For those of you who subscribe to New Scientist, their magazine’s cover story this week is a feature entitled “THE AMAZING THEORY OF (ALMOST) EVERYTHING”. In the feature is an overview of the Standard Model (which describes all known fields and particles, excepting gravity, with amazing accuracy, but leaves a plethora of puzzles unaddressed) and includes a final section (edited by Abby Beall) with short articles by six scientists about their current views regarding the Standard Model, among them myself. [This website’s introductory article on the Standard Model is here; see also here.] . . .
The other five scientists who contributed are
- Jon Butterworth, a senior physicist at the ATLAS experiment at the Large Hadron Collider (LHC), well-known for his public outreach in the UK, and the author of several books for general readers about physics;
- Adam Keshavarzi, a physicist at the g-2 experiment measuring the magnetic properties of the muon (and finding a result that deviates slightly from the current Standard Model prediction);
- Clare Burrage, Surjeet Rajendran and Emily Adlam, three accomplished theoretical physicists with highly creative and wide-ranging approaches to the problems of the Standard Model. They’re younger and much more involved in the details of possible solutions than I am, so keep an eye on what they’re doing.
The experimenters, of course, are hoping their experiments will shed some new light on the puzzles that the Standard Model leaves open. I don’t want to get into those details today, but I’ll come back to the g-2 experiment at some point soon.
In my brief contribution to the feature, I make simple points concerning the following issue. So far, other than the Higgs boson, the LHC hasn’t discovered any new elementary particles or other dramatic unexpected effects. This poses a conceptual crisis, because there were strong arguments (based on quantum field theory and on experiments) that Higgs bosons shouldn’t appear alone. That crisis both justifies and motivates the work by professors Burrage, Rajendran and Adlam, along with other young physicists.
In their articles, the other theorists discuss their approaches. Rajendran, whose work has covered many research areas, examines the potential role of new experiments aimed at finding evidence of particles whose interactions with all known particles are extremely weak. Burrage, thinking along similar lines, describes a subtle form of new force whose effects depend on the environment that it is in, and which can’t be observed without specially designed experiments, including ones that she and her colleagues have proposed. Adlam has a more radical and more speculative proposal: that not only is our way of thinking about time wrong (which by itself is plausible, given how confusing time is to us), our misunderstanding of it may have an impact even on the Standard Model.
As of yet, neither they nor anyone else seems to have an exceptionally compelling idea. But out of these new lines of thought, intriguing proposals for entirely new types of experiments are emerging. This all to the good; as is often said, we should never let a crisis go to waste. If our current confusion leads to a novel set of experimental questions about the world, that’s real progress. And if one of those new experiments turns up something no one (or almost no one) was expecting, that’s priceless.
20 Responses
Hi Proff Matt, the lack of discoveries in the LHC that reinforces the stting theory, impoverished it a lot, and even made many theorists of this field to abandon it. Do you agree that? That is, what happened prof Matt that nothing comes out of LHC in favor of this theory? Would it be all wrong? So What happens?
I suspect that what you’re asking is this: some scientists tried to claim that supersymmetry would be a sign of string theory. By that logic, the absence of supersymmetry at LHC would be an absence of a sign of string theory. [By incorrect logic, it would be evidence against string theory.] So what is in fact the implication of the LHC’s lack of discoveries?
But in fact there’s simply no connection between string theory and supersymmetry at LHC energies. You can have string theory with or without supersymmetry at LHC energies. You can have supersymmetry with or without string theory (unless string theory is the only possible theory of quantum gravity, in which case the LHC is irrelevant to the question.) You can have a non-supersymmetric world at LHC energies with or without string theory.
So we have learned nothing at the LHC that bears on string theory. The only linkages between the two are propaganda. And the reason is simple: the difference in energy scales between the two theories is as much as a million billion. You don’t learn about quarks by studying DNA molecules, and you don’t learn about strings by studying top quarks and Higgs bosons, either.
Congratulations on getting your article in New Scientist. Good job, and great article.
Thanks, I’m glad you enjoyed it!
Great to see that you’re increasingly coming to the attention/re-attention of the mainstream media, in time for your book release next year.
What happened to your last blog posting on: telescopes looking back in time; which doesn’t link correctly?
https://profmattstrassler.com/2023/07/06/how-can-telescopes-look-back-in-time/
I didn’t mean to post it! It was a scheduling mistake… and I hadn’t proofread it. Worst of all, it had a serious error, the sort you make when it’s late at night and you don’t look it over in the morning. [Specifically the sunset claim was wrong, as a moment’s thought reveals.] The problem is that it’s not clear what to replace that example with. I’ll fix it someday but haven’t got a good idea yet.
