A couple months ago I recorded a podcast with Lex Fridman, it’s now available here.

A lot of Fridman’s other interviews are well worth watching or listening to, and I thought we had an interesting conversation. I can’t stand listening to or watching myself, so not sure how it turned out. But happy to answer here any questions about what we were discussing.

Very cool! I love this blog and Lex’s podcast so what a great treat!

“I can’t stand listening to or watching myself . . . ”

I know the feeling!

Was there a mutual softball agreement when it came to the topic of Eric Weinstein? Surely you or Lex must be aware of the technical criticisms of his Geometric Unity theory that’s been out for awhile now (the only one in existence by Nguyen and Polya).

Jason S.,

If I’m going to spend time specifically criticizing people’s ideas, it’s because I think there’s a problematic situation with the ideas, that they’re getting significant attention and funding within the research community, crowding out better ideas. I don’t see any point to spending time discussing technical criticisms of Weinstein’s work (or Garett Lisi’s, or any number of other similar if less well-known research programs).

What I thought was worth talking about (and from what I remember, did talk about with Fridman) is the underlying fundamental problem that Lisi/Weinstein’s ideas share with mainstream ones that are now in the textbooks (GUTs/SUSY). If you try to get unification by embedding the SM symmetry groups in a larger group, you have to then introduce new physics to break the symmetry group down to the observed SM one. Generically, this removes most if not all of the explanatory power of your idea about unification.

Anyway, happy to discuss that point more, I think it’s very much underappreciated. I’ll leave debating pro/con the work of Lisi, Weinstein, Wolfram and others to those who feel it’s a good use of their time, don’t want to host that here.

Peter:

While your answer makes sense and explains why you would not criticize such theories on your platform, it would seem that the right metric for answering a question on a podcast is whether ideas are getting podcast attention (vs scientific community attention). So it looks to me like a missed (deliberate?) opportunity to give a non-generic comment when one seemed possible. If there wasn’t a point to evaluate Weinstein’s (or anybody else’s) work, the question would not have been asked.

I wasn’t aware of Lex Fridman or his blog before this. He seemed to understand almost nothing that you said, judging by his inane follow-up questions, silly reformulations of your points, etc.. Was he having a bad day or is this representative of his work? You say his blog his interesting, so I suppose it was a bad day…

At ~7:00 you mention that recent developments in Number Theory “fit into a context where the theory is kind of four-dimensional.” Could you elaborate what in particular you were referring to?

Jason S.,

For me, what’s worth giving attention to, on a podcast or elsewhere, is exactly those topics that are interesting and not getting attention.

jjohn,

Fridman’s own expertise is far removed from math/theoretical physics. I think you underestimate how hard it is for someone who hasn’t spent a lot of time following controversies in physics to understand what is going on and carry on a thoughtful conversation about them. I’ve often run into people trying to do discuss or write about such issues who are well-meaning but completely clueless. Given the challenges I think he did quite a good job. It was clear that his own interests are mostly in different directions than mine, but he found common ground .

Also worth noting is that he interviews a large number of people, with very different interests. The sheer number of interviews he has done is remarkable, and from what I’ve seen the quality is pretty high.

DF,

What I had in mind specifically was Witten’s reformulation of geometric Langlands in terms of a four-dimensional QFT. It’s true this is geometric, not number theory Langlands, so more of an analogy. I also had in mind the dictionary relating knots and 3 manifolds with number theory, in which a number field is three-dimensional. See here

https://web.ma.utexas.edu/users/vandyke/notes/langlands_sp21/langlands.pdf

for notes from a recent course by David Ben-Zvi in which he relates this knot/3 manifold point of view on number theory with the 4d QFT.

Haven’t visited this page in years, but the Lex Fridman podcast brought me back! Great to be here. Your conversation with Lex was great.

That was a very good interview, be interesting to hear more approachable discussions like this, that touch on the potential of spinors/twistors for physics! (though having it broken up with other varied/interesting topics, like in this interview, helps :))

I very much enjoyed your podcast with Lex. Thank you.

Hi Peter,

I think there may of been some string theory hype back in September that you may of missed, since I don’t see that you made any blog post about it. Apparently there’s a paper that was published in Physics Review D that claims to of found gravitational wave spectra of merging “fuzzballs” by numerical computer modelling that are different from different from those predicted by ordinary GR for merging black holes. The authors appear to claim that these could be potentially detected by current or future gravitational wave detectors. It was reported here:

https://physics.aps.org/articles/v14/s110

and the pre-print is here:

https://arxiv.org/pdf/2103.10960.pdf

I’ve already taken a look at the paper. Do you have any comment on this?

