | Sure, but the Copenhagen interpretation is basically | rejected as absurdist and is unnecessary for the exact | same reason. It's also trying to give a physical | explanation for an artifact of _one_ of the many | mathematical representations of quantum mechanics. | Schrodinger 's Cat is a reductio ad-absurditum to | _disprove_ the Copenhagen interpretation! | danbruc wrote: | _Contrary to some misunderstandings of it, it doesn 't | "add" extra worlds; it removes the concept of "wave | function collapse", and leaves all the other known laws | of quantum mechanics completely unchanged._ | | Yes, it gets rid of the collapse postulate, but no, it | actually introduces many worlds. You can wiggle a bit | around, claim that prior to the wave function collapse | there are also many worlds in Copenhagen or whatnot, but | in the end many worlds makes a metaphysical claim that | two cats exist, one dead, one alive while Copenhagen | claims only one cat exists in the end. | tbabb wrote: | _it actually introduces many worlds_ | | No, this is the misunderstanding that I'm talking about. | | The extra "worlds" follow directly and exclusively from | the existence of the various basis states in a wave | function, and the laws of entanglement. No other | postulates are needed. | | Before the measurement/entanglement, the system and | environment are independent, and can be written (|0> + | |1>) [?] (|0> + |1>). After the entanglement, the wave | function of the universe can no longer be factored that | way, and the system and environment are in a joint state | of |00> + |11>. The |00> and the |11> are the multiple | "worlds", they show up-- in both interpretations-- | whether you want them to be there or not. | | Copenhagen doesn't want them to be there, so it says that | one of the |00> or |11> goes away... at some point... | because [waves hands and mumbles]. Many worlds merely | declines to do this, and that is legitimately the only | difference between the two. | danbruc wrote: | _The extra "worlds" follow directly and exclusively from | the existence of the various basis states in a wave | function, and the laws of entanglement. No other | postulates are needed._ | | The many worlds are in the entangled state but then the | collapse postulate reduces them to one world. If you | remove the collapse postulate you put them back in. And | sure, the collapse postulate is an awful solution | breaking unitary evolution and you have every right to | reject it, but that does not change the fact that many | world introduces - or at least not removes - additional | worlds that are not there in Copenhagen. | tbabb wrote: | The distinction between "adding" and "removing" a | postulate is an important, non-arbitrary one. | | The "worlds" are there in _both_ theories; Copenhagen | adds a new phenomenon (non-unitary evolution) which makes | some of them disappear at unspecified times. The | "worlds" are direct consequences of suppositions _shared | with Copenhagen_. | | Many worlds has N postulates, Copenhagen has no fewer | than N+1. One theory is a _strict subset_ of the other 's | premises. It is not at all accurate to say that many | worlds is the one that "introduces" suppositions. | narrator wrote: | Or, in the transactional interpretation, the other guy's | marble sends a signal from the future back to your marble | to change its color when you look at it. | 0majors wrote: | That's not quite correct. There are no good analogies between | classical objects like marbles or socks and entanglement. | | In fact, Bell's inequality was stated as a collaboration game | that can only succeed if you use entangled particles. No | classical object will get you the same results. | | You still can't communicate faster than light but the reason | is more subtle. The article does a good job but for a deeper | explanation I'd refer to Sean Carrol: | https://youtu.be/yZ1KSJbJAng | Retric wrote: | All analogies are flawed because the underlying reality is | different. They can still be useful if they can communicate | some more abstract idea. | | An analogy I like for entanglement is to picture two atoms | that will both decay at the same time. You could place them | on other sides of the planet and until one is observed to | decay nobody learns anything because the timing is | unpredictable. After the observation people agree with that | timing independent of distance but can't communicate | anything because the timing was random. Still, having two | people both knowing some fact at the same time which can't | be observed by outsiders is a useful in it's own way. | | What I like about this is it's clear what's going on is | different from what's being described, it's describing a | property of something, and it separates information from | communication. On the other hand it's got plenty of it's | own problems. | 0majors wrote: | The problem with that analogy is it gives an illusion of | understanding while being completely misleading about | what Bell's inequality actually tells us about nature. | | The whole point of Bell's inequality is that quantum | entanglement is fundamentally different than classical | correlation between two objects which have some opposite | properties the observer simply does not know about before | observing one of them. | | It's not helpful to use an analogy which teaches the | reader the exact opposite of the point you are trying to | make. | | Your example with decaying atoms suffers from the same | misunderstanding. Quantum entanglement is not about lack | of information about some specific states, if that was | the case, why would anyone talk about loss of locality? | | Understanding entanglement and Bell's inequality requires | a completely different ontology than your everyday | experience with classical objects. I highly recommend the | video I linked above for an approachable explanation. It | is not as simple as these analogies but at least it gets | to the actual point of this result which tells us | something profound about how nature works. | Retric wrote: | No so fast, Bell's inequality only invalidates local | hidden variables. It's your interpretation that's | suggesting some local variable like a ticking clock was | determining when those atoms would decay, but that's not | part of the analogy. | | The many worlds interpretation is analogous to global | hidden variables, and while out of favor, perfectly | consistent with modern physics. That said, the core issue | is IMO only a one dimensional property was correlated | which hides a lot of the oddities involved. | normac2 wrote: | You describe that as an analogy, but I always took that | to be what it actually _is_ (or at least one very simple | example). Are you saying that that is how we interpret | our experience intuitively, but we need a more radical | account under the various mainstream interpretations of | quantum physics (Many Worlds, Copenhagen, etc.)? | 0majors wrote: | That's right. Not only it's an analogy, it is also a bad | one and completely misleading, at least according to | physics of the last 50 years. Note how the article frets | about the loss of locality. | normac2 wrote: | Hmn. Is that at least what we _experience_ if we try it | as an experiment (even if the underlying physics is quite | different than what it seems)? | Retric wrote: | The only thing we experience from preforming at an | experiment is the data it provides. As such from the data | from existing experiments is where all the _spooky action | at a distance_ is actually observed. | | https://en.wikipedia.org/wiki/Bell_test | tbabb wrote: | I don't think this criticism is correct, at least in | response to what was said. | | Yes, a classical bag containing classical balls doesn't | reproduce quantum behavior, because of Bell's theorem. But | GP's description isn't classical; it explicitly invokes | multiple universes. Once you've done that, quantum behavior | is reproducible, because (just as Bell's theorem says) it's | no longer possible to ascribe a single hidden state to the | ball/bag system, because you can't eliminate the extra | universes. | morpheos137 wrote: | Personally I prefer the superdeterminism arguement: i.e. the | state of every "future" entanglement was already set "before" | the big bang. The anthropocentric corollary is that "free | will" is an illusion. | mensetmanusman wrote: | The universe seems to have surely went to great lengths to | trick its own atoms into believing they have free will. :) | bronzeage wrote: | Or maybe you give too much power to free will. Could a | Maxwells demon pick the correct timing to close/open