The first paper they link to is not about string theory. It's using math that was developed for string theory, and is perfectly valid outside it, to make predictions that can be (and are) experimentally validated.
It has exactly none of the problems of string theory, and I am not sure why it's clumped with a physics paper in the blog. How is it a problem to say "hey they used string theory tools!" in a press release? If anything it might get other people to look at the math and get something good out of it...
This quote explains why the author thinks that it is a problem :
> with string theorists now virtually unemployable unless they can figure out how to rebrand as machine learning experts.
Their issue is (seemingly) not with the paper, but with the claim that these headlines feed a hype that attribute to string theory capabilities it doesn't have.
To be clear this is OP's argument, not mine. I am not sure I buy it, except perhaps for the fact that every other academic is expected to rebrand as an ML expert nowadays. It has more to do with ML hype than with string theory hype.
The professor whose student worked on this problem is a network theorist. He's never done string theory and has no need to "rebrand as machine learning expert". So yeah I don't buy it either.
Left this on his blog but it’s awaiting moderation:
It would be helpful to have more clearly targeted and titrated criticism, because you’ve mentioned press releases, a sciam article, the paper, and Sabine all without differentiation.
I hope it’s clear enough the paper itself is legit and doesn’t seem to make any inappropriate claims. Beyond that, the PRs seem to be the real offenders here, the sciam article less so (could be argued that’s healthy popsci), and I’m not sure what comment you’re making about Sabine. The title of her video may be click baity but the content itself seems to appropriately demarcate string theory from the paper.
I'm certainly a lay person here, so take this with a grain of salt. But my understanding is that this is part of the problem, or more the issue that people criticize.
I think it's largely uncontroversial that the math in string theory could be useful in other areas. But if that's your argument for the legitimacy of string theory then the question arises what string theory is and if it is still part of physics. Because physics has, of course, the goal of describing the real world, and, my understanding is, string theory failed to do that, despite what many people have hoped.
If string theory is "just a way of developing math that can be useful in totally unrelated areas", it's, well, part of mathematics. But I don't think that's how the field sees itself.
And why would that be a reason to attack people who don't care at all about the physics, but acknowledge that the mathematical ideas they use originated in string theory? Should they omit that just because the physics side of string theory has been more or less fruitless?
Peter Woit, the Columbia maths department computer systems administrator, makes his bread by googling the word String Theory and then posting what ever latest results come up in a disingenuous way on his blog to stir reactions from his readers.
Because, unfortunately, a terminal degree is not always a guarantee of future productivity.
String theory came into the public consciousness about two decades ago, followed by a backlash from a relatively small but persistent set of professors. String theory has largely dropped out of the public focus, but those researchers continue to hammer at it.
Woit is one of those. He's known primarily for his objections to string theory. His own work is just fine, but nobody outside of his discipline knows it.
It reminds of this quote from Roger Penrose's book, Fashion, Faith, and Fantasy in the New Physics of the Universe:
“My nervousness was perhaps at its greatest because the illustrative area that I had elected to discuss, namely string theory and some of its various descendants, had been developed to its heights in Princeton probably more than anywhere else in the world.”
“Moreover, that subject is a distinctly technical one, and I cannot claim competence over many of its important ingredients, my familiarity with these technicalities being somewhat limited, particularly in view of my status as an outsider.”
“Yet, if only the insiders are considered competent to make critical comments about the subject, then the criticisms are likely to be limited to relatively technical issues, some of the broader aspects of criticism being, no doubt, significantly neglected.”
The fact that Penrose felt nervous criticizing string theory has made me think less of string theory (or rather, the humans behind it) ever since.
That's from 2003, when the string theory theorists were riding high and attacking string theory was bad for a physicist's career. Now, "with string theorists now virtually unemployable unless they can figure out how to rebrand as machine learning experts...", the situation has reversed.
String theorists understand high-dimensional math, so maybe they can do something for machine learning theory. Probably not, but we can hope. It's frustrating how much of a black box machine learning systems are.
Well... Penrose got himself into serious trouble speaking on issues beyond his expertise. I respect that he is now being more careful. And it's entirely possible that he isn't up to date on their tech. Why would you doubt his own words?
Thanks for illustrating my point. Eviscerating someone is not how science should be conducted. On the contrary, it's how we got here: decades invested in an untestable, unworkable theory.
Well, it is a surprisingly natural path from Quantum Field Theory (QFT). So many things we get for free (primarily: gravitation), I would be surprised if it were just a random coincidence.
Yet, no one knows how to turn it into an actual theory in physics. It feels like we had QFT but weren't able to create the Standard Model.
It is, obviously, possible that the String Theory framework is just too broad. Or that it is in principle true, but we reached a level where it is too hard. Or it is just a step in the right direction, but we are missing something.
