[HN Gopher] How Bell's Theorem proved 'spooky action at a distan...
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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?
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