THE MODERN VIEW

Wanganui Chronicle, Volume 75, Issue 140, 16 June 1932, Page 9

THE MODERN VIEW

SCIENCE AND COSMOS THE THREE UNIVERSES WIDER CONCEPTIONS The universe, as viewed by the astronomers of thirty years ago, was a comparatively small affair. Comparatively small, we say; in reality, immensely great. Professor Simon Newcomb. the eminent American astronomer, one of the greatest authorities on the subject, brought out in 1901 a book entitled “The Stars: A Study of the Universe,” in which he summed up all that was then known and surmised. He concluded that “that collection of stars which we call the Universe is limited in extent, with a diameter of three thousand light years” —a light year being roughly six billion miles; and he admitted at the same time that “far outside of our Universe there may be collections oi stars of which we know nothing.” says the astronomical correspondent of the Manchester Guardian. Since then knowledge has grown from more to more, and the problem has been attacked from several standpoints, with, a great measure of success. There arc three different methods by which the problem can be tackled. The astronomer can work outwards from the earth and the solar system, getting first the individual distances of the nearer stars, then the average distances of the more distant. Or be may work from without inward—that ie to say, he may seek by getting the distances of very distant objects to get a kind of skeleton-image of the system and fill in details bit by bit. Or he may proceed from theoretical and mathematical considerations. As a result of the use of these different methods we have now three cosmological concepts —called, for brevity, the Kapteyn Universe,” the “Shapley Universe,” and the De Sitter Universe.” From Two Men. It would be more correct to apeak of the “Kapteyn-Van Bhijn Universe,” for the concept is due to both. Jacobus Cornelius Kapteyn was one of the half-dozen greatest astronomers of the last generation. For over forty years he filled the Chair of Astronomy in the University’- of Groningen, Holland, and for quarter of a century directed the famous astronomical laboratory there. He died in 1922. During the last aLx or seven years of his life he had the assistance of a brilliant young astronomer, Pieter Johannes Van Bhijn, who now occupies the Chair and presides over the Laboratory.

These two astronomers, getting tho average distances of stars of any given magnitude, worked outwards from the sun as centre and were able to determine the star-density in the stellar system. They found, that the stars thinned outward gradually, but they were able to throw out their surrounding line to a distance of nearly 5090 light years. “In the di* rection of the pole of the Galaxy,” they write “this brings us to what many will be inclined to take as practicaily the limit of the system. In any direction along the plane of the Milky* Way this same limit, must be eight times more distant.” The 1 ‘Kapteyn-Van Rhijn Universe.” therefore, is a vast, disc-shaped cluster of stars with a thickness of about 10,000 light-years and a diameter of about 70,000. But it is quite evident that this is by no means tho whole universe. Apart from tho globular clusters and the spiral nebulae it leaves out of account tho more distant star-clouds of the Milky Way. The “ KapteynVan Rhijn Universe,” as the latter himself admits, represents simply that part of the stellar system which can be investigated by statistical methods. The “Kapteyn-Van Rhijn Universe.” indeed, appears, to be but a small pa T t of the “Shapley Universe.” Shapley’s View. Dr. Harlow Shapley, from whom the “Shapley Universe” takes its uame is by common consent the greatest of modern American astronomers. A native of Nashville. Missouri, where he was bom 45 years ago, Dr. Bhapley after a brilliant student darter was for seven years observer at Mount Wilson, California, where he had the use of the great 60in. reflector, then the greatest telescope in the world. For the past teu years Dr. Shapley has been Professor of Astronomy at Harvard College and director of the world-famous observatory there. Eighteen years agu Shapley began the study of the remarkable and comparatively rare class of objects known as the globular clusters. By means of new methods of measurement, based on thp period-luminosity law deduced from the behaviour of certain variable stars called Cepheids, Shapley was able to get the distance of pighty-six of these clusters. He found these distances to range from 20,000 to 220,000 light-years. Further, he found that they formed a great ellipsoidal system divided by the plane of the Milky

I Way. and remarkably enough, that • the plans of this system of globular clusters correspond with that of the Milky Way. “We naturally infer that the galatic system and the assemblage of globular clusters are co-extensive. and that the centre of the two systems may be the same.” Studies of the distant star-clouds of the Milky Way also con vinced Shapley of the vast extent of the stellar system, and so he reached the conclusion that the stellar system is really an assemblage of smaller systems —local clusters to one of which the sun belong. The extent of this system, or systems, is 3000 light years, and the thickness about .10,000; and it is ringed round by a hundred smaller sub-systems the globular clusters, dependent on and subordinate to the greater system. This was the original “Shapley Universe.” but within the last few years Shapley has been studying the distant objects misnamed spiral nebulae. These are independent stellar systems, at distances from 1.000,000 Light years from the earth. He has fixed the distance of the “Coma-Virgu system” as 10,000.000, and of the Centaurus system as 100,000,000 light years. The Shapley Universe has recently been extended by Dr. Hubble of Mount Wilson. Working along the same lines, he finds that about two million galaxies exist within a distance of 140,000,000 light years from tho sun. De Sitter’s Universe. Altogether more awe-inspiring than the Kapteyn or Shapley Universe is the De Sitter Universe. Dr. William De ISitter, a former assistant to Kapteyn, is now Professor of Astronomy in the University of Leyden. He is first and foremost a mathematician, and has come into the public eye of late years by reason of his work in developing the Einstein theory. For that be received a year ago the Gold Medal of the Royal Astronomical Society. The picture of the universe which De Sitter unfolds to us in the result of deductions from the Einstein theory as to the amount of matter in the universe and the distribution of it. The space-time universe, finite yet unbounded, is, according to De Sitter, two thousand million light years in radius, a distance fourteen times as great as the distance of the most distant object photographed by the lUUinch reflector at Mount Wilson. This universe, De Bitter maintains, consists of 80,000 million galaxies. Dr. A. C. D. Crommelin, in a recent outline o£ De Sitter’s theories, remarks that “au electron bears about the samo proportion to a pin-bead that, the pin-head does to tho sun or the sun to the galactic system. . . . But the ratio of the diameter of space is much larger, say. 1 to 40 000; thus the tightness with which galaxies are packed in space is much greater than that with which protons and electrons are packed in the stars, or even in the pin head, or than stars are packed w each galaxy,” The “Kapteyn Universe” would appear to consist of our local cluster and perhaps some adjacent systems — a comparatively small part of the stellar system. The “Shapley Uni* verse” consists of the stellar system — —“our galaxy’’ —and adjacent galaxies. But this is a very small part of the much greater De Sitter Universe. According to Van Rhijn, the stellar population of the Shapley Universe, irrespective of the globular clusters, is about 30,000 million. Inclusive of tho globular clusters, it will be considerably greater, but as our stellar system seems to be a bit above the average in size and population we may take 30,000 millions as a fair estimate of the average population of » galaxy. We have to multiply this huge figure by 60,000 million to get a minimum estimate of the number of blazing suns in the whole De Sitter Universe.