When the universe was newborn (just a couple of microseconds old) it displayed a handedness, or chirality, that, according to a recent article in Science, physicists are finally able to reproduce in the laboratory. Dmitri Kharzeev and his team at the Relativistic Heavy Ion Collider at the Brookhaven National Laboratory noticed that the strong force behaves differently when things get hot enough. At temperatures of four trillion degrees Celsius—the hottest temperature ever measured in a lab—protons and neutrons, smashed out of gold nuclei, turn into a flowing plasma of quarks and gluons. The plasma, which behaves like a liquid, seems not to be mirror symmetric. Click for an animated video.
In general, the universe conforms to certain symmetries. For instance, there doesn’t seem to be any preferred direction in space—no experiments performed in an isolated spaceship could tell you which direction you were facing. However, the universe emphatically does not respect other symmetries. For instance, the weak nuclear force (one of the famous four: gravity, electromagnetic, strong and weak), only acts on left-handed particles, such as the neutrino—an experiment, for example, measuring beta decay, in your isolated spaceship could tell you whether the universe is right- or left-handed. While this came as quite a shock when it was experimentally verified in 1957, it was believed to be the only exception.
However, Kharzeev’s experiment, in which local magnetic fields preferentially separate charged particles, suggests that the strong force, at least at the beginning of the universe and at very high temperatures, like the weak force, is not mirror symmetric either. Perhaps most intriguingly, this asymmetry may help explain why matter is more prevalent than anti-matter. So, while the New York Times headline, “Scientists Briefly Break a Law of Nature,” isn’t quite right (laws, by definition, are true of our world!) it nevertheless captures how interesting and surprising these results really are.
By Mathias Frisch , The University of Maryland
(Vol. 3, December 2008)
By Graham Nerlich , The University of Adelaide
(Vol. 4, March 2009)