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Comment by K0balt | Hacker News Reader

This seems a bit self referential, if viewed from a many worlds interpretation.

The infinity of universes in which you can exist is reduced to a lesser infinity by the reverse time travel, since you could only have travelled backwards from universal states in which those specific conditions still existed, ergo reality appears to the traveller to be self healing.

That’s one of the things about MWI that is irritating, even though it still seems the most likely to me. It covers the testing parameters so completely that it is impossible to test. You always end up in a lesser infinity, but an infinity nonetheless. What we need is a way to quantify randomness in such a way that we might detect a change in the dimensions of infinities or something, but that seems improbable at best.

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The issue with Copenhagen is that it doesn’t describe when precisely wave-function collapse actually happens, i.e., when the physical process deviates from the Schrödinger equation. It is not a proper theory in that sense. There are objective-collapse theories that do, and therefore provide different predictions from Many-Worlds (which simply says that the Schrödinger equation always holds). We haven’t come up with experiments yet that could test those different predictions, but we may in the future.

I remember reading somewhere wave function collapse would have some energy signature and that someone failed to detect it, indicating the many worlds interpretation could not be ruled out.

The only thing I can think of that you might be thinking of is that as far as I know, MWI really requires QM be perfectly linear.

I'm not 100% sure, but wave function collapse might involve some non-linearity somewhere, whichight also be detectable in some fashion.

Bohm's Interpretation is experimentally indistinguishable from MWI.

On the other hand, Bohm's interpretation seems pretty ad hoc. And it also includes all of the other worlds that MWI has in it via the pilot waves that continue to exist and propagate forever. (The pilot waves never collapse.) It's just that only one of those many worlds ends up being "real".

Yes, Bohmian mechanics seems like MW with added complications, all the “worlds” still exist. It’s not clear how it is ontologically different from MW, other than that painting one of the worldlines green.

What I don't follow with the ideas about MWI is the idea of discrete universes at all. Why would one not be able to perceive the entire subset of universes in which one can exist? (in which you were born, didn't get hit by a bus, etc)

Necessarily, this lesser infinity of universes would tend to be extremely similar, and would average out to some kind of consensual reality, with the variation noise only becoming evident if one looked very closely (superposition, casimir effect, uncertainty principle, etc)

So the act of observation would merely divide this lesser infinity into two lesser infinities which would be distinct unless they were reunited by a reverse-time coherence such as many quantum experiments have demonstrated.

I would suspect that statistically, such reverse-time coherences are pretty common inside of one's personal light cone, so in this respect, I would guess that the "universe bandwidth" is probably quite robust and requires a pretty significant (macroscopic scale) effect in order to divide permanently into distinct infinities for a given observer.

Of course this is all just metaphysical conjecture, but Id be interested if anyone is seriously thinking along similar lines.

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