Bohmian mechanics and String theory

[TheHeraclitus]

TL;DR Summary

Is String theory compatible with Bohmian mechanics? Does string theory prefer some interpretations of QM more than others?

Is it easy to combine them or impossible? Is there a tension due to the non-locality found in Bohmian mechanics?

Thank you!

 

[ohwilleke]

AFAIK, string theory assumes that strings are subject to the same QM rules as fundamental particles in the SM. It isn't obvious how the analysis of Bohmian mechanics v. other QM interpretations is change in the context of string theory.

There are some who argue that Bohmian mechanics is flawed in QM and is the wrong interpretation, and that criticism could carry over to string theory. I suppose that the one thing that could be a problem in Bohmian mechanics in string theory but not in QM is if you assign a level of reality of pilot waves in Bohmian mechanics that could be explained with a BSM mechanism in QM which isn't available in string theory that purports to be a true TOE.

 

[mitchell porter]

String theory contains many features - relativity, fermions, gauge symmetries - which are already a problem for Bohmian mechanics at the level of field theory.

 

[Demystifier]

There is no much work on the relation between string theory and Bohmian mechanics. Well, except by me:
https://arxiv.org/abs/hep-th/0512186
https://arxiv.org/abs/hep-th/0605250
https://arxiv.org/abs/0705.3542
https://arxiv.org/abs/hep-th/0702060

 

[Demystifier]

String theory contains many features - relativity, fermions, gauge symmetries - which are already a problem for Bohmian mechanics at the level of field theory.

See the last paper on my list above.

 

[Demystifier]

I suppose that the one thing that could be a problem in Bohmian mechanics in string theory but not in QM is if you assign a level of reality of pilot waves in Bohmian mechanics that could be explained with a BSM mechanism in QM which isn't available in string theory that purports to be a true TOE.

What BSM mechanism do you have in mind? And by the way, in modern "string theory" (such as M-theory), strings themselves are not fundamental objects.

 

[martinbn]

There is no much work on the relation between string theory and Bohmian mechanics. Well, except by me:
https://arxiv.org/abs/hep-th/0512186
https://arxiv.org/abs/hep-th/0605250
https://arxiv.org/abs/0705.3542
https://arxiv.org/abs/hep-th/0702060

Given that string theory is relativistic and Bohmian mechanics practitioners believe that relativity is "wrong", how could they be compatible?

 

[Demystifier]

Given that string theory is relativistic and Bohmian mechanics practitioners believe that relativity is "wrong", how could they be compatible?

The same question one could ask about relativistic quantum field theory (RQFT) and Bohmian mechanics. You and me already had a lot of discussions on that, so if you remember what I said about RQFT in that context, the same can be repeated about string theory.

In short,
1. The idea that relativity is fundamentally wrong is the simplest, but not the only, way to formulate Bohmian mechanics.
2. If one takes a simpler Bohmian route and accepts that relativity is wrong in a fundamental sense, it can still be right in an effective sense.

In addition, I would add that some versions of M-theory (which is supposed to be a fundamental non-perturbative formulation of string theory) are not relativistic in a fundamental sense.

 

[martinbn]

The same question one could ask about relativistic quantum field theory (RQFT) and Bohmian mechanics. You and me already had a lot of discussions on that, so if you remember what I said about RQFT in that context, the same can be repeated about string theory.

In short,
1. The idea that relativity is fundamentally wrong is the simplest, but not the only, way to formulate Bohmian mechanics.
2. If one takes a simpler Bohmian route and accepts that relativity is wrong in a fundamental sense, it can still be right in an effective sense.

In addition, I would add that some versions of M-theory (which is supposed to be a fundamental non-perturbative formulation of string theory) are not relativistic in a fundamental sense.

The way I understand this is that Bohmian mechanics is incompatible with string theory as much it is incompatible with quantum field theory.

 

[Demystifier]

The way I understand this is that Bohmian mechanics is incompatible with string theory as much it is incompatible with quantum field theory.

Or, that Bohmian mechanics is compatible with string theory as much it is compatible with quantum field theory.

 

[Demystifier]

Is String theory compatible with Bohmian mechanics?

Yes.

Does string theory prefer some interpretations of QM more than others?

No.

Is it easy to combine them or impossible?

Once you know how to combine Bohmian mechanics with relativistic quantum field theory (RQFT), it's relatively easy.

Is there a tension due to the non-locality found in Bohmian mechanics?

There is some tension, but not more than with RQFT. Perhaps the tension is even smaller, because string theory has some nonlocal aspects (T-duality, AdS/CFT, ...) which RQFT does not have.

