For many years, editions here of This Week’s Hype were mainly devoted to bogus claims that someone had found a way to get a testable prediction out of string theory or other “evidence for string theory”. Recently there have been many fewer such claims, with consensus in the string theory community that there is now no hope to get a prediction from string theory about observable physics at accessible energies. One can watch the recent talks here on Steven Weinberg and his legacy to get a good idea of what this current consensus looks like: you can’t test string theory since string effects occur at much too high an energy scale, and Weinberg showed that such things will just look like the Standard Model sort of QFT at observable energies. In addition, Weinberg is also credited with the anthropic CC argument, taken as evidence for the otherwise unobservable string theory landscape. Taken together, the consensus of leading particle theorists has become that there’s no point to trying to do any better than the Standard Model, with the only answer available to anyone who asks questions about higher energies is “string theory, whatever that is”.
With particle physics abandoned, theorists have focused on quantum gravity as the only legitimate issue to study. For many decades the hope was that a consistent answer to the unknown question of what string theory really is (often called “M-theory”) would be found, and that would provide a final end to the subject of fundamental physics. This final theory would be untestable, but it would self-consistently explain why one could not hope to test it. In recent years though, after decades of no progress towards a consistent M-theory, string theorists have essentially given up on this hope.
This situation has lead to a recent trend in string theory research: instead of looking for positive evidence for string theory, try to find an argument that resistance is hopeless, string theory is the only theory possible. The arguments of this kind I’ve seen make no sense to me, but they are gaining in influence. One place I noticed this is in this recent white paper about the interesting topic of celestial holography, which has little to do with string theory. There the authors write:
A crowning achievement for the celestial holography program would be for it to determine concretely whether string theories are the only consistent theories of (asymptotically flat) quantum gravity.
Today Quanta magazine has more of this sort of thing, with an article whose title shows up on the web as A Correction to Einstein Hints At Evidence for String Theory. The sub-headline tells us that
In a quest to map out a quantum theory of gravity, researchers have used logical rules to calculate how much Einstein’s theory must change. The result matches string theory perfectly.
which sounds pretty impressive. The article starts off with quotes such as:
The hope is that you could prove the inevitability of string theory using these [bootstrap] methods,” said David Simmons-Duffin, a theoretical physicist at the California Institute of Technology. “And I think this is a great first step towards that.
and
Irene Valenzuela, a theoretical physicist at the Institute for Theoretical Physics at the Autonomous University of Madrid, agreed. “One of the questions is if string theory is the unique theory of quantum gravity or not,” she said. “This goes along the lines that string theory is unique.”
The paper at issue is this one which appeared on the arXiv nearly a year ago. It’s not about string theory or about conventional quantum gravity in four space-time dimensions. The topic is graviton scattering in maximally supersymmetric theories in ten flat space-time dimensions, and the argument is that the basic principles of supersymmetry, Lorentz invariance, analyticity and unitarity imply a bound on the coefficient of the lowest order correction term. The only relation to string theory is that a string theory calculation of this correction coefficient satisfies the bound (as expected, since string theory is supposed to satisfy the assumed basic principles). Much is made of the fact that in string theory one can get any value of the coefficient consistent with the bound. This is taken as evidence for the “inevitability” of string theory, but I don’t see this at all. It’s more accurately evidence for the usual problem with string theory: it’s consistent with anything. If the authors of this paper had found that the string theory bound was different than their bound, they could have written a paper arguing that they had finally found a way to falsify string theory (measure the coefficient, if it was found to be in the region allowed by general principles but not by string theory, string theory would be falsified).
The article does get right the motivations behind these claims:
Some physicists hope to see string theory win hearts and minds by default, by being the only microscopic description of gravity that’s logically consistent. If researchers can prove “string universality,” as this is sometimes called — a monopoly of string theories among viable fundamental theories of nature — we’ll have no choice but to believe in hidden dimensions and an inaudible orchestra of strings.
To string theory sympathizers, the new bootstrap calculation opens a route to eventually proving string universality, and it gets the journey off to a rip-roaring start.
and it gives a little space to skeptics:
Other researchers disagree with those implications. Astrid Eichhorn, a theoretical physicist at the University of Southern Denmark and the University of Heidelberg who specializes in a non-stringy approach called asymptotically safe quantum gravity, told me, “I would consider the relevant setting to collect evidence for or against a given quantum theory of gravity to be four-dimensional and non-supersymmetric” universes, since this “best describes our world, at least so far.”
