Spooky Action (at a distance)

Einstein's name for quantum entanglement, a phenomenon where two particles become linked so that measuring the state of one instantly determines the state of the other, no matter how far apart they are.

I've always found this phenomenon to be mind-blowing. For example, say there are two sister electrons, with + and - spin, on either side of the universe. I take electron + and flip it's spin to -. It's sister will instantaneously flip from - to +, even though it is millions of miles away. How could that be possible? 

Archival Print (color)