These galaxies, while standing absolutely still, are racing from us, in some cases, faster than the speed of light. The spacetime between us and everything else grows larger by the minute, pushing the galaxies in this image to a distance of over 47 billion light years. Because of universal expansion, the farther something is away from us, the more it's light is shifted toward the red and the faster it appears to be moving.
Edwin Hubble himself discovered this by measuring the redshift of many galaxies. Redshift is a measure of the amount of shift in a galaxy's spectrum toward the red and measures not only speed, but distance as well.
Recently, hubble scientists put the icing on the cake. Using the measured redshifts of all the galaxies inside the image, they made a 3D model of the Ultra Deep Field. This is how it looks when we apply the distances of the galaxies in the most important image ever taken.
There are over 100 billion galaxies in the universe. Simply saying that number doesn't really mean much to us because it doesn't provide any context. Our brains have no way to accurately put that in any meaningful perspective. When we look at this image however, and think about the context of how it was made, and really understand what it means, we instantly gain the perspective and cannot help but be forever changed by it.
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