Figure 1
To find out how to use the expanding Universe to measure distances, we must look again at our balloon. Let us take three points in a line on the surface of the balloon (Figure 1) and look at the distances between them.
Figure 1
Let us suppose that the balloon is expanding so that the distance between the points A and B increases by 2 cm every second. If the balloon expands regularly, the distance between points B and C will also increase by 2 cm every second. After 1 second the balloon will look like Figure 2. After 2 seconds, it will look like Figure 3. If we now consider the distance between A and C, we find that it goes from 4 cm to 8 cm to 12 cm - increasing by 4 cm a second. From the point of view of A we see that C is twice as far away as B and is going away twice as fast. In fact we can show that for any point, the further away it is, the faster it recedes.
Figure 2
Figure 3
* Click here to see how this applies to the real Universe