Quantum entanglement shows that reality can't be local • Hacker News Board

Re: Quantum entanglement shows that reality can't be local

#101

Post by nessus42 » Tue, Oct 30, 2012, 9:41 PM UTC

kybernetikos wrote: post #86

nessus42 wrote: post #23

This article completely ignored the Many Worlds Interpretation, which preserves all of realism, locality, and Relativity.

Can you explain how MWI is local? In the period of time before the observer is 'entangled' into the same system as the observed particles, the different possibilities can interfere with each other. If this can happen even if the entangled particles are separated by a lot of space, surely that is the same as nonlocality. Maybe my confusion is that I'm not sure a which point the universe splits. Suppose I entangle two…

> Maybe my confusion is that I'm not sure a which point the universe splits.

The answer to that is that the universe never really splits. It remains one big very complicated universe, with very very very messy superpositions of state in it. But different components of these superpositions lose "coherence", which gives the appearance to us of wave collapse, even though there actually is no wave collapse.

Lookup "decoherence" for more info on this.

Re: Quantum entanglement shows that reality can't be local

#102

Post by ramidarigaz » Tue, Oct 30, 2012, 9:47 PM UTC

DanBC wrote: post #53

ChuckMcM wrote: post #3

This is for me the most interesting part of the whole teleportation / entanglement research. When these papers started coming out we debated the notion of 'faster than light' communication. The counter argument was that you had to move the particles apart and that was constrained by the speed of light. Then the question of "when" the state was resolved was pondered. There were two thought experiments proposed at this…

Greg Egan - I can't say more because spoilers.

Diaspora?

Re: Quantum entanglement shows that reality can't be local

#103

Post by krsunny » Tue, Oct 30, 2012, 9:55 PM UTC

zellyn wrote: post #69

fixermark wrote: post #4

One thing I've never understood about interpretation of quantum entanglement experiments: Based on what I've learned of these experiments, it seems to me that the least mind-bending interpretation is that the entanglement event results in two particles that have some complementary property k (i.e. one particle has k and the other has ~k) and which one of the two, k or ~k, is had by one of the particles is unknowable…

Nobody seems to like my theory that the programmers of the simulation we're all living in were deferring procedurally generating that level of detail until it was necessary because we'd actually examined it closely. They're probably still cursing our Hubble telescope, not to mention computers with their decreasing semiconductor scales. This comment probably just triggered their simulation-awareness detector. :-) Actu…

That's because the simulation is telling everyone to reject your theory and ridicule you for presenting it.

Re: Quantum entanglement shows that reality can't be local

#104

Post by joe_the_user » Tue, Oct 30, 2012, 9:56 PM UTC

yummyfajitas wrote: post #85

joe_the_user wrote: post #75

Ok, as far as I can tell, this all just a rehash of EPR paradox and the weirdness of the Copenhagen interpretation of QM. The many worlds interpretation resolves everything with full locality. http://en.wikipedia.org/wiki/Many-worlds_interpretation Just consider, if I take a black marble and a white in hand, shake them up and put them in two boxes so I don't know which marble is in which box and put the two boxes on…

Your description is wildly incomplete. What you've just described is merely ordinary probability theory. To see the effects of QM, build a device to flip a quantum-mechanical coin. If it comes up heads, put the marbles into the two boxes. If it comes up tails, put the marble into the two boxes in a slightly (but unmeasureably) different way. I.e., whichever procedure you chose, P(white in right)=0.5. However, when yo…

Sure, I never claimed to describe all of QM.

However, while are many amazing effects there, I don't see how your particular example of QM weird or others relate make the information transmittal at a distance part. IE, the interference part isn't directly related to the entangled at a distance except it provides a box that you can't look into.

Re: Quantum entanglement shows that reality can't be local

#105

Post by nessus42 » Tue, Oct 30, 2012, 9:58 PM UTC

Ingaz wrote: post #67

nessus42 wrote: post #23

This article completely ignored the Many Worlds Interpretation, which preserves all of realism, locality, and Relativity.

Correct if I'm wrong, but I think that Many Worlds Interpetation does not explain a thing. It's like religion - one can think it's possible, other - impossible. But it can't be proved or disproved

I'm pretty sure that, in theory, all the major interpretations of QM are experimentally distinguishable from each other. The feasibility of ever being able to perform some of these experiments, however, is rather questionable.

Two exceptions to this are (1) that the Many Worlds Interpretation is experimentally indistinguishable from the Bohm Interpretation, unless you want to commit suicide many times with a quantum revolver; and (2) the Copenhagen Interpretation doesn't define what a "measurement" is, so scientifically determining whether it's correct or not is impossible.

None of this implies that any of this is "like religion".

Re: Quantum entanglement shows that reality can't be local

#106

Post by joe_the_user » Tue, Oct 30, 2012, 10:01 PM UTC

ealloc wrote: post #81

joe_the_user wrote: post #75

Ok, as far as I can tell, this all just a rehash of EPR paradox and the weirdness of the Copenhagen interpretation of QM. The many worlds interpretation resolves everything with full locality. http://en.wikipedia.org/wiki/Many-worlds_interpretation Just consider, if I take a black marble and a white in hand, shake them up and put them in two boxes so I don't know which marble is in which box and put the two boxes on…

What you are describing is a "hidden variable theory", but it has been shown (See "Bell's Theorem") such a theory cannot be true. QM is stranger than that.

