What exactly are interpretations of quantum mechanics?

[ynon]

atyy: "Ocean waves can be counted using integers, would it be equally as proper to refer to an ocean wave as a particle? "

I don't see how one could do that but that doesn't preclude wave-particle duality at the quantum level. A bowling ball has a wave function but I don't think of it as a particle.
Wave-particle theory is old fashion but so am I.QM particles and waves are one and the same and we only view different aspects of the same phenomena. We can elect to view either but we change nothing by simply observing or verifying a state..No matter how the cat is alive or dead it is never both.. QM is strange and nowhere near completely understood by anyone but one does not alter reality by only observation in QM or the macroscopic universe of which there can be only one by definition. The universe is defined as, " The Universe is all of time and space and its contents" Wikipedia. All means everything unless physicists have their own special definition of all or universe. QM isn't known to split the universe and alternate time lines are proposed but unproven. Great for Sci-fi story lines and like religion fun to read or debate but a matter of faith. IMO

" God is so great he does not even need to exhist" from a rabbi in a story by Victor Weisskoph

 

[stevendaryl]

I don't consider MW as logically consistent, in its derivation of the Born rule it presupposes common sense, but I see no way to justify the applicability of common sense in MW.

If MW fails in a non-circular way to derive the Born rule, that isn't actually an inconsistency. A theory is inconsistent if it allows the derivation of a contradiction, but failing to derive something doesn't imply inconsistency.

 

[Splizard]

We don't know what Interpretation is correct until we measure it.

 

[craigi]

What exactly are interpretations of quantum mechanics? Is only one of them correct?

Contrary to popular belief and posts in this thread, many of what are commonly termed interpretations, do have subtley differing implications which can in principle be differentated.

Some examples can be found here:

http://link.springer.com/article/10.1007/BF00670071
http://www.researchgate.net/publication/253061131_Gravitational_Collapse_of_the_Wavefunction._AN_Experimentally_Testable_Proposal

However, with current technology, it is not possible to perform these experiments.

 

[stevendaryl]

Contrary to popular belief and posts in this thread, many of what are commonly termed interpretations, do have subtley differing implications which can in principle be differentated.

Some examples can be found here:

http://link.springer.com/article/10.1007/BF00670071
http://www.researchgate.net/publication/253061131_Gravitational_Collapse_of_the_Wavefunction._AN_Experimentally_Testable_Proposal

However, with current technology, it is not possible to perform these experiments.

As Ilja pointed out, ultimately the goal of thinking about alternate interpretations IS to find empirical ways to distinguish them. It might be that two interpretations are currently indistinguishable (even in theory), but different interpretations suggest different extensions of current theories, which might be empirically distinguishable.

For example, a Lorentz-type ether theory can be constructed that is indistinguishable from Special Relativity. But they have different extensions---an ether theory has the possibility of extensions that violate Lorentz symmetry.

 

[Ilja]

If MW fails in a non-circular way to derive the Born rule, that isn't actually an inconsistency. A theory is inconsistent if it allows the derivation of a contradiction, but failing to derive something doesn't imply inconsistency.

Ok, let's add that common sense essentially assumes that there is only one world which would actually happen.

 

[stevendaryl]

Ok, let's add that common sense essentially assumes that there is only one world which would actually happen.

Well, "common sense" really amounts to a naive theory of physics that is good enough for practical purposes. There is no logical reason to think that something being common sense makes it true.

If a theory is logically consistent and is also consistent with our experience, then we can't rule it out on the grounds of logic alone. We can rule it out based on aesthetic criteria of being more convoluted than it needs to be to account for the facts, but that's not really conclusive. Why should we expect nature to be simple? It's nice for us if it is, but why should it be?

To me, it's ultimately a practical matter. We don't have time to investigate every possible theory, since there are infinitely many of them, so we confine our attention to the ones that are simple enough that we can hope to make some progress on. But it's ultimately subjective, how we choose which theories are worth considering, and which ones are not worth our time.

 

[Ilja]

Well, "common sense" really amounts to a naive theory of physics that is good enough for practical purposes. There is no logical reason to think that something being common sense makes it true.

Yep, the point was the following:

Common sense presupposes single world. The derivation of Borns rule presupposes common sense. MW, if it uses this derivation, therefore, presupposes common sense, therefore presupposes a single world, logical contradiction.

Of course, there is a lot of room for disagreement, for the simple reason that common sense is much too vague. The "common sense" which presupposes the single world, in principle, may be different from the "common sense" used to derive Borns rule. But I see no way for this, Born's rule requires probabilities, and I see no base for probablity in many worlds.

 

[Jazzdude]

But I see no way for this, Born's rule requires probabilities, and I see no base for probablity in many worlds.

Subjective probability in the frequency sense arises naturally from the branching idea. That's why the first approach for deriving Born's rule was based on branch counting. Of course, the result of that counting cannot depend on the weights of the branches and therefore the rule cannot be recovered. That's why Everett introduced a cutoff that, if chosen adequately, results in the right statistical prediction. It's not hard to see that his derivation is arbitrary and wrong. Later attempts to fix this didn't give much better results. Other problems with branch segregation arose in addition and led the community to believe that branch counting is inherently flawed, as branches are already an ill-defined concept.

That's where the story of MWI ends for me. Without the concept of branches and the natural way of introducing probability by branch counting, there is no way to have any natural notion of probability in the interpretation. All attempts to introduce it must lean just as far out of the window as any other interpretation and instantly kill all the appeal of Everett's approach.

With this preamble I agree with your statement. There's no satisfying way of speaking of probability in MWI.

Cheers,

Jazz