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...about 4 trillion particles enter the bulb in one second, the agitated gas gets dense enough to support a sort of chain reaction. A few atoms spontaneously lose their extra energy, which they emit in the form of photons (units) of radio microwaves about 21 cm. (8.3 in.) long. The newborn photons hit other hydrogen atoms and make them emit photons too. Then a pulse of microwaves bursts from the bulb and is gathered as high-frequency current by apparatus outside...
Universal Waves. Another scientist much preoccupied with the possibility of messages from civilizations outside the solar system is Harvard's Nobel Prize-winning Edward Mills Purcell, who with Harold I. Ewen was the first to detect the 21-cm. waves. If nonsolar aliens are sending messages to earth, theorizes Purcell, their first problem is to select the proper radio frequency, and their most likely choice is 21 cm., the sharpest and most universal radio waves that flash through space. Such aliens would reason that if earthlings have an electronic technology, they would know about the 21-cm. waves...
There is no doubt that radio messages can span interstellar distances. Dr. Purcell estimates that the total power of all the 21-cm. waves that bathe the earth's surface is equal to the power of only one watt, but modern antennas can pick them up easily. And this week's Project Ozma is a first small step in an effort that might take one year or 10,000 to turn a dream into reality...
...radio waves pass through cosmic dust clouds. By tracking the 21-cm. waves given off by hydrogen, radio astronomers have been able to probe deeper and deeper through the Milky Way toward the galaxy's center. Recently, Dutch Astronomers G. W. Rougoor and J. H. Oort of Leiden Observatory reported that they had been able to peer into the mysterious nucleus itself. They found there a strange pinwheel of rapidly spinning hydrogen...
...happy chance, it turned out that the neon lamps light up when exposed to radar waves with a power density of only 5 or 6 mw. sq. cm.-about half the permissible dose for man. So they are perfect for the purpose, and last indefinitely, Dr. Johnson and two Navy medical colleagues report in the United States Armed Forces Medical Journal. Photo flashbulbs can also be used for a one-shot warning: they go off when exposed to still smaller doses of microwave radiation...