Ava Anthony, age 15, of Staten Island, New York, for her question:
What happens to matter and antimatter when they meet?
Uranium is radioactive because particles of its matter keep turning into energy. A nuclear reactor also converts matter into energy. So we know that, under certain dramatic conditions, matter can be converted into powerful doses of energy. However, particles of matter and antimatter do not wait for dramatic circumstances. When these opposites meet, they instantly annihilate each other creating a spurt of highly energetic radiation.
The theory of antimatter is rather new and to understand it we must know a bit about matter. The gases, liquids and solids in our world are ordinary matter, made from ordinary atoms. The ordinary atom, of course, is a well organized unit of infinitesimal atomic particles. A fair sized atom has a swarm of electrons around a nucleus stuffed with protons and neutrons, assorted mesons and about a couple of dozen other particles.
Physicists have figured out the weight of about 30 different particles of ordinary matter, also their magnetic and electrical qualities and several other properties. They now know that there are anti particles to match each of them. For example, the electron is a particle of matter with a negative electrical charge. Its matching particle of antimatter is the positron, which has a positive electrical charge.
In a tank of water, there are uncountable zillions of ordinary energetic electrons. Now suppose a positron enters this picture. It might have a chance to travel a centimeter and exist perhaps for one millionth part of a second. Then, maybe sooner but hardly later, it would come within close range of one of those teeming electrons. This spells instant annihilation for both the electron particle of matter and the positron particle of antimatter. The pair of opposites becomes a spurt of gamma rays and other dynamic energies.
The larger proton particle of matter has a positive electrical charge. Its matching antiproton has a negative charge. When they meet they annihilate each other into almost 1,000 times more energy than did the electron positron pair. Both the neutron and the anti¬neutron are electrically neutral, though they have opposite magnetic and other opposite properties. They too annihilate each other and become energy.
Obviously antimatter cannot exist for more than a moment in our world of ordinary matter. But in other parts of the universe, separated by vast oceans of space, things may be different. It has been suggested that the mysterious quasars may be powered by fantastic conflicts between vast quantities of matter and antimatter.
Cosmologists are wondering how antimatter fits into the entire structure of the Universe. It has been suggested that half the cosmic material may be ordinary matter and the other half antimatter. Maybe there are entire stars and even galaxies of antimatter, where stray particles of ordinary matter would meet instant annihilation. However, antimatter stars and galaxies could exist only if they were separated from ordinary stars and galaxies by vast oceans of outer space.