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Approaching 50 Years of String Theory

• ekjhgkejhgk 11mo ago
  [flagged]
  • tgv 11mo ago
    From the FAQ * Be kind. Don't be snarky. Converse curiously; don't cross-examine. Edit out swipes. * Comments should get more thoughtful and substantive, not less, as a topic gets more divisive. * Please don't fulminate. Please don't sneer, including at the rest of the community. * Eschew flamebait. Avoid generic tangents. Omit internet tropes. * Please don't post shallow dismissals, especially of other people's work. A good critical comment teaches us something. * Please don't post insinuations about astroturfing, shilling, brigading, foreign agents, and the like. It degrades discussion and is usually mistaken. If you're worried about abuse, email hn@ycombinator.com and we'll look at the data.
    • Dumblydorr 11mo ago
      Wow their comment history isn’t much better, is there downside or anything that repeat low-value commenters face?
      • exe34 11mo ago
        I've had dang on my case, threatening to ban me if I kept it up.
  • setopt 11mo ago
    Physicist here. Would you like to enrich our world view by linking to counter-examples? My understanding was that string theory being more "hypothetical physics" than "theoretical physics" at this point is still a pretty legit criticism.
    • exe34 11mo ago
      I'm legit interested in hearing more about this, like YouTube series, popsci books, magazines - I've been meaning to read Zwiebach's A first course, but I keep getting distracted with background reading and then never get back to it.
    • ecosystem 11mo ago
      The legit criticism with a legit recommended change is even better. A time and technological gap always exists between theory and a plan for experimental confirmation. Some gaps are fairly short. String theory's gap is undoubtedly long, not for lack of resources. This gap justifies tapering the allocation of attention and research resources (funding, students, etc), which got lopsided following the strong marketing campaign driven by Greene.
      • setopt 10mo ago
        I tend to agree. Science funding is unfortunately a limited resource, and I would like to see different approaches explored in more detail, which unfortunately would imply less (but not zero) funding to string theory. Not zero, because we also don’t want the competence built up in string theory groups to die out completely, in case that remains our best lead. To borrow a compsci analogy, we tried the depth-first search going in the string theory direction, maybe it’s time to switch to breadth-first for a while, to see if there are any viable and useful theories with less distance from the ones we have today. Maybe it doesn’t have to be a "theory of everything" either, we can initially settle for a "theory of more".
    • ekjhgkejhgk 11mo ago
      Physicist here. My PhD is in an area that was spawned into existence due to inspiration coming from string theory, not string theory proper. I've made some comments here [1] to discuss how I see the situation. It's difficult to be thorought in the world of research, and even more so in an HN comment. I'll be writing more as the subject pops up in HN. [1] https://news.ycombinator.com/item?id=46336655 https://news.ycombinator.com/item?id=46336655
  • jfengel 11mo ago
    I don't entirely understand where that comes from. The Standard Model and General Relativity are both tested to extreme precision. Any experiment unifying them will have to involve insane energies. It's not as if there is some other model with easy tests that we've agreed to ignore. As far as I can tell, it seems to come from the developers of Loop Quantum Gravity, who feel left out of funding. And maybe that's true. But their theory doesn't offer practical tests, either. It would be weird if it did.
