Why the sky is dark at night

FEB 01, 1974

In a universe uniformly filled with stars we would expect the sky to be ablaze with light from all directions, according to a 250‐year‐old paradox we are just beginning to understand.

DOI: 10.1063/1.3128443

Edward R. Harrison

Let us imagine that stars similar to the Sun are uniformly distributed in an infinite and static universe. Edmund Halley in 1720, J. P. Loys de Chéseaux in 1744, and H. Wilhelm M. Olbers in 1823 showed this seemingly reasonable 16th and 17th century model of the universe leads to a remarkable paradox. For whatever direction we look in the sky our line of sight eventually intercepts a star, and the whole sky should therefore be ablaze with light as bright as the Sun. This startling disagreement between theory and observation is nowadays referred to as “Olbers’s paradox.”

References

1. E. Halley, Phil. Trans. 31, 22 (1720, https://doi.org/PTRSAV
and E. Halley, 31, 24 (1720).https://doi.org/PTRSAV , Philos. Trans. R. Soc. London
2. J. P. L. de Chéseaux, Traité de la Cométe, Bousquet, Lausanne (1744); appendix II, page 223.
3. H. W. M. Olbers, “Ueber die Durchsichtigkeit des Weltraums,” in Astronomisches Jahrbuch für das Jahr 1826, (J. E. Bode, ed.) Späthen, Berlin (1823); page 110.
4. O. Struve, Sky and Telescope 25, 140 (1963).https://doi.org/SKTEA3
5. J. D. North, Measure of the Universe, Clarenden, Oxford (1965).
6. S. L. Jaki, The Paradox of Olbers’ Paradox, Herder, New York (1969)
and Am. J. Phys. 35, 200 (1967).https://doi.org/AJPIAS
7. H. Bondi, Advancement of Science 12, 33 (1955).https://doi.org/ADSCAH
8. H. Bondi, Cosmology, Cambridge U.P. (1960).
9. G. C. McVittie, Fact and Theory in Cosmology, Eyre & Spottiswoode, London (1961).
10. G. J. Whitrow, B. D. Yallop, Mon. Not. Roy. Astr. Soc. 127, 301 (1964) https://doi.org/MNRAA4
and G. J. Whitrow, B. D. Yallop, 130, 31 (1965).https://doi.org/MNRAA4 , Mon. Not. R. Astron. Soc.
11. G. C. McVittie, General Relativity and Cosmology, 2nd ed., University of Illinois Press, Urbana (1965).
12. D. W. Sciama, Modern Cosmology, Cambridge U.P. (1971).
13. S. Weinberg, Gravitation and Cosmology, Wiley, New York (1972).
14. See also popular texts: G. Gamow, Sci. Am., March 1954, page 54;
F. Hoyle, Frontiers of Astronomy, Harper, New York (1955);
D. W. Sciama, Unity of the Universe, Faber, London (1959);
R. A. Lyttleton, The Modern Universe, Hodder & Stoughton, London (1956);
G. J. Whitrow, Structure and Evolution of the Universe, Hutchinson, London (1959);
J. Singh, Great Ideas and Theories of Modern Cosmology, Constable, London (1961);
C. A. Rowan, Changing Views of the Universe, Macmillan, New York (1961);
W. Bonnor, Mystery of the Expanding Universe, Macmillan, New York (1964);
I. Asimov, The Universe, Avon, New York (1966);
P. W. Hodge, Galaxies and Cosmology, McGraw‐Hill, New York (1966);
E. Schatzman, Origin and Evolution of the Universe, Hutchinson, London (1966);
D. H. Menzel, F. L. Whipple, G. de Vaucouleurs, Survey of the Universe, Prentice‐Hall, Englewood Cliffs, N.J. (1970).
15. M. Scharzschild, Structure and Evolution of the Stars, Princeton U.P. (1958).
16. G. F. R. Ellis, E. R. Harrison, Comm. Astrophys. Space Phys. (in press).
17. E. R. Harrison, Nature 204, 271 (1964); https://doi.org/NATUAS
E. R. Harrison, Mon. Not. Roy. Astr. Soc. 131, 1 (1965).https://doi.org/MNRAA4
18. R. Weymann, Astrophys. J. 145, 560 (1966).https://doi.org/ASJOAB
19. A. Sandage, PHYSICS TODAY, February 1970, page 34.
20. W. Rindler, PHYSICS TODAY, November 1967, page 23.
21. W. B. Bonnor, Mon. Not. Roy. Astr. Soc. 128, 33 (1964).https://doi.org/MNRAA4
22. Discussed by R. Schlegel, Am. J. Phys. 26, 601 (1958).https://doi.org/AJPIAS
23. H. Bondi, T. Gold, Mon. Not. Roy. Astr. Soc. 108, 252 (1948).https://doi.org/MNRAA4
24. F. Hoyle, Mon. Not. Roy. Astr. Soc. 108, 372 (1948) https://doi.org/MNRAA4
and F. Hoyle, 109, 365 (1949).https://doi.org/MNRAA4 , Mon. Not. R. Astron. Soc.

More about the Authors

Edward R. Harrison. University of Massachusetts, Amherst.