Essentially from the point of view of the massive object, the interaction with space-time acts as some decoherence process.
Well, the question is, can we use gravity in the same way that we use quantum processes, i.e., in a coherent way? If we can, e.g. using it to establish entanglement, then the theory you describe cannot hold.
Edit: I maybe semi take this back, it actually may be the case that this particular weird model of gravity would provide a way to distinguish between the interpretations of QM because of how grossly it violates the usual assumptions of QM. It seems too implausible for me to really dig into but I don't entirely grok how they propose melding the proposed inherent but non-quantum randomness with the rest of quantum physics in a way that still makes things line up well in the face of observation/collapse (or the equivalent in many-worlds). They might lean enough on assumptions about how that happens to break the observational equivalence?
https://www.scientificamerican.com/article/this-simple-exper...
You were taught wrong
So we'd be evolving from a pure to a mixed state?
A good entry point to CQ is Oppenheim's [hep-th] https://arxiv.org/abs/1811.03116
"... invariant under spatial diffeomorphisms ... consistent ... completely positive, norm preserving, and linear in the density matrix ... the metric remains classical even when back-reacted upon by quantum fields ... the dynamics here, while stochastic, can leave the quantum state pure -- it is rather the classical degrees of freedom, which gain entropy."
It's a heavy couple dozen pages (part V is a mountain for mountaineers (I am nowhere near the summit) and the foothills are also hard work, though most of it shouldn't pose technical comprehensibility problems anyone who's done QFT (GKSL is prominent [short intro <https://arxiv.org/abs/1906.04478>], and the Lindbladian is the generator of time-translations) and who has encountered Lagrangian and Hamiltonian formulations of gravitation, especially if they've glanced at Birrell & Davies. A crash read or refresher of Wald's QFTCS https://arxiv.org/abs/gr-qc/9509057 might be useful if like me you've mostly spent time in one of the two fundamental silos and want a bit more meat than what's in the first couple pages of Oppenheim 2018's part I. The general relativistic constraint equations are also important, and there is a good overview at https://link.springer.com/article/10.1007/s41114-020-00030-z
The meat, for me, is the potential for a better approximation than semiclassical gravity when quantum fluctuations are large: "[even if not fundamental, CQ gives] the ability to consistently study back-reaction effects in cosmology and black-hole evaporation ... [but] care should be taken, since an effective theory might violate our assumptions of Markovianity or complete positivity at short time scales or when the gravitational degrees of freedom have not fully decohered.", "This theory serves as a sandbox in which to understand issues around the quantisation of the gravitational field. After all a probabilty density \rho and the Liouville equation have a lot in common with the wave function \psi and the Heisenberg equations of motion. [and the rest of that paragraph just before (eqn 2)]".
It's one of those things that could be true and explain all of QM but also is kind of a cop out. "Of course your two detectors are giving correlated results, they were tightly coupled 13.8 billion years ago and now they are forever linked like all things."
That's just determinism. Superdeterminism additionally posits that the results of those experiments are all correlated so as to make it appear to us as if local hidden variable theories were false. Pick the settings on two polarimeters for a Bell-type experiment by measuring the spins on photons emitted 10 billion years ago from two different galaxies, and you'll find (or rather, won't find, because it's being hidden from you) that they were arranged, long before the Earth was formed, just so as to trick you. The universe is conspiring against us, and the whole scientific project is a farce.
That, or superdeterminism is false.
And we’re just measuring those.
We know two things:
- universe was small enough everything was tightly coupled
- non-local phenomena occur
Insisting that our beliefs reflect an ideology (eg, you can segregate off portions of reality to study in isolation) which seem contrary to observed reality (eg, the points above) is religion — not a scientific investigation of the universe.
To say that QM is in fact a local hidden variable theory because everything was once touching billions of years ago, without positing any mechanism for it is a cop out.
At least instrumentalism admits that there are interpretational questions, even if we don't need to answer them.
- because it was touching;
- and because we observe non-local information stored in braiding of the wave equation; even when we separate the constituent (quasi)particles.
The belief that you can reduce a system by decoupling a particle or system from outside influences is at odds with that second fact. We’re storing the hidden variables in those non-localities; when you measure a system where both particles are part of a non-local phenomenon, they’re coordinating through that non-locality.
What has literally no proposed mechanism is suggesting such non-local quasiparticles disappeared — by what specific mechanism did primordial anyons dissipate?
No. Also superdeterminism doesn't have non-local phenomena. The idea is that measurements are predetermined to look like quantum.
