The Possibly-Not-Quite-As-Elegant-As-We-Were-Hoping Universe

Galleons, we begin today’s post with a crash course in supersymmetry. And by crash course, I mean that I’m going to toss some words around, do a crappy job of explaining them, pretend you understand my prattling, then talk about some science news.

I apologize in advance.

We begin with plain ol’ symmetry. In terms of physics, symmetry is a property in which, under certain transformations, aspects of a physical system remain unchanged. Rotation is a type of symmetry. So is reflection.

In particle physics, there are a number of types of symmetry. There is charge symmetry (C-symmetry), which states every particle has an antiparticle, and that replacing every particle with its antiparticle would yield a universe indistinguishable from our own. Parity symmetry (P-symmetry) states that a universe where everything appears as if reflected in a mirror would be indistinguishable from the one we know.

Unlike on Star Trek, where a Mirror Universe counterpart can be easily identified by a well-groomed goatee:

Supersymmetry (also called SUSY, which is fucking adorable) is just another type of symmetry. This particular brand of symmetry relates to bosons and fermions, two types of subatomic particles. Bosons are particles with integer spins (like photons and gluons and the Higgs, if it’s out there). Fermions have half-integer spins (electrons, quarks, neutrinos). According to supersymmetry, there are fermion superpartners for the bosons and boson superpartners for the fermions. These superpartners have spins of 1/2 a unit less than their regular partners (for example, electrons are spin-1/2 particles, so they should have a spin-0 superpartner):

The problem is, there are no existing particles that can act as superpartners for the others. Instead, what we have is a hypothetical zoo of ridiculously-named new particles: squarks, winos, zinos, sneutrinos, gluinos, etc. And, while scientists have done a lot of grumbling about this theoretical type of symmetry doubling the amount of particles in our existing standard model… supersymmetry also acts as an elegant solution to some problems in the realm of particle physics, one of which is string theory.

Before supersymmetry, we had a form of string theory known as bosonic string theory. The first incarnation of string theory, bosonic string theory dealt solely with the vibrational patterns of the bosons. However, because bosonic string theory contained no fermionic (half-integer) vibrational patterns, it was incomplete. You can’t have a theory that’s supposed to describe the universe blatantly ignore huge swathes of it, now can you?

So, in the 1970s, scientists began working on incorporating fermionic vibrational patterns into a modified string theory. What emerged was a theory where bosonic and fermionic vibrational patterns appeared in pairs.

That’s right- the revised string theory incorporated (and, in fact, heavily relied on) supersymmetry.

And that’s how supersymmetric string theory (commonly called superstring theory) was born.

***

As you are probably aware, I’m a big fan of superstring theory. It is, without a doubt, one of the most beautiful scientific theories ever produced. By reducing our most basic building blocks to strings, we set the stage for a universal symphony. Superstring theory makes the universe into a song, an orchestration, a living, lilting pattern of harmonics and melodies. I cannot think of a description of the universe more lovely than one that compares it so readily to music.

One of the basic things about a string is that it can vibrate in many different shapes or forms, which gives music its beauty. ~Edward Witten

String theory appeals to our sense of aesthetics while happily satisfying our driving need to spin order out of chaos, to find the underlying patterns that make up the world.

But that’s all it is- a theory. And while it’s easy to get caught up in the torrent of string theory excitement, we have to constantly remind ourselves that string theory has yet to be experimentally verified. Elegant though it may seem, all it will take is a few pieces of hard data to shatter the theory into tiny little pieces.

***

Enter the LHC.

Physicists have been hoping for years that the LHC, the Holy Grail of supercolliders, would be able to provide the necessary data to solidify or scrap our current model of string theory.

Recent findings suggest that we might be leaning toward the latter.*le gasp!*

CMS and ATLAS (they’re two-of-a-kind) have spent the past year hunting for super particles. And they’ve seen no sign of the beasties. The LHC has doubled the mass limit previously set by the Tevatron, showing no evidence of squarks (quark superpartners) at energies up to about 700 gigaelectronvolts.

“We’re painting supersymmetry into a corner,” says Chris Lester, a particle physicist who works with ATLAS.

The LHC continues to ramp up the energy level, and the higher energies it accumulates data at, the more territory it rules out for these super particles. This creates a bit of a problem for dear SUSY, as increasing the mass of these super particles causes them to cease canceling out quantum fluctuations (a big reason why supersymmetry is so important is it can be used to cancel out quantum fluctuations in equations, which also helps keep the theoretical Higgs boson in an acceptable mass range). In order to keep SUSY alive, scientists will have to assume very specific masses for the super particles. Ironically, supersymmetry was created to prevent that very same type of fine-tuning of mass for the Higgs boson.

By the end of the year, the LHC will reach 1,000 gigaelectronvolts — potentially ruling out some of the most favored variations of supersymmetry.

“A lot of people think that the situation is not good for SUSY,” says Alessandro Strumia, a theorist at the University of Pisa in Italy. “This is a big political issue in our field. For some great physicists, it is the difference between getting a Nobel prize and admitting they spent their lives on the wrong track.”

The loss of supersymmetry seems imminent, and the aftershocks from such a discovery (or lack of a discovery, if you will) will shake the core of modern physics. Theoretical physicists will be sent back to the drawing board, looking for a new solution to the problems with the standard model (problems string theory seemed to correct).

Personally, I think this is an amazing time for physics. We have the technology to finally perform experiments to test the theories we’ve been working on for the last 50 years. And no matter how much I may like superstring theory, it may be nothing more than the spontaneous generation of our age. We may be completely off the mark with it. But whether the LHC disproves supersymmetry or finds the Higgs, we’re looking at a real turning point for particle physics.

So, while I find this bit of news surprising and a bit sad, I’m also thrilled. This is why I love science- it’s a constant search for truth. Even though we’ve spent years and years believing supersymmetry and string theory are the answers we’ve been looking for, all it takes is data like this to prove us wrong. This is not religion. We pursue truth, whatever that might be.

And sometimes we are wrong.

And so we keep searching. Because that’s science.

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