Dr. Strassler:
Does your new book give any detail about the differences and/or similarities of QFT and string theory? I know the two theories attempt to describe the “fundamental” things we call particles, but what is the difference between the two theories? Is string theory a kind of field theory? I have attempted to find, online, any articles addressing this question, but have had negative results.
This book doesn’t address this very directly, because it’s really not about string theory, but rather about those things that are established experimentally. String theory (as a “theory of everything”) only comes up a couple of times. But it does say this:
“The universe’s fields, from the electric and magnetic fields to the Higgs field, have been extensively studied in experiments, and we know a great deal about them. String theory, sitting at the next level of potential knowledge, represents an attempt to explain where the fields come from.”
Now this point of view is not widely expressed, so let me flesh it out a bit here so you can see why I said it this way.
The conceptually simpler point (but incomplete) is that in string theory, a single type of string can represent a very large number of different types of particles, because a string that vibrates in different ways, or is wrapped around an extra dimension, can appear as a large variety of different types of particles with different properties—with different masses, electric charges, spins, and so on. In other words, all the particles we know and many, many more may all (in principle) be summarized in a single string moving in the right type of complicated geometry.
We don’t understand string theory entirely, so we don’t know the best way to think about it more completely. But one possibility is that one should use what is called a “string field”, which represents an infinite number of fields. The string field’s quanta would be strings, which represent an infinite number of types of particles, the quanta of the infinite number of fields.
Thus string theory and field theory are not in competition; string theory is simply more ambitious, and also completely speculative, while field theory, though limited, has an extremely firm experimental basis.
NOTE: This is not to be confused (though it easily could be!) with the original application of string theory, not as a theory of everything but as a theory of hadrons (protons, neutrons, pions, etc.) Back then people thought that protons and neutrons and pions might be strings… and in a sense, they are (well, that’s a long story, see for instance the discussion of strings and branes in https://profmattstrassler.com/2018/02/05/a-brilliant-light-disappears-over-the-horizon-in-memory-of-joe-polchinski/ ). There field theory and string theory *were* in competition; field theory won, although string theory came back as its partner, through what is known as the gauge/string (or “AdS/CFT”) correspondence. But this is a *different* application of the same theory, less ambitious and less precise, and not to be confused with attempts to make string theory a theory of quantum gravity and everything else fundamental.
Ahh, ok. Thank so much for that extremely detailed response. I believe I understand your response as follows: In QFT each “fundamental” particle has its own field. What we “call” a particle is an excitation of that particular field. All these fields co-exist with one another permeating all of space. However, one field can shove its energy into another field creating a “particle” in that field, such as what happens in high energy collisions.
In string theory, all particles are just different vibrations of, in a sense, the string field. I realize that’s very “laymen”
Also, when is your book being released, and will it be available on Amazon?
Precisely! Well put. Better than many physicists would say it.
Book is due March 5th and it will be on Amazon, Barnes and Noble, and all the other usual sites. In fact it’s already there, for pre-order.
A theory that explains everything except for gravitation sounds like a theory that explains the Sahara desert except for the sand.
I would say that the Standard Model is more like a theory that explains how the desert works in detail — all its dunes and their motion, its oases and their wildlife, and its daily weather — without explaining the bigger questions, such as the long-term climate (why has it been dry there for so long) or the particulars of its sand (why is there so much of it, and why do its sand grains have the size distribution that they do.)
Although the New Scientist editors chose to call the Standard Model, “The Theory of (Almost) Everything”, I would not myself have done so; I think it’s quite far from that. (In fact I emphasize its many gaps in the my upcoming book.)
Nevertheless, don’t sell the theory short. It explains how protons, neutrons, atoms, molecules and thus all ordinary materials emerge from quarks, gluons and electrons, and in many cases it does so with high precision; it explains why (once they form via gravity and magnetism) stars burn and shine as they do; it explains why radioactivity occurs and how its mirror-asymmetric details are nevertheless compatible with certainly elementary particles having rest mass; and it explains all the details of the emission, absorption and transmission of light, all across the universe.
But it does not explain why quarks, gluons, photons and electrons exist, or why their masses are what they are, or why the non-gravitational forces come in the number and strength that they do. Nor does it explain most of the properties of the universe, much less why our universe exists. And it has nothing to say about gravity.
So let’s take a middle ground here: the Standard Model is an impressive human accomplishment, and yet just a stepping stone along a long, ongoing journey.
