17 February 2010

Notes: work up feeling 100 percent better than yesterday, though I am not completely well. I am skipping workouts today and tomorrow. I’ll go in to work early and hopefully get caught up a bit.

One quick science note You’ve heard the sensationalist headlines about physicists doing experiments which violated the laws of physics. Well, that is untrue. What has happened is this:

This latest result has to do with a violation of parity — the symmetry you get by reflecting around one axis, like when you view something in a mirror. (Unfortunately there is a completely different transformation known as mirror symmetry, which this new result has nothing to do with, despite potentially confusing titles.) Quarks and gluons interact in interesting ways, and in the many fluctuations that happen in these high-temperature collisions we can get “bubbles” that pick out a direction in space. In the presence of these bubbles, quarks treat left and right differently, even though they treat both directions exactly the same when they’re in empty space. The phenomenon is known as the chiral magnetic effect — “chiral” means “distinguishing left from right,” and it happens when you put the quark-gluon plasma in a magnetic field.

It’s worth mentioning that, while this result is interesting and very helpful to our quest to better understand the strong interactions, it does not represent the overthrow of any cherished laws of physics. On the contrary, it was predicted by the laws of physics as we currently understand them — and by human beings such as Dimitri Kharzeev and others. Parity is an important idea in physics, but it’s broken all the time — very famously by the weak interactions. Heck, even biologists know how to break parity — most naturally occurring amino acids are left-handed, not right-handed. (I think the reasons why are still mysterious, but can be traced to accidents of history — hopefully someone will correct me if that’s off base.)

The interesting thing is that the strong interactions don’t seem to violate parity under ordinary circumstances; it would be very easy for them to do so, but they seem not to in Nature. When things could happen but don’t, physicists are puzzled; this particular puzzle is known as the Strong CP Problem. (”CP” because the strong interactions could easily violate not only parity, but the combined operation of parity and charge conjugation, which switches particles with antiparticles.) This new result from RHIC doesn’t change that state of affairs, but shows how quarks and gluons can violate parity spontaneously if they are in the right environment — namely, a hot plasma with a magnetic field.

Surf to the link to read about the actual experiment.