Another anti-physics issue of SciAm

High energy physics is undoubtedly the queen and the ultimate reductionist root of all natural sciences. Nevertheless, during the last decade, it has become immensely fashionable for many people to boast that they're physics haters.

The cover of the upcoming May 2014 issue of Scientific American looks doubly scary for every physicist who has been harassed by the communist regime. It resembles a Soviet flag with some deeply misleading propaganda written over it:

A crisis in physics?

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If supersymmetry doesn't pan out, scientists need a new way to explain the universe. [In between the lines]

Every part of this claim is pure bullshit, of course. First of all, there is no "crisis in physics". Second of all, chances are high that we won't be any certain whether SUSY is realized in Nature. Either SUSY will be found at the LHC in 2015 or soon afterwards, or it won't be. In the latter case, the status of SUSY will remain qualitatively the same as it is now. Top-down theorists will continue to be pretty much certain that SUSY exists in Nature in one form or another, one scale or another; bottom-up phenomenologists and experimenters will increasingly notice the absence of evidence – which is something else than the evidence for absence, however.

But aside from this delusion, the second part of the second sentence is totally misguided, too. Supersymmetry isn't a "new way to explain the universe". It is another symmetry, one that differs from some other well-known symmetries such as the rotational or Lorentz symmetry by its having fermionic generators but one that doesn't differ when it comes to its being just one aspect of theories. Supersymmetry isn't a theory of the universe by itself (in the same sense as the Standard Model or string theory); supersymmetry is a feature of some candidate theories of the universe.




To be sure that the hostility is repetitive (a lie repeated 100 times becomes the truth, she learned from Mr Goebbels), editor-in-chief Ms Mariette DiChristina introduces the May 2014 issue under the following title:

Does Physics Have a Problem?

What does it even mean for a scientific discipline to have a problem? Claims in science are either right or wrong. Some theories turn out to be right (at least temporarily), others turn out to be wrong. Some theories are viable and compatible with the evidence, others have been falsified. Some scientists are authors of right and/or important and valuable theories, others are authors of wrong ones or no theories at all.

Some classes of questions are considered settled so they are not being researched as "hot topics" anymore; others are behind the frontier where the scientists don't know the answers (and sometimes the questions): they are increasingly confused by the questions behind the frontier. This separation of the realm of questions by a fuzzy frontier of ignorance is a feature of science that applies to every scientific discipline and every moment of its history. One could argue that there can't be "crises in physics" at all but it's doubly bizarre to use this weird word for the current era which is as ordinary era of normal science as one can get.




The main article about popular physics was written by experimenter Maria Spiropulu (CMS, Caltech) and phenomenologist Joseph Lykken (a self-described very smart guy at Fermilab). They're very interesting and sensible folks but I would have objections to many things they wrote down and I think that the same thing holds for most high energy physicists.

They say that most HEP physicists believe that SUSY is true but add:

Indeed, results from the first run of the LHC have ruled out almost all the best-studied versions of supersymmetry. The negative results are beginning to produce if not a full-blown crisis in particle physics, then at least a widespread panic. The LHC will be starting its next run in early 2015, at the highest energies it was designed for, allowing researchers at the ATLAS and CMS experiments to uncover (or rule out) even more massive superpartners. If at the end of that run nothing new shows up, fundamental physics will face a crossroads: either abandon the work of a generation for want of evidence that nature plays by our rules, or press on and hope that an even larger collider will someday, somewhere, find evidence that we were right all along…

I don't have – and I have never had – any strong preference concerning the masses of superpartners i.e. the accessibility of SUSY by the collider experiments. All of them could have been below \(100\GeV\) but they may be at \(100\TeV\) or near the GUT scale, too. Naturalness suggests that they (especially the top squarks, higgsinos, and perhaps gluinos) are closer to the Higgs mass but it is just a vague argument based on Bayesian reasoning that is moreover tied to some specific enough models. Any modification of the SUSY model changes the quantification of the fine-tuning.

But even if it doesn't, the word "natural" is a flexible adjective. If the amount of fine-tuning increases, the model doesn't become unnatural instantly. It is a gradual change. What I find preposterous is the idea presented by the authors that "if the 2015 LHC run finds no proof of SUSY, fundamental physics will face a crossroads; it will either abandon the work altogether or press for a bigger collider".

You can make a 2016 New Year's resolution and say that you will stop thinking about SUSY if there is no evidence from the LHC for SUSY by that time. You may even establish a sect within high energy physics that will share this New Year's resolution with you. But it is just a New Year's resolution, not a science or a decision "implied" by the evidence. There will be other people who will consider your group's New Year's resolution to be premature and just downright stupid. Physics isn't organized by deadlines or five-year plans.

Other people will keep on working on some SUSY models because these models will be attractive and compatible with all the evidence available at that moment. Even if SUSY were experimentally proven to require a 1-in-1,000 fine-tuning – and it really can't be due to the model-dependence of the fine-tuning scores – most people will still rationally think that a 1-in-1,000 fine-tuning is better than the 1-in-1,000,000,000,000,000,000,000,000,000,000 fine-tuning apparently required by the Standard Model. Maria and Joseph know that it is so. In fact, they explicitly mention the "prepared reaction" by Nima Arkani-Hamed that Nima presented in Santa Barbara:

What if supersymmetry is not found at the LHC, [Nima] asked, before answering his own question: then we will make new supersymmetry models that put the superpartners just beyond the reach of the experiments. But wouldn’t that mean that we would be changing our story? That’s okay; theorists don’t need to be consistent—only their theories do.

