Last year physicists commemorated the centennial of the discovery of
the atomic nucleus. In experiments carried out in Ernest Rutherford’s
laboratory at Manchester in 1911, a beam of electrically charged
particles from the radioactive decay of radium was directed at a thin
gold foil. It was generally believed at the time that the mass of an
atom was spread out evenly, like a pudding. In that case, the heavy
charged particles from radium should have passed through the gold foil,
with very little deflection. To Rutherford’s surprise, some of these
particles bounced nearly straight back from the foil, showing that they
were being repelled by something small and heavy within gold atoms.
Rutherford identified this as the nucleus of the atom, around which
electrons revolve like planets around the sun.This was great science, but not what one would call big science. Rutherford’s experimental team consisted of one postdoc and one undergraduate. Their work was supported by a grant of just £70 from the Royal Society of London. The most expensive thing used in the experiment was the sample of radium, but Rutherford did not have to pay for it—the radium was on loan from the Austrian Academy of Sciences.
Nuclear physics soon got bigger. The electrically charged particles from radium in Rutherford’s experiment did not have enough energy to penetrate the electrical repulsion of the gold nucleus and get into the nucleus itself. To break into nuclei and learn what they are, physicists in the 1930s invented cyclotrons and other machines that would accelerate charged particles to higher energies. The late Maurice Goldhaber, former director of Brookhaven Laboratory, once reminisced:
The first to disintegrate a nucleus was Rutherford, and there is a picture of him holding the apparatus in his lap. I then always remember the later picture when one of the famous cyclotrons was built at Berkeley, and all of the people were sitting in the lap of the cyclotron.
After World War II, new accelerators were built, but now with a different purpose. In observations of cosmic rays, physicists had found a few varieties of elementary particles different from any that exist in ordinary atoms. To study this new kind of matter, it was necessary to create these particles artificially in large numbers. For this physicists had to accelerate beams of ordinary particles like protons—the nuclei of hydrogen atoms—to higher energy, so that when the protons hit atoms in a stationary target their energy could be transmuted into the masses of particles of new types. It was not a matter of setting records for the highest-energy accelerators, or even of collecting more and more exotic species of particles, like orchids. The point of building these accelerators was, by creating new kinds of matter, to learn the laws of nature that govern all forms of matter. Though many physicists preferred small-scale experiments in the style of Rutherford, the logic of discovery forced physics to become big.
by Steven Weinberg, NY Review of Books | Read more:
Photo: Superconducting Super Collider Laboratory/Photo Researchers
