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Quantum entanglement shows that reality can't be local

arstechnica.com

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

#121

Post by Symmetry »

pfedor wrote: post #112
nessus42 wrote: post #105

Earlier 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.

Well, all the theories of quantum mechanics that rely on waveform collapse all predict that waveform collapse happens, while those that don't don't. Observing that larger and larger objects still have tinier and tinier but still existent quantum effects is evidence against collapse. And if you can demonstrate quantum effects in people, then you've pretty much ruled out the Copenhagen and von Neumann interpretations. Those experiments are inconceivably difficult with our current level of technology, though.

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

#122

Post by ealloc »

joe_the_user wrote: post #106
ealloc wrote: post #81

Earlier quoted context omitted.

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.

Fair enough, if it's just an analogy I agree it gives the right intuition.

To be clear, what really happened under MWI is that the wavefunction "branched" into two around the time you created the two particles, and the two branches spearated from each other in configuration space just as the two marbles in your analogy separated in physical space. When you did the measurement, you merely realized which branch you are in.

Where the analogy fails is that the probabilities in QM are inconsistent with there actually having been some hidden choice of marbles made beforehand.

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

#123

Post by cs702 »

btilly wrote: post #77
cs702 wrote: post #44

I've always found classical Newtonian physics, the Special Theory of Relativity, and (to a lesser extent) the General Theory of Relativity to be understandable at an intuitive level, but quantum phenomena just baffles me, even when I think I "understand" it. PS. IvoDankolov: I find it difficult or impossible to think intuitively about quantum phenomena.

Let me make it worse. Ever heard of chaotic systems? Any dynamic system that shows extreme sensitivity to initial conditions is chaotic. For instance smoke curling from a cigarette, planetary orbits over time, weather, water dripping from a tap - all of these show extreme sensitivity to initial conditions. Here is the fun thing. In quantum mechanics everything evolves linearly. Therefore extreme sensitivity to initia…

Thanks. A perfect example of the outright weirdness of quantum phenomena.

I read the first section of that paper ("Why quantum chaos?"), and its proposition makes no sense to me. None other than Poincare PROVED (proved!) ages ago that the motion and position of just three little points attracted to each other according to Newton's formulas are extremely sensitive to infinitesimal changes in their initial motions and positions (i.e., the system is chaotic in the classical sense). And as you point out, the world is full of cases that demonstrate such hyper-sensitivity. Yet, according to this paper, such a system is impossible in nature. I don't get it.

Instinctively, I have to believe there must be a more fundamental underlying explanation for this and other apparent contradictions... it's just that at the moment no one knows what this explanation might be.

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

#124

Post by UnFleshedOne »

ecliptic wrote: post #20

If you were able to construct a rigid beam 25 million miles long wouldn't you be able to transmit data (push a button) on the other end faster than the speed of light?

Even if you create a rigid beam (ignoring the fact that it isn't possible), once you start turning it with a certain speed, its end will start reaching speed of light and start acquiring mass. As the speed aproaches speed of light, the mass of the beam will be approaching infinity.

To think about it, if you have a sufficiently long beam you won't be able to give it any angular momentum at all, regardless of how much force you apply. It will be fixed in space. Perfect starting point if your hobby is moving stars with a combination of chains and pulleys.

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

#125

Post by gus_massa »

rorrr wrote: post #87
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…

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.

No. If you annihilate one of the particles, the other particle continues "unaffected". Whatever you do to one of the particles, the other particle continues "unaffected". Quantum mechanic is a little more complex, so it is difficult to explain what "unaffected" really means.

It's clearer with an example. Let's suppose that you and I have each one a particle that is a half of an entanglement particle pair:

* If you don't do anything with your particle, for each measurement that I can do there are some possible results with some probabilities.

* If you do any measurement to your particle, for each measurement that I can do I have exactly the same possible results with the same probabilities.

* If you do annihilate your particle :( , for each measurement that I can do I have exactly the same possible results with the same probabilities.

* Whatever you do with your particle, for each measurement that I can do I have exactly the same possible results with the same probabilities.

In that sense my particle is "unaffected". I can't do any measurement to know what you have done with your particle. So you can't use your particle to transmit information to me.

The strange effect is that if we later meet and compare notes, we will see that the results you get with your particle and the results I get with my particle are related. Some measurements always are equal, some have the opposite value and some are related in more complex ways.

Each measurement (yours and mine) alone are perfectly normal. The strange effect appears only when the result are compared.

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

#126

Post by svedlin »

mixedbit wrote: post #94

Are you aware of any attempt to explain quantum superposition (and entanglement) on the information theory basis? Is it possible that superposition is an optimization that allows the Universe not to compute stuff that does not have any observable effect? Maybe classical Universe would be much more computationally expensive?

Nice observation. I believe there was a recent paper that touches on this topic:

http://phys.org/news/2012-03-quantum-physics-matrix-efficien...

http://www.nature.com/ncomms/journal/v3/n3/full/ncomms1761.h...

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

#127

Post by cpeterso »

cpeterso wrote: post #95
cpeterso wrote: post #92

Earlier quoted context omitted.

Your theory reminds me of Fassbinder's 1973 film Welt am Draht ( World on a Wire ). The technical director of a simulated world project slowly realizes he lives within a larger simulation. https://en.wikipedia.org/wiki/Welt_am_Draht

Your theory reminds me of Fassbinder's 1973 film Welt am Draht ( "World on a Wire" ). The technical director of a simulated world project slowly realizes he lives within a larger simulation. He tries to outwit the simulation's programmers, as they deactivate or reprogram his friends and co-workers to stop him. https://en.wikipedia.org/wiki/Welt_am_Draht

doh! I replied to my own post instead of editing it in place. This is getting pretty meta. <:)

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

#129

Post by CoffeeDregs »

klodolph wrote: post #50
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…

> short story about someone doing this and discovering that it was the galactic equivalent of 'shortwave' radio and have the alien equivalent of the FCC come out to the planet to arrest the scientists for transmitting without a license "Fine Structure" -- bits of a soft-SF story you can read online http://qntm.org/structure http://everything2.com/?node=fine+structure It's of varying quality, I think people usually li…

Thank you. I had never seen "Fine Structure" and enjoyed it.

    It's of varying quality
It's worth a lot more than what I paid for it. ;)

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

#130

Post by Anderkent »

kybernetikos wrote: post #78
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…

Could you explain why your example isn't just a hidden variable explanation, which as we know from measurements of Bell's Inequality ( http://en.wikipedia.org/wiki/Bell%27s_theorem ), cannot result in a theory compatible with both locality and the predictions of quantum mechanics.

The example is a hidden variable explanation, simply because you cannot do metaphors for quantum physics using classical physics.

Perhaps another approach will be clearer:

Imagine magical filter goggles, of two types: red and blue. People wearing red goggles can only see other people wearing red goggles, people wearing blue goggles can only see other people wearing blue goggles.

You put a pair of red and blue goggles to each box, then have four people pick a pair of goggles each.

The result is that each person only sees one other person, near the second box, wearing the same colour goggles.

This is more or less how many-worlds works, except instead of both red and blue goggles in the box you have a single pair of goggles that is both red and blue, but not at the same time (decoherence), and thus instead of two people wearing different kind of goggles, you have a single person wearing goggles that are both blue and red.

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