Here's a question I would bet you've never pondered: Why is the nighttime sky dark?

Now before you exclaim, "Because the sun has set, you dolt!" and accuse me of having way too much free time, let's actually think about this for a moment. In the evening, the sun sets. Or, more accurately, our part of planet Earth turns away from the sun. Without sunlight to illuminate our atmosphere, the sky becomes dark and the much fainter stars appear. The end. Right?

Not so fast. If the universe is infinite, as early astronomers and natural philosophers believed, then our sky should never become dark.

Think about it this way. Imagine that stars are evenly distributed on crystalline spheres, much like the layers of an onion, which surround us. Let's say, for example, on the sphere closest to us, stars appear nice and bright. The shell twice as distant would also contain stars, but each would appear four times fainter; those on the shell three times farther would appear nine times fainter, and so on.

It might seem easy to conclude that, because the most distant stars would be so terribly faint there would be no way we could see them. But remember that, with the increasing shell sizes come more stars. And, while stars on the shell twice as distant are four times fainter, there are also four times as many of them. On the shell three times farther, there are nine times as many; and so on.

In other words, each shell would contribute exactly the same amount of starlight to our sky, no matter how far away it is. And an infinite number of stars — and shells of stars — would produce a nighttime sky as bright as the sun itself!

It's a mind-bender, to be sure. This apparent contradiction between theory and reality — now known as Olber's Paradox — is named after Heinrich Olber, who tried to explain it in 1826. Interestingly, it's still being pondered today. The explanation could be as simple as there not being an infinite number of stars, or as profound as an infinite universe having an origin, and the light of the most distant stars hasn't yet had time to reach us.

Whatever the answer, go outside tonight and gaze skyward. You might find that the dark nighttime sky now takes on a totally new meaning.

To find out more about Dennis Mammana and read features by other Creators Syndicate writers and cartoonists, visit the Creators Syndicate website at www.creators.com.

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