I have a few questions on the speed of light and how that relates to the age of the universe. I will preface these remarks with the disclaimer that while I have read a bit on relativity from time to time in an attempt to understand it, I unfortunately have found that most of it seems to be beyond my ability to grasp. I was pondering recently while reading an article about the Big Bang and the age of the universe. It was probably one of numerous recent articles about Einstein's life. From my understanding, Einstein determined that because the speed of light is constant, there must be variability in time to make up for this. This explains why time moves slower or faster for two relative observers. So here is the meat of my question. I read in books and magazine articles about the age of the universe. Since time is relative, what does it mean that the universe is so many billions of years old? Don't we need to know billions of years in relation to something? Does that just mean that given the current size of the universe (as we have measured it) is so many light-years across? Or does our age-estimate have more to do with the rate of expansion extrapolated over time? If two beams of light are leaving the Big Bang at the same time traveling in opposite directions, what is their time relative to each other? If they travel for one year in their time are they two light years apart? Or is it less because if they are two light years apart, they would be traveling at two times the speed of light relative to each other? Thanks in advance for any light that can be shed on this. :) Aaron