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#18 www.reddit.com/r/askscience/comments/1bb3og/why_cant_quantum_entanglem

Let's say I have a grey marble. I can split this marble into two other marbles, and I tell you that as a fundamental law of the universe this property of 'color' will be 'conserved'. So if I split this marble into two marbles one must be black and one must be white. When I run my grey marble through the splitting machine you and I each pick up our new marble (unseen) and walk far away, to the edges of the Universe. Despite the distance, the color of our two marbles remains 'entangled'.

The important, and tricky, thing to understand about entanglement is this: it is not true that one of us picked up the black marble, and one of us picked up the white marble, and we simply do not know which is which, rather both of our unseen marbles are simultaneously black/white and will only 'collapse' into one of those colors (randomly) upon observation.

If I look at my marble, and see it has collapsed into a white marble, yours will instantly become a black marble even though we could be many light years apart. This is because the universe will not tolerate us violating conservation of color, even for an instant.

So at first glance it seems this may gives us a loophole in FTL communication, but when you think about it you'll see it can't. After all, I can't control which color my marble collapses into. And though the color I see determines the color of your marble, you won't know that your marble's color has collapsed unless I also send you a conventional message at light speed (or slower) with my observation.