When scientists start pondering the bizarre nature of infinity in nature, some perplexing things start happening. If the universe extends infinitely in any given direction, and there are infinite stars, then the night sky should be as bright as the sun.

The concept of this paradox essentially breaks the sky into sections or points in order to account for stars at varying distances from Earth. Assuming an even distribution of stars throughout the sky, there would be 100 times the number of stars at a given point at 10 times the unit of distance. This slightly confusing mathematical proposition boils down to the conclusion that every point, regardless of the number of stars, should collectively be the same brightness.

We can trace the origins of this paradox all the way back to Kepler in 1610, though it wasn’t popularized until the 19th century by Heinrich Olbers, a German Astronomer. In large part, the paradox demonstrates a proof that the universe is not static nor infinite.

Since we do know that the night sky isn’t as bright as a star in every location, we’re left with many questions that aren’t as easy to answer as you might think.
Explaining The Darkness of the Sky

Astronomers and scientists have to explain Olbers’ paradox in 5 possible lines of thinking:

1. Dust is obscuring distant stars, causing dark spots.
2. There are in fact, not an infinite number of stars.
3. Stars aren’t evenly spaced across the universe.
4. The universe is expanding, so distant stars disappear thanks to redshift.
5. The universe is too young to see the most distant stars.

Addressing these in order, we’re left to understand how cosmic dust might obstruct parts of the sky and create the illusion of “darkness” here on Earth. While the theory of dust blocking light makes sense here on Earth, in space, dust that would block or absorb the light energy from distant stars would itself start to glow or produce light. This is the reason why nebulae glow when they don’t have any internal energy source.

Assuming then that the universe has a finite number of stars is a valid conclusion, but it doesn’t solve the paradox. It could theoretically be possible that the universe has a finite number of stars, but just the number of stars we can see in the observable universe is enough that the night sky should be fully illuminated. Astronomers currently estimate there are 100 thousand million stars in the Milky Way alone and roughly 10^24 stars in the entire universe. While that number isn’t infinite, it’s enough that it doesn’t explain the paradox.

Next, we move on to ponder whether maybe the stars aren’t evenly spaced across the universe. Perhaps they group together and form clusters that look like singular stars in our night sky? This solution is the first that could be correct. There’s no definitive reason to think that stars would be evenly distributed and perhaps they do in fact clump together leaving large chunks of dark sky.

However, just like that question you annoyingly got wrong on that high school science test, that answer isn’t the most correct.
The Likely Solution

In 1929, Edwin Hubble discovered that the universe is expanding, leading way to the understanding that the universe is likely finite in nature. Part of the way Hubble made this discovery was by realizing that we can measure the speed at which things are moving away by focusing on how the wavelength of their radiation has shifted. This is known as Redshift.

We understand that galaxies that are further away from us are moving faster, so it’s possible – if not probable – that their light has been redshifted far down in the light spectrum no longer visible to the human eye.

Coupled with this likely solution, it’s also probable that the universe as a whole is too young to see the most distant stars. Essentially, the universe is only an estimated 13.7 Billion years old, so we wouldn’t be able to see any objects further away than 13.7 Billion light years. This means that our observable universe is as far as we can see and the darkness comes from the absence of the light we can’t see.

These two final propositions to explain the darkness, redshift and a “too young” universe present the most likely solutions to Olbers’ Paradox.

Now, thanks to Olbers’ Paradox, the next time you look up at the night sky, you’ll wonder not about the beauty of the stars you can see, but about the beauty of those you can’t.

Edited by Gaurav Mishra
Written by Trevor English

Music: Break Through by Tom Fox

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