Gravity is unlikely to be the cause of quantum collapse, experiment suggests

Post by ClumsyPilot » Tue, Sep 08, 2020, 1:21 AM UTC

akvadrako wrote: post #30

tsimionescu wrote: post #27

Earlier quoted context omitted.

But this doesn't answer the question. If you claim that all of these possible observers 'exist', how does this have a physical meaning? This is what I never understood about MWI, in what physical sense can the many worlds be said to exist? Where are they in our universe? What direction would we have to travel to find them? Do they exert gravity on us? If not, then how can we claim that they exist in a physical sense?

Existence isn't based on something affecting our world, obviously - that's just absurdly self-centered. But anyway, the other worlds do effect our world - that's why we get interference patterns in double slit experiments.

Post by alpineidyll3 » Tue, Sep 08, 2020, 1:45 AM UTC

GuB-42 wrote: post #34

alpineidyll3 wrote: post #15

Earlier quoted context omitted.

Collapse is only mysterious to people who never learned thermofield theory, or non-equilibrium quantum dynamics. Unfortunately this is also a sizable fraction of all physicists. Thus we have articles like this :/ Basically all the work in getting large scale quantum computers to work lies in these fields. They will continue to grow.

I am not a physicist but isn't it an instance of "if you think you understand quantum mechanics, you don't understand quantum mechanics"? The measurement problem, which deals with collapse is still unsolved. It is also the reason why there are so many weird interpretations of quantum mechanics and that even top physicists can't agree on one. In fact the same physicists tend to sweep the problem under the rug and inst…

Post by zeofig » Tue, Sep 08, 2020, 2:38 AM UTC

alpineidyll3 wrote: post #44

GuB-42 wrote: post #34

Earlier quoted context omitted.

I am not a physicist but isn't it an instance of "if you think you understand quantum mechanics, you don't understand quantum mechanics"? The measurement problem, which deals with collapse is still unsolved. It is also the reason why there are so many weird interpretations of quantum mechanics and that even top physicists can't agree on one. In fact the same physicists tend to sweep the problem under the rug and inst…

There is no measurement problem. It so happens that most measurement apparatus are macroscopic and at a temperature much higher than the quantum gap of the system being probed. Measurements in qm imply a rotation between systems, and mixture with an incoherent thermal state implies a quantum superposition will lose coherence. Full stop. This is all understood in full, grab any text on non equilibrium quantum dynamics…

Post by mgraczyk » Tue, Sep 08, 2020, 4:35 AM UTC

Post by Xcelerate » Tue, Sep 08, 2020, 4:55 AM UTC

alpineidyll3 wrote: post #45

LittleTester wrote: post #41

Earlier quoted context omitted.

Decoherence doesn't really solve these issues. It gives you an approximately diagonal density matrix for the macroscopic degrees of freedom, but: (a) Not exactly diagonal (b) There isn't a unique decomposition of the macroscopic density matrix even after decoherence thus it cannot be taken as simply ignorance of some set of macrostates. You need something stronger, namely superselection or irreversibility.

That's correct, But there are numerous good methods to propogate irreversible dynamics in qm. Many of these are exact in the limit of a noninteracting bath of bilinearly coupled oscillators which is sufficient to describe a measurement collapse. There's no mystery or inexact proscription to such a simulation of a collapse process. It's just complicated.