How old was the universe when the light of the Big Bang went out?

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Dan Kuehn

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Dan Kuehn asked the Naked Scientists:
Hi from New Mexico,

I've listened to all your shows - thanks for posting to iTunes U. 

Questions, questions...

Why do we say the most distant galaxies are moving away from us, the farthest moving fastest, when if fact, if we're the newest thing we can observe, then it must be us who are moving away and accelerating, even though we perceive ourselves always at the centre?

Conversely, isn't it true that somehow all those extremely distant galaxies, seeing them 13 billion years ago, are not so much moving away from us but converging, towards whatever is at the beginning, yes?

If we could see even further, the entire sky would be filled with the light of that original dense crush of the simplest stuff.

How old was the universe when the light of the original miasma winked out, as spacetime began to inflate faster than the speed of light?

I love to make my head spin.

Thanks for a great show,


What do you think?
« Last Edit: 26/11/2011 08:30:02 by _system »


Offline Soul Surfer

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I cannot answer your questions specifically because your misunderstandings are complex and would take too long.  Can first I try to clarify what is going on

The first point is that just our point if view.  Anybody living on a planet round a star in any galaxy right out to the furthest would see and could say exactly the same thing so no one has a special position.

The second important thing to remember is that the galaxies everywhere are moving around with respect to their neighbours at much the same sorts of speeds (well below the speed of light).  What is creating the perceived motion is that space itself is expanding with time and it is the expansion or creation of new space that is the main feature of the big bang.

We can see the light of the "simplest stuff" as you say it is called the cosmic microwave background and if we could see it it would be quite bright.  Someone suggested that it would be like moonlight!  when it formed it was as bright as the sun and about the same colour it has just been red shifted by a factor of one thousand by the expansion of space ever since it happened around 13 billion years ago so it is now radio waves.

Finally all this happened around 300-500 thousand years after the instant of the bang itself when the universe had cooled down to the surface temperature of a star.  The reason for this is critical because it is the same reason why stars emit light and why we use it to see by.  This is the temperature at which most atoms start to loose and regain electrons and form what is known a a plasma and until  the universe and stars coo below this temperature they are not transparent .

If you want to look at the full time line of the big bang according to currently favoured theories look at

when you talk about inflation that occurred much earlier as you will see from the reference.

Learn, create, test and tell
evolution rules in all things
God says so!