Eichhorn pointed out that there might be unitary, Lorentz-invariant descriptions of gravitons in 4D that don’t make any sense in 10D. “Simply by this choice of setting one might have ruled out alternative quantum gravity approaches” that are viable, she said.
Another critique, though, is that even if string theory saturates the range of allowed α values in the 10-dimensional setting the researchers probed, that doesn’t stop other theories from lying in the permitted range. “I don’t see any practical way we’re going to conclude that string theory is the only answer,” said Andrew Tolley of Imperial College London.
I don’t at all understand why Quanta chose to cover this. All it does is help to spread hype and further the cause of the “resistance is futile” campaign from proponents of a failed research program.
Update: This kind of hyped story turns into the expected PR result:
Evidence for String Theory –In a quest to map out a quantum theory of gravity, researchers have used logical rules to calculate how much Einstein’s theory must change. The result matches string theory perfectly, reports Natalie Wolchover for Quanta.
“Much is made of the fact that in string theory one can get any value of the coefficient consistent with the bound. This is taken as evidence for the “inevitability” of string theory, but I don’t see this at all.”
The funny thing is, you don’t even need to know much to notice the vast hole in this argument. You just need to pay attention to the overall logic. It’s a bit like claiming I’m a good weatherman because I predict the probability of rain is somewhere between 0% and 100%. I’m “inevitably correct” in some sense, but it doesn’t mean I’m any good.
How can anyone be fooled by this, unless they want to be?
The fact that this whole argument is about universes unlike our own – maximally supersymmetric theories in ten flat space-time dimensions – requires a bit more technical expertise to notice, at least if people are trying to hide it. But this, at least, is pointed out in the article: “Eichhorn pointed out that there might be unitary, Lorentz-invariant descriptions of gravitons in 4D that don’t make any sense in 10D. ”
In other words, we should only think this whole calculation is relevant to real-world physics if we already buy into string theory.
It’s sad that Quanta is talking about this when there is really interesting physics being done.
@Peter Woit and John Baez, I find it hard to understand your skepticism. The article is addressing the important question whether there are consistent theories of quantum gravity other than string theory. It gives partial evidence that at least in 10D with maximal susy, the answer is no. I think that is pretty exciting! There are a lot of people doing fantastic and honest work along these lines nowadays and if anything, their work should be covered by science journalists more, not less.
Dalimil Mazac,
I’ve read the paper carefully and I see nothing there about any evidence there are no consistent quantum gravity theories other than string theory, even in the 10d maximal susy setting. The quote from Andrew Tolley (who I gather works on bootstrap methods) makes the relevant point: that string theory has alpha in the allowed range says nothing about whether or not there are other theories with alpha in the allowed range.
I completely disagree with you that bogus claims that only string theory can describe quantum gravity deserve more coverage by science journalists and are “exciting” and “fantastic”. They’re the opposite of good science, part of a campaign to convince people that a failed research program is the only way forward.
@Peter Woit, the main point of the paper is not that string theory satisfies a bound (I agree that on its own would not be very interesting). Rather, the point is that the lower bound coming from the bootstrap constraints seems to coincide with the lowest value attainable in string theory. This was by no means guaranteed from the getgo.
Of course, this is not a proof of uniqueness of string theory, but no one is claiming that it is. However, it is a first step of such a proof in the sense that it would become a proof if it could be extended from alpha to all the higher-order terms of the S-matrix.
Finally, I can assure you that most people who work on these ideas would be equally excited if their work lead to the discovery of a previously overlooked quantum gravity theory, as they would be to prove the uniqueness of string theory. There is really no hidden agenda besides trying to understand new facts about nature using rigorous bootstrap methods.
Dalimil Mazac,
I’m still not seeing how string theory allowing any alpha consistent with general principles has anything to do with whether or not there’s another theory also consistent with these principles.
You can hope, like Chew and many others did during the 1960s, that your list of general principles constrains the S-matrix to be something unique. And you can hope that that thing is string theory (and that results in maximally supersymmetric 10d have something to do with non-supersymmetric 4d). But calling this result a “first step in a proof” of this I’m afraid well deserves the term “hype”.
