[Book Review] The Trouble with Physics

post by lsusr · 2020-01-05T01:47:26.368Z · score: 25 (15 votes) · LW · GW · 16 comments

Lee Smolin's book The Trouble with Physics: The Rise of String Theory, the Fall of a Science, and What Comes Next is ostensibly about why string theory can't solve what he calls the Five Great Problems in theoretical physics:

  1. "Combine general relativity and quantum theory into a single theory that can claim to be the complete theory of nature" i.e. "the problem of quantum gravity".
  2. "Resolve the problems in the foundations of quantum mechanics, either by making sense of the theory as it stands or by inventing a new theory that does make sense."
  3. "Determine whether or not the various particles and forces can be unified in a theory that explains them all as manifestations of a single, fundamental entity."
  4. "Explain how the values of the free constants in the standard model of particle physics are chosen in nature."
  5. "Explain dark matter and dark energy. Or, if they don't exist, determine how and why gravity is modified on large scales. More generally, explain why the constants of the standard model of cosmology, including the dark energy, have the values they do."

Actually, The Trouble with Physics is about a much broader problem—disruptive innovation as described in Clayton Christenson's The Innovator's Dilemma and Thomas Kuhn's The Structure of Scientific Revolutions. In Smolin's view, the scientific establishment is good at making small iterations to existing theories and bad at creating radically new theories. It's therefore not implausible that the solution to quantum gravity could come from a decade of solitary amateur work by someone totally outside the scientific establishment.

Extraordinary claims demand extraordinary evidence.

He [Carlo Rovelli] got so many e-mails [from string theorists] asserting that Mandelstam had proved [String Theory] finite that he decided to write to Mandelstam himself and ask his view. Mandelstam is retired, but he responded quickly. He explained that what he had proved is that a certain kind of infinite term does not appear anywhere in the theory. But he told us that he had not actually proved that the theory itself was finite, because other kinds of infinite terms might appear. No such term has ever been seen in any calculation done so far, but neither has anyone proved that one couldn't appear.

Smolin's book is full of evidence like this. I find his argument convincing because it aligns with my personal experience. I earned a bachelor's degree in physics because I wanted to help figure out the Great Problems. I wanted to discuss big ideas with Einsteins, Feynmans and Hawkings. In their place I encountered narrowly specialized postdocs. These PhDs are good at math but tend to have little education in the broader history of science. To them, the physical laws might as well have been handed down on stone tablets. Physicists' job is that of a madrasa.

This might be tenable if the foundations of physics (general relativity and quantum theory) were plausibly true. But general relativity and quantum theory contradict each other. They cannot both be correct. Therefore at least half of physics is wrong.

The scientific establishment isn't structured to resolve problems of this magnitude. Until we restructure the institution of physics so that it promotes diversity of thought (unlikely anytime soon) it's not inconceivable that the answers to the Five Great Problems could come from an amateur.

Smolin's book has inspired me to begin working [LW · GW] on a theory of quantum gravity. I'll need to learn new things like quantum field theory. I might give up before getting anywhere. But at least I know I don't understand basic physics. That puts me in good company.

I think I can safely say that nobody understands quantum mechanics.

― Richard Feynman

16 comments

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comment by shminux · 2020-01-05T05:40:45.998Z · score: 18 (10 votes) · LW(p) · GW(p)
But general relativity and quantum theory contradict each other. They cannot both be correct. Therefore at least half of physics is wrong.

Your first sentence is correct, your second is missing a qualifier, your third is plain wrong. GR and QM are valid each in their own domain. They don't mesh together well, so something has to give in between the two domains. A modification, a wholly different model, something else we have no idea about. It's a consensus in the field that a new revolutionary idea is needed, you are right. And that thousands of smart but "narrowly specialized postdocs" are unlikely to get us there. The five great problems are a good summary of our current views, but I suspect that to make progress in solving, say, #1, the problem itself would have to be restated completely differently. But good luck with learning more about fundamental physics. It's a difficult and thankless task, as close to an efficient market as possible, with no profit to be made unless you have something that the likes of Witten have overlooked. You'll need a lot of sweat and a lot of luck.

comment by waveman · 2020-01-06T08:02:26.513Z · score: 3 (3 votes) · LW(p) · GW(p)
GR and QM are valid each in their own domain.

Their domain is supposed to be the universe, I think. Later people said GR is for the large scale and QM is for the small scale but nothing in the theories actually says this, AFAICT.

