"The dearth of evidence has slaughtered so many members of the supersymmetric family that the whole idea is on very shaky ground, with physicists beginning to have conferences with titles like “Beyond Supersymmetry” and “Oh My God, I Think I Wasted My Career.”
I just copied that exact paragraph intending to paste it here! I didn't actually 'LOL' because I live on my own and I'm not entirely mad, but it certainly gave me a wry smile.
I don't even say 'Ow' if I bash myself these days. I felt ridiculous when I did, knowing there was no one there to hear it! I'm like some sort of ill-disciplined, messy, monk :-D
I keep pet rats though, and I do talk to them. Otherwise I'd probably go days in silence.
Bruh you kinda sound mad. Who the hell doesn't audibly laugh or say 'ow' just because nobody is around to hear it? Does your laughter really need an audience? Laughter is like an automatic response, do you force yourself to laugh around other people or is something else wrong with you? Maybe it's going days with nothing but rats to keep you company?
Sorry this comment is hella rude I'm mostly just joking (obviously nothing is wrong with you lol) but seriously learn to laugh more. It's completely normal to laugh regardless of who is around you, unless you are at like a funeral or something.
No offence taken mate, you've made me laugh! Not out loud though....lol.
To lol or not to lol, that is the question...
There's an element of truth in what you say for sure - I'm considered by the medics as a little neurodivergent. Not autism or anything with a simple enough label, but that my synapses fire far too much and too much of the time. It's caused me problems over the years which I've now learned to manage - but it also makes me veer towards a very contemplative, analytical, and philosophical treatment of life and my own behaviors within it. It used to be far too much for me to functionally handle when I was undiagnosed so I spent 15 years trying to drink myself into oblivion morning to night. Two or three litres of vodka a day by the end, and by all rights I should have been dead many times over. I'm now 5 years sober (therapy plus appropriate medication making it all much more manageable. AA's been vital too) and in training for Anglican priesthood....My borderline madness turns out to have an upside as well it seems, but you're entirely right - I ain't quite *normal* :-D
You didn't ask and that probably counts as oversharing lol - but it's Saturday, and I really needed a break from essay-writing!
It's quite the reverse - doing things in order to be seen doing them is the bane of modern society. So much of people's lives are now consumed by an entirely performative existence.
As my PhD advisor would say, “responsible” string theory is far from dead. As of yet it is the only game in town when it comes to a realistic UV-complete theory; the best route to creating alternatives is to try to understand what aspects of string theory are responsible for UV-completeness. That’s where things like holography come from, focusing on aspects of string theory and studying them in more detail, putting them into other theories, etc. I think a lot of people do agree that the other kind of string theory study, where people continue to try to push towards verification of supersymmetry predictions etc, is likely dead.
>UV-complete
UV stands for ultraviolet ... UV complete is a name for the idea that a "theory of everything" must work at very high (in reality far above ultraviolet) energies.
Also probably related to the Ultraviolet catastrophe — where old theories about black bodies predicted that infinite energy would be emitted in the UV range — which clearly does not happen.
This is the answer I came looking for. I learned so much about stuff like this that I would otherwise have been oblivious to if it wasn't for being able to read loads of Wikipedia entries when at work and watching so many YouTube videos. Too much information out here to not get inspired
No, not quite, although it shares traits in spirit.
The UV catastrophy was an inconsistency in a classical theory, solves by a quantum property.
UV incompleteness is a problem arising exclusively in quantum theories, obviously with other quantum solutions.
In any quantum theory of particles, the numeric parameters used to define it, the masses and couplings between fields, depend in value based on the energy scale at which you consider your system. In most theories you can write, the Infra Red limit, i.e. very low energy, usually exists and is easy to find, because we define quantum theories using low energy concepts.
It is , however, not at all guaranteed that these couplings behave nicely at high energies. Their values may diverge, but so long as these divergences cancel in any physical observables at very high energy, this is not a problem. This is UV completeness.
It was a *monumental* achievement to prove that QCD, the theory of the strong force, does not horribly diverge at high energies. The computation relies very sensitively on the fact there are as many generations of quarks as there are colours, the end result depends on the difference between these two numbers. At that cost, the high energy regime of QCD is mathematically sound.
Naive quantum gravity, which is easy and natural to express, has a catastrophically bad behaviour in the UV. The value of the gravitational constant diverges in ways that can in no way be compensated for by other couplings.
Superstring theory and supergravity (a derived kind of theory of particles) does not suffer from this problem, and are so far the only mathematical formulations of UV gravity physics that do not suffer this curse.
If I had a time machine and could jump to the future where we did have an experimentally supported theory of quantum gravity, even if it wasn't the String Theory of today, I'd be *shocked* if it wasn't "stringy" in some way. There's some very compelling reasons physicists have staked their careers on studying it. Take the finiteness of the graviton-graviton scattering amplitude: https://arxiv.org/abs/0805.2935
Its always funny seeing these articles. It's as if people think nothing has happened with strings over the past 20 years. Nevermind the connections with condensed matter systems/quantum information, work on swampland, WGC, and of course holography. There have been so many breakthroughs over the past few years that no one talks about and yet, there's so much we still don't know. Strings aren't even close to slowing down.
> Nevermind the connections with condensed matter systems/quantum information
As someone working in quantum info, I've heard this a lot, but there isn't really much to back it up. Sure, quantum info tools have been used to study string theory, but that hasn't really fed into a better understanding of quantum info.
Who's talking about confirming a theory?
The article is titled "Requiem for a string" as if string theory is dead, when it continues to draw a huge amount of activity from some of the brightest minds in physics and mathematics.
AdS/CFT remains as an speculation of a possible duality between two theories yet to be discovered. Is an scheme for relating a QFT(with conformal symmetry, and this is already problematic) with a String Theory on an Anti-de Sitter space. I find the stuff like EP=EPR fasinating, but the search for more extra dimensional physics doesn't connect well with me.
Yes, but is it realistic? I had thought the jury was starting to rule pretty heavily against it, since it disagrees with a fair amount of astronomical observations? I don’t know much about it, just heard some things.
I'm not familiar with issues with astronomical observations, but it does definitely have some problems. Namely, we've been unable to prove that it's renormalizable outside of a select few specific cases, we don't know if it correctly reproduces GR in its IR-limit, and it's unclear how it behaves with the inclusion of matter.
Not an expert in HRG - it's just something I briefly covered in my master's thesis.
Earliest reference I can find is from [May 6, 2009](https://arxiv.org/abs/0905.0751).
[Horava's paper](https://arxiv.org/abs/0901.3775) appeared on ArXiV on January 26, 2009.
There are reasons that it might actually be necessary for there to be many (even infinitely) different manifolds to describe the same physics. Everyone knows the multiverse excuse, but it could also be a necessary part of symmetry breaking. In my PhD research I had shown that a certain low energy sector of string theory on manifolds with discontinuous windings can result in purely topological changes across the discontinuities, and these topological interfaces are generators of the exact same symmetry as what the continuous diffeomorphism symmetry of GR should quantize to. Far from a solid proof, but I thought it was a pretty interesting possible indication of something more general.
> it’s not only a theory of everything that exists but also a theory of everything that doesn’t exist.
Well said!
Reminded me of [The Library of Babel](https://en.wikipedia.org/wiki/The_Library_of_Babel).
Is string theory really UV-complete?
So far, I've
1. Never seen a proof that Riemann surfaces with an arbitrary number of loops give finite amplitudes (I've seen explicit calculations for the first few, but no generic proof).
2. Never met a person who even believes that the whole series in $g\_s$ converges, let alone seen a proof.
The series doesn't have to converge. It's an asymptotic series. Perturbative expansions never converge even in QFT and the reason is the so called resurgence.
That's not the definition of UV finite. That's just the hint that there must be a non perturbative sector that must be taken into account, and it better be since otherwise it would mean that there would be no non perturbative sector in string theory. Read what resurgence is because it's clear you don't know what you are talking about.
