Big Bang or Big Ball?

SREW

Please help - I'm sure there's a simple answer to this question, so any explanation would be very welcome:

If you looked out into the night sky with an ultrapowerful telescope, in principle you could see back to the Big Bang no matter which direction you pointed it (suppose for a moment that the big bang was accompanied by a sudden creation of a bit of light). How can a near singularity, with miniscule dimensions, be visible everywhere in the universe?

PS I know no light was around at the big bang, but my point is that all points in the night sky might contain light from the universe when it was very small - how can this be?

Also, if the universe started as nothing and then ‘exploded’, why did it have to start “small” and then “grow” – why not start at any size or shape? Why not start as a big ball, from whose inner surface materials emerge and then diffuse towards the centre? This would make sense of my first question.

TheTechNoir

You are correct that, loosely speaking 'no light was around at the big bang' or rather light was being rapidly absorbed and the universe was opaque. That said, with no light or meaningful travel of photons there is no electromagnetic/visual (in any spectrum) observations that can be made by us. It was not until an estimated 380,000 years after the big bang before the temperatures cooled sufficiently to allow for atoms to coalesce and photons were able to travel in a way meaningful to our current observation. At this stage in time the universe was not tiny. Also consider that the distance between us and the edge of the observable universe is expanding.

The universe did not have to start small, in fact it may be more common amongst cosmologists to lean towards the universe starting infinitely large. Also expansion is a better word to use than growth as describing the big bang with words like 'growth' and 'exploded' can be understood as them growing into an already existing space. I am having trouble understanding precisely what you are suggesting with your last question but it seems to be linked to your misconceptions of the big bang.

TheTechNoir

Upon re-reading this I have a better idea I think of what you are asking. To think of the universe as starting as a large empty ball with the big bang being the introduction of dense matter along the outer perimeter which diffuses towards the center is just completely wrong. This implies a center for starters which all cosmological data we have contradicts. Additionally if you were trying to use it as an explanation for us seeing things so distant and in all directions around us would place us right at the center. This should be enough reason for why this could not be the case, but if more reasons are needed someone could list endless reasons. The universe would simply be different in all possible ways and rules and I would imagine not conducive to life as we know it (that is if such a universe were possible to exist, which I do not think so as it implies a boundary).

SREW

Okay, forget the idea of a 'big ball', it was just a thought and I realize the data doesn't support it.

But on the first question you say "It was not until an estimated 380,000 years after the big bang before the temperatures cooled sufficiently to allow for atoms to coalesce and photons were able to travel in a way meaningful to our current observation. At this stage in time the universe was not tiny." Even if it was not tiny, surely it was still smaller than the universe is now. So my problem is still unexplained. If I look out into our universe that is bigger today, if I look far enough, no matter where I look I can see it at a time when it was smaller... how is this possible?

Nabeshin

I'm really failing to see the confusion here... Light, of course, has a finite propagation speed. This means that whenever we are looking at anything, we are seeing it as it was when the light was emitted, not at our current time. So what we observe is ALWAYS the way things were in the past. So once that's understood, since the universe is expanding, this implies that back in time it was smaller. So whenever we observe cosmological objects, we're observing them in an era when the universe was smaller.

SREW

I agree with all of this - but this isn't the question. Okay a thought experiment to simplify the question. Suppose the universe was 1cm wide 300,000 years after the Big Bang, when light starts to appear. Today the universe is 100cm wide. How come when I look north today, I can see light from when the universe was 1cm wide, and when I look south, I can also see light from when the universe was 1cm wide. Surely the distance separating these spots of light is 100cm? And no matter where I look, I can see light from when the universe was 1cm wide. How can something 1cm wide occupy a space so large today? Is it that space has expanded during the time it took for the light to get to me?

IsometricPion

If the co-moving distance (the distance in the frame in which the the CMB is at rest and was emitted all at approximately the same instant) to the points we are receiving the CMB from today were 1cm away at that time, then the speed of light would be ~7.09x10^-16cm/s and the co-moving distance today would be ~10.9m (1090cm). Different ways of measuring distances give different answers in General Relativity ref.: Wikipedia- Distance measures (cosmology).

In short, the answer is yes, the distance has expanded. There are further complications if you want to talk about what occurred at extremely early times (e.g., fractions of a second after the Big Bang), but none of those complications apply to the above calculations (since they pertain to a much better-understood time period).

SREW

Thanks! That's what I was trying to get at.