It’s depressing that the world is currently in a place where (a) “believe science!” is a major campaign and (b) the world’s smartest physicists seem to have bet the farm on a very straightforward example of affirming the consequent.
(Of which, I must say, Dr. Mazac’s two posts, in tandem, seem a clear illustration.)
More and more it seems to me that the information environment we’re in is characterized by the fact that there is just no safe consumption algorithm to teach anybody other than “be an extremely sophisticated consumer of information and mistrust everything you can’t evaluate for yourself.”
Which is just terrible.
Since no one’s ever seen a graviton, they may for all we know not exist and the entire question is moot. When I refer to “quantum gravity” I always stress that this refers to any way to resolve the inconsistency between the SM and GR. It does not necessarily mean you actually quantize gravity. The question whether a quantization of gravity is internally consistent is different than the question whether a theory consistently combines qft and gr. The commonly named example is that you don’t get a theory of atoms by quantizing water. Likewise, you may not get a theory for the fundamental constituents of space-time by quantizing gravity.
In case you got lost in the previous paragraph, I am saying that the question these people are trying to address isn’t the question we want an answer to. They’re two separate questions. And I agree with Tolley that there’s no way mathematical proof will give us an answer to the question we actually want an answer to (how do we remove the inconsistencies between the SM and GR), simply because no proof is better than its assumptions, and you can’t ever prove the assumptions. It’s unfortunate how many physicists confuse physics with math (& good that Tolley isn’t one of them).
Incidentally, the entire idea that you can somehow derive a more fundamental theory from a less fundamental one makes no sense because if you could it wouldn’t be more fundamental.
(None of this is to say that I am a fan of emergent gravity or think string theory is wrong.)
And why Quanta keeps covering stuff like this is a good question indeed. I’ve been wondering for a while what’s going on there. They also seem obsessed with black hole information loss despite the fact that there’s nothing to learn from this “research”.
Only interesting thing I learned from this is that Astrid seems to be affiliated with a place in Denmark.
“It’s depressing that the world is currently in a place where (a) “believe science!” is a major campaign and (b) the world’s smartest physicists seem to have bet the farm on a very straightforward example of affirming the consequent.”
In your opinion, what is the risk of the situation as you have described it fueling further ignorance against science in among members of the public?
Let me chime in something from a person actively working on bootstrap techniques. There’s no doubt that the paper of Vieira et al. is remarkable and probably one of the most exciting results that ever came out of the S-matrix bootstrap. They demonstrate that at the subleading order in the low-energy limit, string theory in 10D is compatible with S-matrix axioms such as unitarity, analyticity, etc. and moreover it seems to saturate this compatibility among theories with maximal supersymmetry in 10D (in a well-defined sense). However, Quanta’s coverage of this topic is extremely disappointing and I don’t understand why they decided to put a weird “string theory vs. the world” spin on it, instead of letting the result speak for itself. Completely unnecessary.
This is something I find myself wondering as well, and it’s not the first time Quanta has fallen prey to this kind of hype–and I characterize it in that way to be generous to Quanta in the face of my cynicism. So I decided to waste a couple of hours to come up with the following:
Quanta provides a bare bones explanation of their publishing process on it’s “About” page, making it as clear as it can that the Simons Foundation has no say or control over what gets published. This seems to be a bit misleading, however, because Quanta’s current Editor-In-Chief’s (Thomas Lin) bio states that he joined the Simons Foundation in 2012 with no indication that he is no longer a member of the Foundation. If you wanted to truly keep the Simons Foundation out of what you’re publishing, it might be a better idea to not have a member be your Editor-In-Chief.