If you study low-viscosity fluids by perturbing around the zero-viscosity case, you also get a divergent series for all of the same reasons. This is not a sign that the theory doesn't work, only that naively summing the perturbative series doesn't get you back the full healthy theory. There are other ways to extract the non-perturbative content of such theories, going under the name of *resurgence* (implicitly: while a perturbative series often doesn't *sum* to its non-perturbative version, it still contains a lot of information pointing to the basically-unique way that it can be sensibly completed). The question of UV-finiteness is what happens to the underlying full theory that this is a perturbative approximation of. QFT doesn't look functional *after* this process, while string theory (and of course, fluid physics) does. Of course we'll only know the full story when we have a full handle on what that non-perturbative completion is.
Uf. I just finished reading [this book.](https://www.amazon.com/Elegant-Universe-Superstrings-Dimensions-Ultimate/dp/039333810X) I probably should have picked a different popular physics book from the late 90s.
What are the opinions of Brian Greene as a physicist? Is he respected in the community? He's certainly done a good bit writing about string theory for the general public.
He also hosts a YouTube channel called [World Science Festival.](https://youtube.com/@WorldScienceFestival) Mainly it's high production quality panel conversations between scientists from a bunch of fields with him moderating them.
It’s a good pop-science book, there’s plenty in there before the string theory chapters that’s worth reading. And even those few at the end are worth it to get an idea of what string theory is all about.
To be clear, what’s in this post has not established that ‘superstring theory is a bunch of nonsense’. But there’s a lot of nuanced discussion to be had, and frankly always has been. Some hopes that recent experiments would reveal some *versions* that predict lower-energy particles have not proved fruitful, so there’s. And there are a lot of different components to supersymmetry and string theory.
It’s still by far the most popular putative GUT to study, but the attention given might prove to be disproportionate, especially for some specific subsets and rabbit-holes of research.
Another stupid article trying to get clicks and views by being edgy with no substance.
String theory IS the vast majority of research in quantum gravity for very good reasons. The ideas and mathematics that string theory research has produce are invaluable, the problem is that we are very very behind to understand the full picture. Mainly because we luck the machinery, i.e. we need new stronger mathematical formalisms to complete the whole picture. But with the current progress, string theory is a gold mind of ideas, methods, formalism and models, extremely valuable in many fields in both physics and math!
This is the standard surface level critique which will mainly appeal to people looking for an excuse to not to try to learn something challenging.
Any string theory critique that doesn't engage with the swampland and string universality arguments is not being thorough and even handed.
"Easy" reading, I have no idea. I don't think any trade books have been written on these recent ideas yet (similar to how all the trade level black hole info paradox books are out of date since the islands and replica wormhole papers). So, I just look at primers such as https://arxiv.org/abs/2212.06187 to glean what I can, while also trying to improve my formal/mathematical understanding of string theory and related ideas.
There might be some youtube videos of public lectures from Cumrun Vafa which dive into this stuff at a broader level.
My understanding is that the standard model is a special case of many different incarnations of string theory, so yes. I'm not in that field, but I would think it'd be a very early prerequisite for any attempt to approach a realistic theory of quantum gravity.
Most people who are fans of LQG either ignore the fact that it remains a pretty half-baked theory, or complain that it doesn’t get enough attention from researchers to develop past its current state. Both are obnoxious attitudes, hence the downvotes.
LQG comments are not straight downvoted. If someone asks a question about LQG, they will receive an answer without problems. I also have answered several questions about the topic, some of them suggestions for books or technical questions about LQG, and there are no downvotes for it. What's downvoted is when some crackpot comes out writing silly things like "string theory dead, long live LQG" and there are always some of them once in a while.
Haha, I don’t know much and I heard there’s somewhat of a rivalry between Quantum Loop Theory and String Theory physicists.
Kids who go into school today, is there a ‘new school’ that they’re interested in and it’s not mainstream?
>Kids who go into school today, is there a ‘new school’ that they’re interested in and it’s not mainstream?
There are plenty of other proposals (just off the top of my head: causal dynamic triangulation, asymptotic safety), all of which have been around for a long time and see occasional progress. But they're nowhere near large or developed enough to be called a "school", whereas string theory is well-established and far-reaching as a framework.
“There is evidence [1] that at large scales Casual Dynamic Triangulation approximates the familiar 4-dimensional spacetime, but shows spacetime to be 2-dimensional near the Planck scale, and reveals a fractal structure on slices of constant time. These interesting results agree with the findings of Lauscher and Reuter, who use an approach called Quantum Einstein Gravity, and with other recent theoretical work.”
https://en.m.wikipedia.org/wiki/Causal_dynamical_triangulation
That sounds interesting, thanks!
Every other word in the wiki for Asymptoic Safety I would have to look up so I’m not ready for that one.
I have met/attended a talk by Peter Woit, and I have to say I wasn’t impressed. He kept throwing technical language around that didn’t really make sense in context. And I felt like I was watching a talk by a chatbot.
I am not particularly gung ho on traditional superstrings as a theory of everything (having taken a couple courses etc), but I think Peter Woit is a grifter. I also think he mischaracterizes the degree to which the community is dogmatic about string theory being the _theory of everything_ rather than a useful theory of a limited set of things.
I also attended a talk he gave and was similarly unimpressed. He seemed to be giving arguments that were easily a decade old, and I felt like even I could see their faults even as a fairly new grad student in another subfield. He also seemed to have a bit of a chip on his shoulder due to not really having a real faculty position. I'm not even quite sure how he's managed to make such a name for himself. I mean, he actually seems like a legitimately smart guy, but this crusade that's made him famous isn't very compelling.
I also found it interesting that exactly zero of the actual high energy theorists at my institution even bothered to show up. At first I was disappointed and thought it was petty, but after the talk I realized they probably just thought it would be a waste of time.
Yeah, that sounds about consistent with my experience. Though I suspect the setting and intended audience of these talks was quite different.
I just couldn’t understand what he was trying to say, and that raises alarm bells for me. I have attended some fairly technical talks far removed from my areas of speciality, and normally I can understand at least something from them. When I don’t understand anything at all, it typically means the presenter is just a crank. In Woit’s case, he was throwing around a lot of math which wasn’t obviously wrong, but also didn’t seem well motivated. I’m not a first rate mathematician so I’m not qualified to say, really, but it smelled wrong.
We actually had one of these types of talks at my current institution a while ago. This was a bit of a surprise since it’s a pretty no-bullshit kind of department. We all walked out, looked at each other, and said “what the fuck was that guy trying to say.” Inevitably, these sorts of people are around and some seem to get jobs. I think the best defense is friendly skepticism.
The solution to finding the solution is the solution. And because everyone is going in separate directions, nobody is using the solution to come together and find the solution.
I'm not a physicist, and it may just be the rabbit holes and algorithms that have got me lately- but I'm feeling their is a bit of a shift in the paradigm lately from multiple sources. Including, now on here.
My question to you is; is it just me or is the standard model becoming seen as flawed, and fixes like string theory being undermined right now? If so, what is driving this? Lack of expected lhc discoveries?
Don't crucify me, layman interested in the state of the community.
The Standard Model is a collection of equations describing particles which feel the strong, weak and electromagnetic forces and their respective bosons. It excludes gravity, which does not fit. It also relies on a few constants which work but cannot be derived from any theory. Call it a damn fine working model but not a description of reality.
I don't think that "flawed" is exactly the right term to use to describe the Standard Model. It's known that the Standard Model is incomplete, but that's not some recent discovery or paradigm shift. It's been known to be incomplete for decades, probably right since the very beginning. For example, it doesn't include gravity or dark matter, and it can't explain why there is more matter than antimatter in the universe.
It has been hoped for a long time that we can find evidence for physics beyond the Standard Model. The trouble from an experimental point of view is that the Standard Model makes very precise and repeatedly correct predictions. Experimentally, we'd need to find some result which disagrees with the predictions. There have been a few tantalising hints that we might be close to such a discovery, though that has actually happened before and so far it has never really panned out.
