3 ms·

The measurement device gets entangled with the spin - which is in a superposition - and then I get entangled with the measurement device and for got measure the

The measurement device gets entangled with the spin - which is in a superposition - and then I get entangled with the measurement device and for got measure the entire environment. How does this avoid the many worlds? If the measurement device only sees half of the entangled spin state and I only see half of the entangled measurement device - say I see the spin measured up because the measurement device saw the spin up - how does this avoid the necessity of a second world where the spin was down? What breaks the symmetry? What makes the spin down half of the entangled state go away? There is also another weird asymmetry. For the spin we say that its superposition exists in my [slice of the] world but for the measurement device we say only half of the entangled state, the outcome I become aware of, is part of [my slice of the] world, what justifies this?

Joker_vD 2y ago
> What breaks the symmetry? Nothing. It keeps existing, and (1/sqrt(2) * <I think spin is down|⊗<device shows spin is down|⊗<spin was down| + 1/sqrt(2) * <I think spin is up|⊗<device shows spin is up|⊗<spin was up|) keeps evolving, and since QM is linear, the summands evolve independently. Yes, to the outside observer (the one who could look at the whole of the universe from the side/above without interacting with it) this does look very similar to MWI. But we are not outside of the universe, we exist inside it as a part of it, so for us it looks like spontaneous collapse of the wave function.
- danbruc 2y ago
  Maybe I am wrong, but that is exactly what I always assumed the many world interpretation to be. Especially I think many worlds also requires an outside of the cosmos observer to look at all the worlds, I do not think I ever heard someone claim that many worlds allows you and me to see or even move between different worlds.

Joker_vD 2y ago

> What breaks the symmetry? Nothing. It keeps existing, and (1/sqrt(2) * <I think spin is down|⊗<device shows spin is down|⊗<spin was down| + 1/sqrt(2) * <I think spin is up|⊗<device shows spin is up|⊗<spin was up|) keeps evolving, and since QM is linear, the summands evolve independently. Yes, to the outside observer (the one who could look at the whole of the universe from the side/above without interacting with it) this does look very similar to MWI. But we are not outside of the universe, we exist inside it as a part of it, so for us it looks like spontaneous collapse of the wave function.

danbruc 2y ago
Maybe I am wrong, but that is exactly what I always assumed the many world interpretation to be. Especially I think many worlds also requires an outside of the cosmos observer to look at all the worlds, I do not think I ever heard someone claim that many worlds allows you and me to see or even move between different worlds.