Shedding some light on the dark night sky

Why is it dark at night? Oh sure, the sun is on the other side of the earth. But if the universe is infinitely large, holds an infinite number of stars, is homogeneous and static, the night sky would be luminous. Wherever you looked there would be another star to light up the sky. 

Honestly, don’t people who come up with this kind of stuff have a job to do or something? When I sit around and make up stories that are patently not true, I’m called a liar. Personally, I prefer using the term historical fiction.

Obviously the night sky is dark. All you have to do is look. So one or more of the above assumptions must be false. This quandary is known as a paradox, where logical conclusions are contradictory of fact.

My wife could argue that my life is a paradox because my logical conclusions are usually inconsistent with the facts. You may wonder why she stays. I do. I think the truth is that she is secretly an adrenaline junkie.

The “dark sky paradox” is commonly attributed to the German amateur astronomer, Heinrich Wilhelm Olbers, who described it in 1823. It is often called the “Olbers’ Paradox” in his honor. That is, if it is an honor to come up with stuff that is paradoxical. 

The first person to suggest a solution to Olbers’ paradox was Edgar Allan Poe. Oh, yes, the poet! He pointed out that either some stars must be so distant that their light has not reached us, or that some stars were still moving away from us at a high rate of speed. Of course, he didn’t know about the Big Bang or the “speed of light” in 1849. So his was an impressive observation. 

Poe published his proposed solution in a book-length work entitled “Eureka” in 1849, shortly before he died. It is one of his lesser-known works, probably because it was his only venture into cosmology and astrophysics. That’s hard to understand, though, because cosmology is such a big seller in the book world.  Anyway, he pointed out that since the universe is finitely old and the speed of light is finite, only finitely many stars can be observed within a given volume of space visible from Earth. The density of stars within this finite volume is sufficiently low that any line of sight from Earth is unlikely to reach a star.

The Big Bang theory introduces a new form of the paradox. Following the Big Bang, assuming there was one, the universe was basically filled with dust. As the dust settled and the universe became transparent, all points of the local sky in that era would have been of comparable brightness to the surface of the sun, making the entire sky light. 

Hello! It’s dark out at night. Darkness, then, is claimed to be evidence that the universe is not infinitely large, doesn’t have an infinite number of stars, or is not homogeneous and static. Well, that narrows it down quite a bit. 

Of course, we believe now that the universe is not static but expanding because of the initial explosion. However, knowing this does not change the paradox of a dark night sky significantly. Numerous explanations have been proposed, although unless you are one of the proposers, none of them is completely satisfactory. It is a little disconcerting when we discover that science can’t explain why it’s dark at night! 

Poe’s explanation may not be right. Scientists like to point out that his book, “Eureka,” does indeed evoke some modern scientific thought, but it does so in a very blurry way. I think it’s just professional jealousy. I mean, for Pete’s sake, Poe was a poet, not a scientist. 

Admittedly, considering the source, Poe’s ideas may have been drug-induced. Maybe cosmologists could use a little help in this same manner. Their present theories are only about that useful.

Gary McCallister, .(JavaScript must be enabled to view this email address), is a professor emeritus of biological sciences at Colorado Mesa University.


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