Expert: Jayendra Upadhye - 9/7/2005

Question
My co-workers and I are trying to figure out this question.  If we are correct, we are assuming that all objects are moving away from the center of the universe.  We were under the impression that the fastest moving material is at the edges of the universe and that the slower moving material would be closer to the center of the universe.  If this is so, then under what circumstances does an object in the night sky show a blue shift toward the Earth?  We are all moving away from the center, but what could cause the speeds of the objects closer to the center of the universe to be greater than our galaxies speed?  Does it have anything to do with our position in our orbit around the sun, or in our solar system's position in its orbit around the center of our galaxy?  

Answer
Debbie..Debbie..
You and your co-workers have got it all wrong!
(No problem, understanding the expanding universe is a bit difficult initially. Lot of thought-experimentation and visualisation goes into it.)

Actually the expansion of the universe is "center-less"!
There is NO center to it. (And if there is , it lies outside of the 3 known dimensions!).

Visualise (in a thought experiment) that our universe appears as a bubble/balloon to a superior being from the 4th dimension.

To it, all the matter in the universe resides in the syrface of this expanding balloon.

On that surface, any two points will recede faster from each other if they are more distant from each other, as compared to a set of two other points "closer" to each other.

ie recession rate is proportional to distance.

But the center of this whole expanding stuff will be "not inside" of the expanding surface, well "inside" volume enclosed by the balloon.

Coming back to real physical space, stars within a galaxy do not show appreciable recession from each other as the distance of one galactic diameter is not great enough.

But galaxies as far away as the virgo super-cluster of galaxies DO show recession.

Hope you got the drift of what i have been saying so far.

Red/blue shifts are often associated with the observation of vast 3 dimensional structures like spiral galaxies in our neighbourhood or the elliptical old galaxies.

There stars move towards us and away from us as they move about their galactic centers. (much like our sun).

As the stars approach us, their light is blue shifted, and as the go away from us, it is red shifted.

The mean gives the recession rate of the whole galaxy from us.

Also a study of these "differential" red shifts tells us something about the galactic "rotation curve" and the amount of hidden dark matter in the spiral arms..but that is another matter altogether..!

So please dont go looking for a univers-center..there is none withing 3 dimensional space.

Jayen