Approaching 50 Years of String Theory
math.columbia.edu
math.columbia.edu
One day some unusual observation will come along from somewhere, and that will be the loose end that allows someone to start pulling at the whole ball of yarn. Will this happen in our lifetimes? Unlikely, I think.
Your implicit point is a good one. Is it sensible to have a huge chunk of the entire theoretical physics community working endlessly on a theory that could well end up being basically useless? Probably not.
It mostly hasn't worked out and now people are moving on to other things.
The single worst thing that happened though was the populism: a small group of people with credentials started putting out pop-sci books and doing interviews, well in excess of what their accomplishments should mean. People are like "so many people are working on this" because there were like, 3 to 5 guys who always said "yes" to an interview and talked authoritatively.
[1] https://nyuad.shorthandstories.com/strings-conference-abu-dh...
I agree that people should be "moving on to other things," but I'm not seeing the evidence that they actually are.
And there is no known single real world experiment that can rule out string theory while keeping general relativity and quantum mechanics intact.
More accurately, string theory is not wrong (because it just cannot be wrong). Because it does not predict anything and cannot invalidate anything, it does not help to advance our understanding of how to integrate general relativity and quantum mechanics.
It should not be called theory - maybe set of mathematical tools or whatever.
Then people managed to calculate those predictions, and they were wrong. So the people working that theory up relaxed some constraints and tried again, and again, and again. So today it's that framework that you can use to write any theory you want.
That original theory was a good theory. Very compelling and just a small adjustment away from mainstream physics. The current framework is just not a good framework, it's incredibly hard to write any theory in it, understand what somebody else created, and calculate the predictions of the theories you create.
so it's javascript?
In logic this is either the principle of "contradiction elimination" or a "vacuous truth". Depending on how you look at it. i.e. given sufficiently bad premises, you can prove anything.
Later, non-Euclidean geometry was actually essential to modern physics.
It's intellectually sketchy to judge future value by the present.
I imagine this is what you would have sounded like 100 years ago.
The only truly exponential technological progress we’ve ever had, transistors, only scaled by ~5 orders of magnitude in feature size. Thermal engines went from maybe 0.1% to ~50%, less than 3 orders of magnitude, in about 200 years. There’s very fundamental physical laws that suggest that engines are done, and transistor scaling as we have known it for 30 years is also done. Perhaps very clever things might give us 5 more orders of magnitude? E.g. truly 3D integration somehow? Then we’re still 5 orders of magnitude off from our target. I can’t think of any technology that ever improved by more than 10^6, perhaps 10^9 if you count some derivative number (like “number of transistors on chip”, rather than actual size), and that’s from literally zero to today. Not from already-pretty-advanced to Death Star scale.
Another perspective is that, to get to those kinetic energies, we need accelerators as large as the solar system. Possibly the galaxy, I can’t quite remember. Will you concede that galaxy-wide objects are so far from current reality that there’s no point seriously talking about them?
Not to mention you entirely missed the point of what I said. There is research into the most niche, useless fields imaginable, because not every endeavor taken by every human being needs to be profitable or applicable. Sometimes people are just really good at making jigsaws or want to make a stinky chemical or get fascinated with properties of prime numbers.
And then, sometimes, those turn out to be the fundamental underpinnings of an entire generation of economic and military strategy. You can't often know what spurs what in that sense.
I did indeed miss your point, it was well hidden under a lot of sarcasm. I think it is of course completely valid. People should be free to research what they want, and I’m sure string theory must be beautiful mathematics.
But if your goal is unifying QM and GR, and/or achieving a theory of everything (as is for most theoretical physicists), then me and a growing fraction of physicists think that it’s not a promising avenue. I’m not advocating for only working on “useful” things, because such a theory is not likely to yield much profit to anyone in the foreseeable future anyway. But if you state that a unifying theory is your goal and seek funding for that goal, then string theory should move to the backstage. The mathematics department would rightfully be happy to house you otherwise.
Progress is weird.
There's maybe a couple or few hundred-ish in the whole world that focus on it. And they don't need much money because it's pretty much all math.
Is this a typo? I see a lot of words being censored these days and I assumed it's because of some algorithms and visibility. That shouldn't be the case here tho..
