Why is Space Black?

We all know that Space is huge. It’s so huge that you can even say it’s infinite. Which means if you look in any direction, you’re basically looking at a star!

So the light coming the stars should illuminate the night sky and it shouldn’t be dark or black in color. So why is Space black?

This is exactly what Heinrich Wilhelm Olbers (a german astronomer whose name I can’t pronounce correctly) asked in 1823. We call this the Olbers paradox!

The paradox goes like this: if the Universe is infinite, static and has existed forever, then everywhere you look should eventually hit a star.

But we know this is not the case!

So by proposing this paradox, Olbers knew the Universe couldn’t be infinite, static and timeless. It could be some of these, but not all three.

In the 1920s, Edwin Hubble discovered that the Universe isn’t static. In fact, galaxies are speeding away from us in all directions.

This led to the theory of the Big Bang, that the Universe was once gathered into a single point in time and space, and then, expanded rapidly. Our Universe has proven to not be static or timeless. And so, the paradox was SOLVED!

Well, not exactly! There are stars all around so we should still be seeing a bright sky at night. But we don’t.

This is because, as the Universe expanded, the wavelengths of that initial visible light were stretched out and out and dragged to the wide end of the electromagnetic spectrum until they became microwaves.

This is Cosmic Microwave Background Radiation. And yes we can detect that in every direction we look in.

So Olbers was right. If you look in every direction, you’re seeing a spot as bright as a star, it’s just that the expansion of the Universe stretched out the wavelengths so that the light is invisible to our eyes.

And that’s exactly why we see a black or a dark sky at night 🙂