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Physicists provide support for retrocausal quantum theory

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Re: Physicists provide support for retrocausal quantum theory

#11

Post by woliveirajr »

> First, to clarify (...) It does not mean that signals can be communicated from the future to the past(...) instead, retrocausality means (... it) can influence the properties of that particle (or another particle) in the past, even before the experimenter made their choice. In other words, a decision made in the present can influence something in the past.

So, hard to explain in layman words: future can't transmit information to the past, but an action that will be taken in the present can influence some properties of a particle in the past.

Take two particles, separate them enough, do some "A" thing to one of them and the other instantaneously will have the only possible state that doesn't break the universe.

And one viable explanation is that when we've done the "A" thing, this information was transmitted to the particle in the past. We just couldn't measure this before (in the past) because measuring interferes with it, and that property can only be revealed at the same time that we've done the "A" thing.

Is that it? Kinda of information is transmitted to the past, just can't be read before some time ?

Re: Physicists provide support for retrocausal quantum theory

#12

Post by Koshkin »

naasking wrote: post #4

> But by allowing for the possibility that the measurement setting for one particle can retrocausally influence the behavior of the other particle, there is no need for action-at-a-distance—only retrocausal influence. I don't quite get it. According to GR, non-locality and retrocausality are equivalent. So how is retrocausal QM different from Bohmian mechanics/pilot wave theories?

I agree that retrocausality does not look at all surprising knowing GR and the long-established non-locality of QM. (Whether this is equivalent to what the pilot-wave interpretation has to say about the character of QM may require a complicated proof.)

Re: Physicists provide support for retrocausal quantum theory

#14

Post by lucozade »

naasking wrote: post #4

> But by allowing for the possibility that the measurement setting for one particle can retrocausally influence the behavior of the other particle, there is no need for action-at-a-distance—only retrocausal influence. I don't quite get it. According to GR, non-locality and retrocausality are equivalent. So how is retrocausal QM different from Bohmian mechanics/pilot wave theories?

> So how is retrocausal QM different from Bohmian mechanics

From what I can tell from this, there's no difference in the sense that it's experimentally indistinguishable.

It's different in the sense that Bohmian mechanics relies on a non-local pilot wave to match QM results. This frees the other assumption i.e. causality to get to the same answer.

TBH I can't see either get much attention until someone comes up with a way to make them produce different results compared to standard QM approaches. Either that or someone finds a way to make QM calculations substantially easier using these approaches. In other words, if they produce new physics or have practical value.

Re: Physicists provide support for retrocausal quantum theory

#15

Post by ridewinter »

The many-worlds interpretation of quantum mechanics is the only one that's easy to understand. All others seem to bend over backwards to realistically explain quantum effects. It's so rare to find clear explanations, but they do exist.

My favorite from David Deutsch, a main creator of the idea of quantum computing:

To those who still cling to a single-universe world-view, I issue this challenge: explain how Shor’s algorithm works. I do not merely mean predict that it will work, which is merely a matter of solving a few uncontroversial equations. I mean provide an explanation. When Shor’s algorithm has factorized a number, using 10^500 or so times the computational resources than can be seen to be present, where was the number factorized? There are only about 10^80 atoms in the entire visible universe, an utterly minuscule number compared with 10^500. So if the visible universe were the extent of physical reality, physical reality would not even remotely contain the resources required to factorize such a large number. Who did factorize it, then? How, and where, was the computation performed?

Re: Physicists provide support for retrocausal quantum theory

#16

Post by ajuc »

FeepingCreature wrote: post #9
naasking wrote: post #7

Earlier quoted context omitted.

> This would allow us to predict the future and potentially allow for time travel as well. It doesn't actually, they discuss this in the article. The laws of thermodynamics impose an arrow of time via boundary conditions, and something similar would apply here.

Purely as an amateur, it seems unelegant to have something that violates causality as a mechanism, but doesn't give you a way to violate cause and effect at a higher level. It's like the universe is conspiring to keep its awesome tricks from you.

So, universe is like Haskel ;) Purely functional API, but under all of that there's still imperative machine code.

Also, the conspiracy may be a good thing. If you have self-replicating and mutating code on your computer you should put some sandbox around it, or it might evolve to buy more RAM on ebay. Or, more realistically - will crash the system.

Re: Physicists provide support for retrocausal quantum theory

#17

Post by pron »

ridewinter wrote: post #15

The many-worlds interpretation of quantum mechanics is the only one that's easy to understand. All others seem to bend over backwards to realistically explain quantum effects. It's so rare to find clear explanations, but they do exist. My favorite from David Deutsch, a main creator of the idea of quantum computing: To those who still cling to a single-universe world-view, I issue this challenge: explain how Shor’s al…

I don't understand David Deutsch's philosophical justification. Is he suggesting that quantum computing steals computational resources from other universes? If so, in this "quantum computing as theft" view, aren't many of those universes (those similar to ours, doing a similar computation at the same time) stealing computational resources from ours at the same time, yielding the original question again?

Re: Physicists provide support for retrocausal quantum theory

#19

Post by petters »

woliveirajr wrote: post #11

> First, to clarify (...) It does not mean that signals can be communicated from the future to the past(...) instead, retrocausality means (... it) can influence the properties of that particle (or another particle) in the past, even before the experimenter made their choice. In other words, a decision made in the present can influence something in the past. So, hard to explain in layman words: future can't transmit…

That explanation still seems to allow faster than light communication.

Re: Physicists provide support for retrocausal quantum theory

#20

Post by ridewinter »

pron wrote: post #17
ridewinter wrote: post #15

The many-worlds interpretation of quantum mechanics is the only one that's easy to understand. All others seem to bend over backwards to realistically explain quantum effects. It's so rare to find clear explanations, but they do exist. My favorite from David Deutsch, a main creator of the idea of quantum computing: To those who still cling to a single-universe world-view, I issue this challenge: explain how Shor’s al…

I don't understand David Deutsch's philosophical justification. Is he suggesting that quantum computing steals computational resources from other universes? If so, in this "quantum computing as theft" view, aren't many of those universes (those similar to ours, doing a similar computation at the same time) stealing computational resources from ours at the same time, yielding the original question again?

No, nothing stolen. The quantum computer's calculations take place in parallel universes. The difficulty is arranging it so that the parallel universes are identical to eachother other than those calculations in the computer itself. That's the only way that this universe can get the answer back. That's my understanding of the many-worlds explanation of quantum computing. Nice and simple.
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