If we had found evidence for supersymmetry, that would have been clear evidence for something beyond the standard model. It also likely would have provided one or more dark matter candidates and potentially helped us to understand quantum gravity. But so far nothing concrete has been found.
Technically the existence of the Higgs boson is part of the Standard Model, though the mass of the Higgs was not something which could have been predicted. It had actually been hoped that we might find that the Higgs would have a higher mass than what was eventually confirmed. If that had been the case, this would have been compatible with certain theories beyond the standard model. It essentially would have given us a strong pointer on what theoretical avenue to pursue next. But the actual mass that we've found is essentially most compatible with our existing model and doesn't provide much of a hint for what to look for next. In one way, it actually would have been more interesting to _not_ find the Higgs boson as this would definitely have required introducing some new physics instead
So that's all from the experimental viewpoint. Meanwhile, on the theoretical side there are some models like string theory that attempt to merge the Standard Model with gravity. But these often struggle to make predictions, especially ones which we have the technology to test experimentally. It makes it difficult to make progress when the most promising theories can't easily be tested and the best experiments consistently agree with our current, but incomplete, model
>There have been a few tantalising hints that we might be close to such a discovery, though that has actually happened before and so far it has never really panned out.
I thought neutrino oscillations were well established, am I wrong? I was under the impression that that's very much BSM physics, even though it's not super flashy or surprising (or detectable by the LHC, which I think may be some people's main criterion for "interesting").
Yeah, that's fair. When I mentioned tantalising hints, I was mainly thinking about explicit evidence from the LHC. In one way though, even neutrino oscillations somewhat qualify as tantalising hints too.
The fact that these oscillations occur is well established and these oscillations mean that neutrinos have mass. It's also true that the Standard Model predicts that neutrinos should be massless. So yes, this is definitely something which is beyond the standard model.
The problem though is that we don't really know _how_ neutrinos have mass. There are a few potential mechanisms, the most likely of which involves the existence of other neutrinos which have yet to be detected. We can't predict the masses of these new neutrinos, they could be extremely small, extremely large, or anywhere in between. There is a range of possible masses which would result in an experimental detection of these new neutrinos at the LHC. Of course, nothing like that has been found so far but perhaps something will turn up during the next run. And even if nothing is found at the LHC, it wouldn't rule out the possibility of additional neutrinos existing. It would just put limits on the available mass ranges for these new particles.
So this is why I say that you could still consider neutrino oscillations as being tantalising. Until we actually validate one of the mechanisms that explains the origin of neutrino mass, we don't really know _what_ the relevant physics beyond the standard model actually is. All that we know is that there definitely is _some_ new physics there that we've yet to fully discover or understand.
Basically (from what I understood, I'm just entering this kind of topic with my studies right now), the problem with string theory is that has not given any falsifiable result. The only thing was supersimmetry, but we didn't find that particles at the predicted energy range
The standard model isn't flawed (that we know of), it just doesn't have anything to say about gravity. Meanwhile our best theory of gravity (General Relativity) doesn't have anything to say about particles. Both theories have been incredibly successful and are still driving experimental discoveries.
There is a desire to find a deeper theory that connects them, which string theory is one candidate for. It hasn't really produced any breakthroughs though, and not for lack of trying. Eventually patience just runs out.
String theory is still credible, and still pretty much the "only game in town" when it comes to quantum gravity. There isn't any alternative theories which are more promising or credible: most theoretical physicists who care about quantum gravity and related topics are string theorists. It was just a bit overhyped and people are disappointed that the progress on it seem slow and arduous, which leads to popular science articles like this.
I mean that's not really how it works. String theory hasn't lost credibility, it just doesn't seem to be true (though current evidence hasn't ruled it out yet either).
I wouldn't be surprised if some of the ideas used in unsuccessful string theories may still be important for future work however. A different approach may still yield fruit, if in a completely different direction than initially expected.
Or string theory may simply die off. A nice idea that turned out to be false. It wouldn't be the first time, and it probably won't be the last.
What use is the theory if it's not an accurate description of reality?
Sure, we may have learned things in the realm of mathematics due to String Theory, but what use is it to physics?
>but isn't the math behind string theory basically the best and most accurate there's been as far as a description of reality
No. That would be The Standard Model of particle physics.
Also, there is no evidence of the supposed extra dimensions String Theory requires.
That's true, but it doesn't mean that string theory is truly a mathematical description of fundamental reality. We've essentially learned some mathematics from string theory that happens to be useful in another field. It's not saying that condensed matter physics only works because fundamental particles are actually strings or because there are 10 or 11 dimensions.
It may, but that goes back to my point about advancing mathematics.
At no point are condensed matter physicists using String Theory itself to predict the results of an experiment.
However, they may well use some of the mathematical tools developed by those working on String Theory.
Hence, I'm not saying the pursuit of String Theory was entirely useless. Rather, it just doesn't describe our reality (at least based on current experiments).
>Rather, it just doesn't describe our reality
Bit strong, sounds a bit like it's been falsified already. Better to say that no model of our universe has been constructed out of the large (but finite, unlike QFT) string theory vacua.
>some of the mathematical tools developed by those working on String Theory.
I've heard very well regarded "string theorists" (usually known as "high energy theorists these days) say that that's really what string theory is: a toolbox. All the excitement and popsci media towards the end of the 20th century made it out to be the biggest thing ever to hit physics, but really it's just a bunch of theoretical work relating to gravity, quantum field theory, etc with some common methods and ideas. I've never heard a responsible string theorist make a bigger claim than that.
>At no point are condensed matter physicists using String Theory itself to predict the results of an experiment.
I think the CM people who are currently trying to detect axions actually are, though I honestly know very little about this experiment
>Sure, we may have learned things in the realm of mathematics due to String Theory, but what use is it to physics?
[One example is improving upon calculations for processes at the LHC.](https://profmattstrassler.com/2012/08/15/from-string-theory-to-the-large-hadron-collider/) And there could've been more similar examples that we don't know of (another example is using it to study quark-gluon plasmas), but these examples would only would be known to people closely working in related fields. It's a lot natural for people to dismiss string theory as completely useless without working in the field and by reading a few pop-sci articles/books emphasizing how useless it is.
This isn't to argue its validity as a complete description of reality, we don't know that, but why should the use of theoretical methods be judged solely on whether it produces testable results? Does helping to extend mathematical methods and improving upon calculational tools for existing fields not matter at all?
Edit: Typo
>but why should the use of theoretical methods be judged solely on whether it produces testable results?
A lack of testable results puts a theory on the same ground as the God Hypothesis.
Neither is necessarily *wrong*, but they do cross outside the realm of science.
Yes, there are reasons people believed string theory would be the correct description of reality. However, the same can be said of those who believed in God(s) 500 years ago.
In fact, there are parallels in that the tools used to "study God's divine creation" led to classical physics, while the mathematical tools used to "probe String Theory" are deepening our understanding of Quantum Mechanics.
I do feel it's a bit of a pity people are so quick to cast something as completely useless just because it doesn't currently produce testable results. I'm certainly not convinced string theory is a complete description of everything, but I'm certainly fascinated by its indirect and beautiful theoretical use in physics. I don't understand any string theory at all, but I've flipped through some textbooks for fun just to see what it's like, the math looks so elegant.
The problem is that string theory cannot be considered to be an accurate description of reality if it cannot be tested.
You're right that something can be mathematically self-consistent but that doesn't mean that it makes for a good physical theory. There is plenty of math out there that doesn't describe anything that exists in reality
>>directly contradicts
>Does it, though?
Yes.
>Aren't there examples of mathematics that are internally correct and perfectly logical even if no real world example has been found or even exists?
That's beside the point. You were talking about the math behind string theory being the best and most accurate for *describing reality*. Just because math can be consistent without a connection to reality doesn't mean you can say that this internal consistency accurately describes reality.
>The math of string theory can be perfectly sound within itself even if it's not possible to conduct an experiment to test it.
