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← Cosmic distance record 'broken'

Steve Zara's Avatar Jump to comment 8 by Steve Zara

Comment 2 by ZenDruid

I may be mistaken here, but logically if we see light which originated at a certain point 13.14 Gya, wouldn't that indicate a point close to the 'center of expansion' of the universe? Is there any particular area of the sky where these old/distant objects are found? Could a correlation be made?

I realise this may sound very strange, but no, it isn't a point close to the centre of expansion.

Imagine a very, very small lump of dough with raisins in. Now, let's add some special 'Inflationary Yeast' and the right amount of cosmic sugar, and leave it somewhere warm to rise. The dough will rise, with the same rate of expansion everywhere, with each raisin moving apart from all the others. There is no centre of expansion. Wherever you are in the dough, it will appear as if everything is moving away from you, and further things from you will move faster away than nearer things, as there will be a greater length of dough expanding between you and those further things.

Now, imagine the raisins are very, very hot indeed. They are positively glowing. Also, at first, the dough expands very, very, very fast indeed (the inflationary period). After a while, it settles down and expands at a more steady pace.

Finally, and I know this is stretching[sic] things a bit, but imagine that the dough is transparent. You can see other raisins wherever you are.

Now, wherever you are, as time passes, you will be able to see more and more raisins as their light (they are glowing hot) reaches you. Light travels (obviously) at the speed of light, so after one second you can see raisins 1-light-second away. After a year, you can see them 1-light year away. Because of the delay you will be seeing those raisins as they were a year ago.

As the point where you are ages, more and more will be visible, from longer and longer ago. If the rising dough was our universe then after 13.14 billion years you will be able to see, very faintly, things that are 13.14 billion light years away that were as they were 13.14 billion light years ago.

There is no special place to be to see these things, and there is no special place to look. Wherever you are in the dough, if you can look between the close-up raisins and you have a very sensitive telescope you will see things as they were a very long time ago.

If where you are is X years from the origin of the universe, then you can see at most things X light years away. Well, not quite. What I had said is almost right. The thing is, that the dough does not stand still as that distant light travels to reach us. It keeps on expanding. So, light may have only(!) travelled through 13.14 billion light years of distance, but the continuous expansion of the dough means that where it came from is now many tens of billions of light years away. It's as if light has been travelling on a moving walkway: in terms of the walkway (space) light never goes faster than lightspeed, but space carries light with it.

I hope that makes things clearer.

Wed, 25 May 2011 20:44:38 UTC | #630898