[MJA]

Originally Posted by neutralino In this thread I intend to present some of the observational evidence for, firstly, the expansion of the universe, and secondly why we think the universe is accelerating in its expansion today. So, what does this all mean? Well, since Hubble has shown that, for a range of different galaxies, the velocity of recession is proportional to the distance, then we can say that every galaxy is moving away from us. Since we believe in the cosmological principle [6], we know that we cannot be in a special place in the universe, and so we can say that every galaxy is moving away from every other galaxy. This implies that the universe must be expanding.

Hi N,

Thanks for the explanation that ultimately proved Einstein's cosmological constant incorrect.

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?

Or a simply analogy would be: if the grass is green in my front yard, it does not necessarily mean that all grass is green everywhere in the infinite universe.

Or if one measures the motion of a river, it is truly moving in a single direction.
But it is also true that parts of the river are heading in infinite directions too.
So does a river move in a single or infinitely different directions?
If you test or measure a river by throwing a stick in it to see the direction of flow,
you will see its imeasurably infinite in all direction.

Is the universe expanding and contracting in places too?
What is the universe, should that be answered first?


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MJA