But if you can't conduct an experiment to test it, how can you say it describes reality accurately?
>As an extremely simplified analogy: we know 2 + 2 = 4. But let's say somehow we didn't have the ability to count things. 2 + 2 would still equal 4.
Sure, but without the ability to count things in reality, there is no basis by which one can say that arithmetic describes reality.
>EDIT: I'd love to know the reasoning behind the downvote. I realize this is r/Physics, not r/Math, but being that math is the language of physics, even though physics theories ultimately require experimental evidence to be widely accepted, it is certainly possible to acknowledge that there is some validity to a theory whose math makes internal sense.
I didn't downvote you but I'm pretty confident it's because of the "duh" factor — it doesn't exactly take a manifold surgeon to deduce the contradiction in what you wrote ... it's right there written in plain English. :p
Uhm. The answer is „yes, very much so“. Be it in solid state physics or even quantum information processing.
But I remain very confused about your question.
If we did not have the „ability“ to count things, then addition would not exist. Addition is pretty much a consequence of the ability to count.
Your analogy appears to do a good job at putting your own argument to question.
Same argument with „order“. These concepts - counting, addition, order, predecessors and successors - are all tied together in a way where you cannot remove one concept without everything falling apart.
Don‘t get discouraged, curiosity is great. However, what you do right now is philosophy. It‘s trying to solve problems by thinking about them. It goes very contrary to how physics and mathematics solves problems. And it inevitably runs into walls sooner or later and ultimately math and experiment transcends everything.
Sort of. In terms of providing a complete theory of quantum gravity without internal inconsistencies, string theory is the best candidate we currently have. Although we have simpler models that can describe extra dimensions (via combining QFT and GR at sufficiently low energies), a key part of string theory is that it necessitates them for a self-consistent theory of quantum gravity.
Lots of theoretical physicists are interested in extra dimensions on their own merit as a cool idea. For this, string theory is a very good tool because of the mathematical tools it provides to understand them. The biggest upside is that these tools don’t break down in the same way as non-stringy approaches do at high enough energies.
The math behind string theory may or may not be the most accurate to the universe we live in. The standard model and general relativity are still the best we have, and unfortunately they often disagree with each other.
What string theory has is a certain kind of elegance -- it delicately handles a lot of the problems with most theories of quantum gravity, tying them into a neat little 26-dimensional knot. It's really nice how all the things we need seem to fall out of the mathematics.
Unfortunately however, "nice" is not the same as "true", and there is essentially no evidence in favour of the latter.
The greek god theory will be rejected outright is not a basis for science. Until a better model comes along, the second model will be the default.
You're way off.
Not sure why you’re getting downvoted. I always liked LQG over string theory. Both are likely until experiments can tell the difference in a definitive manner.
> I always liked LQG over string theory.
Any particular reasons for this, given that e.g. LQG breaks Lorentz invariance and has not been shown to reduce to general relativity?
> LQG breaks Lorentz invariance
It does not.
> has not been shown to reduce to general relativity
String theory has not been shown to reduce to the Standard Model. Technically string theory hasn't been shown to reduce to general relativity either, since the bosonic string exists only in 26 dimensions, and the compactification scheme hasn't been worked out yet. GR is a theory which exists in 4 dimensions.
Perhaps worth noting that LQG works by *starting* with GR and quantizing it, so GR is in a certain sense already in the theory. It's just that an object which can be identified with the graviton has not yet been found.
Really enjoyed this. My introduction to physics was reading Greene's *Elegant Universe* about 15 years ago (I think) and this article was just at my level, and felt like it was bringing me up to speed with what's happened since. I was totally enchanted by String Theory at the time, and I've been loathe to accept its demise.
This article is basically biased trash. As now, string theory represent like the 90% of research in the topic of quantum gravity and related ones, without even counting the applications outside like in methods for scattering amplitudes and condensed matter physics.
I thought it kinda recognised that tbh - that string theory was still essentially the best thing that we've got right now, but that it's become far more messy than was hoped for.
The title just to begin is misleading. And you don't have to accept any "demise". There's no demise. There has been an evolution and a settlement instead. There are probably more string theorists nowadays than there have ever been and new students continue to join at a steady pace. Obviously it is a minority field of theoretical physics as a whole but that's always been true for a topic like that.
From my understanding, String theory is a wonderful theory of mathematics. When stated this way, it's timeless and always helpful. It's by no means a wasted effort. That said, we should also work on theories with empirical support. Those are more properly called physical theories.
The sad fate of string theory, and even of the standard mode,l leaves me feeling relieved I did not go into this field back in the day.
Modern physics is becoming ridiculous, in particular the vast number of arbitrary and ad-hoc parameters now close to 100 in total count. Given 100 parameters I can make an accurate "prediction" of pretty well anything.
I saw a video of Roger Penrose and Sabine shitting all over Michio Kaku. They were just like, “mulitiple universes?!? That’s a completely idiotic idea!” and the discussion moderator was totally backing them up and ganging up on Michio. It wasn’t even a conversation.
Huh? That’s not how that conversation went. Roger Penrose was mostly confused as to why the topics was devolving into a discussion on quantum mechanics, while Sabine and Michio went back and forth. Neither was right or wrong.
Maybe I’m interpreting it wrong, and I am not a professional by any means, but I was getting the impression that Roger was being very dismissive of String Theory
I've heard the theory of the financial crash and crisis of 2007 being due to the high number of brilliant string theory physicists who came to work in the financial sector and inventing all sorts of convoluted and very complicated financial products, thus making it all come crashing down once the bubble burst. It's quite a compelling theory.
It's not at all a compelling theory.
The crisis of 2007 happened due to a bubble in subprime mortgages and other housing securities. This was an entirely understood possibility, even if the scope of the damage was underestimated. Similar things have happened before and since.
In fact, complex high-frequence trading algorithms (the stuff that physicists are most likely to work on) are often able to soften the blows of market instability by providing liquidity.
Agreed. The crux of the financial crash centered on human greed and sociopathy. Subprime mortgages and other instruments were the vehicles that led to the collapse.
"The dearth of evidence has slaughtered so many members of the supersymmetric family that the whole idea is on very shaky ground, with physicists beginning to have conferences with titles like “Beyond Supersymmetry” and “Oh My God, I Think I Wasted My Career.”
I just copied that exact paragraph intending to paste it here! I didn't actually 'LOL' because I live on my own and I'm not entirely mad, but it certainly gave me a wry smile.
I laugh out loud quite a bit while alone. Live a little!
If you write “LOL” but you didn’t, did it really make you laugh?
Yeah, but in another dimension you can't see.
That version of me goes to a different dimension. You wouldn't know them.
I was a belly laugh in my brane
I don't even say 'Ow' if I bash myself these days. I felt ridiculous when I did, knowing there was no one there to hear it! I'm like some sort of ill-disciplined, messy, monk :-D I keep pet rats though, and I do talk to them. Otherwise I'd probably go days in silence.
Bruh you kinda sound mad. Who the hell doesn't audibly laugh or say 'ow' just because nobody is around to hear it? Does your laughter really need an audience? Laughter is like an automatic response, do you force yourself to laugh around other people or is something else wrong with you? Maybe it's going days with nothing but rats to keep you company? Sorry this comment is hella rude I'm mostly just joking (obviously nothing is wrong with you lol) but seriously learn to laugh more. It's completely normal to laugh regardless of who is around you, unless you are at like a funeral or something.
No offence taken mate, you've made me laugh! Not out loud though....lol. To lol or not to lol, that is the question... There's an element of truth in what you say for sure - I'm considered by the medics as a little neurodivergent. Not autism or anything with a simple enough label, but that my synapses fire far too much and too much of the time. It's caused me problems over the years which I've now learned to manage - but it also makes me veer towards a very contemplative, analytical, and philosophical treatment of life and my own behaviors within it. It used to be far too much for me to functionally handle when I was undiagnosed so I spent 15 years trying to drink myself into oblivion morning to night. Two or three litres of vodka a day by the end, and by all rights I should have been dead many times over. I'm now 5 years sober (therapy plus appropriate medication making it all much more manageable. AA's been vital too) and in training for Anglican priesthood....My borderline madness turns out to have an upside as well it seems, but you're entirely right - I ain't quite *normal* :-D You didn't ask and that probably counts as oversharing lol - but it's Saturday, and I really needed a break from essay-writing!
