Quanta magazine has just put out an impressive package of material under the title The Unraveling of Space-Time. Much of it is promoting the “Spacetime is doomed” point of view that influential theorists have been pushing for decades now. A few quick comments about the articles:

- String theory is barely even mentioned.
- There is one article giving voice to an opposing point of view, that spacetime may not be doomed, an interview with Latham Boyle.
- The big problem with the supposedly now conventional view that spacetime needs to be replaced by something more fundamental that is completely different is of course: “replaced with what?”. A lot of attention is given to two general ideas. One is “holography”, the other Arkani-Hamed’s amplitudes program. But these are now very old ideas that show no signs of working as hoped.
Thirty years ago Lenny Susskind was writing about The World as a Hologram. The idea wasn’t new then and seems to be going nowhere now. It was 17 years ago that Arkani-Hamed started re-orienting his research around the hope that new ways to compute scattering amplitudes would show new foundations for fundamental physics that would replace spacetime. Years of research since then by hundreds of theorists pursuing this have led to lots of new techniques for computing amplitudes (twistors, the amplituhedron, the associahedron, now surfaceology), but none of this shows any signs of giving the hoped for new foundations that would replace spacetime.

Instead of saying any more about this, it seems a good idea to try and lay out a very different point of view which I think has a lot more evidence for it. This point of view starts by noting that our current best fundamental theory has been absurdly successful. There are questions it doesn’t answer so we’d like to do better, but the idea that this is going to happen by throwing the whole thing out and looking for something completely different seems to me completely implausible.

One lesson of the development of our best fundamental theory is that the new ideas that went into it were much the same ideas that mathematicians had been discovering as they worked at things from an independent direction. Our currently fundamental classical notion of spacetime is based on Riemannian geometry, which mathematicians first discovered decades before physicists found out the significance for physics of this geometry. If the new idea is that the concept of a “space” needs to be replaced by something deeper, mathematicians have by now a long history of investigating more and more sophisticated ways of thinking about what a “space” is. That theorists are on the road to a better replacement for “space” would be more plausible if they were going down one of the directions mathematicians have found fruitful, but I don’t see that happening at all.

To get more specific, the basic mathematical constructions that go into the Standard Model (connections, curvature, spinors, the Dirac operator, quantization) involve some of the deepest and most powerful concepts in modern mathematics. Progress should more likely come from a deeper understanding of these than from throwing them all out and starting with crude arguments about holograms, tensor networks, or some such.

To get very specific, we should be looking not at the geometry of arbitrary dimensions, but at the four dimensions that have worked so well, thinking of them in terms of the spinor geometry which is both more fundamental mathematically, and at the center of our successful theory of the world (all matter particles are described by spinors). One should take the success of the formalism of connections and curvature on principal bundles at describing fundamental forces as indicating that this is the right set of fundamental variables for describing the gravitational force. Taking spin into account, the right language for describing four-dimensional geometry is the principal bundle of spin-frames with its spin-connection and vierbein dynamical variables (one should probably think of vectors as the tensor product of more fundamental spinor variables).

What I’m suggesting here isn’t a new point of view, it has motivated a lot of work in the past (e.g. Ashtekar variables). I’m hoping that some new ideas I’m looking into about the relation between the theory in Euclidean and Minkowski signature will help overcome previous roadblocks. Whether this will work as I hope is to be seen, but I think it’s a much more plausible vision than that of any of the doomers.

**Update**: John Horgan has some commentary here, taking the point of view that discussions of “Beyond Space-time” are fine, as long as you realize what you’re doing is “ironic science” not science.

As a side note, I have to say that was some pretty impressive presentation work on the part of whoever is doing the web ui for that article. Really very nice and kind of cutting edge as far as I am aware. You can see the evolution towards a more magazine-style “i’m turning these glossy pages” kind of experience.

Dan Winslow: To the contrary, I find this style of presentation pretty much unreadable/un-navigable. Luckily, it seems the articles themselves are accessible from the normal landing page in the normal way.

One of the linked articles in the main one that I found more interesting was about the ‘Long-forgotten math’ of von Neumann’s algebras. The mathematician who rigorously grounded the third type, namely Alain Connes, has been the primary architect of noncommutative geometry. In that setting, spinors are the elements of the Hilbert space on which the Dirac operator acts. I wonder if you have found anything useful from this spectral formalism.

Georgi Ivanov,

My interest generally has been in very specific examples, hoping to get a deeper understanding of the Standard Model. Using the general theory of operator algebras is kind of at the other end of things, useful to say things independent of any specific theory (which is why theorists without a theory doing quantum gravity find it useful).

Non-commutative geometry a la Connes is a different story, pretty much off-topic.

Dear Peter (thanks for this extremely interesting post, mentioning Boyle’s interview)

and Georgi Ivanov (thanks for touching on the “operator algebra point”),

The problem with the now standard view that “space-time is only emergent”, and hence not fundamental, is huge: (as I already mentioned in previous messages here) essentially all of the main current approaches to quantum gravity are in agreement on this!

