What does the expansion look like?

Here are some dots representing galaxies at time 0.

Now we let them expand, giving this picture at time 1.

Now lets overlay the blue galaxies on the red galaxies to appreciate what it looks like.

The x marks the spot, say our galaxy, where I superimposed the images.

We can try it with another spot.

No galaxy is special. No galaxy is at the center of the expansion.

Also, the universe has no edge. At least we don't see an edge and there is no reason to think that it has one.

So the simplest picture is that at any one time, the universe just goes on forever.

Going backwards in time

Here is the universe at one early time.

If I bring the red galaxies closer together, here is what we get.

Let's draw some lines to show how the galaxies have moved.

It is expanding. There is no center of the expansion. There is no edge.

If we go backwards in time, it goes from this,

to this

Each galaxy has some motion in addition to being carried along with the general Hubble flow.
- Two galaxies may be in orbit around each other.
- All of the galaxies in a cluster may be in orbits around the center of the cluster.
- A galaxy all by itself may have its own additional motion.
- For simplicity, my pictures don't show this.
If we go back far in time, galaxies were different.
- For instance, galaxies could merge.
- For simplicity, my pictures don't show this.
If we go back very far in time, we get back to a time before galaxies were formed.

Davison E. Soper, Institute of Theoretical Science, University of Oregon, Eugene OR 97403 USA soper@bovine.uoregon.edu