Question: how is quantum entanglement possible?

Lauren Burns answered on 8 Jun 2018:

If you are puzzled about quantum entanglement, then you are not alone! Even Einstein was sceptical of the phenomenon. Effectively, quantum entanglement is learning something about one quantum system, tells you something about another physically separate quantum system. Imagine if you had two cats (we know how much physicists love cats!); one white, one black. You put them in two separate boxes, it doesn’t matter how far apart you put those boxes, once someone comes along (who knows the colour options of the cats) and opens one box, they now know, not only what colour the cat in the open box is, but also what colour the cat in the other box is. Physicist would describe the colour of the cats as being entangled, as once you know the colour of one, there is only one option for the colour of the other.

Obviously, with quantum mechanics it is not as simple as colours, they refer to something called magnetic spin – but that is a conversation for another time!!