 

[Fractal matter]

Yes.Nnce you know how to combine Bohmian mechanics with relativistic quantum field theory (RQFT), it's relatively easy.There is some tension, but not more than with RQFT. Perhaps the tension is even smaller, because string theory has some nonlocal aspects (T-duality, AdS/CFT, ...) which RQFT does not have.

I have a suspicion Ads/CFT is local. There are superdeterministic theories around. It the causality that makes holography happen, it seems.

 

[Sunil]

Given that string theory is relativistic and Bohmian mechanics practitioners believe that relativity is "wrong", how could they be compatible?

That's not given. Bohmian mechanics is compatible with the original interpretation of relativity (usually namen "Lorentz ether"). But that's only a difference in interpretation. The empirical predictions are the same.

 

[martinbn]

That's not given. Bohmian mechanics is compatible with the original interpretation of relativity (usually namen "Lorentz ether"). But that's only a difference in interpretation. The empirical predictions are the same.

That is what I said. Bohmists believe that relativity is fundamentally wrong and need to imagine some preferred frame, or ether, or some such thing.

 

[Demystifier]

That is what I said. Bohmists believe that relativity is fundamentally wrong and need to imagine some preferred frame, or ether, or some such thing.

But you asked how they can be compatible? The answer is that they are compatible in the sense of making the same measurable predictions.

You may be worried that they are incompatible in some fundamental principles like Lorentz invariance. But even without Bohmian interpretation, incompatibility in some fundamental principles cannot be avoided when dealing with quantum physics. For example, Copenhagen QM and classical mechanics clearly have incompatible fundamental principles like quantum uncertainty vs classical certainty. So, to paraphrase your objection, Copenhagenists believe that classical ontology is fundamentally wrong and need to imagine some uncertainty, or complementarity, or some such thing. And yet, a defender of Copenhagen QM will rightly point out QM and classical mechanics make the same measurable predictions for purely macroscopic phenomena, in the sense that QM laws for macroscopic systems can be well approximated by classical laws. In the same sense, a defender of Bohmian QM will rightly point out that Bohmian QM and Copenhagen QM make the the same measurable predictions for phenomena in which "hidden variables" are not directly observed.

 

[martinbn]

But you asked how they can be compatible? The answer is that they are compatible in the sense of making the same measurable predictions.

You may be worried that they are incompatible in some fundamental principles like Lorentz invariance. But even without Bohmian interpretation, incompatibility in some fundamental principles cannot be avoided when dealing with quantum physics. For example, Copenhagen QM and classical mechanics clearly have incompatible fundamental principles like quantum uncertainty vs classical certainty. So, to paraphrase your objection, Copenhagenists believe that classical ontology is fundamentally wrong and need to imagine some uncertainty, or complementarity, or some such thing. And yet, a defender of Copenhagen QM will rightly point out QM and classical mechanics make the same measurable predictions for purely macroscopic phenomena, in the sense that QM laws for macroscopic systems can be well approximated by classical laws. In the same sense, a defender of Bohmian QM will rightly point out that Bohmian QM and Copenhagen QM make the the same measurable predictions for phenomena in which "hidden variables" are not directly observed.

There is a very big difference. There are observable predictions of QM that are incompetible with the classical paradigm.

 

[Demystifier]

There is a very big difference. There are observable predictions of QM that are incompetible with the classical paradigm.

Are you saying that Bohmian approach would be more interesting if it was making new observable predictions?

 

[martinbn]

Are you saying that Bohmian approach would be more interesting if it was making new observable predictions?

No, I am saying that it would be less meaningless if it didn't make up unobservable things.

 

[PeroK]

Are you saying that Bohmian approach would be more interesting if it was making new observable predictions?

Definitely!

 

[Fractal matter]

Definitely!

"Louis de Broglie Realistic Research Program and the experimental detection of Quantum Waves"
Annales de la Fondation Louis de Broglie, Volume 46, no 1, 2021

"We propose and discuss “yes-no” type experiments to physically detect quantum waves, independently of the associated corpuscles."

There is also a video, but I'm not going to post it, cause moderators don't like it.

 

[Demystifier]

No, I am saying that it would be less meaningless if it didn't make up unobservable things.

Would you say that string theory (in the standard interpretation of quantum theory) makes up unobservable things?

 

[Demystifier]

Definitely!

https://www.physicsforums.com/threads/problems-with-paper-on-qm-foundations.1007991/post-6553007

 

[ohwilleke]

No, I am saying that it would be less meaningless if it didn't make up unobservable things.

