How do we know Q entanglement exists if particles stop being entangled as soon as we observe them?
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Lets understand the theory a bit better.
Particles have some kind of angular momentum, we call it their spin. They aren’t spinning but we lack a better word. Angular momentum, without a doubt, is conserved. So if we look at a particle that has 0 spin and we split (or it decays) it into two particles where each of them have some non zero spin like ½, our conservation law states that they have to sum up to 0.
So particle A has ½ spin since I measured it and now I know that particle B has to have -½.
But these states are not predetermined for either particle. There is a 50-50 chance I measure ½ or -½ for particle A. And you can experimentally show that it’s in fact not predetermined. So we have this probabilistic nature for measuring states, this is experimentally proven, and we also have the conservation of angular momentum. Entanglement logically follows from this.
So entanglement is a consequence of superposition and the conservation of angular momentum. Of course we need to show that superposition exists and we don’t have hidden variables that predetermin the spin of our particles. This video explains just that: https://youtu.be/hiyKxhETXd8
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