The supersymmetry calamity

It sounds esoteric, like an episode of The Big Bang Theory, and maybe someday it will be. But even in the fields of physics, supersymmetry is esoteric. What is supersymmetry? What is the calamity? Why should you care?

The standard model is the crown jewel of physics. All you need to know is it describes subatomic particles and the forces that affect them. It has 16 kinds of particles: six quarks, six leptons and four bosons. Lately, headlines tell us add the Higgs. The standard model depicts the world at the smallest scale physics has reached so far. With exquisite precision, it calculates results of smashing particles. But it explains nothing. Indeed, it leads to unsolved mysteries like: Why doesn't the entire universe collapse into black holes? And: What is dark matter?

Some 40 years ago, our particular superheroes came to the rescue. Imagine a comic-book world called superspace. A fourth dimension where each particle physicists have found has a partner-particle they haven't found. Why a comic-book world? Well, the whole idea of supersymmetry is still imaginary. Decades ago, the authors of Superspace (a serious text) said:

The most striking feature of the relation between supersymmetry and the observed world is the absence of any experimental evidence for the former in the latter.

This is still true. Even so, for four decades physicists have manipulated the math of superparticles to show how they solve standard model mysteries. Meanwhile, they have built the world's biggest machine to find experimental evidence of superparticles. It's a particle smasher (the Large Hadron Collider or LHC). It got off to a shaky start. But now it's working; and now -- as the Music Man says -- there's trouble in River City. After scanning many trillions of smashes, the LHC sees not a single superparticle! My quote-of-the-year award goes to American physicists Joseph Lykken and Maria Spiropolu:

"The negative results are beginning to produce if not a full-blown crisis in particle physics, then at least a widespread panic."

So here are my predictions for hot physics news in 2015: The LHC will work up to full power. It might find a superparticle. If so, the particle will get an ugly name that starts with s. Then physicists will hunt more superparticles. They will need a bigger atom smasher costing multi-gigabucks. With it they will expand the standard model on a firmer foundation. The main effect of superparticles on you and me will be we'll share the costs. The effect on the world economy will be modest; we won't notice it.

But what if the LHC works up to full power and finds no superparticles? Then: No superheroes, so no rescue. The standard model will be ridiculed: the standard muddle, 40 years of fundamental physics consigned to the comic books. Funds for smashing atoms will be in short supply. Physicists will drive cabs. The main effect of all those trillions of non-events on you and me will be: They will transform our world. How so? Well, the world economy is getting sluggish. It needs new physics. We will find new physics when old physics crumbles. New physics will create a new economy as inconceivable to us as smartphones, social media and Google were 40 years ago. Spending all those gigabucks to show there are no superparticles will seem a steal.

Which way will it go? What do you think? My bet: The old physics is all set to crumble.

Colin Gillespie is a physicist and author whose most recent book is Time One: Discover How the Universe Began. He writes a weekly web log Science Seen.

It's true that this is a serious crisis for believers in Supersymmetry. I'm not sure it's a serious crisis for physics in general, or for the Standard Model in particular.

Supersymmetry solves two well known problems, one of which is a bit of clutter [the statistics problem] and the other is serious, the so-called hierarchy problem.

The statistics problem does not seem to be a big issue to me. In fact, I would call it a non-issue. [It would be interesting to have some real physicists weigh in.]

Classical particles are not fermions. But they are also not bosons, and the "correspondence principle" still heavily leaned on in many basic physics texts as a note-added-in-proof is not taken all that seriously by most physicists anymore.

We see non-classical behavior in "large" systems, and we see non-classical behavior in statistical mechanics at all temperatures and in large ensembles as well, and that's just all there is to it.

In fact, I would guess most physicists these days would take the opposite conceptual approach and say, "well, if quantum physics appears to reduce to classical physics in some scenarios, that's great. But it doesn't mean anything conceptually. You just have to account for why classical physics is a good approximation in some cases, without expecting that to always be true, even in the everyday world."

A great example of that is the behavior of metals. I got into an extended dust-up a number of years ago with a FReeper who called himself RightwingProfessor [who got himself banned for his nastiness on the Crevo Threads.] He maintained that you really don't need quantum mechanics "except in situations that never arise in ordinary life." This is complete baloney. It's impossible to explain the properties of either metals or semiconductors without Band Theory, which relies very heavily on Fermi-Dirac statistics, which in turn is completely unexplainable without a hallmark of quantum physics: indistinguishability. I don't think any practicing physicist today would claim that we have to find a way to reduce Band Theory to Newtonian physics to convince people that it works. [Another great example: lasers; which can't possibly be created in Newton's World. Thank God we don't live there.]

The hierarchy problem, on the other hand, is a serious issue. Basically it boils down to: "we don't understand why the weak force is so much stronger than gravity." That is a problem, but there are alternative explanations for it that don't require supersymmetry. So it is not an intrinsic weakness in the Standard Model. Extra dimensions is a known dodge, which might turn out to be correct if Supersymmetry isn't.

