Is Nature Symmetrical?

The discovery of antiprotons at the University of California (TIME, Oct. 31) was a basic physical discovery which had far-reaching effects. In Britain's Nuclear Power, Professor O. R. Frisch of the University of Cambridge tells how the discovery has affected scientific reasoning about the smallest things in the universe, the sub-atomic particles, and about the biggest thing, the universe itself.

According to the laws of electrodynamics, nature should be "symmetrical." There should be atoms with negative as well as positive nuclei. But for years after the discovery of atoms, all the evidence seemed stubbornly intent on proving that matter was unsymmetrical. The heavy, charged particles (protons) in the nuclei of atoms were always positive. The light particles (electrons) surrounding the nuclei were always negative. Never could the scientists find a "reversed atom" (negative protons, positive electrons) to back up the principle of symmetry.

Pair of Creation. In 1932, physicists discovered that positive electrons (positrons) are created out of energy by cosmic rays. They can also be made artificially by high-energy gamma rays from radioactive elements. Positrons do not last long; as soon as one of them hits a normal electron, both particles are annihilated, turning back into the energy out of which they were made. But the proof that positrons exist was a victory for believers in nature's symmetry. Better still was the fact when a positron is created, it always appears in a "pair" with an ordinary negative electron.

If positive electrons exist, why not negative protons? Scientists searched for them for years in cosmic rays, but found only a few doubtful cases. They hoped to create them in the laboratory, but no existing cyclotron had enough power. It took the Berkeley Bevatron to create an antiproton out of energy. Like the positron, it, too, appears only paired with an ordinary proton, and destroys itself as soon as it collides with a proton.

Anti-Matter. With the antiproton found, scientists assume that "antimatter" is possible--a symmetrical "mirror image" with all the outward characteristics of ordinary matter but with its electrical charges reversed. Obviously, antimatter could not exist within reach of ordinary matter as it exists on earth. But it may even be common in other parts of the universe. Some of the distant galaxies may be made of such reversed matter. The light from a star of antimatter, says Professor Frisch, would be just like the light from normal stars.

If a space ship from earth were to land on a planet of antimatter, it would I vanish in a puff of energy. But if a galaxy made of antimatter were to collide with an ordinary galaxy, their stars might not annihilate each other. In the vast emptiness of space, even within a galaxy, direct collisions between stars are extremely unlikely. But dust and gas between the stars would certainly come in contact. Each particle of normal matter would annihilate a particle of antimatter. The result would be a great increase in brightness. No such glowing collision has been observed, says Professor Frisch, but "since collisions between galaxies are anyhow very rare, this might have been overlooked."

If there are no galaxies made of antimatter, the cosmologists should try to explain why they do not exist. An explanation is relatively easy for those cosmologists who believe the universe was formed in a vast, single explosion. "The universe," explains Professor Frisch,"must have been very dense at first, and annihilation would have weeded out all but one kind of matter." But for those who hold that matter is being created continuously in space between the galaxies, the antiproton is more of a problem. Their theory will have to explain, says Professor Frisch, why only one kind of matter is being created.

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