Given the effort of the smartest minds and still no progress (I do not think there is any hype left), it is possible that we need to wait for something more. Like the revival of artificial neural networks in the 2010s, after decades of slumber.
Unfortunately my understanding of physics stops at general relativity and quantum mechnics (which I did study both at uni, with some mathematical framework of understanding).
How would I advance from this point, what should I read to get a grip on string theory, including the concepts and maths involved? Could you recommend some resources?
Like why did they come up with the concepts they came up with, how does that help explain established theories and experimental phenomena on a deeper level, etc.
Also I've noticed there are several competing theories in this domain (like Quantum Gravity, String Theory, hope I'm not wrong), what are the odds that these theories end up being equivalent?
As others have pointed out, compared to classical physics, quantum mechanics describes the world of tiny distances and energies in greater detail while relativity becomes useful at the opposite end.
How would one construct an experiment whose results depend on both phenomena?
I would argue that you don’t need to learn string theory as it currently does not predict anything we can realistically observe (as you need energies that occurred only at the big bang). If string theory is correct we could observe a “supersymmetric” twin of all known particles, however we haven’t seen these, and they could exist even if string theory is false.
String theory aims to explain all physics as manifestations of a mathematical concept best understood as a vibrating string.
Initially, the hope was that string theory could predict the particle masses we observe, but that hasn’t worked as it turns out there were many different predictions possible.
String theory has also struggled to develop a version of the theory that does not contradict known properties of our actual universe.
Loop quantum gravity is not equivalent to string theory, except that it also tries to unify gravity and quantum physics.
As things stand, string theory is not falsifiable, while that is the case, you could argue it does not count as physics.
But, by multiple accounts, it is interesting math, which can be worth doing for its own sake, and it’s happened often enough that interesting math turned out to be useful somewhere. Just not for explaining physics.
The easiest book that's not popsci but actual physics is Barton Zwiebach's "A First Course in String Theory".
It does not presuppose a background in QFT. It does require you to know quantum mechanics. Mind you, it's not as deep as the standard texts (Polchinski et al. or Kaku's work prior to going off the rails) or my favourite which is the two-volume "Quantum Fields and Strings: A Course for Mathematicians". But it makes reading the others possible.
I’m no expert in string theory but with all the bagging on string theory I tried to get to the guts of what's going on without as much "opinion". I did watch this great video which interviewed a bunch of scientists working on various aspects of string theory, and overwhelmingly it seems there's still a lot of interesting questions to be answered (even if string theory doesn't describe this universe), unfortunately I can't seem to find it at the moment.
I think the main thing is, even if string theory turns out not to describe reality, it shows that quantum mechanics and general relativity can be reconciled within a single, mathematically consistent framework. The tension between the two is gone and it's actually needed for physical correctness. Simply knowing that such a reconciliation is possible is already a meaningful result.
String theory emerged from attempts to quantize gravity. I think the most interesting thing is that when a relativistic string is quantized, a massless spin-2 particle inevitably appears in the spectrum. This particle behaves exactly like a graviton, meaning that gravity is not introduced by hand but instead arises naturally from the theory.
Competing approaches may possibly be all compatible, much like different interpretations of Quantum Physics.
The main difficulty with experimental tests is that the relevant energy scales and distances are far beyond what we can currently probe in the laboratory. This is not a weakness unique to string theory, but a general problem for any theory of quantum gravity. The Planck scale is simply too extreme to access directly with present technology.
As for experiments that depend on both quantum mechanics and general relativity, in principle these would involve situations where quantum coherence and strong gravitational effects are both important. Examples include black hole evaporation, aspects of early-universe cosmology, and possible quantum effects in curved spacetime. These are extraordinarily difficult to study experimentally, but they are what motivates the search for a theory of quantum gravity in the first place.
Among theoretical physicists there is little doubt that Edward Witten is currently the greatest living theoretical physicist. Here is an interview with him from a few weeks ago:
Yeah Witten is unusual. He's not just a little bit better than everyone else, he's on a different league.
I knew a someone who was a temp visitor at the Institute for Advanced Studies who was given temp office next to Witten. And he said he wouldn't hear a noise, and the one day he starts typing and doesn't stop until 100 pages of paper are written, like he has it finished in his mind before he starts typing. Somehow I'm inclined to believe it can't be far from truth.
Hasn't stopped Weinstein from publishing. That nobody takes him seriously isn't Witten's fault. At least... not directly. Witten just happens to be very rigorous and a very gifted mathematician, so he sets a high bar for the rest of the field.
Yes, and RFK Jr. says certain vaccines have never worked.
I guess what I want to convey is how sad your comment makes me. What went wrong that makes you, and anyone really, trust that man's opinion on physics?