There are also some other things that Supersymmetry neatly explains. That's not surprising. Some very smart people -- a lot smarter than me -- have been working on it for a really long time. IIRC, something like, 60 years. But there are some alternatives which also explain, or take a stab at explaining these things without abandoning the Standard Model as well...

We shall see.

The article is a little light on details.

I've read two quotes, before this, by physicists who very carefully suggested that the “evidence” for Higgs may not be conclusive.

I was not surprised.

Not because I understand the physics, but because of the way the audience of CERN physicists responded after the Higgs announcement was made.

In spite of the whoops and hugs and high fives, I clearly sensed that much of the “excitement” was forced, and that a lot of the scientists in that room had real doubts about what actually had been discovered.

I also wish the author would have explained in more detail which “superparticles” CERN plans to look for, and why that procedure would be any different than hunting for the Higgs.

Don't we already know that some superparticles exist anyway?

We use positrons in human medicine, and we know experimentally that antiprotons and antiquarks exist.

Not because I understand the physics, but because of the way the audience of CERN physicists responded after the Higgs announcement was made.

You are an astute observer of human behavior. Initially all CERN could really say was they had found a new boson [impressive enough in and of itself] with the correct mass to within 5σ [impressive also, but the usual criterion is 6σ although we have accepted 5σ in the past.]

However, over the last two years, more and more of the predicted properties required of the Higgs Boson have been confirmed for this particle. It's increasingly unlikely that this particle is not the Higgs Boson.

That is not to say that the Higgs has every property that's possibly been attributed to it. For example, does the Higgs Field give mass to every particle? Probably, but this isn't necessary for the Higgs Boson to be the symmetry breaking particle for the Electroweak Unification, which is what Higgs was theorized for to begin with. Is the Higgs Field the same field as the Inflaton Field [which caused the very early universe to expand at faster than the speed of light?] We will probably not know that for a while. That's also a "nice" proposed property of the Higgs Field, but not a necessary one. The Inflaton Field may manifest itself in a different particle.

Don't we already know that some superparticles exist anyway?

No.

We use positrons in human medicine, and we know experimentally that antiprotons and antiquarks exist.

Superparticles are not antimatter. They are complementarymatter. Here's the deal: Quantum particles with the same quantum numbers are indistinguishable from each other. This means that every electron [for example] in the universe is exactly the same as every other. This is completely different from classical physics, where, in principle, it's possible to label two distinct electrons in an atom and keep them straight. This is actually not possible in quantum mechanics. For example, in Helium, which has two electrons, there are not really two distinct electrons. There is simply a system which has two electrons in it, and there is no "electron 1" and "electron 2."

In order to make this work, the wave function you get when you combine two quantum particles into a two-particle system has to be either symmetric or anti-symmetric.

The anti-symmetric elementary particles are called fermions. Electrons, positrons, protons, anti-protons, neutrons, quarks, anti-quarks -- in fact all particles of what we think of as "matter" [and antimatter] -- are anti-symmetric, called fermions, and have 1/2-intrinsic spin quantum number.

The symmetric particles are the ones we usually associate with forces [energy, interaction, etc.] The symmetric particles are photons, gluons, W/Z particles, gravitons. All have integral intrinsic spin [0,1, or 2], symmetric wave functions on exchange, and are called bosons.

"Supersymmetry" is a theory suggests that every fermion has a corresponding "super" boson type particle that hasn't yet been discovered, and every boson similarly has a corresponding "super" fermion. So, for example, the electron [matter] has a superpartner boson called the selectron. The positron [antimatter] has a superpartner boson also, called the spositron. The photon [light, electromagnetic force] is a boson. It has a fermion superpartner called the photino [the photon is its own antiparticle, so there is no anti-photino.]

In the simplest version of the theory, the masses of the complementary superparticles would be exactly the same as their counterparts. An electron has a mass of 0.511 MeV/c² so naively, we would expect its superpartner boson to have the same mass. However, for reasons that I can't explain easily, this turns out not to be true; the superpartners must be more massive than their counterparts.

As a consequence we may not yet have reached high enough energies to have seen the very massive superpartners. However, there are some reasons why if those masses are too much larger, a lot of the benefits of supersymmetry goes away, and there's no reason to try to save the theory any longer. I think 10 TeV/c² is around where most Supersymmetry guys throw in the towel and say if we haven't seen the superpartners at that mass [/energy], then Supersymmetry isn't real.

[If you're REALLY interested, a Czech string theorist by the name of Lubos Motl has a great blog http://motls.blogspot.com/. I do not know him personally, but he is an "out and proud" conservative. His explanations of particle physics are quite accessible to the general reader.]

Supersymmetry allows physicists to come up with explanations for a number of "fine tuning" problems with the Standard Model. However, there are possible other explanations, like extra dimensions. Supersymmetry being "wrong" is not a deal breaker for the Standard Model.

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