    • ekjhgkejhgk 11mo ago
      > I don't entirely understand where that comes from. The Standard Model and General Relativity are both tested to extreme precision. Any experiment unifying them will have to involve insane energies. It's not as if there is some other model with easy tests that we've agreed to ignore. You're absolutely right in everything you said, thank you. Like another commenter posted, the planck scale is 10^19 GeV and we're about 10^15 short. Therefore it follows we won't be testing anything at planck scale for many generations, if ever. Therefore the argument of "I can't test it therefore the theory is useless" is just being defeatist. The fact that such theory isn't testable might be a feature of our Universe, not the theory. As in, these people don't normally make the distinction between something that "could be tested in principle, we just don't have the technology" (like string theory) vs something that "couldn't be tested even in principle" (like how many angels can dance on the head of a pin). They're basically playing with semantics when they say "it's not testable". > As far as I can tell, it seems to come from the developers of Loop Quantum Gravity, who feel left out of funding. And maybe that's true. But their theory doesn't offer practical tests, either. It would be weird if it did. Again, correct on all points. However, I'll add the following. Yes, LQG makes as many directly-testable predictions at the planck scale as string theory, which is to say none, because we don't have the technology to test anything directly at that scale. I keep repeating these things on HNs, but people here fundamentally don't understand how research in theoretical physics is done. I'll try a little exposition: Physics is: make experiments, and try to infer which laws/rules/formulas are common to all experiments or sets of similar experiments, and their domain of applicability. These are called theories. Theoretical physics is: think about theories, and try to observe which laws/rules/formulas are common to all theories or sets of similar theories, and their domain of applicability. These are more general theories from which your directly-experimented theories can be derived. You can keep interacting constructing ever more general theories from an ever smaller set of principles. So a lot of theoretical physics is about arguing which of the principles that you know are true because you've experimentally tested them will hold in circumstances where you can't directly test. As it turns out there's a lot that you can infer about things you've never seem because often times mathematics puts constraints on how different ideas work together. The string theory/LQG thing is that LQG start from the guess that Lorentz invariance doesn't hold at planck scale. The reason why LQG is less appealing to a lot of physicists is that if you follow this through you can never quite make it mathematically self consistent. In string theory what happens in certain sub-domains is that you start with a lot of arbitrary possibilities, but then you demand certain types of mathematical self-consistency and magically it points out that there's only one or a small number possibilities. A classic example is: "how many dimensions does the universe has?" which no theory really gives as answer, but string theory at least points in a direction: "if you assume such and such, the the allowed answers are such and such". This happens a lot in string theory, and it's what drives people to keep digging. String theory on the other hand concludes that Lorentz invariance must hold at all scales "in some string-like theories" if you demand cancellation of divergences, which you must have for your theory to be renormalizable and therefore mathematically self-consistence. So in a sense this is a prediction of string theory. Not that LQG doesn't predict the opposite, that Lorentz invariance doesn't hold. Instead it assumes that it doesn't. String theory instead predicts that it does. The latter is much more impressive; anybody can start from an arbitrarily picked assumption that noone can prove wrong.
  • Certhas 11mo ago
    Eh... mainstream physics by numbers is not HEP and definitely not HEP Th, and there are plenty of serious physicists somewhat critical of the field, and more so of the way it presented itself over the last decades. And while I disagree with some of the criticisms and some of the style of the crtics, it's not like you get an honest appraisal from Greene (and Witten).
  • omnicognate 11mo ago
    Perhaps you could elevate the discussion by providing an actual argument against this view of string theory, which has indeed percolated through social media? For my part, I know a little bit more than "shit" about physics but I know very little about string theory and know better than to have strongly held opinions about things I don't understand. I've heard quite a lot about the criticisms and would like to hear a defense of it.
    • ekjhgkejhgk 11mo ago
      I have a lot more to say, but I wrote a little bit here: https://news.ycombinator.com/item?id=46336655 https://news.ycombinator.com/item?id=46336655
  • JKCalhoun 11mo ago
    Rather than inb4, you'll make a stronger case by rebutting any of those comments you see come up in the thread.
    • ekjhgkejhgk 11mo ago
      Not really a rebuttal, but a discussion of how I see the situation: https://news.ycombinator.com/item?id=46336655 https://news.ycombinator.com/item?id=46336655
  • ecshafer 11mo ago
    Ive been told my multiple High Energy Physicists that String Theory was suspect because it makes no predictions. Being able to make predictions that are testable is a foundation of theoretical science. Not everything is because of influences.
• tuhgdetzhh 11mo ago
  An in half a century we still haven't found a single actually testable prediction.
  • SiempreViernes 11mo ago
    I think that's not quite right: it is reasonably certain that string theory can produce both the standard model and most extensions people have dreamt up, so the problem is rather that all the obviously "stringy" predictions are currently unavailable, while the string theory derived predictions for achievable experiments look like what we get from other theories we already have.
    • atakan_gurkan 11mo ago
      To make this valuable, it should produce a limited set including standard model. If you produce pretty much everything one can dream of, that does not carry predictive power. 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".
      • ecosystem 11mo ago
        Making a hard, arbitrary deadline is a pretty extreme thing to do. ie Higgs Boson was a lot longer between theory and experiment than this.