Thank you, Matt, for taking the time to reply to my (admittedly somewhat snide) remark. I did not mean to belittle the monumental amount of effort and ingenuity that has gone into formulating the Standard Model. However, the partial success it has scored in some areas does not necessarily mean that with the application of further effort and ingenuity it will provide answers to the remaining very major questions. Thus I would beg to differ with your concluding statement. The great success enjoyed by Ptolemaic astronomy in accounting for the motions of the planets did not make it a stepping stone to Copernican astronomy. Copernican astronomy was built on its ruins. The number of arbitrary assumptions necessary to make the Standard Model work is rather large, and seldom stated outright. Not only is the existence of gravity taken as a given, so is the existence of the three other basic forces, among them the Strong Force, invented by Wigner specifically to save the Rutherfordian atom. When the Rutherfordian atomic model showed itself to be fundamentally unstable, due to the closely-packed positive charges (protons) in the atomic nucleus, there were two possible approaches: 1) scrap the model and devise one in which the atomic nucleus is inherently stable (e.g., protons are decay products, not present as such within the nucleus); 2) invent a new force that would *make* the model stable, while coercing it obey some arbitrary rules (the Pauli Exclusion Principle). For better or for worse, mainstream physics chose the latter course. But there is a cost to such an approach. Physics is saddled with a single-purpose force, entirely unrelated to any other. Each such invention that is necessary to make the model work (e.g., quarks and gluons) reduces the likelihood of the model being a correct representation of physical reality. Has anyone compiled a list of assumptions aka inventions, or arbitrary rules needed to make the Standard Model work? If not, I’d like to try my hand at it.
As for physical magnitudes, that is a different story. Since our units of measurement are arbitrary, the natural units, such as the speed of light or the unit of atomic mass, can only be evaluated experimentally.
Well, I would argue that Greek astronomy was indeed a stepping stone to Copernicus, but that’s a long discussion to be had over a meal. The predictions of Greek astronomy were pretty accurate — they understood the Moon’s orbit and Earth’s shape very well — and set a standard that Copernicus had to try to beat. He didn’t, either, since he didn’t have the tools. It was only really Brahe and Kepler who did so.
Your complaints about the strong nuclear force are interesting, but quite strange to me. In no sense does this force stand alone, from my perspective. I would have said this:
* it uses the same quantum field theory mathematics as the electroweak forces,
* is integrated with the other forces inexorably through ‘t Hooft anomaly matching conditions,
* agrees with data incredibly well (https://arxiv.org/abs/1406.4088 ),
* is essential in our understanding of the Higgs boson production rate https://profmattstrassler.com/articles-and-posts/the-higgs-particle/the-standard-model-higgs/production-of-the-standard-model-higgs-particle/ ,
* has to be accounted for even in the electroweak decays of particles https://profmattstrassler.com/2022/08/01/celebrating-the-standard-model-how-we-know-quarks-come-in-three-colors/ ,
*can’t be neglected in any measurement done at the LHC and several previous experimental facilities (as in https://www.researchgate.net/figure/ATLAS-results-of-the-SM-cross-section-measurements_fig9_330009152, where every measurement to the right of the first three columns requires a complete understanding of the internals of the proton *and* the effects of the quantum behavior of quarks and gluons.)
It’s hardly an ad hoc invention now, even if it was at Wigner’s time — which was a very, very long time ago.
Anyway, I’m not sure how and why you have the impression that it’s somehow ad hoc. If we didn’t know about it and how to make precise calculations with it, we could not have known how to design the LHC and use it to find the Higgs boson.
So, Can I say: althought the SM is accurate in many aspects, it is still the limited understanding about cosmic by human, and it still cannot reflect the whole physical reality of the cosmic.
Then what about the hypothesis of the false vacuum decay of the higgs field, it is also calculated by standard model, but why many scientists still think it is not correct?
False vacuum decay is calculable in the Standard Model, but (a) even within the Standard Model, it depends on the top quark’s mass, which isn’t precisely enough measured yet for us to determine whether we live in a false vacuum or not, and (b) any additional particles beyond the Standard Model that interact with the Higgs field would change the calculation, and we cannot be sure, despite the LHC’s studies so far, that such particles do not exist. So it’s not a matter of correct or incorrect; our information is incomplete, and so we cannot draw a clear conclusion yet.
I am well aware of the fact that Wigner’s invocation of the Archangel Suriel (pun intended), otherwise known as The Strong Force, to save the Rutherfordian atom has by now becomes an indispensable part and parcel of the Standard Model, which cannot function without Suriel’s constant intervention. In more standard language, the Strong Force continues to serve the purpose for which it was designed, but not without the help of a magic spell known as the Pauli Exclusion Principle and a host of other arbitrary rules dictating the behaviour of the ghostly denizens of the subatomic realm.
