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Bounding the speed of ‘spooky action at a distance’

arxiv.org

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Re: Bounding the speed of ‘spooky action at a distance’

#21

Post by tedsanders »

Filligree wrote: post #18
tedsanders wrote: post #10

Suppose you and a distant friend both agree to wave a flag at 1200 GST. To an alien observing Earth, it looks as if the "human flag-raising interaction" is an instant effect that "travels" faster than the speed of light, since the flag raising happens at the same time in two places. But really, nothing is travelling. You and your friend just pre-agreed to do something at the same time at different places. If energy o…

What you're suggesting sounds like a hidden variable theory, which have been thoroughly disproven (Bell's Theorem). Quantum mechanics cannot work through merely pre-arranging actions.

To nitpick: Only LOCAL hidden variable theories are disproven by Bell's theorem.

However, I agree with your point that my example is not compatible with quantum mechanics.

I only meant to give the sense that nothing is travelling, even though you can semantically say something is.

Re: Bounding the speed of ‘spooky action at a distance’

#22

Post by ryanatkn »

This is ignorant speculation, but what if the interaction doesn't depend on distance, and instead always takes the same fixed amount of time? What if that delta t is equal to 1 plank time, one tick in the cosmic 3D simulation? Of course that's an advanced experiment to run, but the implications would be fun.

Re: Bounding the speed of ‘spooky action at a distance’

#23

Post by tedsanders »

It's like you and a friend have a deck of cards.

You each take a card from the deck, and then travel a million miles away.

Then, at the crack of noon (synchronized to GST, of course), you both look at your cards. Your card is the 3 of Clubs.

You travel back to meet your friend, and discover that his card (which he measured at noon, just like you) was the 7 of Diamonds.

You repeat this experiment a gazillion times and are amazed!! No matter how many times you run it, you and your friend never get the same card!!!

It's as if the cards are sending spooky signals to each other!

And after you double check that you and your friend are both looking only at 1200 GST, you realize that this spooky signal travels faster than the speed of light (since the it takes no time to "travel" a million miles).

It's like magic, eh?

Not really. The fact there is one of each card means it's impossible for you and your friend to have the same card. No magical spooky signals are being sent.

(The real question is whether the quantum mechanical case is analogous to this contrived example. I think it is. The important difference in quantum mechanics it that you really don't know what card you have until you look at it. However, that doesn't mean that your card is sending a faster-than-light spooky signal to tell the other card what to be. And you certainly can't use it for signalling or anything useful.)

Re: Bounding the speed of ‘spooky action at a distance’

#24

Post by DanBC »

n3rdy wrote: post #7
ChrisClark wrote: post #5

Earlier quoted context omitted.

Then he didn't understand what you were asking. It can easily be faster than the speed of light because no information can be transmitted through this phenomenon.

> Then he didn't understand what you were asking. It can easily be faster than the speed of light because no information can be transmitted through this phenomenon. If its observable then how could information not be transmitted? I'm the furthest thing from a physicist but if quantum entanglement causes an atoms polarity to change because millions of miles away another atom it is entangled with did the same, that wou…

I have a box. Inside the box my cat is alive and dead until I open the box. I open my box. Now my cat is either alive or dead. The cat in the box a billion miles away is instantly !alive or !dead.

But! Cat_A being alive is paired with Cat_B being dead. We know this. When we discover Cat_A being alive and thus Cat_B being dead we're not really finding out anything about Cat_B; we're just finding out something about the Cat_A / Cat_B pairing, and Cat_A is local to us.

(http://everything2.com/title/Quantum+entanglement+and+faster...)

Also, you can't change the polarity at a whim.

Re: Bounding the speed of ‘spooky action at a distance’

#25

Post by Filligree »

tedsanders wrote: post #23

It's like you and a friend have a deck of cards. You each take a card from the deck, and then travel a million miles away. Then, at the crack of noon (synchronized to GST, of course), you both look at your cards. Your card is the 3 of Clubs. You travel back to meet your friend, and discover that his card (which he measured at noon, just like you) was the 7 of Diamonds. You repeat this experiment a gazillion times and…

What you're describing is a hidden-variable theory, which has been ruled out by Bell's Theorem. Sorry.

Re: Bounding the speed of ‘spooky action at a distance’

#26

Post by eoinmurray92 »

bpicolo wrote: post #14
tedsanders wrote: post #10

Suppose you and a distant friend both agree to wave a flag at 1200 GST. To an alien observing Earth, it looks as if the "human flag-raising interaction" is an instant effect that "travels" faster than the speed of light, since the flag raising happens at the same time in two places. But really, nothing is travelling. You and your friend just pre-agreed to do something at the same time at different places. If energy o…

Except in the case of the top article,as far as I understand, information could in theory be transmitted thanks to time. A spin change can represent a 1 bit, and the lack of a spin change at a time can represent a 0 bit.

It can be used to share a cipher (one-time-pad) because you and I would know the arrangement of bits that the other person has, and no-one else would/could know. However the measurements on the qubit's are probabilistic, so we cannot control the arrangement of bit that we have. We will only know if the are correlated/anti-correlated.

Re: Bounding the speed of ‘spooky action at a distance’

#27

Post by tedsanders »

shardling wrote: post #13
tedsanders wrote: post #10

Suppose you and a distant friend both agree to wave a flag at 1200 GST. To an alien observing Earth, it looks as if the "human flag-raising interaction" is an instant effect that "travels" faster than the speed of light, since the flag raising happens at the same time in two places. But really, nothing is travelling. You and your friend just pre-agreed to do something at the same time at different places. If energy o…

It's still worthwhile to check that it really does work like that. But somehow, no one ever titles these articles "Physics continues to work exactly as expected." :)

I wholly agree. :)

Re: Bounding the speed of ‘spooky action at a distance’

#28

Post by didgeoridoo »

tedsanders wrote: post #10

Suppose you and a distant friend both agree to wave a flag at 1200 GST. To an alien observing Earth, it looks as if the "human flag-raising interaction" is an instant effect that "travels" faster than the speed of light, since the flag raising happens at the same time in two places. But really, nothing is travelling. You and your friend just pre-agreed to do something at the same time at different places. If energy o…

Almost, but spooky action is quite a bit spookier. Suppose you and your friend both agree to MAYBE wave a flag every day at 1200 GST, then communicate no further about it. The alien would always observe that either both flags are being waved, or both are not.

Re: Bounding the speed of ‘spooky action at a distance’

#29

Post by DanBC »

mratzloff wrote: post #11
ChrisClark wrote: post #5

Earlier quoted context omitted.

Then he didn't understand what you were asking. It can easily be faster than the speed of light because no information can be transmitted through this phenomenon.

My understanding is there are scientists working on quantum entanglement communication. If so, I'm not sure why you assert no information transfer. (Not a physicist.)

Isn't that just tamper-proofing, rather than FTL communication?

(http://www.newscientist.com/article/dn12786-quantum-cryptogr...)

Re: Bounding the speed of ‘spooky action at a distance’

#30

Post by jessriedel »

_of wrote: post #17

Watch out for arxiv.org, these papers may or may not have passed peer review. A lot of junk is deposited there.

This same group research group, including the same first author, published in Nature last year.

http://arxiv.org/abs/1205.2024

Since it's common practice to first post to the ArXiv before submitting to a journal (note, for instance, that the first version of their Nature paper was posted to the ArXiv 4 month before being published), I'm confident this paper is or soon will be submitted for peer review. It's always possible they made a mistake or are overstating their findings, but I don't think these guys are a bunch of hacks.

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