Plain old QCD relies upon all sorts of mechanism and interactions of quarks and gluons that aren't directly observable.

Generally speaking, we don't directly observe individual u, d, s, c, or b hadrons or gluons because they are confined within hadrons or are indistinguishable parts of a quark-gluon plasma.

We infer, from a combination of Occam's razor and observations, that there are three color charges (and three anti-color charges) of quarks, and eight possible color charge (including anti-color charge) combinations in gluons. But it is still impossible to identify the color charge of any particular quark or any particular gluon (in stark contrast to the easily observable electromagnetic charges of quarks, charged leptons and on shell W bosons, or the mass-energy charge with respect to the gravitational force of particular particles up to the limit of the Heisenberg uncertainty principle).

The most interesting parts of QM (regardless of interpretation) happen between measurements, and some of the inferred in between observations parts, like virtual particles (which if they were real particles would violate mass-energy conservation, a bedrock assumptions that holds for all observables in physics), are profoundly important to the end results.

Similarly, one of the things that we do to calculate the path integrals of particle propagators in QED, which is considering amplitudes for photon paths in which photons are moving at more or less than the speed of light in a vacuum "c" as part of the total path integral calculation, involve unobservable things that are fundamentally inconsistent with the bedrock principles of special relativity. Classical special relativity (which QED, QCD, and the weak force all follow perfectly at the level of observables) suggests that all photons must always be on paths between points consistent with velocities of exactly c. Yet, we rely on these unobservable things that are contrary to special relativity, and contrary to all experimental observations (statistically significant evidence of Lorentz invariance violations has never been observed), because when we do, we get the right end results of the overall calculation of observable quantities to the greatest precision of any scientific observations ever made by human beings.

We don't directly observe the intermediate imaginary number quantities that go into lots of ordinary classical electromagnetic calculations.

Like those familiar unobservable things, the unobservable parts of Bohemian quantum mechanics are inferred indirectly from observations in ways that, when you are doing it right, should be indistinguishable from, for example, the Copenhagen interpretation, with experiments devised to date that allow us to make these indirect observations.

So, merely predicting unobservable things isn't very troubling if, as in the case of Bohemian quantum mechanics, the unobservable things imply observable things.

The fact that there is more than one possible set of unobservable mechanisms to produce the same results in quantum mechanics that humans can conceive isn't really all that shocking or surprising.

End results that can arise in more than one possible way are well within the realm of human experience.

For example, there are usually many possible different ways that the pieces midway through a chess game could have ended up there and nobody is very troubled by taking on chess problems that don't include the moves that led up to its starting point.

 

[martinbn]

Would you say that string theory (in the standard interpretation of quantum theory) makes up unobservable things?

As far as I know, no it doesn't.

 

[martinbn]

Plain old QCD relies upon all sorts of mechanism and interactions of quarks and gluons that aren't directly observable.

Yes, and that is perfectly fine.

 

[Demystifier]

As far as I know, no it doesn't.

So I guess you would say that extra dimensions, D-branes, multiverses and strings themselves are observable in principle, but we just happen to live in a universe where those are unobservable in practice. Well, the same is the case with Bohmian stuff. It's observable in principle, but we live in a universe in which Bohmian stuff is unobservable in practice.

 

[martinbn]

So I guess you would say that extra dimensions, D-branes, multiverses and strings themselves are observable in principle, but we just happen to live in a universe where those are unobservable in practice. Well, the same is the case with Bohmian stuff. It's observable in principle, but we live in a universe in which Bohmian stuff is unobservable in practice.

You misuderstood me. It wasn't about the unobservable things. It was about making them up. The dimensions in string theory are a consequence they didn't just make them up. If they were like the Bohmists they would say something like: four dimensions are ontological, the rest are not. This is what i meant by making up unobservable things. In this case it is this "property" of being ontological for some dimensions that is an unobservable made up thing.

 

[Demystifier]

The dimensions in string theory are a consequence they didn't just make them up.

Fine, but supersymmetry in string theory is made up (put by hand), it's not derived from a deeper principle. And the very idea that the world is made of 1-dimensional objects called strings is also made up. Of course, you may point out that they are made up for a purpose (in hindsight they turn out to solve some problems), but so is the Bohmian stuff.

 

[Demystifier]

If they were like the Bohmists they would say something like: four dimensions are ontological, the rest are not.

As the only person on Earth who worked seriously on Bohmian formulation of string theory, I can tell that this is not true. In my papers all dimensions are equally ontological.