[jamest (OP)]

Darren wants to know, 'Why can we see the light from the first galaxies. Why hasn't that light already passed us if it is from so long ago when the universe was smaller?'

[paul cotter]

That is an interesting question that seems at first glance to be a bit of a conundrum. What one needs to realise is that, due to the finite speed of light, looking at far away objects entails looking back in time. An object that is, for example, 10billion light years distant will appear as it was 10billion years ago. NB cosmology is not my field of competence and I may not be precisely accurate here as the expansion of the universe complicates calculations but I hope this answer gives some perspective.

[Eternal Student]

Hi.

   It'll probably help to explain which bits of Darren's thinking are correct and then it'll be easier to appreciate which bits would be different.

1.   We cannot see the light from every galaxy when it first formed.   The light from our own galaxy when it first formed has travelled past us.   Light from nearby galaxies like Andromeda when it formed has also gone past us.  So a lot of Darren's thinking is correct.... there's a lot of galaxies whose early development we cannot see, that light has gone past us.

2.   So we can only see some galaxies in an early stage of evolution.

3.   The universe may be infinite.   You could stop thinking about it as having ever been smaller in any meaningful sense involving attempting to assign any real finite numbers to its width, height and length.  It was always of inifnite length, width and depth.   It was denser (more stuff packed into every cubic metre) but it may have always been of infinite extent.  In that case, we can always find a galaxy that is as far away as we like.   There would always be some light hitting us now that has travelled from some remote galaxy that was in an early stage of development when that light left that galaxy.   If the universe is infinite, then we're done and can just leave the discussion here.    The only thing we've adjusted In Darren's argument is the notion that the universe was originally "smaller" in some way.   It was denser but it was always infinite in spatial extent.   This is currently popular scientific opinion.

4.    It's possible though not curently popular scientific opinion that the universe could be of finite extent.   There may be some meaningful finite real numbers and units of distance that we can assign as its length, width and depth.   However, the early expansion of the universe has been at a sufficient rate that it has out-paced the rate at which light could travel and reach us from some remote location.
   You might imagine a hare running as fast as it can down a road but someone has been stretching that road faster than the hare can run, so even after 13.8 billion years it still hasn't reached the end of that road.
    If our current models of cosmology are right, expansion of the universe is accelerating and there will be some light from some remote galaxies that will never manage to reach us.

5.    Current cosmological models use General Relativity where space (and especially spacetime) is not quite like the simple Euclidean geometry we all learnt in school.   As human beings we would want to try and assign meaningful measurements for the length, width and depth of the universe and imagine the universe as some conventional 3-D shape existing in Euclidean space but it isn't going to "play ball" or play fairly.    A direction that seems like it should be "straight ahead to planet earth" while a ray of light is way over there is not going to be the same direction as "straight ahead to planet earth" when a ray of light is right next to planet earth.   So we could just as reasonably adjust our analogy about the hare running down a road that was being "stretched" all the time, instead we could imagine that the road was being "curved" and "distorted" all the time.   The hare never was capable of running in a Euclidean straight line toward planet earth, the universe was distorting and changing the rules of spatial geometry at a pace faster than the hare can travel and reach the final destimation (planet earth).    The main thing is that all of these analogies are just analogies, as human beings we're always going to want to imagine the universe as something sitting inside Euclidean space and either expanding or twisting and curving in some sensible way consistent with how 3-D shapes conform to the rules of geometry we learnt in school.   However, the universe just doesn't play fair and doesn't follow those rules, the length of the shortest path from one place to another can change as cosmological time (or what can also be called co-moving time) progresses even though none of those places (the start or end place) were moved apart in any conventional way that complies with what Eucldiean geometry says must have happened.
    So, without needing to attach any mental image to it we can just say that the behaviour of the universe in early times (which is often called "Inflation") was sufficient to out-pace the ability of light to travel from a remote galaxy to us (here on planet earth).

Best Wishes.