Bump but probably gonna slide. I think I've answered my own question

Anyone? Maybe one more bump

If the Universe were collapsing, distant galaxies would be blue-shifted, as the space between us would be shrinking. The correlation between red-shift and distance is the major thing that tells us it's currently expanding.

Expansion/collapse cycles are effectively irrelevant to the modern age, since upon collapse to a sufficiently small volume everything gets effectively reset anyway. Although there are alternative cosmological models, the earliest we can see back to is just after the Big Bang, so that's all that's really worth "believing" at this time. But we work on other models like cyclical expansion/collapse because one day we might have some observations that fit into them, and it'll be useful to know what to look for when that day comes.

>>7720784
I thought about that. The spectrum from light of distant objects. But how would light and the colour spectrum work in a model of a collapsing universe where time is essentially going backwards? Sorry, pleb. But thanks for your reply. I thought I could recall a doco with michio kaku saying something about this

>>7720784
I mean it's not only space that's expanding but matter aswell, isn't it?

>>7720821
Replying to myself but nah that doesn't make sense. Your right the space between us is expanding. If matter was expanding too then there would be no expansion. Everything would be clumped together like after the Big Bang

So time is lineal?

>>7720841
Linear. Linear. Linear. I don't know why my phone is correcting. Now working. Linear

>>7720847
Not sure what you mean by linear. Does time always go forward? Essentially, yes. Time is best measured by entropy. In an expanding universe or sufficiently sparse collapsing universe, entropy always increases on average (for spontaneous processes), and we observe this as time going forward.

When you get near the end of a collapsing universe, there is actually a tendency for entropy to decrease, but everything is screwed up at that point anyway. It's like everything is on the surface of a black hole. But anyway, that's so far outside the bounds of anything we've observed that it's not worth speculating upon.

But linear... if you mean, does time always go forward at the same rate, then the answer is no. There's a really good book, old, but with no real math to distract you:
> http://www.bartleby.com/173/

>>7720879
Just looked up the meaning of the word just to be sure and I guess I did mean lineal. That's weird. What I meant is a straight line going one way. I guess I'm asking if time would go backwards in a collapsing universe as well? I looked up cyclical models and I'm sort of familiar with m theory, when I say familiar I mean the most basic understanding of course. Which is probably wrong like my basic understanding of physics in general. But I never liked string theory. It bends my mind way too much. I like the "neatness" of relativity. So I guess my question should've been,
In a collapsing universe would time go backwards and would we be able to perceive it? And you've answered that. Thankyou for your reply

>>7720693
By measuring the total gravitational pull of the universe and to take the dark energy difference. We can see if the universe if flat, expanding or crunching.

>>7720693
>How would you know if the universe was collapsing?
when redshift becomes blueshit, we're in trouble

So how WOULD light and the colour spectrum work in a model in which time is going backwards in a collapsing universe? Also if it takes millions of Years for light to reach us from these distant objects, wouldn't it take millions of years for us to see a shift? It could be collapsing now and we won't know till that light reaches us. Thoughts?