Can Quantum Entanglement surpass the speed of light

[freyar]

There are some elements of truth in that analogy, but I think it's going too far with how things change in time; the important point is a little more complicated and much, much weirder.

Since we've been talking about cake, I'll rephrase the photon experiment from earlier in terms of cake. Let's talk about simple cakes which have only two properties, the flavor of the actual cake, which can be chocolate or vanilla, and the flavor of the icing, which can also be chocolate or vanilla. Sorry if you don't like those flavors.

Here is where the weirdness starts. In quantum mechanics, there are what we call "incompatible observables," meaning that you can't know them at the same time. In terms of our cake analogy, you can't know both the flavor of the icing and the flavor of the cake. In experimental terms, what this means is that, say you eat some of the icing, and it is vanilla. Then, if you eat a piece of the cake, half of the time it will be chocolate and half the time vanilla. But suppose you eat some vanilla icing on one cake, then eat some of the cake from that cake (it's vanilla too). Then eat some of the icing from that cake again. There is now a 50% chance that the icing has turned to chocolate! That's because you can't know the flavor of the cake and icing at the same time.

Actually, I suppose that's the 2nd bit of weirdness. The first bit is that the outcomes of experiments are always probabalistic; only the averages of a lot of identical experiments can be determined/predicted by calculations.

The entanglement issue is even weirder. In this experiment, we have two cakes. We know that (somehow), if cake A is chocolate, then cake B is vanilla (or vice versa) AND that if the icing on cake A is chocolate, then the icing on B is vanilla (or vice versa). So if I eat some of the icing on cake A and notice that it's chocolate, then anyone who eats the icing on B will taste vanilla (assuming nothing else happens to the cakes in the meantime), and it doesn't matter if there's time for me to send a light signal in between. Same thing if I eat the cake of A and you eat the cake of B. But if I eat the icing of A and you eat the cake of B, our "measurements" don't influence each other at all.

 

[Puggins]

Maybe someone mentioned this here, but just to reiterate: the cool thing is that the particles are in a quantum state that is not supposed to be able to be predicted.

Let's do another example. I have two d20s. I "entangle" them. Then I start them spinning in little boxes and give one of them to Bob and one to John. Neither of them know what number is going to turn up once the dice stop spinning- these are fair dice. Oh, and I'm crazy good at spinning, so they'll keep spinning until either guy rattles his box.

Bob decides to rattle his box. The die stops spinning and lands on a 17. You now "know" that John's die will land as a 3, regardless of when or where John decides to rattle his box.

Spinning coins would be a bit more accurate, I guess, but I liked the die idea better

 

[Umbran]

Maybe someone mentioned this here, but just to reiterate: the cool thing is that the particles are in a quantum state that is not supposed to be able to be predicted.

Well, our intuition says they could not be predicted. The cool thing is that our intuition is wrong. The two objects, despite the distance between them, are in a sense *one* object.

I mean, if you flipped a coin, and it came up heads, you wouldn't at all be surprised that the other side would read tails. Just take that one flipping coin, put one side on Earth, and the other side on the Moon, and it's a little weird....