What seems to ultimately guide Quanta’s coverage, however, are these two, simple, statements:
There are, as of this comment, 38 articles on Quanta’s website that are tagged with “string theory”. Out of those articles the authorship is broken down in the following ways:
12 are written solely by Natalie Wolchover (“Senior Writer/Editor)*
4 are written solely by Kevin Hartnett (“Senior Writer/Editor”)
3 are written by a collaboration between Natalie Wolchover, Olena Shmahalo (“Contributing Art Director”), and Lucy Reading-Ikkanda (“Former Graphics Editor”)
3 are written solely by Robbert Dijkgraaf (who is credited as a “Contributing Columnist”)
2 are written solely by Erica Klarreich (“Contributing Correspondent”)
1 is written solely by Peter Byrne (“Contributing Writer”)
1 is written solely by Charlie Wood (“Staff Writer”)
2 are written by Sabine Hossenfelder (“Contributing Columnist”)
1 is written solely by Dan Falk (“Contributing Writer”)
1 is written solely by Thomas Lewton (“Contributing Writer”)
1 is written solely by George Musser (“Contributing Writer”)
1 is written solely by Philip Ball (“Contributing Writer”)
1 is written solely by Eva Silverstein (“Contributing Columnist”)
1 is written solely by Patrick Honner (“Contributing Columnist”)
1 is written solely by K.C. Cole (“Contributing Writer”)
1 is written solely by Joshua Sokol (“Contributing Writer”)
1 is written solely by Siobhan Roberts (“Contributing Writer”)
1 is written solely by Jennifer Ouellette (“Contributing Writer”)
*One of Natalie Wolchover’s articles is simply a multimedia presentation titled, “Theories of Everything: Mapped”, so its relevance may be questionable as it may be tagged with numerous legitimate theories.
There are, as of this comment, 17 articles on Quanta’s website that are tagged with “multiverse”. Out of those articles the authorship is broken down in the following ways:
7 additional articles written solely by Natalie Wolchover**
2 additional articles written solely by Charlie Wood
1 additional article written solely by Jennifer Ouellette
1 article written in collaboration between Natalie Wolchover and Peter Byrne
1 article written solely by Thomas Lin (“Editor in Chief”)
The same single article by Peter Byrne referenced above
The same single article by Dan Falk referenced above
The same single article by Philip Ball referenced above
**One of Natalie Wolchover’s articles is tagged with both “string theory” and “multiverse”, it is included in the string theory tally.
Although one can quibble about the content of the articles themselves: “it’s just a Q&A!”,”it’s an editorial column/blog, which ‘is not reviewed by anyone outside of the news team prior to publication…!'”, or “it’s part of their ‘Quantized Academy’ series!” I will concede the possibility that some of the Q&A’s might be interviews with scientists who are critical of string theory, but the fact of the matter is the majority of the articles are giving a voice to string theory/the multiverse. Even if the tone of an article is entirely neutral, it continues to legitimize string theory/the multiverse–even if its only in a small way.
Based on the authorship breakdown above it seems pretty clear that, for whatever reason, Natalie Wolchover is pushing string theory/the multiverse at Quanta–and her role as a Senior Writer/Editor most likely gives her a lot of s(w)ay in what gets put out. But she may not be the only problem, because the current Deputy Editor at Quanta is Michael Moyer, whose bio states: “Before joining Quanta Magazine in 2014, Michael Moyer spent six years at Scientific American, where he was most recently in charge of physics and space coverage and led the magazine’s special editorial projects…”
If I’m remembering correctly, Scientific American is a publication that is rife with string theory and multiverse hype, so having someone who was in charge of physics and space coverage there for six years now the Deputy Editor at Quanta is not a good sign; any skepticism about Moyer’s position is, unfortunately, bolstered by the fact that when you look at the publication dates for articles on string theory in Quanta, there are two articles in 2013, then nothing until 2015, after Moyer is hired (the history of Quanta’s archive regarding the multiverse is a little more even), with healthy coverage of the publication of something on string theory every year since–2019 being an unusually barren year, with only one article tagged with string theory published.
To me, it looks like Quanta–far from “falling prey” to the hype–sadly perpetuates string theory/the multiverse mania, just in a more conservative/limited way.
The result by Vieira et al isn’t really all that interesting. String theory and other 10 dimensional theories are toy models that theoretical physicists like to play in, and it’s great that the S-matrix bootstrap could give a result pertaining to such toy models, but there is no evidence yet that the techniques used with the S-matrix bootstrap could say anything about actually interesting theories relevant to the real world, i.e. theories that are in 3+1 dimensions.
I actually thought the Quanta article was pretty good! It successfully conveyed to an outsider like me both what the result literally says (i.e., the two alpha ranges approximately coinciding in 10D SUGRA), and how string theorists and non-string-theorists very differently interpret that.