the | door just by his power of free will? If your answer is | yes, then free will can break the second law of | thermodynamics. If your answer is no, I will ask, what | about in a single small period of time? What is stopping | the agent with free will from opening the door then? | | I think the same thing prevents Maxwell's demon and a | bell observer from having "too much free will", and that | thinking of free will in terms of single point in time | decisions is also wrong for similar reasons. | morpheos137 wrote: | I don't know what you mean. The number of atoms involved | in the free will delusion is infintesimal compared to the | number of atoms in the universe. | | Number of atoms in 8 billion human brains: | | about 10^35 | | number of atoms in the universe | | about 10^82 | | according to search results. | | Maybe there are no aliens but homo sapiens are just the | first stage of the universe becoming self aware. | fnord77 wrote: | this seems a little fast and loose. you already had the | information the instant you picked the marble, but you didn't | observe it until later. | cycomanic wrote: | But that's essentially the point. The information is not | information until it is observed. | flubert wrote: | "This is the first of a set of papers that look at actual | Einstein-Podolksy-Rosen (EPR) experiments from the point of view | of a scientifically and statistically literate person who is not | a specialist in quantum theory." | | https://arxiv.org/abs/quant-ph/9611037 | | ...I wonder if anyone has ever followed up on Caroline Thompson's | work after she passed away. | | https://arxiv.org/abs/quant-ph/0210150 | miguelmurca wrote: | > really permits instantaneous connections between far-apart | location | | The phrasing in this article is tricky, as it wasn't FTL | communication that was proven; just that there are correlations | between things that _would require_ FTL communication, were they | classical processes. This is an important point: | https://xkcd.com/1591/ | eggsby wrote: | One reason I often hear astrology is not taken seriously by the | scientific community, as in findings like 'athletes often have | aries rising on their birth chart' are ignored and not | evaluated further, is because there is no empirical foundation | for the communication of the effects. | | https://en.wikipedia.org/wiki/Astrology_and_science | wizzwizz4 wrote: | There actually _is_ empirical foundation for the | communication of the effects![0] But the model is strictly | simpler if you remove the astrology from it; astrology has no | _additional_ explanatory power, and its novel claims (claims | not predicted by any other model) are wrong. | | > Such children are more likely to be picked for school | teams. Once they are picked, players benefit from more | practice, coaching and game time -- advantages denied to | those not selected, who are disproportionately likely to be | younger for their selection year. Once accounting for their | biological age, the older players might not have been any | better than later-born children when they are first picked. | But after becoming part of a team, and being exposed to | training and matches, they really do become better than | later-born children who might be equally talented. | | [0]: https://fivethirtyeight.com/features/why-athletes- | birthdays-... | eggsby wrote: | Sorry if my language was unclear, I meant to highlight this | line from the wiki article: | | "There is no proposed mechanism of action by which the | positions and motions of stars and planets could affect | people and events on Earth in the way astrologers say they | do that does not contradict well-understood, basic aspects | of biology and physics." | | Relevant here because it essentially says "there is no | empirical basis for spooky action at a distance" which has | been grounds for dismissal of such action-at-a-distance | claims like 'the relative positions of celestial bodies | influence events on the earth'. | | This kind of empiricism has been used as grounds to not | critically evaluate these claims. Everyone is certainly | free to have their own reasons around why they do not want | to evaluate such claims. For example some people only want | to consider things that are easily falsifiable and subject | to particular scientific practices. The wiki article goes | on to mention how Carl Sagan refused to disavow astrology | on these grounds (i.e. gravity is weak so stellar influence | writ large ought to weak) while still leaving room for a | disavowal if it were on firmer grounds. I do think your | point about simplicity is salient here. | wizzwizz4 wrote: | > _' the relative positions of celestial bodies influence | events on the earth'._ | | Who's claiming that!? The relative positions of celestial | bodies have influenced all sorts of events. For instance, | the horoscopes in the newspaper, or photographs of the | night sky. | | No, what's in doubt is _astrology_ , which is a much more | specific set of (wrong) claims. | naasking wrote: | Not necessarily. Bell's theorem assumes statistical independence, | but that means that either spooky action at a distance is real, | OR that experimenters do not have complete freedom to configure | their instruments (aka superdeterminism). | ThePhysicist wrote: | There's no spooky action at a distance. Let's imagine we have an | entangled qubit system that consists of a superposition of the | states (0,1) and (1,0), i.e. either part A is in state 0 and part | B in state 1 or vice versa. When we perform a measurement on the | first part of the system and obtain 1, it simply means that we | have "branched" into the (1,0) state of the system. This | branching is usually irreversible because of the decoherence | caused by the measurement (which itself is just an ordinary | quantum process). There is no information exchange or any type of | exchange between the two parts of the system going on, we simply | branch into a part of the probability space defined for the | system. The question whether the other branches still exist then | leads to either the "classical" interpretation of quantum | mechanics or the "many worlds" interpretation. The latter seems | to be favored today as we know that there's nothing special about | the measurement process that causes the collapse of a wave | function (it's a quantum process in itself), but in the end | there's not really a way to test this so it's really more of a | philosophical question. | | Articles about "spooky action at a distance" should really | mention this, as we have a much better understanding of the | measurement process in quantum mechanics today than Einstein et. | al. had when they wrote their paper. | virgil_disgr4ce wrote: | If there's one single phrase I wish I could erase from history | it's "Spooky action at a distance." Ugh. It bugs me a lot that | Quanta made these misleading statements that just continue the | confusion over what should be a more widely-understood core | feature of the universe we live in. | | Tangentially, I wish "interaction" would come to replace | "measurement," especially in the context of decoherence. The | universe is branching * _constantly*_ everywhere as various | quantum systems interact. | joe_the_user wrote: | What you're describing could be done with classical physics. | Have one penny and two lockets. Place the penny blindly in one | of the two lockets. Take one locket across the world. Opening | it instantly lets you whether the other locket has contains the | penny. | | And the point of this description is this is _not_ what 's | weird about quantum entanglement. | | What's weird about quantum entanglement is you have two | different measurement types that are non-orthogonal and they | combine according to quantum logic rather than classical logic | [1]. Having a particle in a state of _this_ sort can 't be | explained by any analogy to discreet events occurring | beforehand. | | [1] | https://en.wikipedia.org/wiki/Quantum_logic#Quantum_logic_as... | | Edit: Whether this is "spooky action at a distance" is in the | eye of the beholder. One thing is isn't able to be is fully | reducible to actions happening on something like a "classical | time line" but another thing is isn't to able to do is transmit | information. | lisper wrote: | Note that there is a very important property of entangled | particles that is hardly ever mentioned in this kind of | exposition, which IMHO casts a lot of light on what is really | going on, and that is that entangled particles do not self- | interfere the way non-entangled particles do. For more details | see: | | https://flownet.com/ron/QM.pdf | jfengel wrote: | I don't think the paper justifies the statement as you put it, | though perhaps you can point out what I'm missing. I don't | think you can tell just from looking at the particle itself | whether it has an entangled partner somewhere in the universe. | | It is, however, possible to use the entangled partners to | create systems with decidedly counter-intuitive properties that | change the way the un-involved partner interacts. That's also | the essence of Bell's Theorem. | | It only works when you're controlling the experiment as a whole | and thus not transmitting information faster than light... | though you can set up the experiment in a way that makes the | conventional transmission of information incredibly obscure. | Bell's Theorem requires you to jump through a lot of hoops to | exactly mimic that, which is why it took a long time to | definitively rule out other interpretations of the experiments. | lisper wrote: | See section 4.2, and in particular the paragraph that starts | "Here's the kicker..." | | It is true that you can't tell if a single particle is | entangled or not. But if you have an ensemble of particles | all prepared in the same state then you can tell if that | state is entangled or not. Non-entangled (a.k.a. pure) states | have a preferred basis that produce self-interference. | Entangled (a.k.a.) mixed states do not. | | (The pure-mixed dichotomy is a little misleading because it | depends on your point of view. A single member of an EPR pair | is in a mixed state, but the pair as a whole is in a pure | state.) | gus_massa wrote: | I agree with the GP. If you only have a single member of | the pair, then you will see the same interference pattern | in a double slit experiment than with a not-entangled | particle. | | It doesn't matter if the other particle has collided with a | brick, went thru a double slit experiment, went thru a bad | double slit experiment, or is flying to Andromeda. | | (In spite that the calculation to get the correlation with | any result in the other experiment may be much harder with | the entangled pair than with two non entangled particles.) | lisper wrote: | What can I say? You're wrong. The math shows that you're | wrong (as does the elementary argument presented in the | paper). Find a physicist and ask them if you don't | believe me. | gus_massa wrote: | I have at least 8 Physicist that I email/zoom regularly | (at least twice per month). I also have half a degree in | Physics, with at least 2 courses of Quantum Mechanics | (all the advanced courses also use QM, but there are 2 | courses only about QM). [I also have a degree and a PhD | in Math, but it's not too relevant here.] | | Anyway, I'll read the article thoughtfully and write a | long comment tomorrow. Can you take a look tomorrow? | lisper wrote: | Sure. | | Just to be clear, the part you are wrong about is this: | | > If you only have a single member of the pair, then you | will see the same interference pattern in a double slit | experiment than with a not-entangled particle. | | This bit: | | > It doesn't matter if the other particle has collided | with a brick, went thru a double slit experiment, went | thru a bad double slit experiment, or is flying to | Andromeda. | | is correct. | | Also, there _is_ an interference pattern in the results | of a double-slit run on entangled particles, but it is | not "the same" as you get with non-entangled particles, | and the procedure you have to go through to observe this | interference pattern is radically different. | Gunax wrote: | I've been posting this explaination for more than 10 years now: | | http://www.felderbooks.com/papers/bell.html | | I think I prefer Felder's explaination more than Quanta's. It's | omitting some details (eg. the angles) but is better at | explaining the difficulties of Bell's Inequality--why it seems | like spooky action at a distance and why it cannot be used for | communication. | subroutine wrote: | One thing I've not been able to clarify is whether Bell | accounts for the possibility that passing through a | polarization filter could effect the waveparticle in some way, | like altering its polarization angle. | ericb wrote: | If we were in a simulation, would the speed of light be the | processing speed of the universe as each area re-renders, and | spooky action at a distance be two variables pointed to the same | memory location, populated with a lazy-loaded value, with copy- | on-write semantics? | | edit: seems like it is lazy loaded, so revised my summary. | joe_the_user wrote: | There are no propositions that "we are in simulation" would | imply (unless someone fundamentally lacks imagination). | | Being "in a simulation" doesn't imply that we're in simulation | created by later humans, it doesn't give any indication how | fine-grain the approximations are, etc. etc. | | "We're in a simulation" fundamentally discard Occam's Razor in | the fashion of the belief in God as controlling everything. And | thus this belief has the same weight as belief in the Flying | Spaghetti Monster [1]. | | [1] https://en.wikipedia.org/wiki/Flying_Spaghetti_Monster | UncleOxidant wrote: | It's kind of interesting how people who would never consider | a creationist explanation seem quite willing to embrace the | idea that we're in a simulation. | naasking wrote: | One is an assertion with no logic to justify it, the other | is an assertion with a somewhat persuasive argument | justifying it [1]. They are simply incomparable. | | [1] https://www.simulation-argument.com/simulation.html | UncleOxidant wrote: | But how is the simulation hypothesis not positing a "god" | of some sort (some kind of super-intelligence that they | claim is behind it all)? It seems like the simulation | hypothesis is a theistic hypothesis. Or do they assume | the simulation just evolved? | | Also, why the assumption that post-humans are running the | simulations (as in the paper)? Couldn't it be any ultra- | advanced civilization that's playing with an evolutionary | simulation? | naasking wrote: | The simulation argument is exploring the likelihood that | post-humans would simulate humans. Both post-humans and | humans inhabit a universe with the same laws, so this | isn't a fictitious universe created by a deity. | | > Also, why the assumption that post-humans are running | the simulations (as in the paper)? Couldn't it be any | ultra-advanced civilization that's playing with an | evolutionary simulation? | | Sure, potentially. The paper makes no assumptions about | the existence of other life forms, it instead | extrapolates the likelihood of a simulation given the | only intelligent life we know to exist: us. | | Therefore you can see the simulation argument from that | paper as a _lower bound_ on the probability we live in a | simulation. Positing the existence of other life forms | that run random simulations can only _increase_ the | probability we 're living in a simulation, assuming one | of the other outcomes isn't more likely. | lazide wrote: | If a simulation exists, and there is evidence of it, then | sure we could surmise that someone created the simulator | - and would have some evidence of such? | | I think the parent poster was noting that it is a pretty | fundamentally different argument than say, positing the | existence of a creator, because we exist at all - and | that said creator has certain specific requirements of us | regarding what we do on Sundays, for instance, or with | whom and when we have kids. | UncleOxidant wrote: | > and that said creator has certain specific requirements | | Is that a requirement of every flavor of creationism? | Actually, maybe I shouldn't use 'creationism' in this | context because that's a loaded term with a lot of | baggage at this point. What else to call a hypothesis | that asserts there's some kind of intelligence behind the | universe that we see? Simulationists would seem to fall | into that broader category as would old-school | creationists. | feoren wrote: | Of the 3 assertions in the abstract, the obviously false | one is #2: "Any posthuman civilization is extremely | unlikely to run a significant number of simulations of | their evolutionary history". When you realize that | running a simulation of the universe requires more | processing power than is available in the universe, this | is _very obviously_ false. | | I respect people who believe in a bearded White | omnipotent homophobic God who lives in a sky palace more | than I respect people who believe in this insane drivel | about the probability of living in a