This is just a lie though. Non-Euclidean geometry is a mathematical model of how distances behave on non-linear spaces. Nobody ever believed it to be a "fundamental mistruth", even suggesting it would look ridiculous. It would be akin to denying linear algebra, even the meaning is unclear.
That the physical reality of space is not linear was a shocking revelation, since all human experience and basically every experiment done up until that point indicated otherwise.
> Nobody ever believed it to be a "fundamental mistruth"
https://math.libretexts.org/Courses/College_of_the_Canyons/M...
"Lobachevsky [mathematician contemporary of Gauss, who claimed parallel postulate was unnecessary] was relentlessly criticized, mocked, and rejected by the academic world. His new “imaginary” geometry represented the “shamelessness of false new inventions”"
Further, many claimed premature success in finding logical contridictions in geometry lacking parallel (Euclid's 5th) postulate; which meant they believed a 4-postulate geometry to be fundamentally false.
Energy to vaporize Earth's oceans: ~4 x 10^27 J
For a Planck-scale linear collider at LHC-like collision rates (~10^8/sec):
Beam power requirement: ~2 x 10^17 W
With realistic wall-plug efficiency of ~1%: ~2 x 10^19 W
Annual energy consumption: ~6 x 10^26 J
At 1% efficiency, one year of operation would:
Vaporize about 15% of Earth's oceans
Or vaporize the Mediterranean Sea roughly 50 times
Or boil Lake Superior every 5 hours
Or one complete ocean vaporization every 6-7 years of operation
It's about 1 million times current global power consumption
Or about 50,000 Suns running continuously
Or 170 billion Large Hadron Colliders operating simultaneously
I seriously read that and first thought it was a dig at SPARC chips running hot ...
I also just really enjoy Brian Greene, his books, and the World Science Festival Youtube channel.
I definitely don't walk away from any of Brian Greene's content thinking that String Theory is anything close to a confirmed fact at all.
It's been some times since I read his earlier books, possibly his tone has changed?
I'll also say, I'm far from a professional physicist. I'm reading and watching for fun and intellectual curiosity, not to learn physics with the goal of doing my own research. I always thought of String Theory as being more of a study of math where many people have unsuccessfully tried to apply it to physics. And, that it's lead to some really interesting ideas. I just find him and his work really enjoyable.
I think her point is more that his tone hasn't changed. If you're curious I would just watch the video. Angela comes with the perspective of also having read his earlier books and having liked them.
A few debates between Brian and other notables; Hossenfelder, Eric Weinstein, and Roger Penrose to name a few; have popped up in my youtube feed lately which are typically also engaging.
Hossenfelder has gone off the "the physics establishment is all idiots and they are suppressing the real physics" deep end and has converted specific complaints into trashing the entire field.
Most, but not all
If you do research it becomes pretty apparent that a high number papers are not great. There's varying issues, but a big one is that the funding model incentivises pumping out papers which are often of low quality, researching whatever happens to be in vogue at the moment
Literally everyone I've ever talked to in research as a frank conversation knows that this is a massive problem, but nobody wants to talk about it publicly. Research funding is already completely screwed as it is, and researchers are incredibly aware of how fragile their livelihoods are
Its clearly leading to a big reduction in the quality of the literature. I went on a replication spree recently and found that a pretty decent chunk of the field I was working in was completely unreplicable by me, with a few papers that I strongly suspect 'massaged' their results for various reasons
I wish someone would talk about this who wasn't also in bed with right wing grifters, and was actually credible. We need someone more like ben goldacre for physics
Sabine's most interesting content is the paper reviews, and where she sticks to actually examining the evidence - but it makes up a tiny fraction of what she produces these days, and her support for some truly grim figures is just gross
This is not very persuasive.
To a large degree if you're trying to successfully trying to push for change, it really matters that the person pushing for it is credible. Someone like ben goldacre is able to credibly make a strong push for change within medicine because they've maintained credibility, someone like sabine makes the situation worse because they've chucked it away
Sabine's has a day job as a Youtuber, and she makes her videos from that perspective. She speaks her mind, makes a decent living, and educates some science nerds on the way. Seems pretty nice.