It could be that a straightforward extension of one or the other would solve the problem, somehow embracing or correcting the other. But all the obvious ways to do that have been explored and have failed.

Or it could be that both are fundamentally conceptually wrong, like Newtonian gravity was 'wrong' (though quite accurate most of the time). If that is the case the actual solution would look very different and would then be shown to approximate QM and GR in limiting cases.

String theory is not really a theory of physics; it is more like the idea that a certain type of theory, not yet identified, may work. So it is more of an approach or a program. But even if ST is successful, it would leave a lot of unanswered questions. And after decades their is not much sign of a breakthrough.

To be fair one key problem is a lack of data. If we could build accelerators 10^12 times as powerful as current ones, we may have something to work on. But there are so many possible theories given current data. Given no data, and no way to test theories, physics degenerates into a popularity contest.



comment by shminux · 2020-01-06T08:42:25.849Z · score: 3 (2 votes) · LW(p) · GW(p)
Their domain is supposed to be the universe, I think. Later people said GR is for the large scale and QM is for the small scale but nothing in the theories actually says this, AFAICT.

each one was constructed for their respective domains. Not surprising that they don't automatically keep their validity in other domains. Quantum mechanics came with their own limiter, the ad hoc Born rule without which it doesn't predict anything. GR is too weak for small source masses, so we have no idea when and if it stops applying.

To be fair one key problem is a lack of data. If we could build accelerators 10^12 times as powerful as current ones, we may have something to work on. But there are so many possible theories given current data. Given no data, and no way to test theories, physics degenerates into a popularity contest.

Indeed we need more data, but not necessarily at high energies. If anything, measuring gravitational effects of the sources that contain 100,000 nucleons, not 10^23 nucleons would be more illuminating than a super mega LHC. Or gravitational effects of any system that can be put into spatial quantum superposition (i.e. not just a SQUID).

comment by steve2152 · 2020-01-05T20:32:34.334Z · score: 2 (2 votes) · LW(p) · GW(p)

It's a consensus in the field that a new revolutionary idea is needed

I disagree, I think the consensus in the field is that the fundamental laws of physics are very likely some version of string theory or something closely related to it. It's not a unanimous consensus, but it is probably the majority position among academic theoretical physicists, even among academic theoretical physicists who are not specifically string theorists themselves. (I haven't looked for surveys, I'm just guessing from personal experience.)

comment by shminux · 2020-01-05T22:06:38.614Z · score: 4 (3 votes) · LW(p) · GW(p)
I disagree, I think the consensus in the field is that the fundamental laws of physics are very likely some version of string theory or something closely related to it.

I guess it depends on which bubble one is in. The likes of Susskind and 't Hooft seem to acknowledge that a new paradigm is needed. And it makes sense given the herculean efforts expended on the String Theory in the last 3 decades or so, with very little to show for it. Certainly the AdS/CFT correspondence and the holographic principle in general, as well as a number of other ideas that emerged from the string theory research will have to fit into the new paradigm somewhere, but probably not in any recognizable way. I'd bet 10:1 that the next significant step in fundamental physics would not be a natural extension of the string theory.

comment by TAG · 2020-01-07T09:19:28.348Z · score: 1 (1 votes) · LW(p) · GW(p)

GR and QM are valid each in their own domain

GR and QM give correct predictions in their own domains. They also have different ontological implications, which may or may not be a problem depending on what you expect to get out of physics.

comment by paragonal · 2020-01-15T17:50:30.820Z · score: 3 (2 votes) · LW(p) · GW(p)
In Smolin's view, the scientific establishment is good at making small iterations to existing theories and bad at creating radically new theories.

I agree with this.

It's therefore not implausible that the solution to quantum gravity could come from a decade of solitary amateur work by someone totally outside the scientific establishment.

For me, this sounds very implausible. Although the scientific establishment isn't geared towars creating radically new theories, I think it is even harder to create such ideas from the outside. I agree that most researchers in acadamia are narrowly specialized and not interested in challenging widely shared assumptions but the people who do are also in acadamia. I think that you focus too much on the question-the-orthodoxy part. In order to come up with something useful you need to develop a deep understanding and to bounce around ideas in a fertile environment. I think that both have become increasingly difficult for people outside of acadamia because of the complexity of the concepts involved.

