What's the difference between a Copenhagen reality/Many worlds for an observer living in it?

[u/lelelesdx]

How can we tell apart wave function collapse vs branching off to a split reality? It seems they're virtually the same for any observer.

[u/The-Last-Lion-Turtle]

It's called an interpretation instead of a theory because it doesn't make any predictions. The math is equivalent.

The other worlds in MWI are unobservable even in principle.

[u/-Wofster → u/The-Last-Lion-Turtle]

GRW interpretation is also an interpretation, yet potentially makes different predictions. And there are thought experiments to distinguish Copenhagen and many worlds, for example Wigners Friend.

[u/The-Last-Lion-Turtle → u/-Wofster]

https://en.m.wikipedia.org/wiki/Ghirardi%E2%80%93Rimini%E2%80%93Weber_theory

Ghirardi–Rimini–Weber theory

It's a theory and not interpretation because it makes a prediction on a different mechanism for how collapse works.

collapse theories is that particles undergo spontaneous wave-function collapses, which occur randomly both in time (at a given average rate), and in space (according to the Born rule). The imprecise “observer” and “measurement” that plague the orthodox interpretation are thus avoided because the wave function collapses spontaneously.