MT,
One motivation for my anti-string theory hype campaign has always been that I think is that this kind of hype has already done significant damage to the public perception of science and scientists, and threatens to do even more if it continues. If we’re trying to get the public to “trust science”, this kind of behavior does not promote that at all, quite the opposite.
Ryan Usher,
In trying to understand why this kind of thing happens I think you’re focusing on the wrong people. The source of the problem is that the most prominent scientists in the field are pushing this, not that professional journalists pay attention to such figures. The Simons Foundation, like Simons himself, is focused on elite institutions, and Quanta is going to reflect points of view coming from those elite institutions. When there’s a serious failure of elite institutions like in the string theory/multiverse case, it’s a lot to expect of either the Simons Foundation or Quanta to take on the role of trying to fix that failure.
Scott,
The point that the coincidence of these two ranges doesn’t imply uniqueness of string theory is a straightforward matter of fact + logic. If such straightforward issues become matters of opinion, determined by which tribe you belong to, science is doomed.
In any case, in this example I don’t even think that most members of the string theory tribe are willing to sign onto the incorrect side of the argument. Lubos Motl, as fanatic a member of the string theory tribe as they come, has a long posting about this here
https://motls.blogspot.com/2022/01/how-string-theory-correctly-predicts.html
where he makes some of the same points I made, e.g.
“The authors seem excited about the fact that string theory exploits exactly all the allowed values. Well, it is a double-edged sword. On one hand, you can be reassured that string theory overlaps with the consistent quantum theory of gravity nicely, so we have “the” theory. On the other hand, you could say it is bad news because – as in the swampland reasoning – you would want string theory to impose stronger conditions than those that can be extracted from “possibly naive”, non-stringy arguments.”
He argues for the uniqueness of string theory, but not by claiming that the coincidence of the ranges shows this (he more favors “LQG sux” as a uniqueness argument).
I agree that the coincidence of these two ranges can’t be interpreted, in any way whatsoever, as a “uniqueness proof” for string theory! And I didn’t see the article as claiming that. Rather, it quotes string theorists who *optimistically hope* that this result might be extended to a more general result stating that, if a given correction to GR is consistent with general postulates about quantum gravity, then that correction can also be realized string-theoretically. Even that would really be a “universality statement” rather than a “uniqueness statement” — more a statement that one “might as well” study string theory than a statement that one “must” study it — but it would be pretty important information regardless, no?
Do the other approaches have some results about which Quanta could report? Has anyone suggested to Quanta such results from the other approaches?
Regarding the discussed article, I would mainly prefer if they would write clearly that the 10D thing is about mathematics, and not about physics.
Scott,
I read this as pretty clearly an argument for uniqueness (“This goes along the lines that string theory is unique.”), and for something much stronger than “string theory is a universal framework that can capture any possibility”. That string theory is “unique” implies there are no other non-equivalent possibilities. Thus, no point to work on alternatives, because if you succeed you would just give a different construction of string theory.
I don’t think one can understand any of what is going on here outside of the context that people are trying to defend a proposal for a fundamental theory that is not well-defined and is completely untestable. About the only way you can justify this is by a “no-alternatives” (or uniqueness) argument, according to which all seemingly deadly problems of the theory don’t matter: it has to be true since it is the only possibility.
Martin S.,
I don’t think there’s been much progress in any of the main approaches to quantum gravity. I was going to write that I don’t know of alternatives they should be writing about, then realized that’s not true. There is at least one (euclidean twistors), but they’re not alone in ignoring that….
The “10D thing” is not “mathematics”, it’s an idea about physics (the bootstrap constraints are very much physical principles). I’m very weary of the endless blaming of bad ideas about physics on “mathematics”.