From the perspective of accomplishing institutional change in the academic physics world, this is does nothing. The institutional powers don't react at all to a complaining influencer with an Einstein doll.
And I suspect she's perfectly fine with that. Overturning the Physics establishment is a near impossible task. I would leave that for those mad enough to try.
I don't think you're describing "the" problem with Sabine. She's not what you want her to be but that's a you problem. You're describing your particular problem with Sabine.
I appreciate that she's doing a lot to bring attention to the real issue despite your claim that she is supporting grim figures. I know about the problem because of her work, but I have no idea who Ben goldacre is.
Also no idea what you mean by supporting grim figures. I checked to see if she has come out in support of Jeffrey Epstein or something crazy like that, but no.
Bro she blurbed "The War on Science," a book stuffed with racists and sex pests complaining that they lost their jobs for falling in love with their graduate students, writing them love poetry on tumblr, and then kicking them out of their research group because they could stand to be near them. Or for saying that they "don't shy away from the word superior" when discussing white people being better at running societies and lying about the GPAs of black students. Or for taking joking photographs with human remains.
And yes, the authors of the book include people who provided support in the legal defense of jeffrey epstein.
And its not something that's just a 'you' problem - if you want the actual underlying issues in physics to be fixed, its a massive issue that the spokesperson for fixing those problem currently may be a bigot, or at the very least endorses bigots and sex pests. Beyond just being generally completely unacceptable, it allows everyone to completely dismiss whatever is being said very easily
For the other poster, ben goldacre is someone that's become very well known for making effectively the same points as sabine, but within the pharmaceutical industry. They sat down and basically wrote for decades about how the testing was absolutely broken, multiple books, a column, and producing lots of work on how broken studies were in medicine and talking to anyone that would listen - and as a result, they were actual able to enact effective change. It was a huge win for evidence based science!
Sabine is not someone who can achieve that in physics - her videos would be much more effective if they contained actionable content and concrete analyses of the issues. I'd have a tonne of respect for her if what she did was publish papers or videos showing the degree to which the literature was broken, analysing funding, conducting interviews (even if anonymous) with researchers, looking through examples of bad papers and explaining the problems to a lay audience. Producing a mixture of for-scientist and for-lay person material to break the figures down, in a way that produces a compelling argument
Instead we at best get specific examples plucked out of the air. I know she isn't massively overgeneralising the issue from my own personal experience, but she presents a terribly uncompelling argument as to why there are problems. Where's the data? Why are you writing book blurbs for sex offenders instead of writing papers?
That's why I've come around increasingly to the idea that she's a grifter, even though I used to enjoy her content (before it went out of the window) and think that she does likely genuinely care about the underlying problem to some degree. Its closer to ragebait than anything that feels productive now unfortunately. I don't think its even necessarily on purpose on her end - the right wing has a way of sucking in anyone on the fringes and giving them a home even without them knowing, but also why give her the benefit of the doubt?
I pretty strongly disagree with that categorization of Collier's video, as it makes it sound like string theorists were innocent bystanders and "the big bad media" just ran overboard.
I think she puts the blame squarely on string theorists (e.g. "celebrity string theorists who wrote all these books") as constantly hyping up the field with promises of "in a decade it will be amazing" - a phrase she uses to great dramatic effect throughout the video - despite never acknowledging the fact that it fails miserably at making testable predictions.
When she says "they lied to us", the "they" she's clearly talking about are specific researchers in the field (which she names), and the string research community more broadly, who are hyping up their field, not just "the media".
1. I think there are two reasons why string theory is cool (other people may have different opinions). Please note that none of these two reasons are directly related to the extension of Standard Model. 1.1. String theory is the only theory so far that can mix gravity and quantum mechanics, and it can be even used to derive Hawking entropy of a black hole from "first principles" (see paper by Strominger and Vafa). The obvious trouble is that the black hole in question lives in five-dimensional space and is unrelated to the real-world black holes, but this is way better than what one can get from Standard Model physics (which is, no gravitons for you).
1.2. Through AdS/CFT correspondence, string theory can be used to describe quantum field theories that are not related to string theory by themselves. This gives a very strong tool to study these quantum field theories, and the paper by Maldacena that discovered this correspondence is one of the most important papers in the field.
