No matter which direction we look in, or how far away our telescopes and instruments are capable of seeing, the Universe appears pretty much the same. The number of galaxies, the types of galaxies that are present, the populations of stars that exist within them, the densities of normal matter and dark matter, and even the temperature of the radiation that we see are all uniform: independent of the direction we look in. On the largest of cosmic scales, the average difference between any two regions is merely 0.003%, or about 1-part-in-30,000. The biggest differences that we see, in fact, aren’t a function of which direction we look in, but rather how far away we’re looking. The farther away we look, the farther back in time we’re seeing the Universe, and the greater the amount the light from those distant objects is shifted towards longer wavelengths. A lot of people, upon hearing this, get a particular picture in their heads: the greater the amount the light is shifted, the faster these objects are moving away from us. Therefore, if you look in all directions and reconstruct, “at what point, in space, would we see all directions receding equally?” you can locate the center of the Universe.
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