MT,
Among the biggest fans of this are the intelligent design people, see
https://uncommondescent.com/intelligent-design/string-theory-again-will-a-correction-to-einstein-save-it/
Their argument is kind of a “God universality”: if you try to make sense of the universe sooner or later you will have to give up on conventional scientific notions of evidence and start doing metaphysics/religion. They are welcoming the string theorists to the realm of religion with open arms…
The real issue here is not that string theory as an approach to quantum gravity is degenerative in the Lakatos sense (which it is), but that the entire quantum gravity research program as a physics research program is degenerative, of which string theory is only one branch among many. There is currently no evidence of gravity itself being quantum, as Sabine above pointed out, and it would remain that way until it is discovered in experiment or observation that gravity is indeed quantum. As a result, internecine warfare between different subprograms of quantum gravity over which approach to quantum gravity is more degenerative, such as the assertion in the Quanta article that string theory is the unique approach to quantum gravity, is largely irrelevant in the larger picture. The quantum gravity research program as a whole does not really deserve any attention from the scientific media until actual evidence of gravity being quantum is found, let alone the internal debate over which approach to quantum gravity is less degenerative.
Mark,
It would be helpful it Quanta and other science publications would identify degenerative research programs and put warning labels on stories about them.
I don’t agree though that only an experimental observation can save a degenerative research program and put it on a progressive course. New theoretical ideas that solve the problems that have caused a field to degenerate are possible. What I see as the underlying problem here is a failure of the mechanisms that are supposed to push degenerative research programs out of mainstream science. Failed ideas need to be recognized as such, not promoted by influential people and institutions.
Peter,
I don’t necessarily agree either that only an experimental observation can save a degenerative research program. Cosmology is a field where the current standard model of cosmology, Lambda-CDM, is a degenerative research program, and there is plenty of experimental evidence from dwarf galaxies to large scale structures like the Giant Arc to the Hubble tension showing that Lambda-CDM has significant flaws, and where it is new theoretical ideas, like superfluid dark matter or relativistic MOND or something else, that are needed to put it back on a progressive course.
However, it is the case that some research programs are degenerate for lack of experimental evidence. This was the case with most speculative beyond standard model research programs in high energy physics such as supersymmetry and GUTs, where there is simply an utter lack of evidence of anything beyond the standard model, apart from neutrinos having mass. For a few decades, theorists saw no results after no results of any beyond standard model physics, and merely tinkered with the parameters of their pet SUSY or GUT and waited for the next set of results at the Tevatron or LHC to come out. Eventually, after the latest LHC run, most theoretical physicists have abandoned the BSM research program after the non-detection of anything there, and largely moved on to other fields. SUSY and many other BSM models weren’t actually proven false, some theorists today speculate that evidence for SUSY might not appear until the Planck scale, but it is pointless to spend further time on SUSY models when experimental tests for SUSY at the Planck scale won’t be around for many decades or centuries. No amount of speculative new ideas (apart from neutrinos for which there is already experimental evidence of BSM physics independent of the LHC results) would have saved the wider BSM research program from dying out, unless experimental evidence of new physics was actually discovered at the LHC or some other near-term future experiment.
The quantum gravity research program is another one of the research programs where the degenerative nature of the research program comes from the lack of experimental evidence to signal anything about the theories. Any experimental evidence of quantum gravity is largely speculated to appear at the Planck scale, which once again is decades or centuries away. Theoretical ideas won’t help solve the core issue here, as one simply ends up with a quantum gravity landscape with a multitude of different theories explaining the same phenomena with no experimental evidence to distinguish between any of the theories. So really the only solution here is similar to the solution in the BSM research program, to abandon the quantum gravity research program until the time comes when such experiments can be done.
I agree with you that the underlying problem here is a failure of the mechanisms that are supposed to push degenerative research programs out of mainstream science. However, there is more of quantum gravity that needs to be pushed out mainstream science than just string theory. String theory has been around for 50 years and is merely the most popular and well known degenerative research program in quantum gravity. Loop quantum gravity has been around for 30 years and is also a degenerative research program, suffering from many of the same issues as string theory. The same is true of many other approaches in quantum gravity, such as causal sets, or it from qubit, and so forth. The same mechanism failures that keep string theory alive in the theoretical physics community are also the ones that keep loop quantum gravity alive and causal sets alive and it from qubit alive and so on, none of which can even be proven wrong because of the lack of experimental evidence and the lack of even any theoretical predictions in many theories.
Furthermore, even if string theory ends up disappearing from the face of the earth, so long as the larger quantum gravity research program remains fairly active, it would merely be replaced with other overhyped ideas about quantum gravity such as loop quantum gravity or it from qubit or emergent spacetime from some underlying unknown quantum structure, all as flawed as string theory is right now. And the scientific media will still write bogus claims that they have discovered evidence for this quantum gravity theory and that quantum gravity theory when no such thing has occurred yet.
