The Naked Scientists

The Naked Scientists Forum

Author Topic: How can astronomers 'look back in time'?  (Read 4121 times)

Offline Hop Harrigan

  • First timers
  • *
  • Posts: 2
    • View Profile
How can astronomers 'look back in time'?
« on: 18/08/2011 11:56:02 »
Hi,
I hear astronomers say that using more and more powerful optical and radio telescopes they are able to 'look back in time', possibly even as far as the big bang.
How can this possibly be true? All the matter and all the light in the universe originated at the big bang. The universe has (and still is) expanded since this point. However the speed of the expansion of the mass in the universe must be slower than the speed of light or we would be infinitely heavy. This means that the light from the instant of the big bang would have passed the mass from the big bang in the first nano seconds of the event and is currently much further away from the origin of the big bang than we are (earth). So 'looking back' at the big bang is meaningless huh?


 

Offline graham.d

  • Neilep Level Member
  • ******
  • Posts: 2208
    • View Profile
How can astronomers 'look back in time'?
« Reply #1 on: 18/08/2011 13:06:04 »
Hop, this is quite a tricky subject and is not helped by some simplified media explanations. The big bang is not just a big explosion in an empty space but the start of space-time itself. Space is itself expanding and it is thought that there are distant regions of space-time expanding away from us with a redshift that would imply speeds greater than lightspeed. This view is a result of an incorrect and simplified view of the cosmological model of the universe. It would not be consistant with Special Relativity but is consistant with General Relativity. These regions of space will be forever unknowable to us. The big bang is also not thought to be a single event but a rather stuttered affair. This is expained here:
http://en.wikipedia.org/wiki/Inflation_(cosmology)
 

Offline Hop Harrigan

  • First timers
  • *
  • Posts: 2
    • View Profile
How can astronomers 'look back in time'?
« Reply #2 on: 18/08/2011 15:18:28 »
Hi Graham, thanks for the explanation. Do I take it that this also means that we cannot identify a 'place' or a  'direction' in space where the big bang initiated? ie the red shift is the same in all directions and not greater in the 'direction' of the bang itself?
 

Offline graham.d

  • Neilep Level Member
  • ******
  • Posts: 2208
    • View Profile
How can astronomers 'look back in time'?
« Reply #3 on: 18/08/2011 16:42:05 »
Hi Graham, thanks for the explanation. Do I take it that this also means that we cannot identify a 'place' or a  'direction' in space where the big bang initiated? ie the red shift is the same in all directions and not greater in the 'direction' of the bang itself?

Yes, correct. It is a feature that is demonstrated by the Cosmic Microwave Background which confirms the the universe looks (more or less) the same in every direction.
 

Offline Soul Surfer

  • Neilep Level Member
  • ******
  • Posts: 3345
  • keep banging the rocks together
    • View Profile
    • ian kimber's web workspace
How can astronomers 'look back in time'?
« Reply #4 on: 24/08/2011 09:47:12 »
The simple fact is that light travels at a finite speed and it takes time to reach us.

We see the sun as it was 8 minutes ago

The nearest stars as they were a few years ago

Local galaxies as they were a few million years ago

Remote galaxies as they were a few billion years ago

Now most of this is not important because the universe was very much the same then.  However when you start looking back more than one billion years things were different and this starts to show up in what can be seen.  There were more active quasars and galaxies were much messier and less well organised and of course  as stated above you can get right back to the microwave background which was in fact at the time like a monster flash of starlight when the whole universe was like the surface of a star.

Proving that things had changed with time was the main element in disproving the well favoured continuous creation theory was wrong and the big bang was right back in the late 1950s and 60s when I was young.
« Last Edit: 24/08/2011 09:52:09 by Soul Surfer »
 

The Naked Scientists Forum

How can astronomers 'look back in time'?
« Reply #4 on: 24/08/2011 09:47:12 »

 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums
 
Login
Login with username, password and session length