So I was reading about GN-108036 this morning and for some reason I thought of something which I can't quite wrap my head around and make sense of. It's early morning so maybe coffee hasn't kicked in yet.

If it starts with a central big bang and we now look at something that is 12.9 billion light years away, how can we be here already to "observe" the light if the universe is approx. 13 billion years old?

In other words:

Big Bang, stuff starts expanding.
What will form GN-108036 is part of it
What will eventually form earth is part of it.
Nothing can travel faster than light yet;

12.9 million years after we are at this point "ahead" of the light from GN-108036 to see the light reaching us?


Nothing can travel faster than light yet

The expansion of the Universe itself can.

There are already parts of the Universe receding from us "faster than light". This is because every small part of the Universe is expanding only a little - but if you sum it up over cosmic distances, the expansion speed, total over a large distance, becomes huge.

So, in a sense, nothing actually moves faster than light. It's just that the Universe is so big that this tiny space expansion actually adds up A LOT over large distances. Space itself is growing, and it's not subject to relativistic limitations - only things moving through space are limited by c.

Back to your original question: there was a time, early on, when the Universe expanded much faster than today. It went from essentially nothing to a huge size in almost no time. Things that were previously close together, all of a sudden found themselves separate by large distances. So, those photons emitted 12.9 billion years ago, might have arrived here a very long time ago, if it were not for this sudden "additional" distance in between.

BTW, this is not entirely rigorous, but it's good enough as a pop-sci explanation, and at least will get you started.

  • $\begingroup$ +1 Make sense (if I understood properly) it means that you can go full north at c and I can go full south at c and we are effectively getting further from each other at 2c. Right? Furthermore, things aren't moving in the traditional sense of moving in space as the space doesn't yet exist, that I am not sure I get... $\endgroup$ – jfrobishow Dec 22 '11 at 17:49
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    $\begingroup$ Well, you're not "going", space is. You can't "swim" through space faster than c, but space itself can carry you faster than that, if you compare two points which are distant enough. (I am already committing lots of sins against rigorousness, please understand this is pop-sci talk, not science proper.) $\endgroup$ – Florin Andrei Dec 22 '11 at 19:10
  • $\begingroup$ @FlorianAndrei In your 4th paragraph, you make it sound like Inflation happened after the first galaxies were formed, but it didn't. No "magical" additional distance came between us and the galaxy while the photons were en route, except from the ordinary, everyday expansion of Space. It wasn't "suddenly", it was graudually. The Galaxy was much closer to us than now when the photons were emitted, but during their journey, more distance was being gradually added, kinda like if travelling on the surface of a Giant balloon while it's being blown up. $\endgroup$ – Thriveth Jun 7 '13 at 11:30

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