Here is a cynical but overall rather accurate takedown of Mr. Weinstein:
Hasn't it just been subsumed by AdS/CFT now? IIUC that's a layer of abstraction but still primarily string theory under the hood. That's still an active area isn't it? Or is that dying too?
I've heard AdS/CFT described as a correlation between something that doesn't describe our universe (which is maybe de-Sitter, but definitely not anti-de-Sitter space) and something else that doesn't describe our universe (the fundamental forces are not describable with a conformal field theory).
If string theorists are now unemployable, and they have to rebrand themselves as doing ML, then it seems to me that string theory is disappearing on its own, even if there are still some with tenure who continue to publicly promote it, but will eventually die off. So maybe when a child who was born this year becomes old enough in the future to develop an interest in physics, they won't even hear about it, except as a footnote.
High-energy physics is kind of stuck on that. Most of the interesting questions involve energies or distances way beyond what's reachable by experiment today.
Meanwhile, there's interesting experimental action in low-energy physics, down near absolute zero. Many of the weirder predictions of quantum mechanics have now been observed directly. Look at the list of Nobel laureates in physics since 1990.
A big fraction of them involve experiments with very low energy states,
where thermal noise is small enough that quantum effects dominate.
Some of that work led to useful technology. That's forward progress.
Kind of interesting to think about how the scale (range or magnitude) in which we are able to detect something has such striking implications for the model that gets developed based on these findings.
Even when we are able to operate at higher resolution sometimes the model makers still operate on their own scales. For example, I believe political science and economics ought to be studied from a biological perspective if they are to be fully understood, since gene by environment interaction determines so much. However, there seems to be little interest among political scientists and economists to study the nitty gritty of molecular and population genetics, and little interest among the molecular and population geneticists to study political science and economic theory. And because of this, seems to me such models will always fall short compared to models that operated on a perhaps more appropriate scale of inputs.
One day when I'm not being lazy I might publish a point by point refutation of the usual nonsense anti-string theory memes. Until then, here's what I said on this point 25 days ago, specifically the first paragraph starting with "like another commenter".
OK, but if there are no predictions that we can test for several generations, how do you tell the difference between science and science-sounding nonsense?
> If, then, it is true that the axiomatic basis of theoretical physics cannot be extracted from experience but must be freely invented, can we ever hope to find the right way? Nay, more, has this right way any existence outside our illusions? Can we hope to be guided safely by experience at all when there exist theories (such as classical mechanics) which to a large extent do justice to experience, without getting to the root of the matter? I answer without hesitation that there is, in my opinion, a right way, and that we are capable of finding it. Our experience hitherto justifies us in believing that nature is the realisation of the simplest conceivable mathematical ideas. I am convinced that we can discover by means of purely mathematical constructions the concepts and the laws connecting them with each other, which furnish the key to the understanding of natural phenomena. Experience may suggest the appropriate mathematical concepts, but they most certainly cannot be deduced from it. Experience remains, of course, the sole criterion of the physical utility of a mathematical construction. But the creative principle resides in mathematics. In a certain sense, therefore, I hold it true that pure thought can grasp reality, as the ancients dreamed.
This is his argument that mental experiments are a good basis to construct a theory. If relativity had 0 experimental evidence to this day it would be held in considerably lower regard.
There is no a priori reason why a bunch of meatbags would have the ability to test all laws of physics of this universe. I think we may have gotten lucky for a while there. String theory is so far out there that a new methodology has been developed, namely using beauty or symmetry or Occam's Razor to choose between competing theories. None of these have the pedigree of empiricism, but they may also not be wrong. I hope some aesthetic could be applied to the laws of the universe, but that is also not at all guaranteed.
Occam's razor is perfectly empirical: "entities must not be multiplied beyond necessity". It's what people repeatedly accuse string theory of violating in low-rent popsci criticism.
The other things you refer to are still Occam's razor: symmetry is handy because it eliminates symmetry-breaking entities even though we know they can happen in the standard model (Higgs) and "beauty" is really just another way of saying Occam's razor - you'd prefer your theory to not be full of dozens of free parameters because it starts to fit any possible outputs and be less predictive.
At all points the issue is that unless you've fully explored a simpler space with less entities, don't start adding them because you can always keep adding them to solve any problem but predict nothing (ala epicycles keeping geocentric solar models alive. You could probably run a space program assuming the Earth is the center of the universe, but it would be fiendishly difficult to model).
You seem to be intuiting some kind of chi squared minimization. It is true that fewer free parameters constrain models, but there is nothing in nature that prefers simplicity. That is probably the most annoying thing to us physicists. Even thermodynamics is always shoving us toward disorder. Just look at plasma physics some time for deterministically intractable problems stemming from four little equations (one if you like tensors).
