The brilliant, whimsical popularizing of Sir Arthur Stanley Eddington has made ''the expanding Universe'' almost a household word. But the telescopic observations of a universe which seems to be blowing up like the fragments of an explosive shell have come mainly from Mount Wilson Observatory's brilliant Astronomer Edwin Powell Hubble. Beginning in 1928, Hubble and his coworker, Milton LaSalle Humason, showed that the light from the most distant nebulae (clouds of stars) which he could photograph in Mount Wilson's giant telescope was shifted far toward the red end of the spectrum. Such a redshift is observed in the light of a star known to be retreating from Earth, so it was assumed that the distant nebulae were retreating in all directions. On these observations, and on the theoretical expanding universes formulated by de Sitter and Lemaitre before any observations were made, the case for the expanding universe rested.
Sir Arthur has never lost his enthusiasm for this cosmic soap bubble. But the speeds indicated by the amount of redshift, some of which now equal 25,000 miles per second, have made many astronomers doubt. Other causes for the redshift were suggested, such as cosmic dust or a change in the nature of light over great stretches of space. Two years ago Dr. Hubble admitted that the expanding universe might be an illusion, but implied that this was a cautious and colorless view. Last week it was apparent that he had shifted his position even further away from a literal interpretation of the redshift, that he now regards the expanding universe as more improbable than a non-expanding one.
To the National Academy of Sciences Dr. Hubble communicated the results of his most recent survey of the distant nebulae. The distribution of these bodies in space forced him to conclude that a non-expanding universe theory "is more economical and less vulnerable." If the red-shifts do not really indicate velocity, he wrote, one has a "rather simple and thoroughly consistent picture of a universe in which . . . the large-scale distribution of nebulae is uniform throughout the sample available for inspection." On the other hand, to assume that the shifts really indicate receding velocity forces one to adopt a very curious model of the universe. "The model is closed and very small—a large fraction can be observed with existing telescopes—and is packed with matter to the very threshold of perception—. The rate of expansion has been slowing down so that the past time scale is remarkably limited. In short, the necessary adjustments and compensations suggest that the model may be a forced interpretation of the data." In plainer language, this meant that Astronomer Hubble is now willing to abandon the expanding universe to mathematical cosmologists and philosophers, pending a further development of theory, or the erection in 1940 of Caltech's 200-inch super telescope, which may finally settle the question.