My grandma puts a donut in one of two boxes, closes both, gives one to each of us. You leave for Mars and, at an agreed-upon instant, I open my box. Now I know what is in your box, and you know what's in mine. No faster-than-light, no mystery.
Quantum entanglement shows that reality can't be local
111–120 of 172 posts
Re: Quantum entanglement shows that reality can't be local
#112Earlier quoted context omitted.
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…
Be specific. What experiment do you have in mind that could distinguish between interpretations? Note that if the "experiment" involves dying to see what's on the other side then it doesn't exactly make it seem less like a religion.
Re: Quantum entanglement shows that reality can't be local
#113It would be interesting to see the result of experiment where one electron in entangled pair collides with a positron.
I suspect that this might give some interesting results.
Re: Quantum entanglement shows that reality can't be local
#114The way that I best understand quantum entanglement (and maybe someone like jessriedel can correct me if I'm wrong) is thus: You may be familiar with the Schrodinger equation (HΨ = ih' dΨ/dt) or the more accurate time-dependent Dirac equation. In each of these equations is a function called the wavefunction (denoted with Ψ). This function represents the "quantum state" of your system -- in other words, all the inform…
Being requested by name is too ego-boosting to pass up, so let me take a crack at clarifying at least one apparent confusion.
> For example, you can measure momentum, position, energy, spin etc... and each of these observables has a different corresponding mathematical operation that you perform on Ψ to get XΨ, where X is the mean value of the observable...
>The weird thing though is that what you measure isn't always exactly this value. Instead, the mean value of many measurements will be this value. You can also compute the standard deviation of these measurements using Ψ, but that's about it.
A good QM textbook will actually say something much more precise. It says that (a) the set of possible outcomes of the measurement is equal to the spectrum of the observable being measured and (b) the chance of getting a particular outcome is given by the squared inner product of the wavefunction with the appropriate eigenvalue. (The whole business of calculating means and standard deviations is confusing unless you understand that; unfortunately, this is allowed to happen often in into QM courses.) This means that QM doesn't just predict some statistical properties of the outcome distribution, it completely specifies the distribution.
Also, I figure you know this, but I want to mention that when you say
> you can plot and analyze this data, and what you'll notice for two entangled particles separated by thousands of miles or more is that there are statistical correlations between the two sets of data
it's important to emphasize that these are non-local correlations (in the Bell sense). You can generate mere local correlations using everyday classical systems.
Re: Quantum entanglement shows that reality can't be local
#115This 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…
This doesn't work because there is no moment at which the state is 'known' or 'detangled'. There is no way to tell, by observing one particle, when the other particle was observed. If there was you could send a signal with it, which would be no good. The universe is a strange place.
Plus the other particle could later be "unobserved" through quantum erasure..
Re: Quantum entanglement shows that reality can't be local
#116Earlier quoted context omitted.
The most interesting question to me is - what happens when one of the entangled particles get annihilated. If the other one does too, instantly, then we can use that to communicate faster than light.
(X -> FLT) -> ~X
There's a saying, "Relativity, causality, FTL. Pick two."
Re: Quantum entanglement shows that reality can't be local
#117This 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…
The most interesting question to me is - what happens when one of the entangled particles get annihilated. If the other one does too, instantly, then we can use that to communicate faster than light.
Entanglement is a lot more superficial / complex than that.
QM is so differnet than how we are used to dealing with things the only really useful way to understand it is the Math it's based on. But, decoherence is the hart of a lot of the spooky voodo that really trips people up so it's a much better place to start than the 'cool' vs. trying to extrapilate based on the odd stuff that goes on. http://en.wikipedia.org/wiki/Quantum_decoherence
PS: Also, avoid thinking at the large and small scales at the same time. Sensors really are just more fields and particles just like everything else. Also, decoherence is not an all or nothing event it's more a sliding scale between wave and particle.
Re: Quantum entanglement shows that reality can't be local
#118BTW, while I'm not entirely sure what this article is saying, here's one of the best explanations of "Quantum" I've ever seen. Unlike most, it doesn't start out from physics, but from a mathematical/probability framework ... that allows for negative probabilities. Yeah.
http://www.scottaaronson.com/democritus/lec9.html
I'll quote a bit:
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But if quantum mechanics isn't physics in the usual sense -- if it's not about matter, or energy, or waves, or particles -- then what is it about? From my perspective, it's about information and probabilities and observables, and how they relate to each other.
Ray Laflamme: That's very much a computer-science point of view.
Scott: Yes, it is.
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Re: Quantum entanglement shows that reality can't be local
#119Earlier quoted context omitted.
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…
Be specific. What experiment do you have in mind that could distinguish between interpretations? Note that if the "experiment" involves dying to see what's on the other side then it doesn't exactly make it seem less like a religion.
You might as well say that the Bohm interpretation is "like religion" then, rather than saying that the MWI is.
If your assertion is that we might never know which is true, the Many Worlds Interpretation or the Bohm Interpretation, then you might be right. But, if it comes down to these two, most scientists are going to go with the Many Worlds Interpretation by Occam's razor.
There are many other theories that we reject by Occam's razor that we can't disprove, and yet we don't typically consider these rejections to be a matter of "religion".
Re: Quantum entanglement shows that reality can't be local
#120Ok, 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.
Bell's theorem only shows that local hidden variable theories cannot be true. Non-local hidden variable theories, such as Bohm, are still possible.