2. It is true string theory is unusable as of now to derive the Standard Model physics (and provide extensions for it). Unfortunately, I would say that hardly any papers in high energy _theoretical_ physics currently address Standard Model physics. Roughly speaking, in late 1970s, after quantum chromodynamics was established and the asymptotic freedom was discovered, it turned out that it is extremely hard to compute many things we are generally interested in. At this point, high energy theoretical physics split in two sub-areas: phenomenology (which tries to extend the Standard Model to derive things like neutrino mass) and theory (which is a more formal theory and tries to answer questions like "how to quantize gravity"). One can argue that this makes hep-th an area of mathematics, and I would agree with that (eg in Cambridge theoretical physicists are in the same department with applied mathematicians).
2.1. The things theoretical physicists study tend to pop up in various places, even if the original motivation is misplaced. Even the string theory itself originated as a way to explain the Regge trajectories (which were explained with quantum chromodynaics afterwards), and not to quantize gravity. For a more practical example, Witten introduced topological quantum field theories long before anyone understood how to apply them to real-world physics.
3. I do not agree that string theory dominates the hep-th field. I would say that its popularity changes with the time, going up and down. While the main conference in the hep-th field is called "Strings", the talks at it are not necessarily related to strings theory, and at the 2025 conference I'd say that only 1/3 of the talks were anyhow related to the strings theory. Moreover, there is no hard division between people working on string theory and people working on other hep-th subjects, so that e.g. Witten made many contributions to hep-th which are not anyhow related to string theory.
3.1. As for the push to do string theory that eg Sabine Hossenfelder alludes to, I'd say that I experienced no such push during my MSc and PhD studies. I've written four papers, and worked on a couple of projects that did not become a paper, and out of those, only one was dedicated to string theory.
3.2. On the other hand, the more fringe theories that can provide alternative to string theory are also more high-risk endeavors (as you are quite likely to fail to produce anything coherent within a typical timeframe you allot to write a paper). Hep-th is strongly underfunded, and I believe, that with greater funding (and less need to publish-or-perish) some people would also pursue the more fringe directions in hep-th.
3.3. A comment on the naming: hep-th is a field which is very hard to name. The name I use is the traditional one (and is used as eg a name for the field on arXiv). However, many things derived by the physicists in the field are not anyhow related to the high energy in the literal meaning of the words "high energy". When talking to people at a party, I say that I studied string theory, because the name is catchy and it rings a bell, but this way of referring to the field is definitely a misnomer.
Is that a correct assessment?
Is it just about higher energy particle collisions? Or does it involve things like doing experiments next to a black hole?
or dark matter
>In theories of particle physics based on string theory, the characteristic length scale of strings is assumed to be on the order of the Planck length, or 10E−35 meters
Yet electrons repel each other over distances of many meters by I think the virtual exchange of photons. How on earth would that work? How does your photo string know to head to an electron string trillions and trillions of times it's length away?
As far as I can tell the field became popular for sociological reasons that you could get grants for it and the like rather than any connection to reality(?)
It's hard to visualise in 3D, but if you cut down the spatial dimensions to just 1D (a line), then theories like string theory just turn the infinitely thin mathematical line into a tube. You can picture a tube that vibrates, or has waves in its cross-section. Don't think of the the "strings" as actual little loops moving around in space, they're a modification of what space is.
You can even do the same kind of line->tube extension of a space with even more extra "loop" dimensions than the number of base dimensions. AFAIK the current theories have 10 total, of which 3 are the usual "large" dimensions of space, the rest are "small" and rolled up like the tube example.
"if you cut down the spatial dimensions to just 1D" doesn't sound very physical to me.
I'm maybe being downvoted fairly. I studied physics and it don't think it's a misunderstanding of popularisation or that string theory is untestable, I just think it's straight wrong and not how the physical universe works.
Very roughly: It's possible for point-like (or tiny looped) particles to interact as long as they take every possible path instead of just the one path that would cause a collision. How you interpret this is... up for debate. I prefer the many-world interpretation (MWI), but not everyone agrees.