I'm not saying QM's mechanisms are the same boxing marbles. I'm just saying that separating entangle particles isn't just more interesting than boxing marbles, IE, all the modifications that are going interfere with each can be seen as already having happened - which is why QM doesn't allow you to transmit information faster than light.

Re: Quantum entanglement shows that reality can't be local

#107

Post by kybernetikos » Tue, Oct 30, 2012, 10:02 PM UTC

Symmetry wrote: post #99

kybernetikos wrote: post #86

Earlier quoted context omitted.

Can you explain how MWI is local? In the period of time before the observer is 'entangled' into the same system as the observed particles, the different possibilities can interfere with each other. If this can happen even if the entangled particles are separated by a lot of space, surely that is the same as nonlocality. Maybe my confusion is that I'm not sure a which point the universe splits. Suppose I entangle two…

The splitting is a quantitative rather than a qualitative process. You can observe quantum effects with 100 atom molecules the same way as with single particles, it's just they require far finer observations to detect. If no collapse occurs, the the time entangled complexes reach visible scales there's no way you could ever detect the quantum interference. It isn't that the universe has split, it's that one section o…

Yes, but this complex is growing the whole time, as it entangles with other parts of the universe around it in both locations. That means that I become entangled with it in one location, and simultaneously become entangled with some other part of the universe that is not remotely local to me.

That's why I find the description of it as 'local' somewhat weird, but I accept that I'm probably using the term incorrectly.

Re: Quantum entanglement shows that reality can't be local

#108

Post by jessriedel » Tue, Oct 30, 2012, 10:02 PM UTC

GregBuchholz wrote: post #83

jessriedel wrote: post #61

Earlier quoted context omitted.

Physicist here. NegativeK is correct. Bell's theorem is the key to understanding why your explanation doesn't work. Bell's theorem, and the associated experimental demonstration, has been called the most profound discover of science. It's well worth a few hours of your time to try to understand it. You don't need to know any quantum mechanics or advanced math to do so. Incidentally, I'll mention that your argument is…

Non-physicst here. What do you think of Caroline Thompson's work, like: "Chaotic Ball" model,local realism and the Bell test loopholes http://arxiv.org/abs/quant-ph/0210150 ...I've always wondered if much of the Einstein-was-wrong business is really a category error. I personally liked: Clearing up Mysteries - The Original Goal http://bayes.wustl.edu/etj/articles/cmystery.pdf " ...we must keep in mind that Einstein's…

Based merely on the abstract, I'd guess that I wouldn't find Thompson's paper very interesting. I'm glad there's someone worry about possible loopholes in Bell experiments (just like I'm glad there are physicists working on GRW and astronomers looking out for killer asteroids) but I don't think there's anything to find there.

As far as the philosophy goes, I'd say most people's frustration from Bohr's positivist position is actually due to the real flaw with Copenhagen, which is the ambiguity bundled up into the word "measurement". If you eliminate this ambiguity (which I think is being done incrementally through the study of decoherence), you'll find that a positivist position is actually a lot more attractive. At least, that was how my feelings evolved on the issue.

Re: Quantum entanglement shows that reality can't be local

#109

Post by nessus42 » Tue, Oct 30, 2012, 10:05 PM UTC

kybernetikos wrote: post #96

kybernetikos wrote: post #86

Earlier quoted context omitted.

Can you explain how MWI is local? In the period of time before the observer is 'entangled' into the same system as the observed particles, the different possibilities can interfere with each other. If this can happen even if the entangled particles are separated by a lot of space, surely that is the same as nonlocality. Maybe my confusion is that I'm not sure a which point the universe splits. Suppose I entangle two…

Let me try to explain myself better: Two particles are entangled and separated by a vast distance. At some point, I conduct a measurement on the first particle, causing me to split into two different versions of myself that have measured two different states. Now, the effect of that measurement spreads outwards from the site of the measurement, so I may affect other things based on the measurement, etc. My problem is…

> My problem is that if a measurement is done on the other particle, long before any message from me could possibly have got there, then that measurement and the effects it has on its local environment and the effects they have are all also dependent on my measurement.

Imagine that your friend Joe writes the same word on two pieces of paper, puts them in envelopes and hands one envelope to you and mails the other envelope to Paris. At some point in time, you open up your envelope and read the word "popcorn". At some other point in time, Pierre open up his envelope and reads the same word.

The word that Pierre reads is not "dependent on your measurement". Nothing nonlocal occurred.

Re: Quantum entanglement shows that reality can't be local

#110

Post by Symmetry » Tue, Oct 30, 2012, 10:06 PM UTC

kybernetikos wrote: post #96

kybernetikos wrote: post #86

Earlier quoted context omitted.

Can you explain how MWI is local? In the period of time before the observer is 'entangled' into the same system as the observed particles, the different possibilities can interfere with each other. If this can happen even if the entangled particles are separated by a lot of space, surely that is the same as nonlocality. Maybe my confusion is that I'm not sure a which point the universe splits. Suppose I entangle two…

Let me try to explain myself better: Two particles are entangled and separated by a vast distance. At some point, I conduct a measurement on the first particle, causing me to split into two different versions of myself that have measured two different states. Now, the effect of that measurement spreads outwards from the site of the measurement, so I may affect other things based on the measurement, etc. My problem is…

then that measurement and the effects it has on its local environment and the effects they have are all also dependent on my measurement.

I think that's your trouble there. Those are totally independent of your measurement, the waveform splits at the measurement of the other particle the exact same way, regardless of what happened to you locally.