"The wavefunction never collapses"

[javisot]

What we really need is a theory in which "spacetime geometry" is not built into the foundations at all, but emerges from something else. That's what, for example, loop quantum gravity is trying to do. (String theory? Not really. It still assumes a background--it's just a background with 10 or 11 or 26 or whatever dimensions instead of 4. It doesn't discard the concept completely at the foundational level.)

In string theory (M), are 10+1 dimensions "assumed" in the same way that 3+1 dimensions are assumed in GR?

I understood that problems in string theory have solutions if and only if the problem is embedded in a spacetime with a specific number of dimensions. Unlike other theories where spacetime is a rather malleable tool, in string theory the number of dimensions of spacetime is a consequence, eliminating loopholes. Isn't that emergent? (that the dimensionality of spacetime arises as a necessary consequence to solve something)

 

[PeterDonis]

In string theory (M), are 10+1 dimensions "assumed" in the same way that 3+1 dimensions are assumed in GR?

There are restrictions, at least according to string theorists, regarding what numbers of dimensions allow solutions, yes. But the point is that there is still an underlying spacetime manifold. The spacetime manifold doesn't emerge from something else; it's a fundamental aspect of the theory that's just put in by hand. The only thing the theory predicts is how many dimensions it has to have in order for there to be solutions.

in string theory the number of dimensions of spacetime is a consequence

The number of dimensions is, yes, but the fact that you're using a spacetime manifold at all is not. See above.

 

[Dale]

Of course nature "views them as incompatible"; our current theories are just not yet able to distinguish them.

I don’t at all see this as true. Certainly not “of course”. Simply saying “of course” is not at all convincing.

What actual evidence do you have from nature that indicates that nature views different interpretations of QM as incompatible?

I know lots of people who view them as incompatible. And I know lots of people who believe that nature shares their view. But so far I have seen no indication that nature views different interpretations as incompatible.

 

[javisot]

I know lots of people who view them as incompatible. And I know lots of people who believe that nature shares their view. But so far I have seen no indication that nature views different interpretations as incompatible.

I agree with your point and would add that if by "compatible" we mean being able to explain the same results, then MWI and Copenhagen are compatible.

If by "compatible" we mean something more complex than simply being able to explain the same results, then MWI might not be compatible (depending on the exact requirements for compatibility).

 

[jbergman]

I don’t at all see this as true. Certainly not “of course”. Simply saying “of course” is not at all convincing.

What actual evidence do you have from nature that indicates that nature views different interpretations of QM as incompatible?

I know lots of people who view them as incompatible. And I know lots of people who believe that nature shares their view. But so far I have seen no indication that nature views different interpretations as incompatible.

I think the whole discussion about how gravity fits in here at least suggests that they aren't necessarily all compatible.

Penrose's interpretation is radically different. At this point we don't have any experiment to decide but I personally think it is worth thinking about the implications of the different "interpretations".

 

[Dale]

I think the whole discussion about how gravity fits in here at least suggests that they aren't necessarily all compatible

That is a far cry from “of course nature views them as incompatible”.

 

[Matterwave]

Penrose's interpretation is radically different. At this point we don't have any experiment to decide but I personally think it is worth thinking about the implications of the different "interpretations".

By Penrose interpretation do you mean the Penrose-Diosi model where gravity causes collapse?

That one should actually make some different predictions from standard QM, it just does so at a scale that's not easy to access and there's some parameters that can be tweaked. The simplest version of that theory seems to have been falsified. There's another thread around here on it.

I believe the GRW collapse theories are also in a similar situation.

The above are called theories since they make some different predictions than standard QM so they don't seem to be interpretations.