I think it's better to think of most real world models as being low dimensional-ish, where there is a decaying power law of eigenvalues, and most are quite small, though not zero. You can get quite far by looking at the largest modes and ignoring small ones, but you're not exact, so you're not seeing The Truth, or whatever. Forcing your self to use fewer parameters is a way of denoising, however, that is quite effective.
Mathematics often does apply to the real world, but that isn't the goal. Physics is about the study of the real universe. If you want to call string theory a branch of mathematics I'd be fine with it, but they keep trying to claim they are physicists and that puts a higher bar on what we expect from them.
Of course physicists sometimes do make wrong predictions and it can take some time to figure out the hypothesis is wrong. However the goal is always to make something they can test to prove the hypothesis holds, which string theory has so far failed to do.
Good question, I touch on this on the same comment, in the paragraph starting with "I keep repeating these things on HNs".
The TLDR is that you can never expect the same level of certainty when you don't have direct experiments, but you can still rule out _some_ hypothesis, and see how far other hypothesis take you. This is called theoretical physics. Just because you can't make an experiment doesn't mean you can't do anything.
I heard that there's so many variants of string theory. All theories that have interesting low-energy predictions have lost to standard theory (see: SUSY experiments at LHC). Now we're left with high-energy ones which may actually be wrong too but we can't test them yet.
String theory isn't a theory it's a family of related theories sharing some common mathematical tools.
People talk about this as though it's an attempt at deception, whereas two people notionally working in string theory could in fact be proposing highly incompatible models which would be conclusively ruled out (and a lot of them have been in so far as that can be done - i.e. experimentation has put tight bounds on their possible parameters).
They are getting close to making a testable prediction, any day now. Have been for the last 30 years. History is not always an indication of the future, but it is often a good sign.
I notice not-even-wrong-woit doesn't bother refuting any of the claims on their merits. Just calls it "ridiculous hype" and moves on. It's about the same level of rigor he applies to his research in LQG - Loony Quantum Gravity.
I hear you, but on HN it's crazy. That person is the messia who will tell you the real truth that Big Academia and Mainstream University won't tell you.
It feels like Woit is just being a hater at this point. In a meritocracy, talent and funding gravitate toward the most promising options. If string theory took up a large proportion of people and resources, it’s because it solved technical problems no other framework could. Even if it hasn't yielded a Theory of Everything, the fact that its toolkit is now solving problems in other fields suggests the program has led to some success. Now that the field is in a lull, we're seeing a natural institutional rebalancing. Talent is simply self-allocating toward more fertile ground, which is exactly how a healthy scientific ecosystem should function.
The problem is the 'most promising option' is affected by hype and loud voices. Many of the string theory crowds made predictions that did not pan out at all and still did not acknowledge their mistakes. I think that's the problem. Sure there was a lot beautiful mathematics discovered, and it can be used in some other fields, but the acknowledgement of failure of string theory is needed, rather than trying to point here or there where some of the tools from ST could be used.
(I am a physicist, but nowhere near the strings theory)
I’m reporting a -1 day here because I’m lazy and tired.
Apple passwords are not case sensitive anymore, especially when porting between iPhone and windows
QR codes lol
The first paper they link to is not about string theory. It's using math that was developed for string theory, and is perfectly valid outside it, to make predictions that can be (and are) experimentally validated.
It has exactly none of the problems of string theory, and I am not sure why it's clumped with a physics paper in the blog. How is it a problem to say "hey they used string theory tools!" in a press release? If anything it might get other people to look at the math and get something good out of it...
This quote explains why the author thinks that it is a problem :
> with string theorists now virtually unemployable unless they can figure out how to rebrand as machine learning experts.
Their issue is (seemingly) not with the paper, but with the claim that these headlines feed a hype that attribute to string theory capabilities it doesn't have.
To be clear this is OP's argument, not mine. I am not sure I buy it, except perhaps for the fact that every other academic is expected to rebrand as an ML expert nowadays. It has more to do with ML hype than with string theory hype.
The professor whose student worked on this problem is a network theorist. He's never done string theory and has no need to "rebrand as machine learning expert". So yeah I don't buy it either.
Left this on his blog but it’s awaiting moderation:
It would be helpful to have more clearly targeted and titrated criticism, because you’ve mentioned press releases, a sciam article, the paper, and Sabine all without differentiation.
I hope it’s clear enough the paper itself is legit and doesn’t seem to make any inappropriate claims. Beyond that, the PRs seem to be the real offenders here, the sciam article less so (could be argued that’s healthy popsci), and I’m not sure what comment you’re making about Sabine. The title of her video may be click baity but the content itself seems to appropriately demarcate string theory from the paper.