The evidence you cite doesn't seem to support your assertion: Although Rovelli holds some idiosynratic ideas, his career path led him through typical prestigous institutions. So he certainly cannot be considered to stand "totally outside the scientific establishment".

comment by G Gordon Worley III (gworley) · 2020-01-05T18:47:43.444Z · score: 3 (2 votes) · LW(p) · GW(p)

Does there anywhere exist a community of folks you might work on this with who aren't derisive of this approach, woefully uninformed on the specifics (I think that's broadly the issue here on LW; we're not selecting for physicists of the sort you'd like to talk to even if there are a lot of them here), or cranks?

My experience has been that it's very helpful to have supportive folks who can at least a little bit appreciate what you are doing and offer feedback, even if you are going super deep in some direction such that you are the expert in ways that means they will often be mistaken even if they can help you avoid making obvious mistakes.

comment by lsusr · 2020-01-05T23:23:33.797Z · score: 1 (1 votes) · LW(p) · GW(p)

If physicists of the sort I'd like to talk to are around at all that's good enough for me.

comment by Jay Molstad (jay-molstad) · 2020-01-05T15:02:33.325Z · score: 3 (2 votes) · LW(p) · GW(p)

Look for a system where the predictions of GR contradict, or at least interact with, the predictions of QM. If there is no such system, then the contradictions are more metaphysical than empirical.

I've wondered for a while if the gravitational anomalies ascribed to dark matter/energy could be the result of linear frame dragging through the quantum fields. The basic idea is:

1) QM says there's a lot of "zero-point energy" surrounding us in every direction related to the quantum fields.

2) This energy has no gravitational consequences because it's pulling equally in every direction.

3) Relativistic linear frame dragging might break that symmetry with gravitational consequences.

I don't have the background to go further with the idea, or even to tell whether it's blatantly stupid. It's a stray thought; if you can make something of it, feel free.

comment by steve2152 · 2020-01-05T20:22:29.257Z · score: 4 (3 votes) · LW(p) · GW(p)

Look for a system where the predictions of GR contradict, or at least interact with, the predictions of QM.

There are two main examples: Microscopic exploding black holes, and the Big Bang.

Our current fundamental physics theories are probably adequate to explain literally everything that happens in the solar system, which is one of the reasons I don't think fundamental physics is a particularly time-sensitive topic of research. So we can just wait until we have superintelligent AGI, and ask it what the fundamental laws of physics are. :-)

  1. This energy has no gravitational consequences because it's pulling equally in every direction.

Although I appreciate the intuition that " it's pulling equally in every direction", uniform energy density does in fact have an effect in GR. It causes the whole universe to expand or contract. That's exactly what dark energy is.

comment by lsusr · 2020-01-08T21:09:59.944Z · score: 1 (1 votes) · LW(p) · GW(p)

The Trouble with Physics does address zero-point energy as a possible explanation/alternative for dark energy. Your points 1 and 2 are correct. The problem is that the cosmological constant calculated from vacuum energy is many orders of magnitude greater than the observed cosmological constant.

comment by [deleted] · 2020-01-08T22:22:22.290Z · score: 2 (1 votes) · LW(p) · GW(p)

FYI dark energy probably doesn't exist and therefore doesn't need an explanation: https://phys.org/news/2020-01-evidence-key-assumption-discovery-dark.html

comment by jmh · 2020-01-05T14:19:01.063Z · score: 2 (4 votes) · LW(p) · GW(p)
This might be tenable if the foundations of physics (general relativity and quantum theory) were plausibly true. But general relativity and quantum theory contradict each other. They cannot both be correct. Therefore at least half of physics is wrong.

I also don't think the logic of the argument quite holds.

My take is we can interpret the situation better via a clock metaphor. Specifically the old staying about running and stopped watches. The running one is almost always wrong while the stopped (broken/not running) one is correct twice a day (assuming the 12 hour clock).

I don't disagree with the general sentiment here, but think a better way to approach it might be recognizing the essentially all of physics is incomplete. One of the ways this manifests in the science is that disagreement between the quantum and macro theories.

comment by paragonal · 2020-01-15T17:55:21.426Z · score: 1 (1 votes) · LW(p) · GW(p)
Smolin's book has inspired me to begin working [LW · GW] on a theory of quantum gravity. I'll need to learn new things like quantum field theory.

If you don't know Quantum Field Theory, I don't see how you can possibly understand why General Relativity and Quantum Theory are difficult to reconcile. If true, how are you able to work on the solution to a problem you don't understand?

comment by steve2152 · 2020-01-05T20:38:15.206Z · score: 1 (1 votes) · LW(p) · GW(p)

Do you think that the True Fundamental Laws of Physics are definitely not string theory (or anything mathematically related to string theory)? If so, why?