The Left Hand of Darkness



20 Might 2015

Artist rendering of a gamma ray burst.
NASA Goddard Area Flight Middle
Artist rendering of a gamma ray burst.

One of many fundamental assumptions of cosmology is that the universe is on common the identical all over the place. That’s, it’s uniform and isotropic. This assumption appears to carry up fairly effectively, however naturally there are research completed that search for violations of this assumption. From time to time a analysis mission will discover what appears to be a violation of this assumption, however they often don’t pan out when examined extra intently. However there are points of the universe that aren’t symmetrical, and one of many greatest is named matter/antimatter asymmetry (or baryon asymmetry).

Once we have a look at the universe round us, all the pieces appears to be made up of matter. However from particle physics we all know that each kind of matter particle (proton, electron) has an antimatter sibling (anti-proton, positron) with an reverse cost amongst different issues. We are able to make antimatter particles within the lab, however they at all times kind paired with common matter. For each positron we create, for instance, an electron can also be created. So when the very first matter within the universe appeared quickly after the large bang, one would anticipate an equal quantity of antimatter to even be produced. One would suppose the universe needs to be half matter and half antimatter, but it surely isn’t.

There are many proposed options to this thriller, corresponding to the concept that the early universe had small imbalances that had been magnified by early cosmic inflation. In that means we simply occur to stay in a area of the Universe that’s dominated by matter. In different areas, far past the observable universe, there could possibly be areas dominated by antimatter. However that concept isn’t very satisfying, so a extra widespread mannequin is that some mechanism within the early universe should have made matter extra frequent than antimatter. As unusual as that appears, there’s such a mechanism, and it’s often known as CP violation.

Symmetries in particle physics.
Flip Tanedo
Symmetries in particle physics.

The CP on this case stands for cost parity, that are two symmetries in physics. Right here cost is solely the signal of the cost, thus electrons have a unfavorable cost and positrons a optimistic one. Cost symmetry signifies that universe fabricated from matter and one fabricated from antimatter ought to behave in the identical means. Parity could be described as a mirror picture. For those who maintain up your proper hand whereas wanting in a mirror, your picture will maintain up its left hand. Usually parity is represented by spin, the place one is correct handed, and the opposite is left handed. Parity symmetry principally signifies that if left and proper had been flipped within the universe, nothing ought to change. For those who mix these two symmetries you get CP symmetry. Because of this in the event you flipped matter with antimatter and left with proper all the pieces ought to keep the identical. It may appear fairly apparent that it shouldn’t make a distinction if we referred to as electrons optimistic and protons unfavorable, any greater than if we determined to change the which means of left and proper. Nevertheless it seems that it isn’t so apparent for the universe.

In 1964 it was discovered {that a} impartial particle often known as a Kaon got here in two sorts that had been CP duals of one another. If CP symmetry had been conserved, then these two kinds of Kaons ought to decay on the similar charge. What we discovered was that the 2 Kaon sorts decay at barely totally different charges. The distinction between the 2 is barely about 3 elements in 1000, but it surely isn’t zero. Basically what this implies is that nature distinguishes between matter and antimatter on a cosmic scale. They aren’t merely reversible. So it’s potential that the universe may need barely favored matter over antimatter within the early universe.

Whereas we all know that CP violation happens, the identified mechanisms by themselves aren’t sufficient to account for the matter/antimatter asymmetry seen within the universe. For the mannequin to work, there have to be some mechanism past the usual mannequin that produces a big sufficient impact. It’s a thriller we nonetheless haven’t solved.

At this level all we are able to do is hold researching, and see if the universe ideas its hand.

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