The fundamental point of my critique is this: It is agreed that in beta decay the disintegrating particle is *not* composed of the decay products; rather, the decay products are created at the instant of the reaction. However, in the case of alpha decay, the decay products *are* assumed to be present as such within the disintegrating particle (atomic nucleus) prior to the reaction. The assumed presence of alpha particles *as such* within the atomic nucleus is what made it necessary to invent a strong force, along with the above-mentioned magic spell to “save the phenomena”. Historically, the mentioned assumption was an unwarranted extrapolation of the results of the Rutherford gold foil experiment. I realise this is ancient history, but a history lesson is needed if we are to establish where the train got derailed and why.
I realise my credentials in this field are incomparably inferior to yours, but I do have a publication to my name that you may find of interest, in case you were wondering how it came about that the Period Table is so greatly askew (in comparison to its ideal, symmetrical form):
https://www.academia.edu/105998667/Why_Is_the_Periodic_Table_Askew
Well, I wish you the best of luck on the road you’ve chosen, but you should at least try to understand why the Pauli Exclusion Principle is not, in fact, an ad hoc rule. I do advise you to learn a little more about how quantum field theory works and why the exclusion principle is something that comes out of its math, rather than being imposed from outside.
I know I am testing your patience, Matt, but I do feel I should clarify my position. I am not saying QM doesn’t work mathematically; it obviously does. But physicists admittedly have no clue as to how it could possibly work conceptually and the fact that the preposterous and frankly puerile “many worlds” hypothesis is being entertained at all is surely a sign of desperation. It’s not just a philosophical issue. I am concerned about the barriers to progress that occur as a result of assigning real existence to what are mere mental constructs. I may not have expressed it well, but I actually stand in awe of the success of the Standard Model. The strong force and the Pauli Exclusion Principle are perfectly fine, as long as we use them on an “as if” basis. I have singled out the strong force, but the same objection applies to *all* forces and fields. They are a useful way of describing the observed motions of particles and bodies, but that is where their usefulness ends. The notion that masses exert a force on other masses is a deduction from the observed motions, not an observation in itself. General Relativity tried to look for the solution in a change to the space-time metric, which was a step in the right direction, but Einstein’s decision to embrace Riemannian geometry was a fatal misstep. A much more productive “as if” view of gravitation would be to assume that masses simply reduce the space in their vicinity. Physicists have no trouble believing the outlandish notion that masses literally bend space, so they should have little trouble with the notion that masses negate or eliminate space. It’s a tautology really. The reduction of distance is the observation, which the notion of a gravitational field attempts to explain as the result of the application of a force. But there is no force, and there is no interaction between masses. Masses act “as if” they are eliminating space in their vicinity, which by definition results in a reduction of distance between them. This opens up a whole new avenue of approach to the problem. Just one example of the importance of not accepting the reality of “as if” constructs.
If I understand correctly, the issue that concerns you is that while you appreciate the predictive power of the Standard Model and General Relativity, you don’t like the language used. I would fully agree than any such language is potentially temporary and certainly non-unique, so you’re perfectly free to try to reformulate the language. After all, Newton’s laws were reformulated several times; if you lived in the 19th century and didn’t like the idea of forces, you could use the calculus of variations, or the Hamiltonian, or Hamilton-Jacobi theory, and forces would never appear; instead, completely different concepts would arise. Similarly, Schrodinger quickly proved that his approach to quantum theory was the same as that of Heisenberg, Born, and their friends — wave functions instead of matrix manipulation.
However, the onus is on you, in such an effort, to prove mathematically that your new way of looking at the problem is consistent with all previous experiments. Hamilton did just that, and so did Schrodinger. They knew the rules, and they did exactly what they had to do.
When you say that “[physicists] should have little trouble with the notion that masses negate or eliminate space” — well, sure, you’re right. Physicists consider, propose and discard outlandish ideas before breakfast, it’s part of the job. But it’s not the important part or the hard part. The important part is to ***prove that the idea that masses negate or eliminate space still leads to exactly the same perihelion shift of Mercury, the same gravitational lensing in Hubble images, and the same gravitational wave signals in LIGO.*** This is where most outlandish ideas die. Your ideas don’t bother me per se, but no physicist is going to pay much attention to them until you can explain, in math, why they won’t run into conflict with existing experiments. That requires making the ideas precise and proving that they don’t ruin the basic predictions of general relativity.