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.”

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References

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More about the authors

Edward R. Harrison, University of Massachusetts, Amherst.