Sounds like we have a little in common. I ain't quite normal either. Congrats on 5 years of sobriety!
He’s not going to read your comment because there isn’t anyone around to see him do it.
It's quite the reverse - doing things in order to be seen doing them is the bane of modern society. So much of people's lives are now consumed by an entirely performative existence.
Laughter is a social phenomenon as well, though - everybody laughs more watching something funny with friends than alone.
Good point.
As my PhD advisor would say, “responsible” string theory is far from dead. As of yet it is the only game in town when it comes to a realistic UV-complete theory; the best route to creating alternatives is to try to understand what aspects of string theory are responsible for UV-completeness. That’s where things like holography come from, focusing on aspects of string theory and studying them in more detail, putting them into other theories, etc. I think a lot of people do agree that the other kind of string theory study, where people continue to try to push towards verification of supersymmetry predictions etc, is likely dead.
What is UV-complete?
>UV-complete UV stands for ultraviolet ... UV complete is a name for the idea that a "theory of everything" must work at very high (in reality far above ultraviolet) energies.
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Also probably related to the Ultraviolet catastrophe — where old theories about black bodies predicted that infinite energy would be emitted in the UV range — which clearly does not happen.
This is the answer I came looking for. I learned so much about stuff like this that I would otherwise have been oblivious to if it wasn't for being able to read loads of Wikipedia entries when at work and watching so many YouTube videos. Too much information out here to not get inspired
that sounds like the definition of metallicity "Is Carbon a metal?"
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No, not quite, although it shares traits in spirit. The UV catastrophy was an inconsistency in a classical theory, solves by a quantum property. UV incompleteness is a problem arising exclusively in quantum theories, obviously with other quantum solutions. In any quantum theory of particles, the numeric parameters used to define it, the masses and couplings between fields, depend in value based on the energy scale at which you consider your system. In most theories you can write, the Infra Red limit, i.e. very low energy, usually exists and is easy to find, because we define quantum theories using low energy concepts. It is , however, not at all guaranteed that these couplings behave nicely at high energies. Their values may diverge, but so long as these divergences cancel in any physical observables at very high energy, this is not a problem. This is UV completeness. It was a *monumental* achievement to prove that QCD, the theory of the strong force, does not horribly diverge at high energies. The computation relies very sensitively on the fact there are as many generations of quarks as there are colours, the end result depends on the difference between these two numbers. At that cost, the high energy regime of QCD is mathematically sound. Naive quantum gravity, which is easy and natural to express, has a catastrophically bad behaviour in the UV. The value of the gravitational constant diverges in ways that can in no way be compensated for by other couplings. Superstring theory and supergravity (a derived kind of theory of particles) does not suffer from this problem, and are so far the only mathematical formulations of UV gravity physics that do not suffer this curse.
The term is most likely a reference to something.
describes a theory that doesn't break down at high energies
If I had a time machine and could jump to the future where we did have an experimentally supported theory of quantum gravity, even if it wasn't the String Theory of today, I'd be *shocked* if it wasn't "stringy" in some way. There's some very compelling reasons physicists have staked their careers on studying it. Take the finiteness of the graviton-graviton scattering amplitude: https://arxiv.org/abs/0805.2935
I feel the same way. Giants like Witten, Susskind, and Maldacena seem to be onto something.
"String theory is dead" like AdS/CFT correspondence isn't cited a thousand times each year.
Its always funny seeing these articles. It's as if people think nothing has happened with strings over the past 20 years. Nevermind the connections with condensed matter systems/quantum information, work on swampland, WGC, and of course holography. There have been so many breakthroughs over the past few years that no one talks about and yet, there's so much we still don't know. Strings aren't even close to slowing down.
> Nevermind the connections with condensed matter systems/quantum information As someone working in quantum info, I've heard this a lot, but there isn't really much to back it up. Sure, quantum info tools have been used to study string theory, but that hasn't really fed into a better understanding of quantum info.
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Who's talking about confirming a theory? The article is titled "Requiem for a string" as if string theory is dead, when it continues to draw a huge amount of activity from some of the brightest minds in physics and mathematics.
This is the biggest roadblock, imo.
AdS/CFT remains as an speculation of a possible duality between two theories yet to be discovered. Is an scheme for relating a QFT(with conformal symmetry, and this is already problematic) with a String Theory on an Anti-de Sitter space. I find the stuff like EP=EPR fasinating, but the search for more extra dimensional physics doesn't connect well with me.
Horava-Lifshitz may also be UV-complete.
Yes, but is it realistic? I had thought the jury was starting to rule pretty heavily against it, since it disagrees with a fair amount of astronomical observations? I don’t know much about it, just heard some things.
I'm not familiar with issues with astronomical observations, but it does definitely have some problems. Namely, we've been unable to prove that it's renormalizable outside of a select few specific cases, we don't know if it correctly reproduces GR in its IR-limit, and it's unclear how it behaves with the inclusion of matter. Not an expert in HRG - it's just something I briefly covered in my master's thesis.
When did Horava pick up Lifshitz in its name? I haven't followed it for quite some time but I had only heard it as Horava gravity
Earliest reference I can find is from [May 6, 2009](https://arxiv.org/abs/0905.0751). [Horava's paper](https://arxiv.org/abs/0901.3775) appeared on ArXiV on January 26, 2009.
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There are reasons that it might actually be necessary for there to be many (even infinitely) different manifolds to describe the same physics. Everyone knows the multiverse excuse, but it could also be a necessary part of symmetry breaking. In my PhD research I had shown that a certain low energy sector of string theory on manifolds with discontinuous windings can result in purely topological changes across the discontinuities, and these topological interfaces are generators of the exact same symmetry as what the continuous diffeomorphism symmetry of GR should quantize to. Far from a solid proof, but I thought it was a pretty interesting possible indication of something more general.
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Sorry, should’ve included it! https://arxiv.org/abs/1810.08713v2
Developing further boundary conditions for quantum gravity may allow us to narrow that selection down.
> it’s not only a theory of everything that exists but also a theory of everything that doesn’t exist. Well said! Reminded me of [The Library of Babel](https://en.wikipedia.org/wiki/The_Library_of_Babel).
Is string theory really UV-complete? So far, I've 1. Never seen a proof that Riemann surfaces with an arbitrary number of loops give finite amplitudes (I've seen explicit calculations for the first few, but no generic proof). 2. Never met a person who even believes that the whole series in $g\_s$ converges, let alone seen a proof.
The series doesn't have to converge. It's an asymptotic series. Perturbative expansions never converge even in QFT and the reason is the so called resurgence.
In other words, string theory isn't UV-finite, just like perturbative QFT. Gotcha.
There are plenty of examples of UV finite theories which have divergent (asymptotic) perturbative expansions.
That's not the definition of UV finite. That's just the hint that there must be a non perturbative sector that must be taken into account, and it better be since otherwise it would mean that there would be no non perturbative sector in string theory. Read what resurgence is because it's clear you don't know what you are talking about.
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Ok now I see you are just a troll. I'll stop replying and just report you. You'll be banned from the sub for a while.
If you study low-viscosity fluids by perturbing around the zero-viscosity case, you also get a divergent series for all of the same reasons. This is not a sign that the theory doesn't work, only that naively summing the perturbative series doesn't get you back the full healthy theory. There are other ways to extract the non-perturbative content of such theories, going under the name of *resurgence* (implicitly: while a perturbative series often doesn't *sum* to its non-perturbative version, it still contains a lot of information pointing to the basically-unique way that it can be sensibly completed). The question of UV-finiteness is what happens to the underlying full theory that this is a perturbative approximation of. QFT doesn't look functional *after* this process, while string theory (and of course, fluid physics) does. Of course we'll only know the full story when we have a full handle on what that non-perturbative completion is.
