[securityfreak]

Could someone please explain, how can they know beforehand the other electron in the other diamond is the first one's "sister"? What if those two are NOT entangled and will have identical spins? What defines entangled electrons? Is it a must that once they were e.g. in the same atom? Thank you. (I only completed 2 basic University physics courses which isn't enough :D )

[caf]

They use a process called "entanglement swapping" that allows you to create entanglement between two particles that have never interacted. It's described partway through this article:

http://www.scottaaronson.com/blog/?p=2464

[comboy]

This should make things more clear: https://www.youtube.com/watch?v=ZuvK-od647c

[securityfreak]

Thank you. It does explain what I was missing from the video.

[tim333]

I think that if you had non entangled electrons you wouldn't get the 'spooky' result. You'd just get random electrons arriving without anything statistically significant of interest.