Cosmic Mysteries: What’s at the edge of the universe?

Strange as it may sound, there’s technically no edge

Our universe is constantly expanding and, based on observations in the last two decades, we think it’s getting faster and faster. That begs the question: what’s it expanding into, and what is at the edge?

Well, that’s where things get a bit tricky. Technically, there is no edge of the universe. From our galaxy, we can see a finite distance (about 46 billion light years), which is the most distant light that has travelled to us since the Big Bang. We call this the observable universe, meaning it spans about 92 billion light years in total. But beyond this barrier, there may well be more space, more galaxies, more stars and more planets. Unfortunately, because light has a finite speed, we will never see beyond this limit.

As the universe is expanding, that means galaxies are also getting further and further away from each other. A common analogy is imagining each galaxy as a dot on an expanding balloon. From our position, it looks like all the galaxies are moving away from us. But if you were in any other galaxy, even the most distant one we could see, you would notice the same effect. There is no edge of the universe – space itself is just simply expanding. And it’s not expanding into anything, it’s just growing.

That’s quite hard to fathom; there’s no easy way to wrap your head around it. That’s why it truly is a bit of a cosmic mystery.

Studying the edge 

The most distant galaxy we’ve ever seen is GN-z11. The light from this bright infant galaxy shows it as it appeared 13.4 billion years ago, just 400 million years after the Big Bang. We measure galaxies at the edge by observing their redshift, which is the change in their light as they move away from us. However, this is not technically the furthest thing we can see. We can actually see remnants of the universe as it appeared 380,000 years after the Big Bang. Known as cosmic microwave background (CMB) radiation, this is the heat left over from when the universe went through a period of rapid expansion and then cooled.


This article was originally published in How It Works issue 99, written by Jonathan O’Callaghan 


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