I'm certainly a lay person here, so take this with a grain of salt. But my understanding is that this is part of the problem, or more the issue that people criticize.
I think it's largely uncontroversial that the math in string theory could be useful in other areas. But if that's your argument for the legitimacy of string theory then the question arises what string theory is and if it is still part of physics. Because physics has, of course, the goal of describing the real world, and, my understanding is, string theory failed to do that, despite what many people have hoped.
If string theory is "just a way of developing math that can be useful in totally unrelated areas", it's, well, part of mathematics. But I don't think that's how the field sees itself.
And why would that be a reason to attack people who don't care at all about the physics, but acknowledge that the mathematical ideas they use originated in string theory? Should they omit that just because the physics side of string theory has been more or less fruitless?
Peter Woit, the Columbia maths department computer systems administrator, makes his bread by googling the word String Theory and then posting what ever latest results come up in a disingenuous way on his blog to stir reactions from his readers.
Seems like a disingenuous description of a person with a terminal degree in the subject at hand. Why bother?
Because, unfortunately, a terminal degree is not always a guarantee of future productivity.
String theory came into the public consciousness about two decades ago, followed by a backlash from a relatively small but persistent set of professors. String theory has largely dropped out of the public focus, but those researchers continue to hammer at it.
Woit is one of those. He's known primarily for his objections to string theory. His own work is just fine, but nobody outside of his discipline knows it.
It reminds of this quote from Roger Penrose's book, Fashion, Faith, and Fantasy in the New Physics of the Universe:
“My nervousness was perhaps at its greatest because the illustrative area that I had elected to discuss, namely string theory and some of its various descendants, had been developed to its heights in Princeton probably more than anywhere else in the world.”
“Moreover, that subject is a distinctly technical one, and I cannot claim competence over many of its important ingredients, my familiarity with these technicalities being somewhat limited, particularly in view of my status as an outsider.”
“Yet, if only the insiders are considered competent to make critical comments about the subject, then the criticisms are likely to be limited to relatively technical issues, some of the broader aspects of criticism being, no doubt, significantly neglected.”
The fact that Penrose felt nervous criticizing string theory has made me think less of string theory (or rather, the humans behind it) ever since.
> Penrose book...
That's from 2003, when the string theory theorists were riding high and attacking string theory was bad for a physicist's career. Now, "with string theorists now virtually unemployable unless they can figure out how to rebrand as machine learning experts...", the situation has reversed.
String theorists understand high-dimensional math, so maybe they can do something for machine learning theory. Probably not, but we can hope. It's frustrating how much of a black box machine learning systems are.
Well... Penrose got himself into serious trouble speaking on issues beyond his expertise. I respect that he is now being more careful. And it's entirely possible that he isn't up to date on their tech. Why would you doubt his own words?
What did he say that got him into trouble?
He has some interesting beliefs about the basis of human consciousness.
He's just saying he doesn't want to be eviscerated by Ed Witten, which is a pretty commonly shared sentiment in the community.
Thanks for illustrating my point. Eviscerating someone is not how science should be conducted. On the contrary, it's how we got here: decades invested in an untestable, unworkable theory.
Do you know who has been eviscerated by Ed Witten?
Well, it is a surprisingly natural path from Quantum Field Theory (QFT). So many things we get for free (primarily: gravitation), I would be surprised if it were just a random coincidence.
Yet, no one knows how to turn it into an actual theory in physics. It feels like we had QFT but weren't able to create the Standard Model.
It is, obviously, possible that the String Theory framework is just too broad. Or that it is in principle true, but we reached a level where it is too hard. Or it is just a step in the right direction, but we are missing something.
Given the effort of the smartest minds and still no progress (I do not think there is any hype left), it is possible that we need to wait for something more. Like the revival of artificial neural networks in the 2010s, after decades of slumber.
Unfortunately my understanding of physics stops at general relativity and quantum mechnics (which I did study both at uni, with some mathematical framework of understanding).
How would I advance from this point, what should I read to get a grip on string theory, including the concepts and maths involved? Could you recommend some resources?
Like why did they come up with the concepts they came up with, how does that help explain established theories and experimental phenomena on a deeper level, etc.
Also I've noticed there are several competing theories in this domain (like Quantum Gravity, String Theory, hope I'm not wrong), what are the odds that these theories end up being equivalent?
As others have pointed out, compared to classical physics, quantum mechanics describes the world of tiny distances and energies in greater detail while relativity becomes useful at the opposite end.
How would one construct an experiment whose results depend on both phenomena?
I would argue that you don’t need to learn string theory as it currently does not predict anything we can realistically observe (as you need energies that occurred only at the big bang). If string theory is correct we could observe a “supersymmetric” twin of all known particles, however we haven’t seen these, and they could exist even if string theory is false.
