Curious about this proposition for measuring for FTL

In summary, the conversation discusses the potential for using repeated measurements of entangled particles to communicate between two parties. However, it is ultimately determined that this method is not effective due to the random nature of the measurements and the inability to control the state of the particles. The idea is based on misunderstandings and does not hold up to the proof of the no-communication theorem.
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Hereweald
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I think it's possible to create a propability higher than 50/50 between two sides communicating by measuring a state of quantum entangled particles.

Full disclosure, I do not have credentials in this field, and only watched a youtube video explaining the subject. So if this is wrong, I would love to be explained why!
So the theory relates to measuring yhe state of a quantum particle, say up or down. Specifically this build on the technique described as repeat measurements seen in this video:

I understand why repeat measurements wouldn't work. However what if this series of measurements was done multiple times. In essence we'd have a grid of particles. Then we gave both Alice and Bob the some rules:

- Bob on collum 1 (or the first series of say 5 measurements): Measure until you get the result you want.

- Alice on collum 1: Measure until you percieve a change in direction.

This would not help much yet of course, as Bob it wants could get the result they want on the first particle measured, and thus Alice would be no wiser as to what Bob means.

But here is where we repeat the measurements. And give Bob and Alice new rules:

Bob still measures until they get the result they want, or until they have measured the same number of particles. And Alice also does this exact thing.

In this case, if alice measured more particles then Bob, given enough iterations of this pattern, Alice should notice an inconsistency in their measurements and tgus deduce Bob's answer must be the very first particle measured. Otherwise, Alice's measurement pattern must match Bob's pattern.

The only thing I can think of that breaks this is if there is a situation where all measured particles have the same state, and thus Alice never notices an incosistency. However THAT is a propability, but not a 50/50 one.

If I need to illustrate this example I would gladly do so! However, I am writing this from my phone, rather late in the evening :p (thanks quantum physics).

Super interested in the responses to this!
 
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  • #2
This doesn't work.

The basic problem is that there is no way for either Alice or Bob to know whether the other one has performed a measurement. As particles reach Alice she measures them, and half the time the particle is spin-up and half the time the particle is spin-down.... but did Bob measure the other member of the pair, or did he quit measuring a while back? She can't tell, all she knows is that particles are coming by, she measures them, half the time they're spin up and half the time they're spin down. Maybe Bob measured the other particle and is looking at the opposite result, maybe he didn't measure it so has no result to look at it, but either way Alice is just looking at her meaurement.

This and similar ideas have been discussed in many other threads here. None work - they can't, the proof of the no-communication theorem is quite convincing - and they all turn out to be based on one of several misunderstandings:
a) They think that Bob can control whether his particle is spin-up or spin-down. He can't - his measurement is as random as a tossing a coin, and therefore Alice's result is just as random.
b) They think that Alice can tell by looking at her particle whether Bob has measured his. She can't - in fact the only way that either Alice or Bob can even know that they're dealing with entangled particles is by getting together afterwards and comparing notes, and seeing that every times that one of them had a spin-up particle the other one had a spin-down particle.
c) They hypothesize that the pair creation is biased so that Bob is better than 50/50 to get spin in one direction or the other. If this were possible it would indeed be possible for Alice and Bob to communicate - but the 50/50 probability that says Bob might as well be flipping a coin is fundamental to the math of the entangled pair. (Look at the video around 8:41 and note that the collapse could have gone the other way).
d) They try to use repeated measurements of the same pair. (You've already figured out why this doesn't work).

Anyways, we're leaving this thread open for a while, but please take some time to go through the older threads......
 
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  • #3
Hereweald said:
I think it's possible to create a propability higher than 50/50 between two sides communicating by measuring a state of quantum entangled particles.

Full disclosure, I do not have credentials in this field, and only watched a youtube video explaining the subject. So if this is wrong, I would love to be explained why!
I say no more. Except learn the material before you attempt to discredit it.
 
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