One of my biggest peeves in the physics world is the idiocy of the Everettian Many Worlds interpretation of quantum theory, characterized by this quote from Sean Carroll:

There was nothing stochastic or random about any of this process, the entire evolution was perfectly deterministic. It’s not right to say “Before the measurement, I didn’t know which branch I was going to end up on.” You know precisely that one copy of your future self will appear on each branch. Why in the world should we be talking about probabilities?

There’s a perfectly good reason to talk about probabilities. **We EXPERIENCE them.** I will measure one of a particular group of results, and on repetition of the experiment those results will occur with certain probabilities as given by the Born Rule. The standard quantum theory (Copenhagen interpretation) provides an axiom calling for use of the Born Rule. They don’t really explain why, but then again they don’t really have to – it’s an axiom. Many Worlders, however do not include that axiom, so they’re on the hook for an answer. They provide one, but it’s fairly hand-wavy.

The real annoyance, though, is attitudes like Carroll’s above, where they simply try to wave the whole thing away. In case it’s not obvious, I certainly do not hold with the Many Worlds interpretation – I consider it very far out in left field. But even if we entertain the notion, it’s still necessary to address the probabilities, because they correspond directly to our experimental outcomes, which is really THE WHOLE POINT OF THE ENDEAVOR.

Carroll’s post with the above comment can be found here:

Why Probability in Quantum Mechanics is Given by the Wave Function Squared