String theory aims to explain all physics as manifestations of a mathematical concept best understood as a vibrating string.
Initially, the hope was that string theory could predict the particle masses we observe, but that hasn’t worked as it turns out there were many different predictions possible. String theory has also struggled to develop a version of the theory that does not contradict known properties of our actual universe.
Loop quantum gravity is not equivalent to string theory, except that it also tries to unify gravity and quantum physics.
As things stand, string theory is not falsifiable, while that is the case, you could argue it does not count as physics.
But, by multiple accounts, it is interesting math, which can be worth doing for its own sake, and it’s happened often enough that interesting math turned out to be useful somewhere. Just not for explaining physics.
The easiest book that's not popsci but actual physics is Barton Zwiebach's "A First Course in String Theory".
It does not presuppose a background in QFT. It does require you to know quantum mechanics. Mind you, it's not as deep as the standard texts (Polchinski et al. or Kaku's work prior to going off the rails) or my favourite which is the two-volume "Quantum Fields and Strings: A Course for Mathematicians". But it makes reading the others possible.
I’m no expert in string theory but with all the bagging on string theory I tried to get to the guts of what's going on without as much "opinion". I did watch this great video which interviewed a bunch of scientists working on various aspects of string theory, and overwhelmingly it seems there's still a lot of interesting questions to be answered (even if string theory doesn't describe this universe), unfortunately I can't seem to find it at the moment.
I think the main thing is, even if string theory turns out not to describe reality, it shows that quantum mechanics and general relativity can be reconciled within a single, mathematically consistent framework. The tension between the two is gone and it's actually needed for physical correctness. Simply knowing that such a reconciliation is possible is already a meaningful result.
String theory emerged from attempts to quantize gravity. I think the most interesting thing is that when a relativistic string is quantized, a massless spin-2 particle inevitably appears in the spectrum. This particle behaves exactly like a graviton, meaning that gravity is not introduced by hand but instead arises naturally from the theory.
Competing approaches may possibly be all compatible, much like different interpretations of Quantum Physics.
The main difficulty with experimental tests is that the relevant energy scales and distances are far beyond what we can currently probe in the laboratory. This is not a weakness unique to string theory, but a general problem for any theory of quantum gravity. The Planck scale is simply too extreme to access directly with present technology.
As for experiments that depend on both quantum mechanics and general relativity, in principle these would involve situations where quantum coherence and strong gravitational effects are both important. Examples include black hole evaporation, aspects of early-universe cosmology, and possible quantum effects in curved spacetime. These are extraordinarily difficult to study experimentally, but they are what motivates the search for a theory of quantum gravity in the first place.
Among theoretical physicists there is little doubt that Edward Witten is currently the greatest living theoretical physicist. Here is an interview with him from a few weeks ago:
https://www.youtube.com/watch?v=sAbP0magTVY
I think it is a great watch for anyone with an interest in the field.
Yeah Witten is unusual. He's not just a little bit better than everyone else, he's on a different league.
I knew a someone who was a temp visitor at the Institute for Advanced Studies who was given temp office next to Witten. And he said he wouldn't hear a noise, and the one day he starts typing and doesn't stop until 100 pages of paper are written, like he has it finished in his mind before he starts typing. Somehow I'm inclined to believe it can't be far from truth.
eric weinstein said that witten is the dark lord of string theory; scotching any advance in theoretical physics.
Hasn't stopped Weinstein from publishing. That nobody takes him seriously isn't Witten's fault. At least... not directly. Witten just happens to be very rigorous and a very gifted mathematician, so he sets a high bar for the rest of the field.
Yes, and RFK Jr. says certain vaccines have never worked.
I guess what I want to convey is how sad your comment makes me. What went wrong that makes you, and anyone really, trust that man's opinion on physics?
Here is a cynical but overall rather accurate takedown of Mr. Weinstein:
https://www.youtube.com/watch?v=DUr4Tb8uy-Q
Hasn't it just been subsumed by AdS/CFT now? IIUC that's a layer of abstraction but still primarily string theory under the hood. That's still an active area isn't it? Or is that dying too?
I've heard AdS/CFT described as a correlation between something that doesn't describe our universe (which is maybe de-Sitter, but definitely not anti-de-Sitter space) and something else that doesn't describe our universe (the fundamental forces are not describable with a conformal field theory).
If string theorists are now unemployable, and they have to rebrand themselves as doing ML, then it seems to me that string theory is disappearing on its own, even if there are still some with tenure who continue to publicly promote it, but will eventually die off. So maybe when a child who was born this year becomes old enough in the future to develop an interest in physics, they won't even hear about it, except as a footnote.
All it needs is an experiment that can test it.