It is a big pleasure to see some dissenting voices like Boyle and Peter đ

There is a significant difference between “emergent” and “derived”: space-time can very well have a role and existence at the fundamental quantum level, without invoking “macroscopic emergence”, and still be “derived” (for example in a spectral way) from operationally defined quantum degrees of freedom (for example quantum fields and their operator algebras).

If Peter allows me just one very short excursion into the “off-topic” direction (operator algebras and non-commutative geometry): the interplay between von Neumann algebras (of quantum fields with their Tomita modular theory) and non-commutative geometry (including Connes’ non-commutative standard model features) is still a work in progress and could be much deeper (and interesting for 4-dimensional geometry) … I can assure that there some researchers currently still working on it đ

Best regards (and sorry for the little “off-topic”) đ

Paolo

I also noticed virtually mention of String Theory; wormholes made inside computers malarky, and that.

Does this mean that Quanta has finally got the message on those topics? Or do you think it that the string lobbyists are generally giving up?

Jim Eadon,

I think the people at Quanta ultimately realized there are various problems with the wormhole claims and that these are not supported by most theorists in the field.

Those theorists interested in continuing to make way overhyped claims about string theory or wormholes are now not getting a sympathetic hearing from either their colleagues or most science journalists. They can now only do this without pushback at certain venues like Brian Greene’s panel discussions.

I see that right now you can ask the Quanta journalists questions yourself, at

https://www.reddit.com/r/IAmA/comments/1fqogti/were_physics_journalists_who_have_spent_years/

Pingback: Is Spacetime Unraveling? - 3 Quarks Daily

This was not encouraging:

chevalierbayard

Is String Theory a dead end?

Natalie_Wolchover

I’ve done a lot of reporting and writing about string theory over the past couple of years for my forthcoming book, and it does not at all strike me as a dead end. There’s a huge amount of vitriol about it among certain science communicators, but in my view, they mislead the public on this. Among working theoretical physicists, string theory is a tool for studying quantum gravity and a conceptual framework that’s mathematically consistent, and which is related to quantum field theory – the language of the Standard Model of particle physics. Exactly how or whether string theory is related to reality remains unclear. But it’s part of a web of mathematical languages that is trying to tell physicists something and they aren’t going to stop studying it.

Charlie’s new article, Physicists Reveal a Quantum Geometry That Exists Outside Space and Time, covers fascinating new research that has an interesting tie-in to string theory: https://www.quantamagazine.org/physicists-reveal-a-quantum-geometry-that-exists-outside-of-space-and-time-20240925/

Charlie_Wood42

+1 to what Natalie said. I’ll also add that many theorists consider string theory to be the best working example of what a theory of quantum gravity might look like. It does some impressive and hard to do things like nailing exactly the entropy of a black hole, down to the multiplicative constant. That doesn’t make it right, but it does make it interesting. It also makes it a top contender until someone comes up with a more complete, or more testable framework. Lots of people definitely want that and are working on alternatives, but I don’t think anything has obviously dethroned it yet.

Garrett Lisi,

Yes, that’s the Quanta editors at their worst. No one is arguing that physicists should stop studying string theory, just that string theorists and journalists who listen to them should stop the forty years of often outrageous hype and instead provide an accurate account of the state of the theory. I’m also not a fan of denouncing unnamed “unnamed science communicators” for unspecified statements.

It’s also amazing how successful the hype for the Strominger-Vafa calculation from nearly 30 years ago has been (it got them a 3 million dollar prize). There’s zero chance that Charlie Wood understands that calculation (for example, that it’s not actually a black hole…), but he’s sure about it impressively “nailing exactly the entropy of a black hole, down to the multiplicative constant.” There’s a generic problem with the Quanta coverage of string theory/quantum gravity that that they’re way too credulous about claims made by certain prominent people in this field, with the wormhole fiasco the most egregious example.

“No one is arguing that physicists should stop studying string theory, just that string theorists and journalists who listen to them should stop the forty years of often outrageous hype and instead provide an accurate account of the state of the theory.”

I completely agree with the point about stopping the hype, but, at least for that fraction of string theorists who went into it because they saw it as the key to finding the “holy grail of physics”, doesn’t assessing it realistically imply precisely that they should stop studying string theory?

Also, in the absence of a credible alternative, it might be too difficult to just stop a research program, as a matter of human psychology. It seems to me that as long as people can fall back on justifying what they are doing via “other benefits”, they would rather stay with the familiar, even if it does not work, than venture into the unfamiliar which might not work and doesn’t even provide a fallback.

What would you tell a person in that situation, Peter?

Armin,

I’m just not understanding why anyone would want to spend their life studying an idea that doesn’t work. If your job doesn’t require this why do it? If it does, why not find another one? If you think your string-theory related research program is working, no reason you shouldn’t keep at it. But, it is important though that people not deceive themselves and not be deceived by others about what works and what doesn’t. Here there are a bunch of prominent string theorists (and journalists at Quanta…) who have something to answer for.

I studied physics, but for some weird reason spent most of my time in âthe mediaâ. In the late 1980s, early 1990s, I did some (modest) science journalism. Back then, even if you werenât a specialist, you could have a certain âfeelingâ for new results. And if you didnât, there often was link between the result and a feasible or already performed experiment to check if the results were going in the right direction.

