It is not faster than light.
I think what he wanted to show was a situation, in which entanglement and quantum mechanics, are superior to classical physics. i.e someone using quantum mechanics would have an advantage over someone who don't.
However, as he said, in this situation the two generals could have agreed on something else, like if it was raining or not.
In fact, something they could have done is to flip a coin, and split with a copy of the result, which they only look at when they launch the attack. It would have the same effect.
With a random variable (the coin flip), that is hidden until revealed, we achieve the same results as quantum mechanics.
Scientist call them "hidden values" and Einstein hopped we could explain the "spooky action at a distance" with such hidden variables. But we can't, Bell proposed an experiment with entangle state which measurement could not be explained by such hidden variables, and Aspect did the experiment and obtained the predicted results.
So there exist situation where we can use entanglement to achieve better results, for example in "non-local games", where players sharing entangled state can win with probability 1, when "classical player" with probability < 1
> In fact, something they could have done is to flip a coin, and split with a copy of the result, which they only look at when they launch the attack. It would have the same effect.
Yes but the difference is that in this case, the plan already exists from the moment the coin is flipped until the result is revealed to the generals. In the QM case no one (not even God) knows what the result will be until it is actually measured,but once that happens the result is known "instantly" at both places (assuming both coins arrive at the same time), so in that sense is a FTL communication (of course it is not real communication)
“ So there exist situation where we can use entanglement to achieve better results, for example in "non-local games", where players sharing entangled state can win with probability 1, when "classical player" with probability < 1”
Do you have an example for this? This is really interesting
I think key is that both generals have already agreed on a predetermined "meaning" of each coin flip outcome, rather than having to communicate it on a different, slower medium after the coin has been flipped.
So really it just front-loads that portion (I.e. removes it from consideration as part of the proposed solution) instead of allowing it to slow down solving the overall problem. It requires precomputation/agreement beforehand, rather than during the time allotted to the problem.
The speed of that precomputation would still be unchanged, and still be the slowest portion.
Yes of course that is why it is not real communication, but in a sense is better than a classical solution because nobody actually knows the final decision until the last second. Of course you could get philosophical and say that an enemy can intercept the quantum coin and measure it, thwarting the plan, so in that sense is the same thing that sending just a pic, but then you will be pulled by the same kind of discussion the physicists has spent the last 100 years doing. Check for example the correspondence between Einstein and Born https://www.amazon.com/Born-Einstein-Letters-1916-1955-Frien...
The "communication" of the final decision is FTL. If you choose a non-QM method, like checking it if rained in some place or using the pic of a flipped coin, that final decision can only be "communicated" at a sub-luminar speed.
