If we had a telescope powerful enough to see all the way back to the Big Bang, what direction should we point it?

04 April 2017

Question

If we had a telescope powerful enough to see all the way back to the Big Bang, what direction should we point it?

Answer

We put Richard's question to University College London cosmologist Andrew Pontzen...

Andrew - Well, the great news is we pretty much do have telescopes that are powerful enough to see. Maybe not all the way to the big bang because right after the big bang the universe was sort of opaque so, if you try and go too far back towards the big bang, then you can’t see any further. But, just a few hundred thousand years after the big bang, the universe went transparent and light that was around at that time has remained within the universe, has been travelling ever since, remained within the universe and we can pick it up with telescopes today.

So this question of what direction should you point those telescopes in is a very good one, and the answer to the actual question is any direction. Because, although you might think of the universe as expanding out in a big bang from a tiny point actually, as far as we can tell, the entire size of the universe could be infinite. So, even if the universe has got an awful lot bigger since those very early days, even in the early days it was still infinite because, if you make infinite smaller, it’s still infinite. So it doesn’t really matter what direction you point a telescope in you are still looking in a direction that was there during the big bang.

Chris - Can you just elaborate a little bit on what you mentioned at the start when you said the universe was opaque and then it became transparent? What did you mean by that?

Andrew - If you imagine a very foggy day, you can’t see very far and the physics behind that is that any light that we call “light photons” - it comes in little packets of energy called photons, and those individual photons keep bouncing around. They are essentially bouncing off water droplets in the case of a foggy day. In the early universe, essentially it was the equivalent of a foggy day except it wasn't water droplets it was electrons, little particles called electrons that were making the light all bounce around. So, for that reason, you couldn’t see any further than this fog that you can’t see past.

Chris - Why did that clear, that fog?

Andrew - It cleared because as the universe expands it cools down and, when the universe gets cold enough,  there’s not enough energy to keep those electrons flying around and they get dragged into protons and they start forming what we recognise today as atoms. So the electrons are no longer whizzing around and no longer able to intercept the light.


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