Eberhard assumptions and FTL communication

In summary: There is no strategy that can produce results that satisfy both 1. and 2.. The only way to do so would be for each particle to be individually measured and then the results pooled together.This is not possible because of the entanglement between the particles.
  • #1
zonde
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In this paper http://dx.doi.org/10.1103/PhysRevA.47.R747 Eberhard derives Bell type inequality from these assumptions:
A theory is defined as being "local" if it predicts that, among these possible sequences of events [with the same number of events N], one can find four sequences (one for each setup [(α1,β1), (α2,β1), (α1,β2), (α2,β2)]) satisfying the following conditions:
(i) The fate of photon a is independent of the value of β, i.e., is the same in an event of the sequence corresponding to setup (α1,β1) as in the event with the same event number k for (α1,β2); also same fate for a in (α2,β1) and (α2,β2); this is true for all k's for these carefully selected sequences.
(ii) The fate of photon b is independent of the value of α, i.e., is the same in an event k of the sequences (α1,β1) and (α2,β1); also same fate for b in (α1,β2) and (α2,β2).
(iii) Among all sets of four sequences that one has been able to find with conditions (i) and (ii) satisfied, there are some for which all averages and correlations differ from the expectation values predicted by the theory by less than, let us say, ten standard deviations.

Now the question I am trying to answer is how we could violate condition (i) or (ii) without opening possibility of FTL communication.
Say if we can not find two sequences (α1,β1) and (α1,β2) that are identical at Alice's end then we can communicate by making up a catalog of possible sequences that Alice can see when Bob sets his detector at β1 and another catalog of sequences that Alice can see for Bob's setting β2.
Even if Alice sees some sequences more often for Bob's β1 and some other for Bob's β2 we still can communicate FTL.
 
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  • #2
Hide the violations in the correlations between outcomes, instead of making them apparent in the individual local outcomes, so Alice and Bob can't detect any effects until they get back together and compare notes. That will prevent them from using the violations for FTL communication, because of the note-comparing requirement.
 
  • #3
Strilanc said:
Hide the violations in the correlations between outcomes, instead of making them apparent in the individual local outcomes
Yes, the question is how to do that given that hiding correlations from local outcomes seems to lead to Bell type inequality.
 
  • #4
How is that an issue? You can't use Bell inequality violations to communicate, precisely because Alice and Bob need to get back together and compare notes to detect any violations. Regardless of what Alice and Bob plan to do ahead of time, Bob's expected measurement outcomes are always 50/50 coin flips.

If you're having trouble being convinced about that, go to this blog post. There's a few interactive widgets in it. The third one, about three quarters of the way down the page, is a "try to communicate with entanglement" game. It simulates what happens when Alice and Bob turn and measure their qubits, based on the strategy you enter.

The goal is for Bob's move variable's value to end up equal to what the refChoice variable given to Alice started as. The table below the widget shows how well the entered strategy works. If the results statistically deviate from 50/50 within a column, you're communicating. See if what you have in mind works.
 
  • #5
Strilanc said:
How is that an issue? You can't use Bell inequality violations to communicate, precisely because Alice and Bob need to get back together and compare notes to detect any violations. Regardless of what Alice and Bob plan to do ahead of time, Bob's expected measurement outcomes are always 50/50 coin flips.
You are missing my question, so I will restate it.

QM predicts:
1. Entangled particles can violate Eberhard inequality in certain measurement arrangement.
2. Taken the same setup as in 1. for each side measurement outcomes taken separately but grouped by remote side's measurement settings are completely random within these groups.

Provide strategy how to produce sample that satisfies 1. and 2. Intuitively there seems to be no problem with that but as strange as it seems Eberhard inequality and it's sufficient assumptions seem to suggest that this is not the case. It's hard to believe that so I am asking the question as I might be missing something.
 

1. What are Eberhard assumptions?

Eberhard assumptions are a set of assumptions made by physicist and mathematician Philippe Eberhard in his research on the possibility of faster-than-light (FTL) communication. These assumptions include the existence of a hypothetical particle called the "Eberhard particle" and the concept of "entanglement swapping", where entangled particles can transfer their entanglement to other particles without being physically connected.

2. Can FTL communication violate the laws of physics?

No, FTL communication does not necessarily violate the laws of physics. Eberhard's assumptions suggest that FTL communication may be possible, but it is still a highly debated and unproven concept. Many theories in physics, such as the theory of relativity, do not support the idea of FTL communication. However, some scientists argue that there may be loopholes or exceptions in these theories that could allow for FTL communication under certain conditions.

3. Has FTL communication been successfully demonstrated?

No, FTL communication has not been successfully demonstrated in any scientific experiments. While there have been some studies and experiments that seem to suggest the possibility of FTL communication using quantum entanglement, these results are still considered inconclusive and require further research and testing.

4. What are the implications of FTL communication?

If FTL communication were possible, it would have significant implications for our understanding of physics and the universe. It could potentially allow for instantaneous communication over vast distances, which could revolutionize many industries and technologies. It could also challenge our current understanding of causality and the limitations of the speed of light.

5. Is research on FTL communication still ongoing?

Yes, research on FTL communication is still ongoing in the fields of physics, mathematics, and engineering. While there is currently no concrete evidence or proof of FTL communication, scientists continue to explore the possibility and potential implications of this concept. New technologies and advancements in quantum mechanics may provide new insights and possibilities for FTL communication in the future.

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