If SUSY looks attractive enough, of course that phenomenologists will ignore the previous fashionable beliefs about the lightness of the superpartners and (invent and) focus on new models that are compatible with all the evidence at that moment. The relative fraction of hep-ph papers that are dedicated to SUSY model building may decrease in the case of the continuing absence of evidence but only gradually so simply because there are no any major enough alternatives that could completely squeeze the SUSY research. There can't really be any paradigm shift if the status quo continues. You either need some new experimental discoveries or some new theoretical discoveries for a paradigm shift.

This unshakable fidelity to supersymmetry is widely shared. Particle theorists do admit, however, that the idea of natural supersymmetry is already in trouble and is headed for the dustbin of history unless superpartners are discovered soon…

The word "natural" has several meanings and the important differences between these meanings is being (deliberately?) obfuscated by this sentence. It is almost a tautology that any theory that ultimately describes Nature accurately is "natural". But as long as we are ignorant about all the details about the final theory and how it describes Nature, we must be satisfied with approximate and potentially treacherous but operationally applicable definitions of "naturalness". In effective field theory, we assume that the parameters (at the high energy scale) are more or less uniformly distributed in a set and classify very special, unlikely (by this probability distribution) regions to be "unnatural" (typically very small values of some dimensionless parameters that could be of order one).

But the ultimate theory has different rules how to calculate the "probability distribution for the parameters". After all, string theory implies discrete values of all the parameters, so with some discrete information, we may sharpen the probability distribution for low-energy parameters to a higher-dimensional delta-function. We can just calculate the values of all the parameters. The values may be generic or natural according to some sensible enough smooth probability distribution (e.g. in an effective field theory). But if the effective field theory description overlooks some important new particles, interactions, patterns, or symmetries, it may be unnatural, too.

It's important to realize that our ways to estimate whether some values of parameters in some theories are natural are model-dependent and therefore bound to evolve. It is just completely wrong for Maria and Joseph to impose some ideas about physics from some year – 2000 or whatever is the "paradigm" they want everyone to be stuck at – and ban any progress of the thinking. Scientists' thinking inevitably evolves. That's why the scientific research is being done in the first place. So new evidence – including null results – is constantly being taken into account as physicists are adjusting their subjective probabilities of various theories and models, and of various values of parameters within these models.

This process will undoubtedly continue in 2015 and 2016 and later, too. At least, sensible people will continue to adjust their beliefs. If you allow me to say a similar thing as Nima did: theorists are not only allowed to present theories that are incompatible with some of their previous theories or beliefs. They are really obliged to adjust their beliefs – and even at one moment, a sensible enough theorists may (and perhaps should) really be thinking about many possible theories, models, and paradigms. Someone whose expectations turn out to be more accurate and nontrivially agreeing with the later observations should become more famous than others. But it is not a shame to update the probabilities of theories according to the new evidence. It's one of the basic duties that a scientist has to do!

I also feel that the article hasn't taken the BICEP2 results into account and for those reasons, it will already be heavily obsolete when the issue of Scientific American is out. They try to interpret the null results from the LHC as an argument against grand unification or similar physics at the GUT scale. But nothing like that follows from the null results at the LHC and in fact, the BICEP2's primordial gravitational waves bring us quite powerful evidence – if not a proof – that new interesting physics is taking place near the usual GUT scale i.e. not so far from the standard four-dimensional Planck scale.

So in the absence of the SM-violating collider data, the status quo will pretty much continue and the only other way to change it is to propose some so far overlooked alternative paradigm to SUSY that will clarify similar puzzles – or at least a comparable number of puzzles – as SUSY. It is totally plausible that bottom-up particle model builders will have to work with the absence of new collider discoveries – top-down theorists have worked without them for decades, anyway. It works and one can find – and string theorists have found – groundbreaking things in this way, too.

What I really dislike about the article is that – much like articles by many non-physicists – it tries to irrationally single out SUSY as a scapegoat. Even if one should panic about the null results from the LHC, and one shouldn't, these results would be putting pressure on every model or theory or paradigm of bottom-up physics that goes beyond the Standard Model. In fact, SUSY theories are still among the "least constrained ones" among all paradigms that try to postulate some (motivated by something) new physics at low enough energy scales. That's the actual reason why the events cannot rationally justify the elimination or severe reduction of SUSY research as a percentage of hep-ph research.

If someone thinks that it's pointless to do physics without new guaranteed enough experimental discoveries and this kind of physics looks like a "problem" or "crisis" to him or her, he or she should probably better leave physics. Those who would be left are looking for more than just the superficial gloss and low-hanging fruits. The number of HEP experimenters and phenomenologists building their work on a wishful thinking of many collider discoveries in the near future is arguably too high, anyway. But there are other, more emotion-independent approaches to physics that are doing very well.