High-energy physics is kind of stuck on that. Most of the interesting questions involve energies or distances way beyond what's reachable by experiment today.
Meanwhile, there's interesting experimental action in low-energy physics, down near absolute zero. Many of the weirder predictions of quantum mechanics have now been observed directly. Look at the list of Nobel laureates in physics since 1990. A big fraction of them involve experiments with very low energy states, where thermal noise is small enough that quantum effects dominate. Some of that work led to useful technology. That's forward progress.
> Most of the interesting questions involve energies or distances way beyond what's reachable by experiment today.
Astronomers can observe extremely energetic environments from a great distance.
It's not a controlled experiment, but sometimes they get lucky and see something that suggests new physics.
I have no idea what might be needed to provide astronomical evidence for string theory.
Kind of interesting to think about how the scale (range or magnitude) in which we are able to detect something has such striking implications for the model that gets developed based on these findings.
Even when we are able to operate at higher resolution sometimes the model makers still operate on their own scales. For example, I believe political science and economics ought to be studied from a biological perspective if they are to be fully understood, since gene by environment interaction determines so much. However, there seems to be little interest among political scientists and economists to study the nitty gritty of molecular and population genetics, and little interest among the molecular and population geneticists to study political science and economic theory. And because of this, seems to me such models will always fall short compared to models that operated on a perhaps more appropriate scale of inputs.
One day when I'm not being lazy I might publish a point by point refutation of the usual nonsense anti-string theory memes. Until then, here's what I said on this point 25 days ago, specifically the first paragraph starting with "like another commenter".
https://news.ycombinator.com/item?id=46336655
In other words as we probe lower scales, string theory predicts thtat Lorenz invariance will never break,
as long we have to do with a consistent string like theory.
Is my understanding correct?
OK, but if there are no predictions that we can test for several generations, how do you tell the difference between science and science-sounding nonsense?
> If, then, it is true that the axiomatic basis of theoretical physics cannot be extracted from experience but must be freely invented, can we ever hope to find the right way? Nay, more, has this right way any existence outside our illusions? Can we hope to be guided safely by experience at all when there exist theories (such as classical mechanics) which to a large extent do justice to experience, without getting to the root of the matter? I answer without hesitation that there is, in my opinion, a right way, and that we are capable of finding it. Our experience hitherto justifies us in believing that nature is the realisation of the simplest conceivable mathematical ideas. I am convinced that we can discover by means of purely mathematical constructions the concepts and the laws connecting them with each other, which furnish the key to the understanding of natural phenomena. Experience may suggest the appropriate mathematical concepts, but they most certainly cannot be deduced from it. Experience remains, of course, the sole criterion of the physical utility of a mathematical construction. But the creative principle resides in mathematics. In a certain sense, therefore, I hold it true that pure thought can grasp reality, as the ancients dreamed.
- Albert Einstein
This is his argument that mental experiments are a good basis to construct a theory. If relativity had 0 experimental evidence to this day it would be held in considerably lower regard.
There is no a priori reason why a bunch of meatbags would have the ability to test all laws of physics of this universe. I think we may have gotten lucky for a while there. String theory is so far out there that a new methodology has been developed, namely using beauty or symmetry or Occam's Razor to choose between competing theories. None of these have the pedigree of empiricism, but they may also not be wrong. I hope some aesthetic could be applied to the laws of the universe, but that is also not at all guaranteed.
> I hope some aesthetic
Certainly internal self-consistency will take you a long way if you don't have experiments. Some people find beauty in this :-)
This is good and all but then it is not really physics as it is generally intended
Occam's razor is perfectly empirical: "entities must not be multiplied beyond necessity". It's what people repeatedly accuse string theory of violating in low-rent popsci criticism.
The other things you refer to are still Occam's razor: symmetry is handy because it eliminates symmetry-breaking entities even though we know they can happen in the standard model (Higgs) and "beauty" is really just another way of saying Occam's razor - you'd prefer your theory to not be full of dozens of free parameters because it starts to fit any possible outputs and be less predictive.
At all points the issue is that unless you've fully explored a simpler space with less entities, don't start adding them because you can always keep adding them to solve any problem but predict nothing (ala epicycles keeping geocentric solar models alive. You could probably run a space program assuming the Earth is the center of the universe, but it would be fiendishly difficult to model).
You seem to be intuiting some kind of chi squared minimization. It is true that fewer free parameters constrain models, but there is nothing in nature that prefers simplicity. That is probably the most annoying thing to us physicists. Even thermodynamics is always shoving us toward disorder. Just look at plasma physics some time for deterministically intractable problems stemming from four little equations (one if you like tensors).
