[neutralino]

Originally Posted by MJA Hi N, Thanks for the explanation that ultimately proved Einstein's cosmological constant incorrect.

You're welcome. However, as we'll see when I write my next part of the story, we'll put the cosmological constant back in!

I have always had great difficulty believing it though. My main concern is the belief that because we measure a part or some of our universe as expanding, how is it that we can assume without knowledge of the extent of our yet infinite universe, that the universe is expanding in it's entirety?

I think this is a valid concern to have. However, as I said in my opening post, the reason we believe the whole of the universe to be expanding is due to the cosmological principle. There are various versions of this; one says that (on cosmological scales) no matter where we look in the universe we will see the same distribution of objects. There has been evidence which suggests that the cosmological principle is correct (CMB data, for example) and, besides, if the cosmological principle didn't hold, then we couldn't do cosmology!