> "if you cut down the spatial dimensions to just 1D" doesn't sound very physical to me
That's just a simplification to aid understanding, it's now how the theory actually works.
I think he went into string research because he was good at maths and there was grant money available for that rather than a deep belief that that was the nature of reality, which is kind of what I mean by sociological factors.
I think much string theory may be like that. Interesting maths but not good at figuring where electrons go.
Because at the nanoscale, you in fact can have 1D, 2D and 3D metals. 3D metals are bulk solids - like we're familiar with. 2D metals are planes of single (or very few) atoms. 1D metals are lines - think placing individual metal atoms down in a row - nanotubes are a practical example.
All real, possible structures to build.
When you do measurements on all these structures you get...weird answers. Like is a nanotube a superconductor? And the answer is...yes, but also no. Yes because you'll in fact view superconductivity like behavior, but no because actually it's a ballistic electron conductor - at the right energy level an electron bounces through the thing without hitting it, but not all electrons can do that at all energy levels, so you still measure a voltage across a nanotube between two conductors.
But a nanotube is 1D - we only have 1 dimension things move in (from one end to the other). So - conductive, not a superconductor, but you can kind of use it like one sometimes. And we know 3D metals are conductors - that's obvious right...so what are 2D metals? Presumably conductors right...?
And the answer is...nope, insulators - at least sometimes. And the reason is because the sum of all possible electron paths in a 2D metal is the electron always returns back to where it started - and those grow much faster mathematically then paths where the electron ends up somewhere else.
But only in 2D: in the 1D case most paths take you out of the conductor. And in the 3D case, the number of paths which land you somewhere else grows much faster then those which loop back, due to the extra dimension of freedom. But 2D metals are constrained - for any given path elsewhere, there are mathematically far more that land back where you started. This is observable, measurable behavior which is a topic of research for future semiconductors. Yet it's almost entirely quantum probability based behavior.
In particular your model of electric fields isn't very good. An electric field's flux around a volume reveals the presence of a particle in that volume. That's not because the field, a bunch of vectors in space, "happens" to integrate to something nonzero if there's a particle in that volume: it's because in some sense the presence of a field with a nonzero flux and the presence of a charged particle are the same thing; the particle is the existence of a divergence in the field within that volume.
Moreover in QFT (and this part is handwavey as I only learned enough to vaguely understand this, but it's better than nothing) the presence of the "field" ends up looking like the sum of what you get if you integrate over every possible way of a emitting or receiving a photon at that point; the accumulated integrals destructively interfere in such a way as to produce a value which reflects where the particles are. So very roughly idea of a field existing at a point and having a "value" is like saying: there are a bunch of things out there that I (a charged particle) can detect by exchanging photons, and the accumulated effect, when you consider all the different quantum superpositions of ways of doing that, is a single vector which induces a force on me. Other fields add up to more complicated objects than vectors.
Once you look at things like that, there should be no objection to how strings and electrons might interact. Whatever's going on at that string level averages out over larger timespans to just look like electron field. Not dissimilar from how all the individual charges in an atom average out to look like a single charge (but are perhaps detectable if you get up really close, in dipole and higher moments, or in how the atom deforms / reacts to nearby charges).
It might help to be aware of the concept of a topological defect (https://en.wikipedia.org/wiki/Topological_defect; there's a great explainer article somewhere that I can't seem to find) as a reductive picture of what a particle "is". I've heard this doesn't work for fermions for some technical reason, but in any case it's very useful as an illustration of the sort of thing that a particle "can be": a vortex in a material can act like a particle and even exhibit attractive/repulsive forces. So I picture the string theory model as answering the question: what kind of substrate could produce vortexes and other "defects" that act like the particles we see? Dunno if that's accurate but it seems like a natural question to me, anyway.
What does string theory predict that (1) is within experimental reach in, say, 5 years (2) if not found, would prove it wrong. Was there ever anything satisfying these two simultaneously? AFAIK,the answer is "no".
Everyone is free to pursue what they want. I did not comment on that at all. You click on whatever part of the tech tree you want. However, my expectation is that the string theory does not have the qualities of a scientific theory that improves one's knowledge about universe.