9 ms·

Suppose that Alice and Bob share a seed to a RNG before the game starts. Can you explain how this will allow them to always win the game?

• bscphil 7y ago
  No, but as I said in my parallel comment, I don't understand how you can do any better than having an infinite amount of pre-shared information without actually communicating. If you can explain that, great (I really would be interested), but the important thing here is that without explaining it the article is kind of flawed.
  • dooglius 7y ago
    I'll make an attempt, though I am by no means a domain expert. As I said in another comment, Alice doesn't know which column is Bob's column, and Bob doesn't know which row is Alice's row. Bell-like inequalities allow something interesting to happen: Alice and Bob can measure a qubit at different "basis angles" such that the phase difference in their basis angles is reflected in the correlation of what outputs they observe from the qubit. You can't do this classically; what Alice does with a pre-shared bit and her row and what Bob does with the pre-shared bit and his column, form independent random variables. It may help to point out that (someone correct me if I'm wrong here...) this only works if both Alice and Bob are able to use their hidden information to choose the bases they're using to measure the qubit; if they were stuck with measuring at pre-determined angles, this trick doesn't work.
    • taneq 7y ago
      OK, so if I'm understanding this right - when you give them a pair of entangled particles, they can each do some stuff to their particle to determine what the other party is going to do. How is this not communication?
      • caf 7y ago
        They can determine what the other party is going to do, but can't influence it, so that's not communication.
      • JadeNB 7y ago
        I think (but IANAP) the answer is in two parts: (1) you can’t intentionally send a message—it’s like asking whether ancient civilisations are communicating with archaeologists, to which the answer is surely “only metaphorically”; and (2) even if it is communication in some sense, it’s still surely surprising, no?
        • taneq 7y ago
          Point 1) matches my lay understanding of quantum entanglement; information is transferred somehow between the entangled particles but not in a way that we can use. So if this new thing IS communication via entanglement (and I can't see how it's not, given the description) then that's huge, and opens the door to all sorts of interesting things.
      • dooglius 7y ago
        Not quite, you can do some stuff that affects the correlation between one output and the other, but that can't be used for communication as each output in isolation looks random.
  • dfdz 7y ago
    That’s a very valid question, and I agree the article fails to explain. The problem is that the answer is complicated (see the discussion at the bottom of the notes I posted). So my suggestion is 1) convince yourself sharing a classic seed is not enough to always win 2) read the blog post describing a simpler problem from ahelwer 3) take it on faith that this idea can be used for the magic square game 4) I know this is an unsatisfactory answer, but hopefully it is a start!