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Author Topic: Seeing into the past....  (Read 5343 times)

Offline dentstudent

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Seeing into the past....
« on: 20/06/2007 07:57:57 »
Please help me understand this. Astronomers can look back in time the further away from earth they look due to C. If you are looking at the light from an object at the very edge of the known universe, the light will be representing how and where it was 13.7 billion years ago. If we can see these objects all around us, and all these objects are showing where they where 13.7 billion years ago (ie, a VERY long way away) is there not a paradox with where they should have started 13.7 billion years ago in the Big Bang, in one central place? If we can "see" back 13.7 billion years to when the Big Bang occured, shouldn't they all be in the same place?

(I'm aware that we can "only" see back about 12.8 - 13 billion years at present)


 

Offline DoctorBeaver

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« Reply #1 on: 20/06/2007 08:02:29 »
I asked a similar question a while back. I'll see if I can find the thread.
 

Offline DoctorBeaver

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Offline dentstudent

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« Reply #3 on: 20/06/2007 08:20:53 »
I asked a similar question a while back. I'll see if I can find the thread.

I see I'm going to have to get up earlier in the morning!
 

Offline Soul Surfer

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« Reply #4 on: 20/06/2007 23:32:08 »
Although they are in different directions they are in some ways closer together even if they are not in exactly the same place.  it is very difficult to visualise though.

Remember it is space itself that is expanding with time not things moving apart like an explosion. 

Consider a three dimensional grid of dots each one centimetre apart extending out indefinitely in all directions.  Let that represent the universe as it was a long time ago. Coming forward to now after the universe has expanded a lot close to us, these dots are now ten metres apart but as we look at the grid further and further away we can see dots on the grid at a great distance. looking down one of the lines into the distance and the past we would see them getting closer together like railway lines vanishing into the distance but as we are also looking into the past they ARE getting closer together and when we get back to the time when the dots were 1cm apart they ARE 1cm apart even though they are all around us.

« Last Edit: 21/06/2007 10:10:38 by Soul Surfer »
 

Offline DoctorBeaver

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« Reply #5 on: 21/06/2007 09:37:04 »
 ???
 

Offline dentstudent

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« Reply #6 on: 21/06/2007 09:52:16 »
Although they are in different directions they are in some ways closer together even if they are not in exactly the same place.  it is very difficult to visualise though.

Remember it is space itself that is expanding with time not things moving apart like an explosion. 

Consider a three dimensional grid of dots each one centimetre apart extending out indefinitely in al directions.  Let that represent the universe as it was a long time ago. Toming back to now after the universe has expanded a lot close to us these dots are now ten metres apart but as we look at the grid further and further away we can see dots on the grid at a great distance. looking down one of the lines into the distance and the past we would see them getting closer together like railway lines vanishing into the distance but as we are also looking into the past they ARE getting closer together and when we get back to the time when the dots were 1cm apart they ARE 1cm apart even though they are all around us.



Nope - didn't get that......could be me though....
 

Offline Soul Surfer

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« Reply #7 on: 21/06/2007 10:17:51 »
The classic image of expanding space is dots on the surface of a ballon that is being blown up. But this is just a two dimensional surface I have just extended the idea into three dimensions. 

Think of looking at remote spots in diametrically opposite directions. as we look further away we look back in time  and these spots were closer together  there is absolutely no reason why they can't have been much closer together than  the "distance" that we are looking now because the space has grown in the time that it has taken us to see the objects by the light from them getting to us
 

Offline dentstudent

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« Reply #8 on: 21/06/2007 10:35:29 »

Think of looking at remote spots in diametrically opposite directions. as we look further away we look back in time  and these spots were closer together  there is absolutely no reason why they can't have been much closer together than  the "distance" that we are looking now because the space has grown in the time that it has taken us to see the objects by the light from them getting to us

Yes, but if we're looking back in time to when these spots were closer together, they are apparently where we see them now - of course, they're not there now, as they will have had 13.7 billion years to move. Even if they appear to be closer together then they are in actuality, they're still a damn long way away, and apart, for an event that happened at the time that we're looking at them. BUT, the thread that the Doc posted pretty much answered my initial question. Thanks for the input though!
 

Offline thebrain13

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« Reply #9 on: 23/06/2007 06:42:19 »
when we do look back a long way into the past, does it look any different than what we see in our immediate area?(other than being redder)
 

Offline Soul Surfer

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« Reply #10 on: 23/06/2007 11:56:37 »
Things do look very different.  Firsly there are fewer heavy elements in the universe because these are manufactured in stars.  Secondly there are quasars which are believed to be large black holes on a feeding frenzy these aren't around now thank goodness. Thirdly in the ultra deep field the shapes of ancient galaxies are peculiar, they are much more irregular and gave not settled down into the elliptical and spiral shapes that we see in closer galaxies.  Finally the cosmic microwave background is light that dates from a period when the whole universe was as hot as a typical star and not a few degrees above absolute zero as now.
« Last Edit: 23/06/2007 11:58:08 by Soul Surfer »
 

Offline maff

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« Reply #11 on: 23/06/2007 18:23:16 »
We must remember where the Earth is in conjunction with the original expansion, in other words if the matter from which the Earth was formed is closer to the edge of the Universe rather than the middle it would effect our calculations to Universe evolution calculations.
..maff
 

Offline Soul Surfer

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« Reply #12 on: 23/06/2007 23:09:33 »
Maff that is a load of total rubbish
 

lyner

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« Reply #13 on: 27/06/2007 10:56:14 »
Quote
closer to the edge of the Universe rather than the middle
What 'edge' did you have in mind? How would you know if you were there? Stars one way and nothing in the other direction?
The expression "finite yet boundless"  sums up the situation - the edge of space doesn't have to exist any more than the edge of the surface of a sphere or the end of a rubber band.
 

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« Reply #13 on: 27/06/2007 10:56:14 »

 

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