I spent a lot of my working life stuck in a dark, cold, room with no windows… There I help build and tinker with atomic physics experiments. These days I’ve been trying to cool down atoms to near absolute zero. At these temperatures they become very easy to control, and we try to come up with useful things to do with the atoms. Maybe we could make a quantum simulator for example. We’re some way from doing that just yet though. In years gone by I played around with a different sort of experiment, one that has been in the news recently.
A long time ago, when physicists still looked intelligent by frequent waving of their pipes down at the smoking room, it was thought that the universe had to be symmetrical. The rules that Nature runs on shouldn’t change if suddenly left became right and up became down, nor should they change if time, all of a sudden, ran backwards. I mean you’d still die if you were walking backwards and were hit by a backward going bus, right!? Unfortunately, nature doesn’t have common sense, and in some cases, these symmetries and our common sense is violated. (Don’t get me wrong, it’s always a bad idea to be hit by a bus!)
When physicists discovered this annoying truth about the universe, they decided to mix things up a bit. To explain the universe, they invented a ring, one ring to rule them all….oh no, sorry, it was a symmetry – supersymmetry! It turned out that some theoretical problems in physics could be solved if every particle in nature had a symmetrical twin, who spins a bit differently and weighs a lot.
For 20 years now, supersymmetry has been offering simple explanations where no other theory can. For example, dark matter, the glue that seems to hold galaxies together, might be made up of these heavier supersymmetric particles. Of course we can’t see dark matter, that’s why they call it “dark”. Nor can we see those other particles. Which is very convenient! Yes so far this magnificent theory has evaded detection.
To find the missing stuff, some physicists spent a lot of money, about 30,000 Ferraris’ worth, and built the Large Hadron Collider (LHC) at CERN in Geneva. Probably the most complicated machine ever built, the LHC smashes particles together and sees what comes out. It’s the Jeremy Clarkson approach to physics! (For those who don’t know who Jeremy Clarkson is, you can choose to remain in blissful ignorance or have a look here.)
Meanwhile, other physicists locked themselves in a basement lab in London to produce a machine that can measure the shape of the electron. This, too, could tell us something about supersymmetry. The point-charge of the electron is thought to get smeared out by interactions with particles around it. If supersymmetry exists, the resulting blob should be slightly oval-shaped instead of round. This experiment, which I did my phd on, fits on a family sized dinning table and cost about 10 Ferraris’, has just been started up.
Both these new experiments are now piling on the pressure for supersymmetry. Neither has found any evidence that supersymmetry exists at all! At the LHC last month they released data ruling out the simplest form of supersymmetry. In London, they made the most precise measurement of the shape of the electron ever performed and saw nothing but a round blob. As this experiment becomes ever more sensitive, it could rule out supersymmetric theories all together.
So with both these new eyes fixed on their target, supersymmetry’s days might be numbered.
(LHC Physical Review Letters paper and Arxiv version.
Imperial College London Nature paper.)