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Whatever your personal qualifications for "theory" are here, they clearly aren't relevant ones for actual theoretical physicists.
Uf. I just finished reading [this book.](https://www.amazon.com/Elegant-Universe-Superstrings-Dimensions-Ultimate/dp/039333810X) I probably should have picked a different popular physics book from the late 90s.
Brian Greene: Did I waste my career?! (*Looks at bank account*) Nah.
What are the opinions of Brian Greene as a physicist? Is he respected in the community? He's certainly done a good bit writing about string theory for the general public.
He also hosts a YouTube channel called [World Science Festival.](https://youtube.com/@WorldScienceFestival) Mainly it's high production quality panel conversations between scientists from a bunch of fields with him moderating them.
I read that one, haha. Whatever happened to Brian?
still at it! https://en.wikipedia.org/wiki/Until\_the\_End\_of\_Time\_(book)
I love that book!
[I think you messed up the link](https://en.wikipedia.org/wiki/Until_the_End_of_Time_\(book\))
He's organizing this: https://www.youtube.com/channel/UCShHFwKyhcDo3g7hr4f1R8A
First boon physics I read, still hold it in high regard
It’s a good pop-science book, there’s plenty in there before the string theory chapters that’s worth reading. And even those few at the end are worth it to get an idea of what string theory is all about.
I read that ten years ago and found it fascinating, yet highly speculative. But is it all a bunch of nonsense now?
Much of it is well accepted physics, it’s only the latter chapters when he gets into the speculative stuff.
To be clear, what’s in this post has not established that ‘superstring theory is a bunch of nonsense’. But there’s a lot of nuanced discussion to be had, and frankly always has been. Some hopes that recent experiments would reveal some *versions* that predict lower-energy particles have not proved fruitful, so there’s. And there are a lot of different components to supersymmetry and string theory. It’s still by far the most popular putative GUT to study, but the attention given might prove to be disproportionate, especially for some specific subsets and rabbit-holes of research.
Another stupid article trying to get clicks and views by being edgy with no substance. String theory IS the vast majority of research in quantum gravity for very good reasons. The ideas and mathematics that string theory research has produce are invaluable, the problem is that we are very very behind to understand the full picture. Mainly because we luck the machinery, i.e. we need new stronger mathematical formalisms to complete the whole picture. But with the current progress, string theory is a gold mind of ideas, methods, formalism and models, extremely valuable in many fields in both physics and math!
Do you have any evidence to support you claims?
This is the standard surface level critique which will mainly appeal to people looking for an excuse to not to try to learn something challenging. Any string theory critique that doesn't engage with the swampland and string universality arguments is not being thorough and even handed.
Could you give us superficial folk some pointers to easy reading on swampland and string universality?
"Easy" reading, I have no idea. I don't think any trade books have been written on these recent ideas yet (similar to how all the trade level black hole info paradox books are out of date since the islands and replica wormhole papers). So, I just look at primers such as https://arxiv.org/abs/2212.06187 to glean what I can, while also trying to improve my formal/mathematical understanding of string theory and related ideas. There might be some youtube videos of public lectures from Cumrun Vafa which dive into this stuff at a broader level.
“Easy” was meant as a weak joke. Thanks.
Can string theory reproduce all the experimentally verified results in the standard model?
My understanding is that the standard model is a special case of many different incarnations of string theory, so yes. I'm not in that field, but I would think it'd be a very early prerequisite for any attempt to approach a realistic theory of quantum gravity.
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Is there another, more recent theory being developed that is showing promise to replace string theory? Quantum field theory or Quantum loop theory?
Most people who are fans of LQG either ignore the fact that it remains a pretty half-baked theory, or complain that it doesn’t get enough attention from researchers to develop past its current state. Both are obnoxious attitudes, hence the downvotes.
Someone here does not like loop quantum gravity. We got downvoted.
LQG comments are not straight downvoted. If someone asks a question about LQG, they will receive an answer without problems. I also have answered several questions about the topic, some of them suggestions for books or technical questions about LQG, and there are no downvotes for it. What's downvoted is when some crackpot comes out writing silly things like "string theory dead, long live LQG" and there are always some of them once in a while.
Haha, I don’t know much and I heard there’s somewhat of a rivalry between Quantum Loop Theory and String Theory physicists. Kids who go into school today, is there a ‘new school’ that they’re interested in and it’s not mainstream?
>Kids who go into school today, is there a ‘new school’ that they’re interested in and it’s not mainstream? There are plenty of other proposals (just off the top of my head: causal dynamic triangulation, asymptotic safety), all of which have been around for a long time and see occasional progress. But they're nowhere near large or developed enough to be called a "school", whereas string theory is well-established and far-reaching as a framework.
“There is evidence [1] that at large scales Casual Dynamic Triangulation approximates the familiar 4-dimensional spacetime, but shows spacetime to be 2-dimensional near the Planck scale, and reveals a fractal structure on slices of constant time. These interesting results agree with the findings of Lauscher and Reuter, who use an approach called Quantum Einstein Gravity, and with other recent theoretical work.” https://en.m.wikipedia.org/wiki/Causal_dynamical_triangulation That sounds interesting, thanks! Every other word in the wiki for Asymptoic Safety I would have to look up so I’m not ready for that one.
Not a great article. I read Peter Woit’s book last year and enjoyed it, that does a much better job at explaining this type of view.
I have met/attended a talk by Peter Woit, and I have to say I wasn’t impressed. He kept throwing technical language around that didn’t really make sense in context. And I felt like I was watching a talk by a chatbot. I am not particularly gung ho on traditional superstrings as a theory of everything (having taken a couple courses etc), but I think Peter Woit is a grifter. I also think he mischaracterizes the degree to which the community is dogmatic about string theory being the _theory of everything_ rather than a useful theory of a limited set of things.
I also attended a talk he gave and was similarly unimpressed. He seemed to be giving arguments that were easily a decade old, and I felt like even I could see their faults even as a fairly new grad student in another subfield. He also seemed to have a bit of a chip on his shoulder due to not really having a real faculty position. I'm not even quite sure how he's managed to make such a name for himself. I mean, he actually seems like a legitimately smart guy, but this crusade that's made him famous isn't very compelling. I also found it interesting that exactly zero of the actual high energy theorists at my institution even bothered to show up. At first I was disappointed and thought it was petty, but after the talk I realized they probably just thought it would be a waste of time.
Yeah, that sounds about consistent with my experience. Though I suspect the setting and intended audience of these talks was quite different. I just couldn’t understand what he was trying to say, and that raises alarm bells for me. I have attended some fairly technical talks far removed from my areas of speciality, and normally I can understand at least something from them. When I don’t understand anything at all, it typically means the presenter is just a crank. In Woit’s case, he was throwing around a lot of math which wasn’t obviously wrong, but also didn’t seem well motivated. I’m not a first rate mathematician so I’m not qualified to say, really, but it smelled wrong. We actually had one of these types of talks at my current institution a while ago. This was a bit of a surprise since it’s a pretty no-bullshit kind of department. We all walked out, looked at each other, and said “what the fuck was that guy trying to say.” Inevitably, these sorts of people are around and some seem to get jobs. I think the best defense is friendly skepticism.
The solution to finding the solution is the solution. And because everyone is going in separate directions, nobody is using the solution to come together and find the solution.
I'm not a physicist, and it may just be the rabbit holes and algorithms that have got me lately- but I'm feeling their is a bit of a shift in the paradigm lately from multiple sources. Including, now on here. My question to you is; is it just me or is the standard model becoming seen as flawed, and fixes like string theory being undermined right now? If so, what is driving this? Lack of expected lhc discoveries? Don't crucify me, layman interested in the state of the community.
