[lamontcg]

> which theories are highly speculative.

So QM itself is on very, very solid ground. You're using it now on your computer.

The interpretations of QM and the attempts to reconcile the exceptionally well tested mathematics of QM and the reality that we experience which is not-QM at all are all philosophical with zero evidence. Everyone just tries to make compelling arguments based on things like Occam's razor about why their horse is the best one in the race without actually knowing anything at all.

We have place a few bounds around things like Bell's inequality so we know that local hidden variable theories are ruled out, but that is about it.

The title article is very interesting because its one of the first few actual tests to probe if there really is a transition between QM reality and classical reality. Regardless of who actually wins the horse-race the important thing here is that there's slow progress being made on trying to experimentally test theories. This is why I've always liked the Penrose models of collapse better than the MWI models since the former have some chance of being actually testable, while with MWI you just blindly decide it is true or not and then you argue a bunch about philosophy and never do any experiments, which isn't science. Penrose models of collapse might be wrong but at least they're in principle testable, which is incredibly exciting about this article.

[c1ccccc1]

Many worlds is absolutely testable, since if we observe collapse in even a single one of these experiments then that completely falsifies many worlds. If one of these experiments discussed in the article had actually observed a collapse, then I have no doubt we'd be seeing headlines like "many worlds theory disproven", and Nobel prizes for the physicists involved. It would be the biggest discovery in physics for decades.

[throwaway81523]

We "observe" collapse all the time, and can calculate the probabilities of the different possible collapsed states of a not-yet-observed superposed or entangled state using the Born rule. What we don't know, and can't tell, is whether we have seen an "objective collapse" (we live in just one universe, that undergoes a discontinuous change at the time of measurement) or in something like MWI. That is question for philosophers afaik. The experiment in the title falsifies certain models of objective collapse, but others are harder to falsify.

[c1ccccc1]

I agree that's it's possible to create objective collapse theories that are arbitrarily difficult to falsify, but the difference between objective collapse and regular old decoherence due to interaction with the environment has experimentally measurable implications. In particular, if you expect a certain probability of objective collapse in a certain period of time, then do an experiment with a coherence time longer than that, while keeping your system carefully isolated from interaction with the environment. Then if the wavefunction collapses anyway, that would prove objective collapse and disprove many worlds.

[throwaway81523]

I thought an objective collapse theory was one where the observation (whatever that is) causes the collapse. An observation is necessarily an interaction with the system, where the observer is part of the environment. So if the system is that isolated from the environment, the collapse or lack of it can't be observed. I didn't think it meant the collapse happens after some amount of time like radioactive decay, even without an observation (interaction). Maybe I'm wrong.

[lamontcg]

You don't get there from WMI though. You get there from trying to prove collapse happens and testing some other theories predictions.