In so far that other quantum gravity research programs do and will end up making advances in physics it is in the same way that string theory ended up making advances to physics, in the contributions that such theories makes to mathematics and mathematical physics and in the techniques developed in the theory that are eventually applied to other subfields of physics such as condensed matter physics and quantum field theory. But that has nothing to do with understanding the world at a fundamental level.
It’s interesting to compare this line of work with the swampland conjecture.
Here, string theory allows the full parameter space allowed by basic physics, and this is a positive result for string theory.
In swampland, string theory doesn’t allow the full parameter space allowed by basic physics, and this is a positive result for string theory.
Talk about having your cake and eating it! It would be nice if there was some framework which allowed these people to talk to one another and figure out which one is right…
Mark,
I don’t think it’s helpful to expand an analysis of the problems with this article and string theory in general first to quantum gravity in general, then to mainstream cosmology. Whatever the problems of the Lambda-CDM model, it’s a well-defined model, and there’s a conventional science debate about the details of its relation to observations. In string theory there’s now nothing even remotely like this, or any prospects for such in the future.
Peter,
I feel like you missed the entire point of my post.
I only brought up Lambda-CDM because you stated that I asserted that all degenerative research programs can only be fixed with experimental evidence. I did not assert that all degenerative research programs can only be fixed with experimental evidence, only that the specific cases of string theory and other quantum gravity research programs could only be fixed with experimental evidence. Apart from using Lambda-CDM as an example to correct that specific misunderstanding, and to highlight the difference between research programs that can be fixed with new ideas vs those that can only be fixed with experimental evidence, Lambda-CDM is not relevant to this topic.
On the other hand, it is entirely reasonable to broaden the analysis from string theory to other parts of quantum gravity, because you do so yourself on this blog:
https://www.math.columbia.edu/~woit/wordpress/?p=12472
https://www.math.columbia.edu/~woit/wordpress/?p=11648
There is the same amount of disingenuous hype and obfuscation going on with these alternative approaches to quantum gravity, where they try to link simple quantum experiments and theoretical calculations to vague quantum gravity ideas, which shows that this problems are not entirely contained within string theory but permeates throughout the quantum gravity research program.
Mark,
Sorry for the misunderstanding. I guess one reason I’m less concerned about problems with quantum gravity in general is just that they haven’t had a huge negative impact on the entire field of fundamental theory the way string theory has. If there is a problem with (picking a random example) causal sets hype, it’s not one that I see as having done significant damage or worth spending time worrying about.
I do think we disagree though about prospects for quantum gravity research. I see no reason not to believe that it’s possible that purely theoretical developments in this area, with no input from experiment, will come across an important idea that has been missing so far, and that this will allow the field to move forward.
Scott Aaronson,
In this case “string universality” and “string uniqueness” mean effectively the same thing:
A gravitational S-matrix is a priori parametrized by infinitely many couplings (Taylor coefficients around small momentum). So you can think of a gravitational S-matrix as a point in this infinite-dimensional space of couplings. The 10D superstrings define tiny subspaces in this infinite-dimensional space (type IIA gives a 1d subspace and type IIB a 2d subspace, parametrized by the string coupling).
As a corollary, assuming that a (10D maximally supersymmetric) gravitational S-matrix comes from string theory leads to infinitely many predictions about its small momentum expansion. So much for string theory not making any predictions.
Showing that the most general S-matrix consistent with the bootstrap comes from string theory would amount to showing that the bootstrap constraints cut the a priori infinite-dimensional space down to the respectively 1d and 2d subspaces. This is such a huge reduction of uncertainty that I think it’s more appropriate to call it uniqueness than universality:)
Needless to say, this goal is still very far but the paper by Guerrieri+Vieira+Penedones shows that everything works after projecting the infinite-dimensional space to the first coordinate.
Dalimil Mazac,
Sure, string theory makes an infinite number of predictions, including:
10D spacetime, very specific and intricate spectrum of states and their interactions
Only problem with this infinite number of predictions is that they are all completely wrong…
As Lisa Randall likes to say: “string theory predicts gravity: 10-dimensional gravity”
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