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I have just understood what quantum superposition truly means in terms of the bra-ket vectors and the vector space. From my understanding, two entangled particles affect the probability of each particle's state. For example, if electron A and electron B were entangled and electron B would always have the reverse spin of electron A, then measuring one could inform us of the state of the other.

I wanted to understand that some videos that I watched claimed that this could allow us to pass information faster than the speed of light. Does that mean physically changing the spin of electron A would change the spin of electron B?

Vinay Bharadhwaj
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Entanglement is not only a quantum mechanical effect.

If you know two persons who are "entangled" by being twins, say John and David, and hear that one of them got a job in New York and the other has stayed in your town, if you meet David on the street, you immediately know that John is in New York.

The quantum entanglement comes from the common wavefunction describing the entangled particles. What is a wavefunction? the solution of specific potential and boundary values. To be able to " physically change the spin of electron A " you have to use an interaction. This interaction will be described by a new wavefunction, where the B particle is not included because it is far away, so the spin of B will be what it was when it left the group, it will not be affected.

anna v
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  • I might be wrong, but entanglement is as far as I know, by definition, a quantum effect. Of course, there are also non-quantum correlations, as your first example shows. The point of entanglement is that in quantum mechanics, these correlations can be stronger (in a certain sense) than you'd expect from a classical point of view. Anyway, in the end this is just terminology. – Tobias Fünke May 07 '22 at 10:19
  • Can John and David violate a Bell inequality? – Norbert Schuch May 07 '22 at 22:14
  • @NorbertSchuch Words have definitions independent of mathematical physics. Mathematical physics uses words to define mathematical effects that have a meaning when read/heard so that a meaning can be attached to mathematics. This does not mean that the everyday word follows all the mathematical definitions. The mathematical definitions are a subset of the meanings of the word. – anna v May 08 '22 at 04:04