simulation. At least | the former were indoctrinated as their brain was forming. | UncleOxidant wrote: | The simulation hypothesis seems as theistic as the | creationist hypothesis. Maybe the main difference being | that with the simulation there would likely have been | many creators (programmers) whereas the creationists | would say there is one (although there are polytheistic | creation narratives, so maybe not so different). Other | than that, they both seem to fall into the theistic | category since a higher intelligence is posited who | created (the simulation | the real world). | serverholic wrote: | Isn't it possible that our universe is really just an | approximation meant to look as detailed as possible? You | don't need a universe of processing power to simulate a | universe. You just need to make it look believable enough | that it fools whoever is in your simulation. | cepie wrote: | I agree with you, and even if it's not an approximation, | it doesn't matter; we can't make assumptions about the | size of a parent reality (and its limits on processing | power) relative to our own. | naasking wrote: | > Of the 3 assertions in the abstract, the obviously | false one is #2: "Any posthuman civilization is extremely | unlikely to run a significant number of simulations of | their evolutionary history". When you realize that | running a simulation of the universe requires more | processing power than is available in the universe, this | is very obviously false. | | I think you've expressed a number of confusions. | | First, I think you contradicted yourself. The line you | quote says that posthuman civilizations are _unlikely_ to | create simulations, but you say this is false because a | universe simulation requires more power than available in | the universe. So you 're agreeing with the outcome while | saying you're disagreeing. | | Second, I suggest reading the the paper fully, because | Bostrom explains that we don't need full universe | simulations, we need only _consciousness_ simulations | (kind of like the Matrix). The very premise of a post- | human civilization is that they have knowledge | sufficiently advanced that they have algorithms to | simulate human minds. | | Much like how video games only render the part of the | world that is visible to the players, so a consciousness | simulation only needs to simulate minds and their | perceptions of a macroscopic, classical world, they do | not have to simulate a full quantum universe. Our brains | are great at filling in information that we expect to be | there, so even the parts that we directly perceivedon't | need to be simulated with complete fidelity. | | Frankly, I don't think you've given the argument | sufficient thought, but by a happy accident you picked | exactly the outcome that I think is most likely, and I | elaborate on why here: | | https://higherlogics.blogspot.com/2021/02/why-we-are- | likely-... | joe_the_user wrote: | _First, I think you contradicted yourself. The line you | quote says that posthuman civilizations are unlikely to | create simulations, but you say this is false because a | universe simulation requires more power than available in | the universe_ | | No, they are saying the opposite. The argument that | simulating the universe requires more atoms than the | universe says that a later civilization would not | simulate the entire universe. IE, #2 of the refutations | really true. | feoren wrote: | Fine, you got me: the assertion that is obviously _true_ | , but goes further in that it invalidates the need for | any of this discussion. If your goal was to engage me in | a thought-measuring contest, sure, you win: you've spent | more time thinking about this utterly ridiculous nonsense | than I have. Congrats? | naasking wrote: | If you're not interested in philosophical discussions, | then why engage at all, particularly only to denigrate | people who like exploring thought experiments? | cepie wrote: | I bet you could make your points without insulting | others. What do you think? | suzzer99 wrote: | If the computer code running this simulation is that good | to never have bugs, then the simulation is functionally | identical to the meatspace real universe from our POV. So | I don't know if there's any point thinking about it other | than idle curiosity. But I do worry that for some | simulation believers it could become an excuse to have | less empathy towards fellow humans. | naasking wrote: | > So I don't know if there's any point thinking about it | other than idle curiosity. | | Idle curiosity is drives a lot of human behaviour, | particularly in philosophy! | joe_the_user wrote: | I actually think the singularity is an interesting | concept deserving of exploration. But "singularians" like | Nick Bostrom (author of parent link) have some strange | ideas. | | A. The idea that intelligence beyond human beings would | grant it's possessor power that are in ways _absolute_ in | very specific, rigid fashion. Human being can accomplish | a lot of things. It 's notable those things human beings | do better than computers seem very tenuous. Humans seem | to drive rather haphazardly yet humans drive much better | than computers and driving overall seems a "bucket | chemistry" sort of activity. Humans calculate much worse | than computers and calculation is an exact, defined | activity (arguable, the exact, defined activity). But for | the singularians, transhuman devices will do the | uncertain, tenuous activities that humans do but with "no | mistakes". And for a lot human activities, "no mistakes" | actually might not even mean anything. Despite humans | driving better than computers, humans probably wouldn't | even agree on what absolute good driving even means. | | B. Simulation as exact map. Any human created simulation | of some system is going to be an approximation of that | system for the purpose of extracting particular | phenomena. Some things are discarded, other focused on | and simplified. A model of the solar has to consider | conservation of energy or tiny deviations will produce | instability over time since errors overall on unavoidable | in current hardware. Even a simulation of a computer chip | isn't useful unless one knows the chip's purpose is | logical operations. But for Bostrom and partisans of | | C. Incoherent ontology. If we could produce an exact | model of a thing, which is the real subject and which is | simulation? What if we could produce twenty "exact | simulations", which is real? In a realm of unlimited | hypotheticals and unlimited exact simulations, wouldn't a | least a countable infinite simulations of "everything" | exist. Which is real is quite a conundrum but this | problem itself only exists in a world of multiplied | objects which we actually have no reason to suppose | exists. | dntrkv wrote: | Well, in my case, I don't believe our universe is a | simulation, but I'm open to discussing the idea for fun and | it does seem like a possibility. Whereas, most people that | believe in creationism, believe it 100% to be the case and | if you don't believe the same you are going to hell. I grew | up in an evangelical Christian community and you can't | really compare the two groups. Evangelicals are ready to | die for this belief. | UncleOxidant wrote: | This is mostly the YECs (Young Earth Creationist - "the | earth is 6000 years old" camp). There are other flavors | like ID (Intelligent Design) that tend to hold things a | good bit looser - and there are many different flavors of | ID as well. But yeah, the YEC folks are completely "it's | our way or the hellway!" and the Evangelicals have pretty | much doubled down on YEC - that wasn't always the case, | there used to be a lot of Evangelicals that were theistic | evolutionists and had no problem with a 4.5B year old | earth. | | EDIT: maybe we need another word in this context besides | 'creationist' since it has a lot of baggage in the | culture at this point. What else to call someone who | hypothesizes that there is some kind of intelligence | behind the universe? The simulationists seem to fit into | that category as do the various flavors of 'creationist', | 'intelligent design', 'theistic evolutionist' and | probably even Hindus, etc. | IncRnd wrote: | > "We're in a simulation" fundamentally discard Occam's Razor | in the fashion of the belief in God as controlling | everything. And thus this belief has the same weight as | belief in the Flying Spaghetti Monster [1]. | | You are using Occam's Razor incorrectly. A preference for | parismony in problem solving is not identical with parsimony | being