How can we measure the size of the universe?: "By now you should be getting a pretty good idea how the most distant galaxies can be further away than 13.8 billion light years. For the first part of the trip, the light that is just now reaching us was traveling through a much more compact universe than we have now. As time went on and space expanded, the distance between the photon and where it started increased at 'faster than light.' Again, this doesn't mean that light was traveling faster than light. Anyone watching the beam go by would measure it at 3x108 m/s, the ordinary cosmic speed limit.
Even so, there's a maximum distance that light could have traveled since time began. This is known as the horizon, and based on our best cosmological measurements, it's about 48 billion light years. The light that we see from the Cosmic Microwave Background Radiation is reaching us from a point very near to the horizon."