The What-ls-lt

As science scratches below the surface of the physical universe, it turns up more & more mysterious matters. A very small ghost, much smaller than an electron, now haunts modern physics. Its name, for want of something better, is the "neutrino." No one has ever seen a neutrino, or any trace which one has left behind it, but physicists are pretty certain that neutrinos are real. Just possibly, they may be the most important things in the physical universe.

In the current issue of Physics Today, Dr. George Gamow tells why he thinks that neutrinos are as real as electrons or protons. Physicists, he says, invented neutrinos because they needed something to explain why electrons, shot out of the same atomic nuclei under the same conditions, do not all have the same energy. One way to account for this discrepancy is to imagine a very small, uncharged particle that departs at the same time as the electron, carrying with it some of the energy.

Later, physicists found that the hypothetical particles (which they had come to call neutrinos) were a convenient explanation for other things they did not understand. For instance, when an atom throws off particles, it kicks back like a firing gun. The energy of the particles and the recoiling atom can be measured accurately by studying the tracks of moisture they make in a Wilson cloud chamber. Theoretically, they should balance; but in many cases they do not. Why? Physicists assume that invisible neutrinos have been shot away, too, affecting the recoil of the atom.

Neutrinos are perhaps two-thousandths the mass of an electron, and have no electric charge by which they can be influenced electrically. They pass right through matter as if it weren't there. Physicists have calculated, says Dr. Gamow, that it would take a lead shield 200 million million miles thick to stop speeding neutrinos.

There is a theory that there are not only neutrinos but "anti-neutrinos." When the two meet, they annihilate one another. Dr. Gamow suggests, with bated breath, that neutrino-annihilation may result in the emission of "gravitational waves." In plain language, the mysterious neutrino and the waves it gives off in dying may keep everything and everybody from flying off into space.

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