The edge of the universe

Distance does strange things to our perspective. Astronomers have found a galaxy at the astonishing distance of 13 billion light years. It was born soon after the Big Bang and since its light has travelled so long to reach us, we see it as it was just after it was born. So the image we see is of a very young galaxy, at the same time it is very old, 13 billion years to be precise. Viewing galaxies so far away in our ever-expanding universe, introduces several bizarre twists in understanding. The very old, yet young galaxy is one of the least bizarre. Another thing that happens when you look at something that far away is that it looks bigger than it should at that distance. At the same time it looks dimmer than one would expect. The reason for this is
that space has stretched the image all the way that it travelled, dramatically weakening the light and thus making the image dimmer than you would expect. But why does it appear bigger than you would expect?  This is because our universe expands and the speed at which it does this increases with distance. So when the light left this faraway galaxy, it was only about 3.35 billion light years away. Therefore it is logical that the image appears bigger than you would expect, the size of the image does not change over time. This also means that, although it took the light 13 billion light years to reach us, the galaxy is now actually 30 billion light years away and moves further away from us with increasing speed.

Now consider cosmic boundaries. The first stars or proto-galaxies might have formed as early as 100 million years after the Big Bang. Their size would be of an object just 1.2 million light years away, while their brightness would indicate the inconceivable distance of 1.2 trillion light years! Their actual distance would be about 38 billion light years. This roughly marks the edge of the visible universe, but objects do not end here. Most galaxies were so far away when they formed, that their light would never reach us anyway. This would mean that a large part of the universe lies “over the horizon” and where does that end? No one is sure, but it is likely that the universe was, is and always will be infinite.

This is difficult to grasp and it’s amazing that scientists have discovered so much about things that are so far away and a universe that is so big that we can’t even imagine it. This is one of the reasons astronomy fascinates me so much.

Regards from the bush
Miriam