      • XorNot 10mo ago
        You write this as though reality is a 4X game and we're obviously wasting time not clicking on the other item in the tech tree to optimize the build.
        • atakan_gurkan 10mo ago
          No, I am simply stating what is expected of a good scientific theory in physics. Such a theory should have power to explain things as well as make new, testable predictions. It is valuable to collect our present information under one umbrella, but if everything falls under that umbrella, it may as well not exist. String theory does not have predictive power (mostly because of energy scales mentioned elsewhere in this discussion, unless someone comes up with an ingenious way to probe its domain with low energy experiments), and its explanatory power is not very useful since it explains both reality and things out of reality, indiscriminately. 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.
• mkw5053 11mo ago
  I thought Brian Greene did a great job interviewing Edward Witten (Fields Medal winner) on the World Science Festival Youtube channel [1]. I also just really enjoy Brian Greene, his books, and the World Science Festival Youtube channel. [1] https://www.youtube.com/watch?v=sAbP0magTVY https://www.youtube.com/watch?v=sAbP0magTVY
  • Levitating 11mo ago
    You might not like Angela Collier's video on string theory[1]. [1]: https://m.youtube.com/watch?v=kya_LXa_y1E https://m.youtube.com/watch?v=kya_LXa_y1E
    • mkw5053 11mo ago
      Interesting, thanks for sharing! 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.
      • Levitating 10mo ago
        > It's been some times since I read his earlier books, possibly his tone has changed? 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.
    • michaelcampbell 11mo ago
      Thanks for posting that; as soon as I saw the title here I was going to look that up if no one else had already. Sabine Hossenfelder too, though there's far too much content from her on this to put a list, but anyone interested might like some of her takes. 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.
• grunder_advice 11mo ago
  I wonder what Ed Witten would have accomplished if he had gone into another field instead of choosing to dedicate his life to mathematical physics.
  • tome 11mo ago
    Not sure if you're making a joke about this, but Ed Witten tried a number of fields before settling on theoretical physics.
  • r721 11mo ago
    You reminded me about this Abstruse Goose comic: https://web.archive.org/web/20230202225744/https://abstrusegoose.com/332 https://web.archive.org/web/20230202225744/https://abstruseg...
    • nrhrjrjrjtntbt 10mo ago
      M for Magic
• greenavocado 11mo ago
  The Planck scale where string theory's distinctive physics should appear is around 10^19 GeV. The LHC operates at about 10^4 GeV. That's a factor of 10^15 which is a million billion times too weak. No foreseeable accelerator technology can bridge this gap. The proposed Future Circular Collider (FCC) would reach maybe 10^5 GeV. Still 14 orders of magnitude short.
  • PunchyHamster 11mo ago
    So the grift can continue
    • ecosystem 11mo ago
      Non-Euclidean geometry (geometric axioms in which one postulate is rejected such that the 3 angles of a triangle are not exactly 180 degrees) was considered a meaningless word game and fundamental mistruth. Later, non-Euclidean geometry was actually essential to modern physics. It's intellectually sketchy to judge future value by the present.
      • cess11 11mo ago
        I imagine that elliptic geometry had some use before modern physics.
        • saghm 11mo ago
          Yeah, even just trying chart a course on a ship across a reasonable distance will cause you to need to reevaluate some "obvious" things (like "what path is the shortest between these two ports" being a curve rather than a line).
        • ecosystem 10mo ago
          The specific controversy was whether without the parallel/5th postulate, there existed a logical contradiction, i.e. proving the parallel postulate
      • 11mo ago
• jshaqaw 11mo ago
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  • snapplebobapple 11mo ago
    i dont think it has anything to do with threats to way of life. It has everything to do with public subsidy of physics that has pushed peripherary mathematics forward without much to show for actual physics advancements. New observations cause changes to string theory not validation of string theory. String theorists can keep do*ng their string theory but its time to subsidize something(so else and see if that leads to actual advancement. I think sabbine hossenfelder is largely correct about this
    • jshaqaw 11mo ago
      Theoretical physics is subsidizing a handful of people sitting at white boards. Even accepting the premise that string theory is wrong I can list hundreds of ways the US budget spews money down black holes orders of magnitude bigger. The spending on string theory isn’t even a rounding error compared to the way my tax dollars are allocated to special interest pork. But only string theory impinges on a generation of cranks who are convinced they alone have the insight into the true ToE and would be recognized as the new Einstein were it not for some entrenched cabal. Maybe I shouldn’t reflexively trust “big science” or something but it’s also not great to evaluate science by who is more charismatically narcissistic on a podcast. Again, I don’t have a big axe to grind on the merits here. But it’s hilarious that folks with zero science background past middle school hear some of these cranks on YouTube and feel worthy to decry Witten as an enemy of the people. Between the podcast bro who was just told his ToE was right by ChatGPT and Witten I’ll take Witten.
