Thread: How can a infinite universe compress into a singularity?

if our universe is infinite ... and expanding ... then if we time reversed it ... wouldnt it always be infinite ( albiet at a much smaller scale factor )?

Can someone explain to me how we can extrapolate backwards from an infinite universe to a singularity?

Why must it be infinite?

Originally Posted by grapes

Why must it be infinite?

because I understand how a finite universe would extrapolate to a singularity. ;-)

Is it safe to say that if the universe is infinite then it could never have come from a singularity?

These simple questions make me want to read an(y)other thread.
I try to think about it, try to get my head around the universe and find I have a very big empty space where I thought my mind was.
An infinitely expanding list of things I don't know. (I don't think it's safe to say infinite around here, though.)

Big Bang creates an expanding universe - but that is not like, now, a whole lot of stuff all flying apart and leaving a big empty space in the middle - or is it? Is the observable universe a relatively tiny volume within an expanding shell of universe? - or is it, back then, expanding high energy volume, fairly homogenous throughout, becoming matter and space expanding (not a bang like an explosion - but still all expanding from a point) such that there could be a galaxy at the centre as easily as anywhere else.

And when I think about before, and outside - my mind fills in the blank with void/potentially/infinite

Another, fun, way to imagine the possibilities is to think of our day-to-day existence as two dimensional (because the next step involves the next dimension, and the fourth dimension seems to tax human imagination). In other words, everything we do, everything we see, exists on a flat sheet. Comfortable with that?

OK, now imagine a single point, which is much less than a single sheet. Expand it quickly, so that its surface is a two-dimensional ball. Imagine that our universe is that two-dimensional ball instead of the flat sheet. It's expanding fast enough that we would never be able to see or reach the opposite side. Essentially, it's infinite. Every point on it is moving away from every other point, in the expansion, but some points have an added motion that moves them closer together or farther apart even faster. In that two-dimensional universe, there is no center of the "explosion", everything was at the center at the start.

Now, instead of just two dimensions, imagine the same thing with three.

Originally Posted by tom

because I understand how a finite universe would extrapolate to a singularity. ;-)

Is it safe to say that if the universe is infinite then it could never have come from a singularity?

Off the top of my head, this implies that one must 'believe' in the BB theory whereas those that think along the lines of string theory wouldn't necessarily 'believe' in singularities. Just my $0.02 worth...ymmv....

Would anyone that does not 'grasp' or understand what 'Grapes' just said... please put your hand up and I will get to you later...

I do NOT 'believe' there ever needed to be a singularity... I can not comprehend that moment... but I am sure there was a awfully Big Bang...

and that some as yet unknown force is eccelorating this ongoing expansion...

seems to be as close as we are to get until information is obtained that might change that... until that unfolds..I wait.

I do not see the 'finite but unbound' as being challenged.

A singularity is born from infinite values, a mathematical construct possibly defined as "infinitely small". So in a sense the singularity described at the BB would already be infinite to start with. Its just that this "singularity" appears to be expanding. Remember folks we have to get our heads around that in the theory of the big bang there is no edge to the universe, no before and no outside, time and space were created at that moment. So for me the universe is infinite in a sense either which way you look at it, since there is no before and no after it just "is".

Originally Posted by David M W

A singularity is born from infinite values, a mathematical construct possibly defined as "infinitely small". So in a sense the singularity described at the BB would already be infinite to start with. at that moment. So for me the universe is infinite in a sense either which way you look at it, since there is no before and no after it just "is".

You appear to be saying that zero is infinite?

"If I can help," should read as 'Can I be understood as to wanting to help explain to 'David MW''...?

'IF' there was a singularity... and we do not know there was... than all of the Universe expanded from this single point.

Surely seeing that. Infinite can not be used. A infinite anything can not be contained in anything.. ie a singularity...

Only if you turn your back on 'the' singularity idea and adopt a multi verse with us only having knowledge of the observed Universe then...

and only then can infinite be used to describe the contents of 'The Universe.' just think about it a while.. Other wise its the tried and true..

Finite and Unbound...