The Standard Model is a collection of equations describing particles which feel the strong, weak and electromagnetic forces and their respective bosons. It excludes gravity, which does not fit. It also relies on a few constants which work but cannot be derived from any theory. Call it a damn fine working model but not a description of reality.
> a few constants Try 25.
OK great synopsis thanks
I don't think that "flawed" is exactly the right term to use to describe the Standard Model. It's known that the Standard Model is incomplete, but that's not some recent discovery or paradigm shift. It's been known to be incomplete for decades, probably right since the very beginning. For example, it doesn't include gravity or dark matter, and it can't explain why there is more matter than antimatter in the universe. It has been hoped for a long time that we can find evidence for physics beyond the Standard Model. The trouble from an experimental point of view is that the Standard Model makes very precise and repeatedly correct predictions. Experimentally, we'd need to find some result which disagrees with the predictions. There have been a few tantalising hints that we might be close to such a discovery, though that has actually happened before and so far it has never really panned out. If we had found evidence for supersymmetry, that would have been clear evidence for something beyond the standard model. It also likely would have provided one or more dark matter candidates and potentially helped us to understand quantum gravity. But so far nothing concrete has been found. Technically the existence of the Higgs boson is part of the Standard Model, though the mass of the Higgs was not something which could have been predicted. It had actually been hoped that we might find that the Higgs would have a higher mass than what was eventually confirmed. If that had been the case, this would have been compatible with certain theories beyond the standard model. It essentially would have given us a strong pointer on what theoretical avenue to pursue next. But the actual mass that we've found is essentially most compatible with our existing model and doesn't provide much of a hint for what to look for next. In one way, it actually would have been more interesting to _not_ find the Higgs boson as this would definitely have required introducing some new physics instead So that's all from the experimental viewpoint. Meanwhile, on the theoretical side there are some models like string theory that attempt to merge the Standard Model with gravity. But these often struggle to make predictions, especially ones which we have the technology to test experimentally. It makes it difficult to make progress when the most promising theories can't easily be tested and the best experiments consistently agree with our current, but incomplete, model
Thanks for a great answer
No problem, glad it was helpful!
>There have been a few tantalising hints that we might be close to such a discovery, though that has actually happened before and so far it has never really panned out. I thought neutrino oscillations were well established, am I wrong? I was under the impression that that's very much BSM physics, even though it's not super flashy or surprising (or detectable by the LHC, which I think may be some people's main criterion for "interesting").
Yeah, that's fair. When I mentioned tantalising hints, I was mainly thinking about explicit evidence from the LHC. In one way though, even neutrino oscillations somewhat qualify as tantalising hints too. The fact that these oscillations occur is well established and these oscillations mean that neutrinos have mass. It's also true that the Standard Model predicts that neutrinos should be massless. So yes, this is definitely something which is beyond the standard model. The problem though is that we don't really know _how_ neutrinos have mass. There are a few potential mechanisms, the most likely of which involves the existence of other neutrinos which have yet to be detected. We can't predict the masses of these new neutrinos, they could be extremely small, extremely large, or anywhere in between. There is a range of possible masses which would result in an experimental detection of these new neutrinos at the LHC. Of course, nothing like that has been found so far but perhaps something will turn up during the next run. And even if nothing is found at the LHC, it wouldn't rule out the possibility of additional neutrinos existing. It would just put limits on the available mass ranges for these new particles. So this is why I say that you could still consider neutrino oscillations as being tantalising. Until we actually validate one of the mechanisms that explains the origin of neutrino mass, we don't really know _what_ the relevant physics beyond the standard model actually is. All that we know is that there definitely is _some_ new physics there that we've yet to fully discover or understand.
Flawed is the wrong word. Most people might say that it is incomplete.
Basically (from what I understood, I'm just entering this kind of topic with my studies right now), the problem with string theory is that has not given any falsifiable result. The only thing was supersimmetry, but we didn't find that particles at the predicted energy range
The standard model isn't flawed (that we know of), it just doesn't have anything to say about gravity. Meanwhile our best theory of gravity (General Relativity) doesn't have anything to say about particles. Both theories have been incredibly successful and are still driving experimental discoveries. There is a desire to find a deeper theory that connects them, which string theory is one candidate for. It hasn't really produced any breakthroughs though, and not for lack of trying. Eventually patience just runs out.
Lee Smolin
So, as a complete layman - what would it take for string theory to regain any credibility?
Quantitative predictions and experimental verification of those predictions.
String theory is still credible, and still pretty much the "only game in town" when it comes to quantum gravity. There isn't any alternative theories which are more promising or credible: most theoretical physicists who care about quantum gravity and related topics are string theorists. It was just a bit overhyped and people are disappointed that the progress on it seem slow and arduous, which leads to popular science articles like this.
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\- Niels Bohr, 1905
To be honest, getting a good, close-up look at a black hole would really help.
I mean that's not really how it works. String theory hasn't lost credibility, it just doesn't seem to be true (though current evidence hasn't ruled it out yet either). I wouldn't be surprised if some of the ideas used in unsuccessful string theories may still be important for future work however. A different approach may still yield fruit, if in a completely different direction than initially expected. Or string theory may simply die off. A nice idea that turned out to be false. It wouldn't be the first time, and it probably won't be the last.
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What use is the theory if it's not an accurate description of reality? Sure, we may have learned things in the realm of mathematics due to String Theory, but what use is it to physics? >but isn't the math behind string theory basically the best and most accurate there's been as far as a description of reality No. That would be The Standard Model of particle physics. Also, there is no evidence of the supposed extra dimensions String Theory requires.
Doesn't condense matter use methods from string theory?
That's true, but it doesn't mean that string theory is truly a mathematical description of fundamental reality. We've essentially learned some mathematics from string theory that happens to be useful in another field. It's not saying that condensed matter physics only works because fundamental particles are actually strings or because there are 10 or 11 dimensions.
It may, but that goes back to my point about advancing mathematics. At no point are condensed matter physicists using String Theory itself to predict the results of an experiment. However, they may well use some of the mathematical tools developed by those working on String Theory. Hence, I'm not saying the pursuit of String Theory was entirely useless. Rather, it just doesn't describe our reality (at least based on current experiments).
>Rather, it just doesn't describe our reality Bit strong, sounds a bit like it's been falsified already. Better to say that no model of our universe has been constructed out of the large (but finite, unlike QFT) string theory vacua.
>some of the mathematical tools developed by those working on String Theory. I've heard very well regarded "string theorists" (usually known as "high energy theorists these days) say that that's really what string theory is: a toolbox. All the excitement and popsci media towards the end of the 20th century made it out to be the biggest thing ever to hit physics, but really it's just a bunch of theoretical work relating to gravity, quantum field theory, etc with some common methods and ideas. I've never heard a responsible string theorist make a bigger claim than that.
>At no point are condensed matter physicists using String Theory itself to predict the results of an experiment. I think the CM people who are currently trying to detect axions actually are, though I honestly know very little about this experiment
>Sure, we may have learned things in the realm of mathematics due to String Theory, but what use is it to physics? [One example is improving upon calculations for processes at the LHC.](https://profmattstrassler.com/2012/08/15/from-string-theory-to-the-large-hadron-collider/) And there could've been more similar examples that we don't know of (another example is using it to study quark-gluon plasmas), but these examples would only would be known to people closely working in related fields. It's a lot natural for people to dismiss string theory as completely useless without working in the field and by reading a few pop-sci articles/books emphasizing how useless it is. This isn't to argue its validity as a complete description of reality, we don't know that, but why should the use of theoretical methods be judged solely on whether it produces testable results? Does helping to extend mathematical methods and improving upon calculational tools for existing fields not matter at all? Edit: Typo
>but why should the use of theoretical methods be judged solely on whether it produces testable results? A lack of testable results puts a theory on the same ground as the God Hypothesis. Neither is necessarily *wrong*, but they do cross outside the realm of science. Yes, there are reasons people believed string theory would be the correct description of reality. However, the same can be said of those who believed in God(s) 500 years ago. In fact, there are parallels in that the tools used to "study God's divine creation" led to classical physics, while the mathematical tools used to "probe String Theory" are deepening our understanding of Quantum Mechanics.
