"When light enters a material, photons are absorbed by the atoms in that material, increasing the energy of the atom. The atom will then lose energy after some tiny fraction of time, emitting a photon in the process. This photon, which is identical to the first, travels at the speed of light until it is absorbed by another atom and the process repeats. The delay between the time that the atom absorbs the photon and the excited atom releases as photon causes it to appear that light is slowing down." Answered by: Gary Russell, M.S., Systems Engineer, Reston, VA
You want to look back further in the past? OK, just look up at night. When you see those specks of light that we call stars, you are looking back in time. Some not so far and others quite a ways back. Here is chart that shows what I am talking about:
So, as you see from the above chart, even the closest stars we see are over 4 light years away and the rest a lot further. At these distances, human travel to these other stars would not be easy even if it were possible. Just some things to ponder on. Now, have a great day, you hear?