I think it's better to think of most real world models as being low dimensional-ish, where there is a decaying power law of eigenvalues, and most are quite small, though not zero. You can get quite far by looking at the largest modes and ignoring small ones, but you're not exact, so you're not seeing The Truth, or whatever. Forcing your self to use fewer parameters is a way of denoising, however, that is quite effective.
It might be worth considering what you think research in a field like mathematics actually entails when asking such questions.
Because you can write a lot of mathematics with no practical applications for generations (then whoops: number theory and cryptography!)
Mathematics often does apply to the real world, but that isn't the goal. Physics is about the study of the real universe. If you want to call string theory a branch of mathematics I'd be fine with it, but they keep trying to claim they are physicists and that puts a higher bar on what we expect from them.
Of course physicists sometimes do make wrong predictions and it can take some time to figure out the hypothesis is wrong. However the goal is always to make something they can test to prove the hypothesis holds, which string theory has so far failed to do.
Good question, I touch on this on the same comment, in the paragraph starting with "I keep repeating these things on HNs".
The TLDR is that you can never expect the same level of certainty when you don't have direct experiments, but you can still rule out _some_ hypothesis, and see how far other hypothesis take you. This is called theoretical physics. Just because you can't make an experiment doesn't mean you can't do anything.
If they had that the hype could die. Luckily it cannot be tested so the hype will continue in perpetuity
I heard that there's so many variants of string theory. All theories that have interesting low-energy predictions have lost to standard theory (see: SUSY experiments at LHC). Now we're left with high-energy ones which may actually be wrong too but we can't test them yet.
Heh... as someone on the outside, I feel the need to ask:
Has it been rigorously shown that it can never be tested? Or is that your prediction?
Test which version? Part of the problem is that string theory is a meta theory. There will always be ways to escape any negative experimental result.
> There will always be ways to escape any negative experimental result.
Yeah... except that hasn't been proven. That's just your belief, right?
I don't think anyone has proven that string theory can yield no testable predictions. I think if someone had, that'd be a big deal.
And I don't think we should pretend that an open problem is closed just because we don't like it.
String theory isn't a theory it's a family of related theories sharing some common mathematical tools.
People talk about this as though it's an attempt at deception, whereas two people notionally working in string theory could in fact be proposing highly incompatible models which would be conclusively ruled out (and a lot of them have been in so far as that can be done - i.e. experimentation has put tight bounds on their possible parameters).
They are getting close to making a testable prediction, any day now. Have been for the last 30 years. History is not always an indication of the future, but it is often a good sign.
But yes, not rigorous.
Provide a viable test, and you will be sure that an experimentalist will jump at the chance
Are string theorists any less employable than other physicists? I gather that most physicists end up doing something other than physics.
I notice not-even-wrong-woit doesn't bother refuting any of the claims on their merits. Just calls it "ridiculous hype" and moves on. It's about the same level of rigor he applies to his research in LQG - Loony Quantum Gravity.
Lumpy Quantum Gravy is real. I've seen it at Thanksgiving.
As a general rule of thumb I practice I ignore the complaints about Physics of anyone who cites Sabine Hossenfelder.
I hear you, but on HN it's crazy. That person is the messia who will tell you the real truth that Big Academia and Mainstream University won't tell you.
Now that you edited your post to correct your spelling, people probably have no idea what I'm talking about.
It feels like Woit is just being a hater at this point. In a meritocracy, talent and funding gravitate toward the most promising options. If string theory took up a large proportion of people and resources, it’s because it solved technical problems no other framework could. Even if it hasn't yielded a Theory of Everything, the fact that its toolkit is now solving problems in other fields suggests the program has led to some success. Now that the field is in a lull, we're seeing a natural institutional rebalancing. Talent is simply self-allocating toward more fertile ground, which is exactly how a healthy scientific ecosystem should function.
The problem is the 'most promising option' is affected by hype and loud voices. Many of the string theory crowds made predictions that did not pan out at all and still did not acknowledge their mistakes. I think that's the problem. Sure there was a lot beautiful mathematics discovered, and it can be used in some other fields, but the acknowledgement of failure of string theory is needed, rather than trying to point here or there where some of the tools from ST could be used. (I am a physicist, but nowhere near the strings theory)
Thanks to Michio Kaku.
not a physicist but this video by Angela Collier is a fun watch:
“string theory lied to us and now science communication is hard.
https://youtu.be/kya_LXa_y1E?si=WTfOSS61YeUQbqgf
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I’m reporting a -1 day here because I’m lazy and tired. Apple passwords are not case sensitive anymore, especially when porting between iPhone and windows QR codes lol
People need to get fired
Sabine Hossenfelder seems to think the paper on natural networks is pretty legit: https://www.youtube.com/watch?v=Hj5b0ieVWSo
Even if string theory cannot explain the universe, there may still be some value in it.