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.
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
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