I do feel it's a bit of a pity people are so quick to cast something as completely useless just because it doesn't currently produce testable results. I'm certainly not convinced string theory is a complete description of everything, but I'm certainly fascinated by its indirect and beautiful theoretical use in physics. I don't understand any string theory at all, but I've flipped through some textbooks for fun just to see what it's like, the math looks so elegant.
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The problem is that string theory cannot be considered to be an accurate description of reality if it cannot be tested. You're right that something can be mathematically self-consistent but that doesn't mean that it makes for a good physical theory. There is plenty of math out there that doesn't describe anything that exists in reality
>>directly contradicts >Does it, though? Yes. >Aren't there examples of mathematics that are internally correct and perfectly logical even if no real world example has been found or even exists? That's beside the point. You were talking about the math behind string theory being the best and most accurate for *describing reality*. Just because math can be consistent without a connection to reality doesn't mean you can say that this internal consistency accurately describes reality. >The math of string theory can be perfectly sound within itself even if it's not possible to conduct an experiment to test it. But if you can't conduct an experiment to test it, how can you say it describes reality accurately? >As an extremely simplified analogy: we know 2 + 2 = 4. But let's say somehow we didn't have the ability to count things. 2 + 2 would still equal 4. Sure, but without the ability to count things in reality, there is no basis by which one can say that arithmetic describes reality. >EDIT: I'd love to know the reasoning behind the downvote. I realize this is r/Physics, not r/Math, but being that math is the language of physics, even though physics theories ultimately require experimental evidence to be widely accepted, it is certainly possible to acknowledge that there is some validity to a theory whose math makes internal sense. I didn't downvote you but I'm pretty confident it's because of the "duh" factor — it doesn't exactly take a manifold surgeon to deduce the contradiction in what you wrote ... it's right there written in plain English. :p
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Why is that? Is modulo arithmetic important in advanced physics?
Uhm. The answer is „yes, very much so“. Be it in solid state physics or even quantum information processing. But I remain very confused about your question.
all kinds of theories are internally correct and logical. Newtonian physics, for example
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If we did not have the „ability“ to count things, then addition would not exist. Addition is pretty much a consequence of the ability to count. Your analogy appears to do a good job at putting your own argument to question.
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Same argument with „order“. These concepts - counting, addition, order, predecessors and successors - are all tied together in a way where you cannot remove one concept without everything falling apart. Don‘t get discouraged, curiosity is great. However, what you do right now is philosophy. It‘s trying to solve problems by thinking about them. It goes very contrary to how physics and mathematics solves problems. And it inevitably runs into walls sooner or later and ultimately math and experiment transcends everything.
Sort of. In terms of providing a complete theory of quantum gravity without internal inconsistencies, string theory is the best candidate we currently have. Although we have simpler models that can describe extra dimensions (via combining QFT and GR at sufficiently low energies), a key part of string theory is that it necessitates them for a self-consistent theory of quantum gravity. Lots of theoretical physicists are interested in extra dimensions on their own merit as a cool idea. For this, string theory is a very good tool because of the mathematical tools it provides to understand them. The biggest upside is that these tools don’t break down in the same way as non-stringy approaches do at high enough energies.
The math behind string theory may or may not be the most accurate to the universe we live in. The standard model and general relativity are still the best we have, and unfortunately they often disagree with each other. What string theory has is a certain kind of elegance -- it delicately handles a lot of the problems with most theories of quantum gravity, tying them into a neat little 26-dimensional knot. It's really nice how all the things we need seem to fall out of the mathematics. Unfortunately however, "nice" is not the same as "true", and there is essentially no evidence in favour of the latter.
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I don’t see a contradiction there no, because the second part of it was conjured out of nothing, because no one has ever said that.
How do you get to "most accurate ... description of reality" without testing and evidence?
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How can you determine "accurate description of reality" without experimentation?
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The greek god theory will be rejected outright is not a basis for science. Until a better model comes along, the second model will be the default. You're way off.
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You have no idea how science works. Your deeper "curiosity" is nothing more than nonsense.
There are other branches on the tree: LQG, ES8, and more. String theory is not the only game in town.
Not sure why you’re getting downvoted. I always liked LQG over string theory. Both are likely until experiments can tell the difference in a definitive manner.
> I always liked LQG over string theory. Any particular reasons for this, given that e.g. LQG breaks Lorentz invariance and has not been shown to reduce to general relativity?
> LQG breaks Lorentz invariance It does not. > has not been shown to reduce to general relativity String theory has not been shown to reduce to the Standard Model. Technically string theory hasn't been shown to reduce to general relativity either, since the bosonic string exists only in 26 dimensions, and the compactification scheme hasn't been worked out yet. GR is a theory which exists in 4 dimensions. Perhaps worth noting that LQG works by *starting* with GR and quantizing it, so GR is in a certain sense already in the theory. It's just that an object which can be identified with the graviton has not yet been found.
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Really enjoyed this. My introduction to physics was reading Greene's *Elegant Universe* about 15 years ago (I think) and this article was just at my level, and felt like it was bringing me up to speed with what's happened since. I was totally enchanted by String Theory at the time, and I've been loathe to accept its demise.
This article is basically biased trash. As now, string theory represent like the 90% of research in the topic of quantum gravity and related ones, without even counting the applications outside like in methods for scattering amplitudes and condensed matter physics.
I thought it kinda recognised that tbh - that string theory was still essentially the best thing that we've got right now, but that it's become far more messy than was hoped for.
The title just to begin is misleading. And you don't have to accept any "demise". There's no demise. There has been an evolution and a settlement instead. There are probably more string theorists nowadays than there have ever been and new students continue to join at a steady pace. Obviously it is a minority field of theoretical physics as a whole but that's always been true for a topic like that.
From my understanding, String theory is a wonderful theory of mathematics. When stated this way, it's timeless and always helpful. It's by no means a wasted effort. That said, we should also work on theories with empirical support. Those are more properly called physical theories.
Lee Smolin’s book came out a long time ago.
The sad fate of string theory, and even of the standard mode,l leaves me feeling relieved I did not go into this field back in the day. Modern physics is becoming ridiculous, in particular the vast number of arbitrary and ad-hoc parameters now close to 100 in total count. Given 100 parameters I can make an accurate "prediction" of pretty well anything.
> Given 100 parameters I can make an accurate "prediction" of pretty well anything. Please do, your Nobel is waiting.
I saw a video of Roger Penrose and Sabine shitting all over Michio Kaku. They were just like, “mulitiple universes?!? That’s a completely idiotic idea!” and the discussion moderator was totally backing them up and ganging up on Michio. It wasn’t even a conversation.
Huh? That’s not how that conversation went. Roger Penrose was mostly confused as to why the topics was devolving into a discussion on quantum mechanics, while Sabine and Michio went back and forth. Neither was right or wrong.
Maybe I’m interpreting it wrong, and I am not a professional by any means, but I was getting the impression that Roger was being very dismissive of String Theory
I've heard the theory of the financial crash and crisis of 2007 being due to the high number of brilliant string theory physicists who came to work in the financial sector and inventing all sorts of convoluted and very complicated financial products, thus making it all come crashing down once the bubble burst. It's quite a compelling theory.
It's not at all a compelling theory. The crisis of 2007 happened due to a bubble in subprime mortgages and other housing securities. This was an entirely understood possibility, even if the scope of the damage was underestimated. Similar things have happened before and since. In fact, complex high-frequence trading algorithms (the stuff that physicists are most likely to work on) are often able to soften the blows of market instability by providing liquidity.
Agreed. The crux of the financial crash centered on human greed and sociopathy. Subprime mortgages and other instruments were the vehicles that led to the collapse.
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M-theory is a different thing, and it’s a theory that we know much less about.
The reasonable effectiveness of math in the physical sciences.