Astronomy Edwin Hubble Essay Research Paper THE — страница 7

his proportionate influence nearly unparalleled in modern astronomy. (2). The most curious impression we are left with is his lack of comment on the significance of the redshift phenomenon, which is surely one of the most important discoveries in science. In none of his writings did Hubble comment on the central importance that the form of the redshift-distance law is linear. This single feature is most crucial for the standard model. Heckmann (1942) was perhaps the first to emphasize the singular significance of the linear form. A linear velocity field has two fundamental properties; (a) each observer sees the identical form and expansion rate from any vantage point, and (b) it is the only velocity field that permits all points in the manifold to be “together” at some time

in the past. Discovery of the linear form is usually taken to be as important as the discovery of the expansion itself if the phenomenon has any relevance to “the creation of the universe”. But hardly any hint of this appears in Hubble’s writings, despite his discovery of the linearity. There is also a lack of discussion of how the expansion relates to “beginnings” – a topic emphasized so strongly in modern cosmological writings. We simply do not know if Hubble was impressed with his discovery in these ways. The second puzzling omission is a lack of emphasis on the meaning of the numerical value of the expansion rate (i.e. the Hubble constant). In an expanding model with a singular point, the inverse Hubble rate is related to the age of the model, the exact function

depending on the deceleration. Credence that we are dealing in the redshift phenomenon with an aspect of “a creation event” requires that the “Hubble time”, obtained from the inverse “Hubble constant”, be the same as the “age of the universe” determined in other ways. We are so used to talking in this way that it is surprising to see none of this in Hubble’s writings. Of course, it is true that the three types of cosmological time scales were not well known in Hubble’s time. These are (a) the Hubble time, (b) the age of our Galaxy via its oldest stars, and (c) the age of the oldest chemical elements. The method to age-date the stars had to await the understanding of the Sch?nberg-Chandrasekhar (1942) limit as a departure of evolving stars off the main sequence

of the Hertzsprung-Russell diagram, an understanding that came only by the developments in stellar evolution in the early 1950s. The age of the chemical elements, although known in principle in about 1910 by Rutherford based on the first understandings of radioactivity, was not worked out in detail until, also, the decade of the 1950s. What we take for granted in the current work that is organized to test the agreement of the three time scales to within say 20 per cent was not possible in Hubble’s time. Nevertheless, it remains a curiosity that Hubble did not strongly emphasize the problem publicly, or, if at all, even privately to himself. There was, of course, the embarrassment that the inverse of the Hubble expansion rate (i.e. the Hubble time) was only two billion years on

Hubble’s 1930 to 1953 distance scale whereas the Earth was believed to be a bit older than three billion years even in 1936. It was left to the inventors of the steady state cosmology to emphasize this discrepancy of time scales, pointing out that any of the Friedmann models (sans cosmological constant) that were used to espouse a “beginning” could not be true. The influence of Hubble was so great that errors in his 1930/1936 distance scale were considered to be out of the question in his time. The discrepancies began to appear only when the 200-inch Palomar reflector was put into operation in late 1949 by the heroic and largely unheralded two-year effort by I. S. Bowen. Baade began obtaining data which showed that Hubble’s scale must be modified. We now know that the

scale must be stretched by a factor of a least 5, more likely by a factor a bit larger than 10. But it must be fairly pointed out that some astronomers, not believing that the problem of the distance scale has been solved by the results of the 200-inch programme from 1950 to 1980, have suggested that the value of the Hubble constant can be determined to the satisfaction of the sceptics only by the future use of the Hubble Space Telescope. For this one suspects that Hubble might have been pleased