Re: As we look back in time, y doesnt the universe shrink?

When we look far away in the universe we are looking backward in time: and surprisingly we do indeed see the universe shrink as we look ever further away! By this we mean that it appears galaxies were closer together in the past (although beware, typical galaxies have also evolved internally over the age of the universe, so one has to also try to account for this, which makes things complicated).

Now, this fits in to the idea of the universe expanding, but it seems strange because one naturally wonders how a small universe can be spread across the whole sky! In fact, it turns out that distant galaxies, although closer together, beyond a certain point themselves actually appear larger rather than smaller as they get further away. To be quite clear about this, we don't mean that the galaxies are changing their size, but that exactly the same galaxy would appear to get bigger when viewed from further away. So on that basis if you estimate the volume of the universe using these distant galaxies as yardsticks you find that it is actually much smaller than you'd think it should be using good-old Euclidean geometry. To take it to the extreme, if we were able to look right back to the moment of the Big Bang we'd find that infinitesimally small point would form a complete sphere around us.

Of course, this is very counter-intuitive, but it does seem to be how the universe behaves, and is as predicted for an expanding universe following the laws of General Relativity. It is hard to explain how this comes to be, but we can use an analogy: imagine standing at the north pole and considering all the lines of longitude running away from you in all directions. You could mark out on the ice the lines of longitude corresponding to the eastern and western most points of any given countries. What you'd find is that countries like Greenland would span a large range in longitude thanks to their being so northerly, whereas a similarly sized country at the equator would span a much smaller range. So far so good, but now consider extending this to the southern hemisphere -- and in particular the south pole itself that in some sense spans the full range in longitude, despite just being a single point! This analogy isn't exact, but it does give us a sense of how these distorting effects of space can come to be.