Research into what separates matter from antimatter is accelerating in particle physics experiments around the world. Scientists are hoping the difference will help explain why you, me and all the things around us are made of matter instead of its opposite.

Shortly after the Big Bang theoretically kicked off everything, the universe was a hot soup of equal parts matter and antimatter, scientists say. Why the former came to dominate is a question that physicists have yet to answer fully.

Recent results from the BaBar experiment in California have confirmed one departure between the two substances, but to solve the puzzle more deviations will have to be found.

"This was a very important step on the road to understanding the matter-antimatter asymmetry," said David MacFarlane, a physicist with the BaBar group. "This asymmetry is one of the fundamental questions of cosmology."

With equal mass but opposite electric charge, there are anti-particles that correspond to the proton, the electron, and the whole zoo of fundamental particles that physicists have so far catalogued.

Strange as they sound, these particles do exist, and they can be created. They just don't last long. If the existential partners come together, they completely annihilate each other.

This yin and yang of physics has been fodder for many science fiction plots. And the copious amount of energy that comes out of matter-antimatter annihilations might one day be put to use as a fuel source.

Alien screening

In his 1961-62 lectures, the Caltech professor Richard Feynman had his students imagine a distant alien civilization on an antimatter planet. If we were to contact them through radio, Feynman asked, how would we tell that they were made of antimatter?

Although the charges would all be reversed, their anti-hydrogen, anti-carbon, etc. would weigh as much as our elements. The energy levels would be the same as well. So their chemistry textbooks would be identical to ours.

There are, however, certain high-energy interactions that in our world behave as if left-handed, whereas in the antimatter world behave as if right-handed. But how do you tell someone which way is "left" over an interplanetary telephone? Feynman’s point was that you can’t, if all you can do is compare physics experiments.

The fact that antimatter acts as a mirror image of matter is called charge-parity (CP) symmetry. After Feynman’s lecture, experimentalists observed a few rare occasions where this symmetry was not upheld, and therefore, one could tell whether the alien on the other line was matter or antimatter.

A necessary disobedience

A world that always obeyed CP symmetry would be unlikely to have civilizations, planets, or galaxies. Played out on the matter-antimatter battlefield of the primordial universe, CP symmetry would lead to the complete destruction of everything.

In 1964, physicists discovered that the rules of CP were sometimes broken by particles called kaons. This violation showed up as a difference in the decay of kaons and anti-kaons, but it only happened in four out of a million events. This was enough, however, to give Andrei Sakharov, the Russian physicist, an idea for how the cosmos escaped mutual annihilation.

Sakharov determined that there were three criteria for allowing matter to win out over the Big Bang stalemate. One of these criteria was CP violation.

Before Sakharov, cosmologists did not have a way to approach the matter-antimatter asymmetry. "The discovery of CP violation made it a scientific question," said Michael Dine of the University of California Santa Cruz.

But the problem remained difficult. Much of the work since Sakharov’s revelation has gone into perfecting the Standard Model of particle physics. It took time to figure just how much CP violation was allowed in the Standard Model. It turns out, not very much.

Nearly forty years after CP violation was seen in kaons, scientists are just now beginning to detect the effect in another particle, the B meson.

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