the only state of the world. | | As a side note, which directly applies to your comment, | Occam's Razor was invented by Friar William of Ockham as a | defense of divine miracles. | joe_the_user wrote: | _You are using Occam 's Razor incorrectly. A preference for | parismony is not identical with parsimony being the only | state of the world._ | | "Everything is really under control of invisible stuff" | make it impossible to use parisomy under any circumstances. | It _fundamentally_ discards Occam 's Razor. | | _Occam 's Razor was invented by Friar William of Ockham as | a defense of divine miracles._ | | While I wouldn't personally accept a God that acts in the | world, the argument is about having some sort of evidence | based interpretation of the world. Flying Spaghetti Monster | is response to arguments like "God makes the rain fall" | etc, not to a God that appears in the world but a God that | can essentially be evoked for anything and in any fashion. | IncRnd wrote: | > "Everything is really under control of invisible stuff" | make it impossible to use parisomy under any | circumstances. It fundamentally discards Occam's Razor. | | You are fundamentally misunderstanding Occam's Razor. It | is not a law - Occam's Razor is a preference for how to | view the world, not a law that was violated. [1] | | There are alternate rules-of-thumb, such as one by | Ockham's contemporary, Walter Chatton. Chatton created | Chatton's anti-razor in opposition to Ockham's Razor: | "Consider an affirmative proposition, which, when it is | verified, is verified only for things; if three things do | not suffice for verifying it, one has to posit a fourth, | and so on in turn [for four things, or five, etc.]. | (Reportatio I, 10-48, paragraph 57, p. 237)" [2] | | [1] https://plato.stanford.edu/entries/ockham/#OckhRazo | | [2] https://plato.stanford.edu/entries/walter- | chatton/#AntiRazo | joe_the_user wrote: | _You are fundamentally misunderstanding Occam 's Razor. | It is not a law - Occam's Razor is a preference for how | to view the world, not a law that was violated._ | | Yes, Occam's Razor isn't a law but a method of | understanding reality. My point is that if you throw out | Occam's Razor in total, not in one or another situations, | you're left with nothing to understand the world with. | | The "God wants it that ways" and "because it's | simulation" can be substituted for any proposition at all | under any circumstances and there's not counter argument | to such substitutions. This approach is also "the | paranoid worldview" - "because they want to think that" | also has this "insert everywhere" quality. | | And you're link describing the original ideas of William | of Occam doesn't what you'd imagine. "Occam's Razor" is | broad approach that's evolved over time and just takes | that label for convennience. Virtually no one is evoking | the authority of William of Occam or claiming to follow | his Nominalism or whatever. The generally means that | adding unneeded hypotheses should generally be avoided. | If you can _never_ follow that guide, you 're in trouble. | mrkstu wrote: | "we're in a simulation" is at least something that might | be ultimately testable with the right theory and | experiment. FSM/God isn't w/o them choosing to 'reveal' | themselves to everyone. | lisper wrote: | That's not a bad analogy, but you have to be very careful here | because no classical analogy can be a perfect fit for | entanglement. The wave function is deeply and fundamentally | different than our classical reality, and there is no way to | reproduce its behavior classically. Among the fundamental | differences is the fact that classical information can be | copied but quantum states cannot be cloned. This is IMHO the | single biggest disconnect between the wave function and | classical reality because the nature of our (classical) | existence is fundamentally intertwingled with copying | (classical) information. It is happening right now even as you | read this. Information is being copied out of my brain onto the | internets and into your brain. At the same time, all our cells | are busily copying the information in our DNA, and so on and so | on. | archibaldJ wrote: | But aren't these "informations" just representations of | (something abstract) reflected in a bunch of quantum states | of your neurons? And we humans decide there are homomorphisms | between mine and yours and thus they are representing the | "same informations". But really they were fundamentally | different. There are no copying. Only some kind of lossy | compression mimicking. | lazide wrote: | At that point you would need to decide what 'copying' is, | exactly. Making a terrible VHS recording of a TV show would | still be considered copying by most, even if none of the | relative pixels ever matched. | [deleted] | tylerhou wrote: | A classical analogy for entanglement: suppose I have two | balls in a bag. They are identical in every way, except one | is red and the other is blue. I randomly grab one in each | hand and show my hands closed. Now the states of the ball are | entangled: as soon as you see the color of one ball, that | "determines" the color of the other. (Not claiming that this | is a perfect analogy, but I don't see where it diverges from | how entangled quantum waves would behave.) | | > Among the fundamental differences is the fact that | classical information can be copied but quantum states cannot | be cloned. | | The no-cloning theorem says that there exists no universal | quantum machine that can perfectly clone an arbitrary quantum | state. However, that does not preclude a machine that can | imperfectly clone any quantum state, or machines that can | perfectly clone some but not all quantum states [1]. (Clearly | the information transferred to my brain is not a perfect copy | of your brain's state, and your DNA is not perfectly copied | every time.) | | [1] https://arxiv.org/abs/quant-ph/9607018 | tsimionescu wrote: | The problem with your classical analogy for entanglement is | that it doesn't match the data. Or rather, it only matches | the data for quantum properties that are similarly blue or | red. | | The non-classical properties of entanglement start | appearing once you start measuring combinations of the | redness and blueness of those balls. | | Let's say that instead of looking at the balls, you pass | them through some machine that will let a red ball pass | through with some probability P that you control; if the | ball is blue, the machine will let it pass with probability | 1-P. Let's say further that you have three such machines. | You set the first machine to P=1. You pass each ball | falling from this machine through a second machine, which | has P = 0. You will never see a ball pass through to the | end - if it were red, it would pass the first machine, but | not the second; if it were blue, it would not pass the | first machine at all. | | But, let's say you now put a third machine between the | other two, and you set P = 0.5. With classical balls, | nothing changes - a blue ball doesn't make it past the | first machine, while a red ball goes through the first, may | or may not pass the second, and never makes it through the | third regardless. | | However, a quantum ball actually has a chance to pass | through the 3 machines if you set it up this way. In fact, | that chance is pretty large - more than half of the balls | will start passing once you add the middle filter machine. | | Still, this is easy to explain if we assume that the middle | machine actually paints the ball instead of just detecting | its color. This is where the entanglement experiment comes | in: if you pass the pair of balls through the three | machines, with ball 1 passing through machines P=1 and | P=0.5, and ball 2 passing through P=1, you will find that | sometimes both balls make it through, even though both | balls can't be red at the same time, and they can't | communicate about passing through the P=0.5 machine (you | can repeat the experiment with the balls being taken | arbitrarily far away before passing through the filters). | feoren wrote: | This is a great thought experiment, thank you. I'm not | totally clear how the machines could work without | actually taking a measurement, though. It sounds like | you're saying the 2nd machine (P = 0.5) takes | measurements (and therefore "paints" the balls), but the | other two don't? | | I've heard of the apocryphal "half-silvered mirror", but | I don't get why reflection isn't an | observation/interaction there either. | tylerhou wrote: | Bell's inequality (as you