Everyone knows that the farther away an object is the farther back in time we're seeing it when its light reaches us. But, if the universe began with a singularity or similar, and if the universe is expanding at less than the speed of light, then there has to be some limit to how far back in time we can look. For us to be able to see the light from the big bang, for example, we'd have to have sped out to our present distance faster than the first photons could have gotten here. (Yes, I know space itself is expanding, but you get my drift.) So as the stuff that became our galaxy traveled away from the big bang, up to a certain distance from the original singularity, all photons emitted prior to the time we reached that distance must have passed us by, by now. So what is that horizon? How far back can we really see?