by Dave Adalian
Why is the night dark?
It sounds like one of those questions you have to be stupid to ask, but the answer can lead to a deeper understanding of how our universe works.
To be fair there is more than one answer because there’s more than one reason the sky at night is dark. The obvious reason is that at night we’re on the far side of the planet from Sol in the shadow of the Earth, so it’s dark. Simple.
But, why isn’t the night sky lit with all the shine from the uncountable number of stars aglow in the heavens? It’s the answer to this second question that’s revealing to the inquisitive mind.
If we lived in a finite universe with an even distribution of stars endless daylight is exactly what we’d see. Because the energy would have nowhere to escape, the stars would warm their surroundings until the entire universe glowed evenly with their heat.
But, that isn’t what we see.
It wasn’t until 1829 that it occurred to astronomer Charles Olbers to ask why the night is dark, and he was promptly ignored. No one had an answer for him then.
One hundred years later, another astronomer, Edwin Hubble, noticed the farther away from us an object is the more its light is distorted when it arrives here. The distortion is caused by speed, and the farther away something is the faster it appears to be traveling. The universe, Hubble had discovered, is expanding at an ever greater rate.
So what?
So imagine a party with 200 people in your living room and more on the way. There would be activity everywhere you looked, someone doing something, laughing, drinking, dancing, talking. You’d be overwhelmed like dim starlight on a bright day.
Imagine that same party in an airplane hanger and the place would seem practically deserted, dark and empty.
Now, what if your living room got bigger every time a new guest arrived? No matter how large and raucous the party became your living room would never seem crowded and the guests would never overfill it.
Strange as it seems, that’s how the universe appears to operate. The older the universe gets the larger it grows, and if we had stopped to think about why the sky at night isn’t filled with starlight, we’d have figured this out years before Hubble actually did it.
And, that is why it’s important to ask stupid questions.
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This column originally appeared in the Visalia (Calif.) Times-Delta and Tulare (Calif.) Advance-Register.