allude to) describes how | transformations on quantum wave functions cannot behave | classically. But classical wave functions can certainly | be entangled as entanglement is a property of a wave | function, not transformations on wave functions. | tsimionescu wrote: | I'm not sure what you mean by classical wave functions - | I've only seen the term 'wave function' used for quantum | mechanics. Are you referring to classical wave equations? | I'm not sure how the concept of entanglement is supposed | to apply to classical waves though. | tylerhou wrote: | I'm saying that you can represent probability | distributions of classical objects as a "wave function." | kolinko wrote: | The analogy you mentioned is exactly the wrong one - it | suggest that it's just a matter of a hidden variable. | | A proper (but less elegant) would be: you have two balls | with the same color or a pattern. | | You take one out. If you check the color first, you will | find the other's color the same, but the pattern sometimes | different. If you check the pattern first, you will find | the pattern the same, but the color sometimes different. | naasking wrote: | > The analogy you mentioned is exactly the wrong one - it | suggest that it's just a matter of a hidden variable. | | It is equivalent to a hidden variable, just a non-local | one. | tylerhou wrote: | > it suggest that it's just a matter of a hidden | variable. | | I disagree. Suppose that I create a machine that chooses | which ball to place in each box. This machine makes the | choice based on some measurement of a quantum particle | (electron spin). Then the colors of the ball are | entangled with the state of the quantum particle, which | cannot be described by some local hidden variable. | lisper wrote: | Only if you can completely isolate the balls so their | states don't decohere. That is not practically possible | to achieve, particularly since in your scenario you reach | into the bag and touch the balls. As soon as you interact | with the balls in any way, you become entangled with them | and the behavior of the system becomes classical. | serverholic wrote: | You didn't add anything to his example. This is just | purely to be pedantic. | lisper wrote: | No. The only way you can actually observe entanglement is | in an _isolated_ entangled system (this is the reason | quantum computers are hard to build). It is true that at | a philosophical level there is no difference, but from | the point of view of _physics_ , which is to say, what is | _observable_ , isolation is crucial. Non-isolated systems | behave classically, notwithstanding that they are | actually quantum systems. | tylerhou wrote: | Would you claim that when Einstein developed his theories | of relativity, they were invalid (from the point of view | of physics) because their consequences were not yet | observable? For example, Einstein used thought | experiments to develop special relativity in 1905, but | since kinematic time dilation was only experimentally | confirmed in 1971, his work was not a contribution to | _physics_ until then? | PeterisP wrote: | Reviewing Bell's theorem - described in this article - has | resulted in experimental evidence that all classic | analogies in the style of "some state was embedded in each | particle at the moment of entanglement and the measurement | just revealed something about what was in that single | particle locally at that time" can not be true. | | Bell's theorem describes the highest possible upper bound | of correlations for spin measurements along different axis | if it was as you say. But it turns out that in practice | they are more correlated than what would be possible | according to Bell's theorem, ergo, that analogy (which, in | general, is plausible and reasonable) is not compatible | with the physical reality we live in. | Kranar wrote: | >They are identical in every way, except one is red and the | other is blue. I randomly grab one in each hand and show my | hands closed. Now the states of the ball are entangled: as | soon as you see the color of one ball, that "determines" | the color of the other. | | This gets used to explain entanglement but it really has | absolutely nothing to do with it. This is nothing that the | ancient Greeks wouldn't have known. | | Not to pick on you specifically, but do people really think | it took a major revolution in physics in order to | understand that if there are two balls, one is blue and one | is red, then if you see one of the balls is red, you can | conclude the other ball is blue? | | It's something that I think humans can solve at the age of | 3. | | The failure in your explanation is right when you state | that "one of the balls is red and the other is blue". The | entire point of entanglement is that such a statement is | not possible, that's a strictly classical interpretation. | Rather, both balls are in a superposition of being both red | and blue simultaneously, and it is not possible in | principle to assign a color to either one of them until the | moment a measurement is made. | tylerhou wrote: | > Rather, both balls are in a superposition of being both | red and blue simultaneously, and it is not possible in | principle to assign a color to either one of them until | the moment a measurement is made. | | I don't disagree, and (clearly) I make a measurement when | I show you the color of a ball. Before I show you a ball, | I would also say that the colors of the balls are in a | superposition. | | > major revolution in physics in order to understand that | if there are two balls, one is blue and one is red, then | if you see one of the balls is red, you can conclude the | other ball is blue? | | Entanglement is really just this simple -- entanglement | itself is a statement about a wave function, classical or | quantum. The major revolution in physics is that | _transformations_ of the wave functions do not behave as | we would classically expect. Entangled particles are a | tool that we can use to measure those transformations | (and get surprising results). | Kranar wrote: | Fair enough we'll simply disagree on that. | | Entanglement is not a property about wave functions and | really has nothing to do with waves. It's a logical | consequence of the uncertainty principle and was | ironically deduced by Einstein, Rosen, and Podolsky (EPR | Paradox) as a way to argue that quantum mechanics is an | incomplete description of physical reality. Being that | it's strictly a consequence of the uncertainty principle, | it applies equally well to non-wave function formulations | of quantum mechanics such as the matrix formulation which | does not use a wave function. | | Entanglement is precisely the principle that a physical | system can exist such that no part of the system can be | described without describing the rest of the system as a | whole. Einstein argued that this made quantum mechanics | incomplete, the idea that somehow two properties of a | physical system separated potentially by light years | could not be decomposed into two physical systems that | behaved independently of one another violated basic | notions of local realism. | | The issue is that as soon as you stated that one ball is | red you have made a statement about some property of the | physical system that is independent of the rest of the | system. That is fundamentally what entanglement states | you can not do. All you can state is that there are two | balls that are in a superposition of being red and blue | and there is no way to describe one ball as red and the | other as blue, they are both red and blue simultaneously. | | That is what entanglement is and that is the new | principle that was neither known to the ancient Greeks or | something that a 3 year old could figure out. Not the | idea that if there are two balls and one ball is red and | the other is blue, then if you see the red ball you know | that the other ball is blue. Nothing about that ever | baffled any physicist. | feoren wrote: | While I believe that entanglement is genuinely something | new and interesting, your explanation of it simply feels | like a semantic difference. There is no way in which the | universe you describe would be different from a classical | universe, at least up to the limits of your description. | I'm simply "not allowed" to say that one of the balls is | red and the other is blue, before I've looked? It's just, | what, against the law to say that? There must be more to | it than that. | | There has to be some observation that would be different | in a universe with entanglement than in a universe | without