A simple example is cold fusion. As a physicist (or a chemist) youâd expect that chemical reactions are typically in the eV range. So where the hell does the energy for cold fusion comes from? In labs across the world, experiments were done that didnât show fusion at all. So, if you wanted to report about cold fusion, you had a starting point.

The arrival of string theory changed that dramatically. The subject is so complicated that you had to take the expertsâ word for it. There were no experiments to keep them honest. The space for the âindependent judgmentâ of a reporter â always a delicate thing in science journalism â was reduced to zero.

So what do you do as a science reporter? Iâve been in the media long enough to know the answer: you cover you ass. You create a situation in which you can always say âI was was just reporting what the experts were saying. You got a problem with that? Go and tell the experts.â

Itâs also an ideal situation for a herd mentality. You donât want to be summoned to the chief editorâs desk to be asked âHey, what the f!ck? Everybody else is writing that this result of string theory is the greatest thing since sliced bread, and you are skeptical? Who the f!ck are you? It was in a press release by goddamn Harvard! Goddamn idiot, next time we can forget about an exclusive!â

Herd mentalities are strange things, though. Itâs perfectly possible that somewhere in 2030 the herd will be marching in the opposite direction. â50 years of string theory and you have nothing to show?â And everybody in the herd will be screaming that they already knew in 2024 that string theory was a dead end, physically speaking.

I really wish Quanta would not write so much about the extremely speculative and totally-divorced-from-experiment parts of physics. It misrepresents what most physicists do. I donât know how someone who doesnât work in physics regards this stuff, but as someone who does, I have, for the most part, stopped reading it. As far as their latest cluster of articles on spacetime is concerned, I read the one about Wheeler, because I met him a few times and heard one of his talks. His style was oracular and the talk was quite cryptic. The only other article I looked at was the one that talked about von Neumann algebras, because my thesis advisor worked in algebraic quantum field theory (I never did, but I picked up a little knowledge of the subject). No mention of algebraic quantum field theory in the article, just that these algebras are now interesting because some people in quantum gravity are using them. The other articles in the cluster and the video – well I have better things to do. Some of their physics articles that are not about quantum gravity are very good, and I would like to see more of those.

Hello Peter,

Saying that it’s too early to seek for emergent theories of space-time because (among other things) 4d space-time geometry as we know it has still things to teach us concerning unification issues beforehand (a statement which is arguably sound) is not incompatible with the fact that ultimately space-time will turn out to be an emergent structure from some deeper degrees of freedom of the fundamental laws of physics.

Best,

I read Professor Woit’s Nov 2023 paper, which was reprised in a recent podcast. I find this work so tantalizing and would like to ask if there is likely very long to wait until a new paper outlining any new developments might appear? Thanks.

Bertie,

I was planning a longer and more detailed paper after that, but as writing it realized that the fundamental technical issue of how you wick rotate spinor field theories from Euclidean to Minkowski is something I really need to get carefully sorted out. This is taking a while, with slow progress. Even for charged scalar fields what happens is tricky, spinor fields even more so.

Apologies for this off-topic comment, but…

I just watched Sabine’s latest video, where you are mentioned by name at the end. I followed her blog during its entire active existence and have viewed a number of her videos since, and generally agree with most of her views and diatribes. But I can’t remember ever feeling revulsion over her commentary like I did with her new video. Not only was the title very misleading (conflating a narrow area of physics with physics in general), she decided to accuse certain physicists of intellectual dishonesty by name, without obvious provocation.

Even you were not spared — she sort-of complimented you, but immediately followed with a dismissive comment, one that a listener who is unfamiliar with your lengthy history as a skeptic would likely interpret as a suggestion that your underlying motivation is a desire to “sell” your own theory. (Seriously, Sabine? What theory? Do you mean Peter’s limited writings on an idea he is excited about and actively exploring? Where is he suggesting he has a theory?)

Overall, I find the video disgusting for her careless denigration of some individuals’ character, and of progress in physics overall, even if the actual physics content has merit.

Marty,

For those wondering what this is about, see

https://www.youtube.com/watch?v=cBIvSGLkwJY

I’m much more sympathetic than you to the rant, since I feel exactly like that some days. Like for Sabine, seeing this argument reappear brought back bad memories of twenty years ago, and depressive thoughts about how the field is dead, people are going to just go on repeating the same arguments about failed theories for the rest of my life and beyond.

The problem with such rants, from me or from her, has always been the question “yes, but why don’t you do something more positive than just get outraged about this?” For many years I didn’t have an answer to that. There were general ideas that I would write about that seemed to me worth pursuing, but nothing specific that I could point to as highly promising. A few years ago when I started realizing that a set of ideas I’d given up on could actually work and started writing about them, criticism then shifted from “you should be ignored because you don’t have an alternative” to “you should be ignored because all you are doing is pushing your own speculative alternative”.

Enough time-wasting on this for today, back to trying to figure out exactly what is going on when you Wick rotate spinors…