That actually was an interesting conversation. Now I couldn’t help but noticing that, when string theory became a topic of discussion, you never mentioned the fact that LHC has not found any supersymmetric partners. My understanding is that, given the energy regions that LHC has explored, this already discards most supersymmetric schemes – leaving only those that are highly contrived and therefore far less compelling.

Is this right? If not, do you think LHC is likely to find these partners some time in this decade?

I’m also admirer of Lex Fridman’s interviews. The list of interviewees and breadth of subjects covered are indeed impressive, and I have yet to listen to one for which I would use the word “inane” to describe any part of the exchange.

Enjoyed this one, too.

Jay H.,

No I don’t think there’s any reason to believe in the usual SUSY extensions of the SM. There’s zero evidence for them, and they have exactly the problem I mentioned earlier: you introduce a new symmetry and immediately create a huge problem: how do you break it to explain why we don’t see it? For SUSY this problem is pretty deadly: SUSY-breaking schemes are ugly and introduce lots of new undetermined parameters. A good idea should reduce the number of parameters you can’t calculate, not increase that number. That the LHC did not see SUSY was not unexpected at all for most theorists.

The problem with string theory is different. You don’t really have an understood full theory, all you understand well is a perturbative expansion in 10d space-time of a supersymmetric theory. The problem with trying to use this is that you have to get rid of 6 of the dimensions and there are too many ways to do that, so your theory can’t predict anything. Some string theorists found it convenient for many years to answer people saying their theory predicted nothing and couldn’t be tested by claiming “our theory predicts SUSY, can be tested at the LHC” (which wasn’t really true). This blew up in their face with the null LHC results. That’s a complicated story, best to keep it simple: the theory predicts nothing and can’t be tested, mainly because the only version you understand has six dimensions you can’t get rid of without destroying the predictivity of the theory.

I just listened to the first half and what a great interview!

Peter, you mentioned a fundamental idea about mapping the integers to a geometric space with the function mod p. What is this called and where can I read more about it?

bryan,

The general story is that to a commutative ring R one can associate a “space” Spec(R), with R then in some sense functions on this space. This is at the foundation of modern algebraic geometry, which gets rather sophisticated.

What I was referring to was the case of R=Z, the ring of integers. In that case what happens is that Spec (Z) is basically the set of prime numbers p. Given any integer n in Z, you can think of it as a function on the set of prime numbers, with f(p)=n mod p (so your functions are taking values in integers mod p at the point p).

Peter, thanks! This is going to keep me busy for a while!

Another long-time, non-technical, blog reader. Very much enjoyed the podcast. I think your gentle push back on the relationship between the sceince you and Fridman were talking about and a meaning of life nicely illustrates one of the qualities that I find valuable in your presentations.

One thing I do not think you addressed, and that might have come near the surface of the conversation is a point you have made several times on the blog. If I remember correctly, you have noted that mathematics practice could serve as a useful model for theoretical physics in absence of new experimental data. (Please forgive if I am mischacterizing.)

I was always intrigued by this idea and wondered what sorts of practices these might be? You may have alluded them in a couple places, for example when you touched on Lisi and Weinstein.

You have already dealt with this issue at length elsewhere, and, as you rightly note, life is short and there are many things yet to do.

Thank you and very best.

Patrick Malloy,

There are two different ways I think mathematics practice can help with the current state of physics:

1. Mathematicians are very careful about stating things precisely and making it clear exactly where the line is between what we understand and what we don’t. Physicists traditionally haven’t needed this, they could rely on experiment for guidance, mathematicians have never had this to rely. I’m convinced physicists could benefit from adopting more of these concerns. At the moment, in many physics theory papers it’s hard to impossible to figure out what the exact statement is, and there’s a huge lack of clarity over whether ideas work or don’t.

2. Much more speculatively, I believe there’s a deep unity between fundamental physics and deep unifying ideas in mathematics. Taking this principle seriously gives one at least some very vague guidance as to what is a promising way forward and what isn’t.

I really enjoyed your podcast with Lex. It taught me some things I liked to know. It made me wonder whether your old book was also at the level of Penrose’s books when it comes to explain physical and mathematical concepts. Read some of its reviews, but decided that I would rather read your newer stuff, when I find time to read more of your writtings.