COSMIC RAYS

Press, Volume LXX, Issue 21320, 13 November 1934, Page 19

COSMIC RAYS

♦ DR. MILLIKAN MODIFIES THEORY EXPLANATION OF ENORMOUS ENERGY LONDON, October 5. Dr. Robert A. Millikan has announced a modification of his worldfamous theory that cosmic rays are evidence of a continuous creation and building up of the universe. Years ago, when cosmic rays first began to be studied, Dr. Millikan declared his belief that they indicated the birth of new atoms in outer space. Attacks by British physicists and others failed to budge him. "The universe is running down, like a clock," they insisted, but Dr. Millikan stuck to his guns. Now, before the International Conference on Physics, he has declared that while atoms were being built up by transformations in outer space, some others were being annihilated entirely. The processes of creation and destruction were going on at the same time, he said. Recent stratosphere flights and other high altitude studies of cosmic rays still left him convinced that creation was going on. Cosmic rays of relatively low energy were a result, of partial annihilation and prove the creation of new atoms, he said. At the same time, he admitted that other cosmic rays were so swift and strong that they could pierce the earth's atmosphere at the equator with an energy \>l 10,000,000,000 volts and could be accounted for only by assuming complete annihilation of entire atoms.

View Reaffirmed Because of his own surveys, made at sea level and in aeroplanes flying to a height of 22,000 feet, Dr. Millikan emphatically reaffirmed his belief that primary cosmic rays, like light, consisted of photons and not of particles. If one believed that cosmic rays consisted entirely of particles, he argued, energies of 20,000,000,000 volts would be needed to account for the known phenomena on account of the resistance of the atmosphere, whereas a few billion electron volts would suffice under the photon theory. He found that cosmic radiation consisted of a field-sensitive portion and non-field-sensitive portion. At sea level, in equatorial regions, 93 per cent, of sea-level ionisation was due to non-tield-sensitive rays and only one-sixth of the remaining 7 per cent, was due directly to electrons. The other fivesixths, he said, was due to secondary radiation produced by those electrons. "As far as can be seen," Dr. Millikan continued, "the only possible source of the energies observed in cosmic radiation lies in atomic transformations of matter into energy in accordance with Einstein's equation. The building of the helium atom out of hydrogen would release 30,000,000 electron volts, that of oxygen 116,00J,000, that of silicon" 1216,000,000, and that of iron 46.000,000. "The condensation, or clustering, of hydrogen atoms in hydrogen 'dust' in the intense cold of interstellar space is a necessary antecedent to the act of building up. The conclusion of modern astronomers regarding the existence of such interstellar dust is not out of line with this hypothesis."

I Result of Annihilation i In addition, Dr. Millikan said, a t small number of cosmic ray energies as high as 10,000,000,000 volts had been observed, and for these there seemed no origin except sudden and complete annihilation of whole atoms of hellium, oxygen, carbon, etc. "Any condition which once starts the process of annihilating matter may, in some cases, be checked at a part-way stage or, in extreme cases, may be carried completely through," he added. "If this possibility exists, it would account for the observed uniformity of all cosmic ray bands, of high energy as well as low, over the whole celestial dome—a most extraordinary characteristic of these rays." It was possible, Dr. Millikan admitted, that annihilation was a result of conditions at an earlier stage in the history of the universe different from those now existing. At any rate, he insisted, both partial annihilation of matter, like that exhibited in the building of the common elements out of hydrogen, and complete annihilation of atoms seem to be called for to account for the energies found in cosmic rays. Dozens of the greatest physicists in the world attended the symposium on cosmic rays and heard the new evidence gathered not only from stratosphere ascents, but from high aeroplane flights, from mountain top studies, and from observations made at sea level in far-flung parts of the earth. Dr. Millikan told of aeroplane flights as far apart as Hudson Bav and Peru, and gave the results of studies made on ships sailing round the world. Balloon Tests Described Professor E. Regener, of Stuttgart, communicated the results of balloon ascents with instruments to a height of 31 kilometres, or slightly more than 100,000 feet, while Professor H. Compton, of Chicago, told of studying cosmic rays from the top of Mount Evans, in the Rockies.

Dr. Compton discussed curious bursts of ionisation caused by cosmic rays, a phenomenon first discovered in 1927 by Professor Hoffmann, of Halle University, in Germany. It was unlikely, said Dr. Compton, that the bursts could be ascribed to any kind of nuclear reaction. The frequency of the bursts, he said, was found to increase more rapidly with altitude than the intensity of the total cosmic ray beam.

He based his conclusions on an Investigation by three scientists from thfi Massachusetts Institute of Technology—Professor R. D. Bennett, Dr. G. S. Brown, and Dr. H. A. Rahmel—who took a 20 litre steel chamber to the too of Mount Evans to measure the frequency and intensity of the bursts.