BT: Are we approaching quantum gravity all wrong?

[notFritzArgelander]

Since Ethan Siegel Has dropped SWaB I'll replace it with BT.
This is an interview with physicist Lee Smolin intended to indicate how abandoning Einstein's dream may have been a terrible mistake. It comes close to persuading me that there may be a way to make sense of de Broglie - Bohm pilot wave ideas to replace QM.

https://bigthink.com/surprising-science ... wmrtdbXbww

It's conceptually thick and deep and might repay revisiting.

PS in edit: I'm sufficiently intrigued to have ordered Smolin's book in Kindle format. If anyone is interested I'll consider posting thoughts and reactions in this thread.

[Gmetric]

If anyone is interested I'll consider posting thoughts and reactions in this thread.

Sounds intriguing. Indeed, If you have time, I’m sure we’d all love to hear your thoughts about it.

[notFritzArgelander]

If anyone is interested I'll consider posting thoughts and reactions in this thread.

Sounds intriguing. Indeed, If you have time, I’m sure we’d all love to hear your thoughts about it.

OK then. I'll take it up in a day or two. I'm finishing up a piece of fluff on near east religious movements. So I'll start in on Wednesday likely. It's going to be my new bedtime reading.

[notFritzArgelander]

Well, for once, I'm ahead of schedule.....

I finished the fluffy bit about near eastern religious movements quickly and read the preface. There is almost no physics in the preface but it is an attempt to outline the philosophical and metaphysical underpinnings of Smolin's enterprise. He separates the sheep from the goats by using a series of questions.

1) Does the natural world exist independently of our minds? Well I have to say yes to that, so I agree with him so far.

2) Is the natural world comprehensible to our minds? He says yes. I say that it is comprehensible to the degree exhibited by science but I reserve judgement about complete comprehensibility until such time as there is a complete understanding of all phenomena. I strongly suspect that that goal is not actually achievable.

The fact that I cannot answer yes to both questions places me among the goats, the anti-realists according to him. I think that's overly harsh. I am simply not a naive realist as he claims to be. We've had William Ockham, Hume, and Kant disabusing us of the arrogant conceit that we can know things directly in and of themselves. Naive Platonic Realism as Smolin seems to embrace has been philosophically dead since the 14th century IMO. Mostly it does no harm that it lives, except in the foundations of maths....

He proceeds to say that folks who think about quantum things are not realists since they must say no to one or more of the two questions above. There is then a call to arms, the realist physicist must go beyond QM because QM must be incomplete.

The antirealists are then classified:

• radical antirealists like Bohr who believe that particle properties are created by our interaction with them

• quantum epistemologists believe that quantum physics is merely about the knowledge we have of the particles

• operationalists like Heisenberg who believe that QM is about the questions we can ask particles

I can't go as far as Bohr. I'm happy with operationalism. So that's the kind of goat that I am.

A third question is introduced to further distinguish among the realists:

3) Does the universe look mostly like the everyday world we see?

If yes then you are a full member of his naive realist clique. If not, and you think reality is very different from what we see then you can be a non naive realist who believes in:

• many worlds QM

• multiverse string theorists

• well i think we don't know Reality from what we see we only know reality and I don't believe in many worlds or multiverses

• I'm sure there are other POVs

Nice things, agreeably put, are said about science and religion not really being enemies (except for the extremists, of course).

The preface concludes by describing how Part 1 describes the triumph of Bohr and Heisenberg views over Einsteins. Part 2 describes the revival of realist approaches by Bohm and Bell. Part 3 sketches attempts to complete a realist theory of everything.

[turboscrew]

I wonder what am I, if I think I see some aspects of reality (or universe) and that the theories model (also) those things about reality (or universe) that are not visible. We can't really be sure of either - what we see, and what the models show, but that's the best we can do - and it seems to work astonishingly well, and it gets better when the models get better.

And we humans are developed the way that we can function quite well with only with our experienced "view" of everything. That doesn't mean that what we experience, is "the ultimate truth" (or reality).

I guess, in these situations, there should be some sort of definition of "reality".
Like are dreams real? In the morning, you don't see the consequences of what happened in the dream, so in this sense, no. But you experienced something - in that sense, yes.

[notFritzArgelander]

@turboscrew I think we are in violent agreement here.

Smolin believes in Reality (Platonic Absolute Reality) and that physics can capture that. I don't.

I believe in an underlying objective reality that we perceive as a phenomenal reality. It's Reality versus reality. Confusing mere mental representations of things, like physics equations, dreams, etc. with reality (phenomenal) is bad enough. Confusing them with Reality (Platonic) is highly self flattering and so in the end delusional.

Even so I'll pass over it in the hope that it makes no difference in the end. We'll see how that works out.

It would seem that Smolin, though he sounds like a physics Platonist is NOT a mathematical Platonist! From an article in which he propounds a manifesto of four principles, the fourth is:

4. Mathematics is derived from experience as a generalization of observed regularities when time and particularity are removed.

Read above and below that heading and one will wonder how he can be consistently so Platonist in discussing physical reality.

PS in edit. I forgot to link the article where Smolin declares mathematical Platonisim anathema: https://physicsworld.com/a/the-unique-universe/

[GCoyote]

That was really interesting. I only got fuzzy when they got to talking in equations and I can't simply visualize the relationships.

Need to take a shower and digest this.

[notFritzArgelander]

That was really interesting. I only got fuzzy when they got to talking in equations and I can't simply visualize the relationships.