Second, dismissing superdeterminism is not, as you seem to say, "contrary to observed reality".
The belief that one is capable of forming ideas that bear any resemblance to reality, is justified on account of, in order for one's beliefs or lack-thereof to have any use, it would have to be true.
Things like the no-speed-up theorem (which I admit I'm not super familiar with), and other things of that sort, lead me to expect that, while I don't have a full argument for this, that it isn't possible for computational complexity reasons, for the early universe to be such that it, in effect, encodes predictions of what future measurements people will make, in a way that makes signals determining what measurement directions get used, correlated in the way that superdeterminism requires.
We know that the universe was once highly correlated, due to its size, and we know that such correlations form super-macro structures, from galaxies to filaments. We further know that knots in the wave equation are a non-local phenomena, such as with anyons. The minimal assumption is that any particle we encounter is part of such a non-local phenomenon.
To assume that we can isolated regions of reality uncorrelated to those two phenomena is to assume an ideological belief, unsupported by evidence.
That you didn’t discuss my actual objection to dismiss it with generalities is very telling.
1) Bohmian mechanics seems to require some kind of simultaneity. Various proposals have been put forth for making natural foliations, possibly using the wave function to do so, that allow one to evaluate the positions of all the particles at a given time so as to know which configuration point to use in obtaining the velocity of the particle. This is possible, but it does not feel philosophically satisfactory yet. GRWf does not require a foliation to be relativistic which is a nice feature.
2) Quantum field theory naturally models particle creation and annihilation. Most QFTs are presented in a mathematically incoherent way. While conclusions can be made via renormalization, etc., driving an actual dynamics is tricky from that stuff. By not doing perturbations but rather defining the operators by taking into account the shifting of the probability from one sector of n particles to another of n+1 particles, QFTs can actually be made to make mathematical sense. This has been accomplished in some of the simpler models. It is not a problem whatsoever to define a Bohmian evolution where particles appear and disappear in a probabilistic fashion. The difficulty is purely in having a properly defined wave function evolution and that is on its way to being solved.
3) One needs to define wave functions, their evolution, and the particle evolutions in a curved space-time. This is not a problem whatsoever. It is very easy to translate and interpret what we need into differential geometric language. QM has issues with the usual observables/operators translating (such as a momentum operator), but since these are derived concepts in Bohmian mechanics, no fundamental difficulty arises.
4) In general relativity, the mass distribution is part of the evolution of the space-time metric. The mass is based on where the particles are. To date, the wave function tells the particles what to do, but the particles do not have any impact on the wave function. The wave function is impacted by the space-time metric. Also, there are some suggestions that mass might be entirely a part of the wave function and not associated with the particle, i.e., the particles are really just undecorated points moving about.
Basically, gravity and the wave function need to work it out and the particles will then be guided by both as the space-time metric is what takes the gradient of the wave function or, for Dirac style motion, something analogous to a square root of the metric is floating around. Bohmian mechanics does have the advantage that it just has to be concerned with the evolution of the particle lines and not having to figure out how to define various observables.
In other words, a known space-time metric interfaces just fine with Bohmian mechanics, but figuring out how to evolve the space-time metric is still an open question.
At the current time, I am not aware of any novel ideas coming from a Bohmian or GRWf point of view towards resolving the problem of gravity.
If interested in a good discussion of all these things and much, much more, I highly recommend the recent book Foundations of Quantum Mechanics by Roderich Tumulka which covers what the title says, but also discuss Bohmian mechanics and other interpretations.
> The difficulty is purely in having a properly defined wave function evolution and that is on its way to being solved.
Interesting, could you provide some references?
Avoiding Ultraviolet Divergence by Means of Interior-Boundary Conditions https://arxiv.org/abs/1506.00497 This is perhaps the first of the papers and so may be a good place to start.
Bohmian Trajectories for Hamiltonians with Interior-Boundary Condition https://arxiv.org/abs/1809.10235 This is the Bohmian part of the story.
Multi-Time Wave Functions https://arxiv.org/abs/1702.05282 This explains the trickiness of having interactions with multi-time wave functions (space-time suggests having multi-time wave functions and no single time).
Creation Rate of Dirac Particles at a Point Source https://arxiv.org/abs/2211.16606 This seems to suggest that there is a kind of spiral approach from/to the point of creation/annihilation.
---
The authors have done a variety of papers on this. A key phrase they use is Interior-Boundary Conditions.
They also released a book based on a course covering some of these ideas: Multi-time Wave Functions, An Introduction https://link.springer.com/book/10.1007/978-3-030-60691-6