entanglement, and you haven't described what that | difference is. There must be one out there, though -- | it's just not clear to me what it is. Does it have to do | with the fact that the fastest I can spread the message | "I just looked at ball A and it's red!" is the speed of | light, and ball B could be very very far away? But I | thought entanglement doesn't actually allow FTL | communication? | sawalk4 wrote: | Isn't this distinction exactly what the article is about? | By saying ahead of time, "one ball is red, the other is | blue", you're describing a hidden-variables theory of | entanglement. It may be unknowable (before measurement) | which color the ball in your left hand is, but it has a | color. | | But Bell's theorem provides a very measureable | counterexample to this type of explanation of | entanglement. Sure, in the article they talk about | electron spins instead of ball colors, but the analogy is | that there isn't a well defined "color of the ball" | before it's measured. | | Of course, the analogy breaks down a bit: electron spin | can be measured in multiple axes with somewhat | complicated interactions. | tylerhou wrote: | > By saying ahead of time, "one ball is red, the other is | blue", you're describing a hidden-variables theory of | entanglement. | | No, consider the case of neutral pion decay, which emits | one spin up electron and one spin down electron. We can | clearly say ahead of time one electron will be spin up, | and the other will be spin down. But there is no hidden | variable that determines which. | | If there were a hidden variable, then _knowledge of that | hidden variable would let you predict which electron is | spin up (which ball was red)._ In the macroscopic world, | the hidden variable might be the state of my brain when | it chose which hand to grab which ball. But if you | replaced me with a robot, and that robot used the | measurement of a quantum event (such as an electron 's | spin) to determine which ball to choose, then there is no | hidden variable. | ithkuil wrote: | This a good source for learning this stuff for real | instead of pop-sci approximations: | | https://ocw.mit.edu/courses/physics/8-04-quantum-physics- | i-s... | lazide wrote: | Ah, but that's the tough part - there IS a measurable | difference in behavior of the universe between these two | examples! (albeit hard to experimentally prove exists, | but it has been!) | | They really are in a superposition, not just 'not known' | until one is measured. | | Just like light was proven to (truly, actually) be both a | light and a wave through the double slit experiments. It | doesn't feel right, but it is - and that is where the | progress is made, and why the pushback on some examples. | It hides the actual truth behind a misleading, but easy | to understand example, that teaches people the opposite | of what is really going on. | bdamm wrote: | It could also be that we simply don't understand | something about light phase, and that's causing us to get | confused about superpositions. After all, the experiments | aren't on single photons, they are on beams of photons. | Kranar wrote: | OPs explanation is that entanglement is when there is a | red ball and a blue ball and when you know which ball is | red, you determine that the other ball must be blue. | | My explanation is that entanglement is when there is no | red ball or blue ball, there are simply two balls and the | color of both balls is both red and blue simultaneously. | It's not simply that one ball is red, the other is blue, | but we don't know which one is which until we measure | them. It's that fundamentally there is no red ball and | blue ball, there are just two balls whose colors are in a | superposition of red and blue. | | I will try to come up with an observable difference but | it's hard to do so with colors because the typical | examples used for entanglement involve properties that | can cancel one another out, so that two entangled | particles exhibiting a superposition of two properties | will, after many trials, end up forming some kind of | destructive or constructive interference that would not | be possible if those two particles were in a definite | state. | [deleted] | virgil_disgr4ce wrote: | This comment is the most helpful thing I've ever read | about entanglement. Thank you! | serverholic wrote: | I think you're having a pedantic moment. Nobody claimed | that the red/blue ball example was some big unsolved | mystery. It's merely to give people a taste of | entanglement in a way that your average person can | understand. | | Isn't it true that if you entangle two particles, | separate them, then measure one it'll tell you something | about the other particle? That's all the example is | trying to communicate. | Kranar wrote: | >Isn't it true that if you entangle two particles, | separate them, then measure one it'll tell you something | about the other particle? | | Yes that's true, but that's also true of things that | aren't entangled. I assure you if I went to Socrates, | showed him a red ball and a blue ball, put them in a bag, | and took out a ball at random that happened to be red, | Socrates would have no problem realizing that the other | ball must be blue. I am sure if I went to my 4 year old | daughter, she'd figure it out as well because nothing | about quantum mechanics or entanglement would be needed | to understand this. | | What entanglement tells us is that if two balls had their | colors entangled, then both balls are both red and blue | at the same time and it's simply not possible to reason | about one ball being blue and one ball being red while | they are entangled. They are in a superposition of both | colors and remain so until a measurement is performed. | | Once the measurement is performed, they are no longer | entangled and only at that point can you call one ball | red and the other blue. | unparagoned wrote: | The analogy is fine for explaining entanglement. Sure | it's more complicated when you consider superposition. | tylerhou wrote: | > Entanglement is not a property about wave functions and | really has nothing to do with waves. It's a logical | consequence of the uncertainty principle... | | I don't follow, and I can't find anything online that | makes this claim. Could you explain more? | | Maybe we disagree about the definition of entanglement. | I'll take one from Griffith's Introduction to Quantum | Mechanics. On page 422, Griffith writes [1]: | | > An entangled state [is] a two-particle state that | cannot be expressed as the product of two one-particle | states.... | | (There is no mention of uncertainty in this section | either.) Here I read "state" to mean "wave function" | which implies that entanglement is a statement about a | wave function, as I earlier claimed. "Cannot be expressed | as a product" means not independent, just like the balls | in my analogy (or electrons from neutral pion decay). | | When I say "see the color of one ball," I am collapsing | the wave function of the balls by making an observation | (in the Copenhagen interpretation). This is analogous to | measuring an electron's spin. If you replace "ball" with | "electron," "bag" with "decay of a neutral pion", | "red/blue" with "spin up/down," and "see the color of one | ball" with "measure the spin of one electron," that's a | completely valid statement in QM. | | [1] | https://notendur.hi.is/mbh6/html/_downloads/introqm.pdf | evanb wrote: | Just to be _absolutely_ pedantic, | | "one of the balls is red and the other is blue" | | IS a statement you can make. However, it's surprisingly | not equivalent to asserting (xor (and | (red? 'left) (blue? 'right)) (and (blue? | 'left) (red? 