Quantum Entangelment: What Einstein Called Spooky Action at a Distance Are Plants Using ItI found this explanation of quantum entanglement in the comments section of an article from io9.
By Roklimber "Being a theoretical particle physicist and someone who does not particularly like cats (there's got to be a correlation there somewhere), I feel compelled to provide a more accurate analogy/explanation for quantum entanglement, though nowhere nearly as entertaining as the cat analogy.
Not too long ago, a friend of mine who lives in the US asked me to explain QE in a way that was accurate but not too technical, so I'll just copy my message to him and paste it here.
=== Imagine that you and I each have a coin and that these two coins were "born" together, made from the same process, before I came to Denmark. Now, imagine that I bring my coin with me and that we decide to throw our respective coins and compare results. We devise some means of synchronizing our throws so that they occur simultaneously, that is, each throw of your coin happens at the same time I throw mine.
Now, suppose that our results are:
(T stands for tails, H for heads)
When I look at my results, without knowing about yours, I see that my results are what is expected from a fair coin. In fact, I could apply all kinds of randomness tests and I'd conclude that my coin is behaving like a random fair coin should. When you look at your results, without knowing about mine, you reach the same conclusion about your own coin.
Yet, when we compare our results, we see that they are strongly correlated: every time I get a T, you get an H, and vice-versa. How can that be? The processes are supposed to be *independently* random, but they're not; somehow, their randomness are strongly correlated.
This is what's known as "quantum entanglement." Of course, it doesn't happen with coins, but if you take two electrons created by the same process (some particle reaction), for instance, and move them far away from one another, this is what happens: when you measure one electron's spin, it's either spin up or spin down, and it's a random process. Same with the other electron. However, their spin measurements are correlated just as with the coins.
Fine, you say, there must be some interaction, some kind of force that the electrons are exerting on one another (like electromagnetism or gravity, but not either one, because we understand both and know that they aren't it), so that when you measure one's spin, the other "knows" to flip its own spin the opposite way.
Ok, the problem is, though, that these measurements happened simultaneously, which means that whatever that interaction or force is, it's traveling faster than light, which contradicts the theory of relativity (which is one of the backbones of physics). This is known as the "EPR paradox" (EPR stands for Einstein, Podolsky, and Rosen, the three physicists who came up with it).
Quantum entanglement and the EPR paradox are still not well understood, but quantum entanglement is a real phenomenon, observed experimentally already. Whether the EPR paradox is a true paradox remains a mystery. If it is a true paradox, relativity will need to be fixed.