Cosmology: A search for two numbers

FEB 01, 1970

Precision measurements of the rate of expansion and the deceleration of the universe may soon provide a major test of cosmological models

DOI: 10.1063/1.3021960

Allan R. Sandage

AS RECENTLY AS THE 1950’s about all that observational cosmology had succeeded in establishing was that galaxies exist and the universe expands. But beginning in the 1960’s a flood of new discoveries has enriched our picture of the universe and has begun to provide a basis on which to distinguish between competing cosmological models. There has been a 30‐year effort, now drawing to a close, to get precise measurements of two parameters that will provide a crucial test for cosmological models. The two key numbers are the rate of expansion (the Hubble constant $H_{0})$ and the deceleration in the expansion ${(q}_{0}).$ The hope is that current research, by determining the extragalactic distance scale for nearby galaxies and searching for exceedingly distant clusters where the redshift is large, will measure both of these numbers to a precision of 15%.

References

1. A. A. Penzias, R. W. Wilson, Astrophys. J. 142, 419 (1965).https://doi.org/ASJOAB
2. R. B. Partridge, American Scientist 57, 37 (1969).https://doi.org/AMSCAC
3. A. Sandage, Astrophys. J. 133, 355 (1961); https://doi.org/ASJOAB
Ya. B. Zeldovich, Advances in Astron. and Astrophys. 3, 242 (1965).
4. G. de Vaucouleurs, W. L. Peters, Nature 220, 868 (1968).https://doi.org/NATUAS
5. W. Baade, Trans. I.A.U. 8, 397 (1952).
6. P. Doig, J. Brit. Astron. Soc. 35, 201 (1925).
7. R. Kraft, Astrophys. J. 134, 616 (1961).https://doi.org/ASJOAB
8. A. Sandage, G. A. Tammann, Astrophys. J. 151, 531 (1968); https://doi.org/ASJOAB
A. Sandage, G. A. Tammann, Astrophys. J. 157, 683 (1969).
9. A. Sandage, Astrophys. J. 127, 513 (1958).
10. R. F. Christy, Astrophys. J. 144, 108 (1966); https://doi.org/ASJOAB
D. S. King, J. P. Cox, Pub. Astron. Soc. Pac. 80, 365 (1968);
R. S. Stobie, Mon. Not. Roy. Astron. Soc. 144, 461 (1969).
11. W. Baade, H. Swope, Astron. J. 68, 435 (1963).https://doi.org/ANJOAA
12. W. Baade (ed. A. Sandage), Astrophys. J. (to be published).
13. S. Kayser, Astron. J. 72, 134 (1967).https://doi.org/ANJOAA
14. J. Stebbins, A. E. Whitford, H. Johnson, Astrophys. J. 112, 469 (1950).
15. G. A. Tammann, A. Sandage, Astrophys. J. 151, 825 (1968).https://doi.org/ASJOAB
16. J. E. Solheim, Mon. Not. Roy. Astron. Soc. 133, 321 (1966).
17. H. P. Robertson, A. G. Walker, Pub. Astron. Soc. Pac. 67, 82 (1955).
18. J. B. Oke, A. Sandage, Astrophys. J. 154, 21 (1968); https://doi.org/ASJOAB
A. E. Whitford, Astrophys. J. (to be published).
19. A. Sandage, Astrophys. J. 134, 916 (1961).https://doi.org/ASJOAB
20. H. Spinrad, Pub. Astron. Soc. Pac. 78, 367 (1966).
21. J. B. Oke, Pub. Astron. Soc. Pac. 81, 11 (1969).
22. A. Sandage, Yearbk. Carnegie Inst. Wash. 65, 163 (1966);
J. V. Peach, Astrophys. J. (to be published).

More about the Authors

Allan R. Sandage. Mount Wilson and Palomar Observatories.