My understanding is that pilot wave theory (ie Bohmian mechanics) explains all the quantum physics with no weirdness like "superposition collapse" or "every particle interaction creates n parallel universes which never physically interfere with each other". It is not fully "local" but who cares?
Is there any reason at all to expect some kind of multiverse? Why is the multiverse idea still heavily referenced (eg in acausal trade posts)?
Edit April 11: I challenge the properly physics brained people here (I am myself just a Q poster) to prove my guess wrong: Can you get the Born rule with clean hands this way?
They also implicitly claim that in order for the Born rule to work [under pilot wave], the particles have to start the sim following the psi^2 distribution. I thinkk this is just false, and eg a wide normal distribution will converge to psi^2 over time as the system evolves. (For a non-adversarially-chosen system.) I don't know how to check this. Has someone checked this? Am I looking at this right?
Edit April 9: Well pilot wave vs many worlds is a holy war topic. People have pointed out excellent non-holy-war material:
Perhaps just an infinite universe gives you the same philosophical conclusions/feels as many worlds? Who has already thought that idea through?
Some of the stuff Wikipedia mentions relating to the "many universes different constants" idea (level 2 here) sounds like it might actually have a little rigor?? How to tell?? (These are optimized by the publishing system to sound like they would have rigor.)
I think this is a little tricky as the theory uses the actual continuum for wave functions such that the amount of information is and remains infinite whether we remove far-away branches or not.
On the other hand, we can only ever calculate finite approximations of the true thing and here we definitely can be more or less efficient.
When we "collapse the wave function" during a measurement process, we decide to remove the other branches from our description such that in some sense a pragmatic version of hardly computing any of the pilot wave is the standard approach.
The description of Open Quantum Systems has really helped formalize this perspective and one can find that even just cosmic radiation or gravitational interaction is strong enough to create quick branching of the wave function for anything macroscopic.
Unfortunately a mathematically equivalent simplification is not feasible as technically the distant contributions are not ruled out to become important at some point in the future (e.g. the wave function tends to spread out in configuration space such that in a non-expanding universe we would expect branches to touch at some point), but at least for many situations one can get good effective descriptions which put us closer to a quantum-native description of how classical behaviour comes about. From that perspective, the probabilistic predictions tell us about which part of a simplified pilot wave (/many worlds branch) we expect to update towards.
Edit 2025
My understanding is that pilot wave theory (ie Bohmian mechanics) explains all the quantum physics with no weirdness like "superposition collapse" or "every particle interaction creates n parallel universes which never physically interfere with each other". It is not fully "local" but who cares?
Is there any reason at all to expect some kind of multiverse? Why is the multiverse idea still heavily referenced (eg in acausal trade posts)?
Edit April 11: I challenge the properly physics brained people here (I am myself just a Q poster) to prove my guess wrong: Can you get the Born rule with clean hands this way?
Edit April 9: Well pilot wave vs many worlds is a holy war topic. People have pointed out excellent non-holy-war material: