How big is the universe?

Humans have a long history of looking to the stars. As a race, we have curious fascination with the unknown: the vast expanse of space is about as unknown as you can get. Modern telescopes have expanded our view, but the universe hasn’t given up all of her secrets yet.

One of the most basic features of the universe, its size, is still an enigma. As we look up above, we can see lots of darkness peppered with stars. We know that it is big, but how big is it? Well, scientists don’t always agree. The trouble is that we can’t see that far.

How do we see the stars?

Though we might not be able to see any end to the universe, we can see lots of closer objects: like stars, planets, and asteroid belts. But, when you see the twinkle of a star, you are not really getting a “live” view. The star is so far away, that the twinkle that you are seeing may have happened years ago!

Light is really slow.

Here is what happens when a star twinkles: Deep out in space, the star decides to send out a flash of light. This star is 2 light-years away from earth. The light from this twinkle shoots out into space in all directions. The tiny light particles (called photons) headed in earth’s direction speed toward earth at the speed of light. But, this star is so far away from earth, it takes the photons of light 2 years to reach earth. After this 2 year journey, this photon reaches the eye of a curious star-gazer on earth enjoying the twinkling star.

We can only see anything once the light gets to earth

This presents a problem for astronomers trying to find the size of the universe: we can only see something in space once light from the object reaches earth. The twinkling star in the sky could explode, and we wouldn’t know about it for 2 years!

This is a picture of a star explosion, called a supernova.

The universe isn’t very old

Scientists currently estimate that the universe is about 14 billion (that’s a thousand thousand thousand) years old. This means that the first photons of light were first formed 14 billion years ago. Because light is so slow, some photons formed at the beginning of the universe are just reaching earth now.

Herein lies the problem: we can’t see anything further than 14 billion light-years away. Any further than that, and the light just hasn’t arrived to earth yet.

So how big is the universe?

This question is still open to debate. For the most part, your guess may be as good as most physicists’ guess.

What we do know is that the universe continues for at least 14 billion light-years in every direction around earth. Past that, we just can’t see anything yet. The furthest object we have seen is the Abell 1835 IR1916 galaxy, which is 13.2 billion light-years away.

What do you think?

Do you think the universe is infinite? Is our universe the only one? Leave your thoughts in a comment below.

( star photo credit: Zach Dischner; supernova photo credit: DJ Quietstorm)