      • snapplebobapple 11mo ago
        No, its subsidizing a handful of people sitting at whiteboards at the expense of different camps of people sitting at whiteboards and the result is nefarious because you dont see what could have been if we minimized string theory funding after a decade or two of poor performance instead of going all in on it for five decades. We gave up decades of potentially actually figuring something new out by going harder on string theory instead of diversifying physics spend as performance failed to show up. how the government wastes money elsewhere is irrelevant to the conversation. Its about proper management of research funding and how string theorists managed tp trick us into funding failure for whole academic careers.
• gnfargbl 11mo ago
  People often say that the problem with string theory is that it doesn't make any prediction, but that's not quite right: the problem is that it can make almost any prediction you want it to make. It is really less of a "theory" in its own right and more of a mathematical framework for constructing theories. 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.
  • pfdietz 11mo ago
    Or, that day will never come, because string theory isn't reflective of the actual world, or because there are so many theories possible under the string theory rubric that we can never find the right one, or because the energies involved to see any effect are far beyond what could be reached in experiment.
    • gnfargbl 11mo ago
      It isn't completely implausible that a future civilisation could perform the experiments to gather that data, somehow; but it is hard to envisage how we do it here on Earth. 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.
      • XorNot 10mo ago
        There is not a "huge chunk" of the theoretical physics community working on string theory, and their never was. For one, it is far less common a topic of research now then it was earlier when it was more popular, but even then "huge" was really "a lot of universities had a grant for string theory investigation because it looked promising". 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.
• giardini 10mo ago
  Hasn't ChatGPT solved string theory yet?
• tim333 10mo ago
  String theory has always seemed intuitively wrong to me. From Wikipedia: >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(?)
  • jiggawatts 10mo ago
    You're being somewhat unfairly voted down, it's a legitimate questions because the popular media so grossly misrepresents what string theory is, especially in their visuals. 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.
    • tim333 10mo ago
      Even so I don't get how electrons a meter apart interact through that stuff, as opposed to the electrical fields which spread out through space and so interact with other electrons as featured in quantum field theory which is what physicists use to actually calculate physical results, as opposed to string theory which fails to calculate actual physical results. "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.
• throw4847285 10mo ago
  What would Imre Lakatos say? Is it degenerating or not?
• mishaevtikhiev 10mo ago
  I have a PhD in high energy theoretical physics (hep-th for short) and I've written a paper on string theory, so I'd like to comment on some things: 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.
• nextworddev 10mo ago
  Basically a framework Ed Witten invented for job security
• GMoromisato 10mo ago
  What experiment(s) would we have to run to see deviations from the Standard Model and be able to come up with newer models (maybe String Theory maybe not)? Is it just about higher energy particle collisions? Or does it involve things like doing experiments next to a black hole?
  • machinationu 10mo ago
    we already have experimental data for deviations from the standard model: neutrino mass for example or dark matter
• paulorlando 10mo ago
  30 years ago in college, at a physics club talk, I got my first intro to string theory. I didn't understand it but was intrigued enough to go to a small one-off seminar led by Prof. Greene. About 15 people around a table while he spoke. I kept thinking I was too ignorant of the subject matter to be able to ask a question. But nobody asked any questions.
• Anon84 10mo ago
  Wasting two generations of some of the most brilliant physics minds isn’t exactly a good thing
• belviewreview 10mo ago
  Here is my question to string theorists: suppose some physicists came up with an alternative theory of everything and were able to use it to make unique empirical predictions. Would you accept it as true and abandon string theory?
• eddie_sputz 10mo ago
  Ah yes. So apparently all of you Orange Redditors are string theorists now.