'right))) | | That is, "one is red and one is blue" does not mean that | it's the case that either has a definite color. | | In terms of oft-used Bell pair states to demonstrate what | I'm talking about, you can definitely say that total | S^2=0. | Kranar wrote: | Your level of pedantry is warranted and I agree with it. | mr_gibbins wrote: | No, I'm sorry, I'm not going to pull out heaps of | regurgitated quantum information to back this up but | that's straight-up wrong. | | The red ball and the blue ball exist as physical objects, | it is us, the observers, who are unaware of whether they | are red or blue at either position. There's no | superposition here. They are red, or blue, assigned | randomly. Not both, not none. These are facts - | properties - about the balls that are real, that exist, | but we simply don't have that information at that point. | It is meaningless that there is no observer that can 'see | through' our hands to know which is correct. | ks1723 wrote: | Sorry, this is just wrong. Bell's inequality and the very | related Bell-Kochen-Specker theorem [1] state that local | hidden variables (one ball is blue, one is red, but we | just don't know it) are not consistent with QM. | | [1] https://en.m.wikipedia.org/wiki/Kochen- | Specker_theorem | nikhilgk wrote: | > This gets used to explain entanglement but it really | has absolutely nothing to do with it. This is nothing | that the ancient Greeks wouldn't have known. | | To be fair, this usually crops up in entanglement | discussions to deomonstrate how it can't be used for FTL | communication and not to actually explain what | entanglement is. | renox wrote: | In this case this analogy is _very bad_ because what your | describing is an 'hidden local variables'.. | canjobear wrote: | This is exactly the analogy that Bell's Theorem refutes! | SigmundA wrote: | Speed of light would just be rule, like cellular automata | rules, Planck distance is cell size and the rule is you may | only move one cell per frame in any direction. Processing speed | doesn't matter to us, it could take a million "years" to render | a frame but we experience it in real-time. | | As you say pointer to shared memory location is basically | hidden variable theory, you could also move faster than the | speed of light by simply updating your location to any value, I | have done this in game hacking before you just need a | WriteProcessMemory api, might get caught by anti-cheats. | cecilpl2 wrote: | > Processing speed doesn't matter to us, it could take a | million "years" to render a frame but we experience it in | real-time. | | This is part of the premise of the fantastic novel | "Permutation City" by Greg Egan. | SigmundA wrote: | I read Diaspora which touches on that as well, I really | need to read Permutation City. | dw-im-here wrote: | no | stouset wrote: | It's more like two variables pointing to an uninitialized value | that's lazily randomly generated on dereference. And copy-on- | write. | | Edit: OP edited their original comment to be more accurate. | someguyorother wrote: | It's not really immutable as you can change the parameters of | an entangled pair. You just can't communicate any information | by doing so, because you need a classical signal to make sure | you don't read one of the particles the wrong way. | SV_BubbleTime wrote: | I could be WAY off, but if locality isn't entirely true, and | the "read success" is 33-67%, doesn't that still leave quite | a bit of wiggle room for communicating information in some | fault tolerant method? | wizzwizz4 wrote: | Nobody's ever managed it, the theory all says it's | impossible, and that would violate several "known laws" of | physics. | PeterisP wrote: | You get correlations - you can "understand what you read" | once you have the measurements from _both_ entangled | particles, so you need another channel of communication | (with the associated delays) to get that information. | | One side doing their interaction may cause a "spooky action | at a distance" (according to some QM interpretations), but | if you have only one side of readings and don't know what | the other party measured in their interactions, you can't | tell _anything_ about what "the other side" did, so it | does not help communication at all because you still need | to transmit as many bits in a non-quantum way until you can | do anything. | cma wrote: | Correlations only but no useable communication. You can | both make a decision on the same random info that isn't | determined until later when you are apart, but can't know | anything other than that if they followed the plan they | made their choice based on the same later-determined random | info, correlated with your random info. | | If they didn't follow the plan and measured orhogonal/same | (can't remember which) spins, then your results are | uncorrelated but you can't know until you meet back up | (maybe barring superdeterminism that is also accessible to | the individual). | mrkstu wrote: | If we agree before parting that one of us is going to | Alpha Centari and the other is staying on Earth and going | to assassinate either the President of Russia or America | depending on the observed state on an entangled pair of | particles, once I reach the star system. | | Doesn't the traveler have more information than anyone | else on ship about whether an assassination attempt was | made in Russia or America? and have it faster than the | speed of light? We don't have it with certainty, but we | have shared knowledge that is unknowable to others and | instantaneous. | cma wrote: | I think would, have a shared private piece of correlated | information between each other that wasn't determined | until you made the measurement (though maybe no joint | reference frame to say who made it first), but you can't | choose what it was (communicate with each other). | | The universe either had to break the light barrier to | make the measurements correlated (predetermining the | outcome isn't generally possible because you could choose | how to make the measurement based on another quantum | measurement from something outside of the other | participant's then-current light cone), or make the same | choice through superdeterminism (the other measurement | and all others were predetermined too and exact | simulation of entire future universe's measurement | decisions was shared between every particle when they | were within some distance at big bang or something). But | even though the universe broke the light barrier, you | yourself aren't able to use it for communication. | | In the many-worlds interpretation you've both branched | into the same branch of the multiverse, but couldn't | choose which branch. You do have private knowledge of | which branch you both ended up in though and the | consequences of that, assuming you both followed the | agreed on procedure. | | I think you can use what you are describing in a series | of correlated measurements to set up a provably secure | one-time-pad, and then do secure classical communication | with it. But you don't communicate the actual bits of the | pad, you just both get correlated ones. | jerf wrote: | You're probably interested in something more like the | holographic universe hypothesis. Under that hypothesis, I | believe "entangled particles" end up staying close to each | other in the projected space. 3D space in that case would be an | "emergent phenomenon" that isn't necessarily the "base data | structure" of the simulation. | fallingknife wrote: | Cellular automata have a built in speed limit, so it could be | something like that. If one cell's state depends on only its | immediate neighbors state, then logically no object can move | faster than one cell diameter per frame. And if you had shared | state between two non-adjacent cells in certain limited cases, | that could create "faster than light" behavior. | dvt wrote: | If we were in a simulation, it feels overzealous to make the | assumption that the computing model would be _anything_ at all | like what 've developed. Best assumptions you can make is that | it follows some kind of consistent logic (though there's | caveats here, too). | ericb wrote: | > that the computing model would be anything at all like | what've developed | | Perhaps. I suspect, though, that it would be subject to the | same information theoretical constraints which would provide | convergent evolutionary pressures. | | It seems at least likely that some level of optimization | would be useful if there is any type of cost (energy, | materials, resources, space) to the computing substrate, | whatever that may be, and that would lead to similar | optimizations to what we might be able to imagine. | tick_tock_tick wrote: | The speed of light is the exact kinda of constant a | programmer would add to a system to solve problems. | eigenket wrote: | But quantum mechanics is exactly the opposite of what a | programmer would add. At least as far as we understand it | is (exponentially) harder to simulate quantum systems than | classical ones. | lazide wrote: | Sure, using systems built from inside the system. In said | theoretical world, they may have different constraints | and physics after all. (Only kinda serious) | | Practically, the simulator theory may be testable, but | probably not. Every religion I've run across is pretty | clearly not okay to even test. | | So that's progress maybe? ___________________________________________________________________ (page generated 2021-07-20 23:00 UTC)