Need to take a shower and digest this.

You have company in your indigestion. When, in the article, they started rapping about equations it felt too hand waving. Without a better definition of the varieties of viewables there was only fog. That's why I went ahead and bought the book.

[SkyHiker]

It comes close to persuading me that there may be a way to make sense of de Broglie - Bohm pilot wave ideas to replace QM.

That symptom is known as "the kiss of death" (https://en.wikipedia.org/wiki/De_Brogli ... ave_theory).

The same page tells that Bell supported Bohm's theory, I didn't know that. Trying to understand the difference between non-locality and superdeterminism, I ran into this Backreaction article, https://backreaction.blogspot.com/2019/ ... inism.html . I find it an interesting article, not so much because of the subject but because it's a nice summary of various non-appealing ideas, or questions, really. She talks about statistical locality, what's the difference with locality?

[notFritzArgelander]

It comes close to persuading me that there may be a way to make sense of de Broglie - Bohm pilot wave ideas to replace QM.

That symptom is known as "the kiss of death" (https://en.wikipedia.org/wiki/De_Brogli ... ave_theory).[/url]

I took aspirin and will likely recover from the headache soon! Once I get over it I'll probably revert with relief to the Copenhagenish "Shut up and calculate!" I get these thankfully rare sieges of pilot-wave-itis from time to time and so far have recovered. I think by the time I finish Smolin's book I'll be back in form.

The same page tells that Bell supported Bohm's theory, I didn't know that. Trying to understand the difference between non-locality and superdeterminism, I ran into this Backreaction article, https://backreaction.blogspot.com/2019/ ... inism.html . I find it an interesting article, not so much because of the subject but because it's a nice summary of various non-appealing ideas, or questions, really. She talks about statistical locality, what's the difference with locality?

1) In non locality one has a measurement that determines what would be measured remotely even if the remote experiment were randomized. In super determinism the remote experiment cannot be randomized.

2) Statistical locality is just the quantum version of classical locality.

[notFritzArgelander]

I've finished reading Part 1 (the first 6 chapters) of Smolin's book and am digesting them. I'll distill some thoughts for tomorrow.....

[GCoyote]

The thing that has bugged me most so far is space as an emergent property. I can deal with emergent time, but space not being fundamental is going to take some doing.

[notFritzArgelander]

The thing that has bugged me most so far is space as an emergent property. I can deal with emergent time, but space not being fundamental is going to take some doing.

I'm agnostic so far on what is emergent, if anything. Relativity makes me inclined to have neither space nor time preferred as emergent or non emergent. Picking one or the other seems like asking for trouble.

[notFritzArgelander]

Well there isn't too much to say about Part I of Lee Smolin's book. Chapters 1-6 are essentially an exposition of quantum mechanics peppered with remarks directed against the anti realistic (and normal) interpretations of it.

I am a little put off by the dumbing down of language used to explain the alleged mysteries of QM. For instance the Heisenberg Uncertainty Principle is reduced to "we can only know half of what we need to know in order to predict the future". Later we do get the product of uncertainties in position and momentum being grater than Planck's constant. Bohr's Correspondence Principle is relabeled as the "subsystem principle": "any system quantum mechanics applies to must be a subsystem of a larger system". The classical state of a system consists of all the data needed to predict all future data of the system (i.e. positions, momenta, and Newton). He proceeds to give two rules for the evolution of quantum states. Rule 1) is that an isolated QM system is predictable for all future time and it is identified with unitarity, that all possible outcome probabilities add to 1. He introduces the superposition principle for wave functions in a reasonable way. Measurements are excluded from rule 1, the probabilities of outcomes are given by the square of the magnitude of the wave function and rule 2) once a measurement is made the wave function is completely in the state corresponding to the outcome. That is rule 2.

A reasonable discussion of entanglement and Bell's Theorem follows.

The history of how the alleged anti realist position on interpreting QM is also fairly discussed.

After reading these 6 chapters I am developing a sense of "buyer's remorse". There is a lot of carping about anti realists. The sense I come away with is that Smolin has adopted the philosophical position of Platonistic Realism in physics and is so devoted to that idea that the success in QM making sense of experiments is shoved aside. In mathematics Platonistic Realism is less harmful. There are no experiments to tell you that Platonistic Realism is bad so as long as you shut up and prove theorems it’s ok. In physics the problem is that ultimately experiment is the arbiter of what ideas are good. So far there is no hint that Smolin is going to discuss any hopes for an experiment that his realism will succeed predicting that will falsify QM.

So far the de Broglie - Bohm approach has only succeeded in creating theories that duplicate QM.

Personal rant off the topic of Smolin's book follows:

If I were wanting to revive an old Einstein idea it wouldn't be pilot waves for particles. It would be making the other fields geometric theories that can be directly unified with classical GR first. This has been done for electromagnetism by Kaluza and Klein

https://en.wikipedia.org/wiki/Kaluza–Klein_theory

and although the maths are formidable there are testable results!

https://en.wikipedia.org/wiki/Kaluza–Kl ... ical_tests

Results support Kaluza Klein against more elaborate "brane theory" gravity approaches.

I expect that there exists a theory in 4d spacetime and 1 (electromagnetism gauge group U(1)) and 2 (weak interaction gauge group SU(2)) and 3 dimensions (strong interaction is SU(3) gauge group) for a total of 10 dimension. It is too hard mathematically to test this out. I hope someone does.