Monday, December 12, 2011

The Mystery of Antimatter

Despite the apparent variety of materials in the world around us, we know that everything is made of one thing: matter. But when the universe was born about 14 billion years ago in the Big Bang, two types of matter were created: ordinary matter, which we and everything around us are made, and antimatter, a kind of opposite version of matter. The existence of antimatter was first predicted by the British physicist Paul Dirac in 1928. We know antimatter exists because we can find traces of it in cosmic rays and because scientists have made small amounts of it in particle accelerators. The universe is vast, but it seems to be made almost entirely of matter. So where did all the antimatter go?

Experimental area at CERN’s Antiproton Decelerator The actual antiproton decelerator ring is behind the concrete shielding seen on the left.
   When matter and antimatter come into contact, they annihilate each other, creating vast amounts of energy in the process. A reaction between on gram of matter and one gram of antimatter would release the same energy as exploding 43,000 tons of dynamite. We think that equal amounts of matter and antimatter were created in the Big Bang, but something happened in the first few minutes after the Big Bang to shift the balance in favor if matter so that when matter and antimatter destroyed each other, some matter was left over. This was the matter that went on to form the universe that we know today. Physicists don’t understand why there was an imbalance between matter and antimatter. In fact, this is one of the biggest mysteries in science today. What we do know is that antimatter is a mirror-like reflection of matter, but not quite. Antimatter is said to violate CP-symmetry (CP stands for charge and parity), meaning that there is not total cancellation between particles and their antiparticles. Understanding this process will help us understand why we live in a universe made of matter and not antimatter. But to really understand antimatter we need an experiment that can recreate the conditions just after the Big Bang. 
   Scientist at the European Organization for Nuclear Research (CERN) are attempting to do just that with several ongoing antimatter experiments. Antimatter is difficult to create but even more difficult to keep without it reacting. CERN’s Antiproton Decelerator holds the antiparticles before injecting them into one of several ongoing experiments. They can hold antiparticles for up to 1,000 seconds—a lifetime in the realm of particle physics. These experiments all have one thing in common: they want to pinpoint the differences in antimatter when compared to matter. It is their hope that someday this mystery of the universe will be solved.

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