Word: photons
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Dates: during 1940-1949
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...critics question the "red shift" as a measure of velocity. The usual explanation of the reddening effect is that the luminous body's motion away from the observer "pulls out" the light waves, making them longer (redder) than normal. But since red light contains less energy per unit (photon) than violet light, Bubble's critics suggest that light may lose some of its energy in traversing space, thus turning redder. It may start out from a distant nebula as young, vigorous violet and arrive at the earth after millions of weary years as old, tired red. If that...
...Work. Imbedded in Max Planck's Law of Radiation (published in 1901) was something vastly more important: Planck's "universal constant" (6.624 x 10 -27 erg-seconds), now considered one of the three fundamental figures in the universe.* Planck's constant enabled Einstein to conceive the "photon" (particle of radiation). It also made possible Niels Bohr's model of the atom. It turned up in spectroscopy, in the study of X rays, in electronics. Upon it is based the whole science of quantum (wave) mechanics...
Extra Energy. Radar waves are electromagnetic waves like light and X rays; but since their frequency is enormously smaller, they carry much less energy per "photon."* They therefore provide what scientists call an "elegant" method of dealing out very small quantities of energy. Using a formidable-looking gadget, Lamb & Retherford shot radar waves of the proper frequency through hydrogen atoms in one of Dirac's predicted states. As soon as the energy was added, the atoms turned into the other state. Since energy was required to make the change, the experiment showed that the two states did not have...
...photon (smallest unit of radiant energy) is equal to the frequency of the wave multiplied by Planck's constant h (6.55 X 10(-27)erg-seconds...
...Princeton, 15 years later, Dr. Dirac, who had forecast a particle, theorized about what happens when one particle strikes another. He selected the two simplest: the electron and the photon (unit of electromagnetic radiation, such as light). To explain how they interact, he ploughed through relativistic bafflements, covered a blackboard with lacy mathematics. Many listeners looked as if they had been hit on the head. Dirac himself seemed unsure...