The relativity of time and defining the "age" of the universe I have been doing searches on the relativity of time and its relation to the "age of the universe," among other things. I have come across some insightful Q&A, but I have yet to really see a "solid" response to my innate question (or questions, as it were). I apologize if one has been given on another post; I am new here and haven't had the "time" (pun) to look thru them all yet. So, here are my questions for anyone who might be able to shed some light: 1) From what I have learned/read/seen, time is relative. The passage of time for observer A who is travelling at speed D within space-time (say someone on Earth travelling around the Sun) is different than the passage of time for observer B who is, say, travelling in a spacecraft at 99% the speed of light (.99c, I'll call it D1) within space-time. In essence, the passage of time for A from the perspective of B is faster, while the passage of time for B from the perspective of A is slower; the person travelling really fast (B) seems to be moving through time slower than the person just sitting on Earth (A) from A's perspective, and the other way around. However, the passage of time for each of them with respect to themselves ("personal time"?) seems normal from their own frame of reference (not compared to each other's frame of reference). If I am correct in my explanation here (which I certainly may not be), then my question is this: how can we assign an age to the universe, e.g. how can we say the Big Bang happened so and so many years ago? If the passage of time is relative based on the speed through which you travel through space-time, then how can we even contemplate assigning an age to the "beginning" of it? It would seem to me that it's an arbitrary point; our assignment of the age would be based only on our tiny little perspective (frame of reference) as forced on us by our being on Earth. Maybe I can explain my question better with a hypothetical situation building off my first example. Let's say observer A from above is the same - a person on Earth right now. But now let's say observer B is a person who is still travelling at 99% the speed of light, but they started travelling at that speed 1 second after the Big Bang and have been ever since (throw out biology). Now, right away I see that my question is in and of itself a paradox because I am assigning a time value (1 second) to a question about time, but let's avoid that for now. Would it not mean that the "age" of the universe to B, were he to stop suddenly and land on Earth right now, be much lower than the 13.7 billion years that A seems to think has elapsed since the Big Bang? Wouldn't he have perceived that passage of time to be like maybe only 1 billion years since his passage of time is slower relative to ours since he was moving much faster? I just can't get my head around that concept. And that leads to my second question. 2) I have read that interstellar space travel is possible based solely on the relativity of time (not using "warps" or "wormholes" or anything like that) because if you could travel close to the speed of light, you could traverse say, 40 light years, in like maybe 1 year. Is that true? Again, I just can't get my head around it. Is that because the "40 light years" we assign as a distance to another star system is relative since it is based on a unit of time, and even though light does technically take 40 of "our" years to reach us from there, if we were travelling on the light beam, the passage of time from our new perspective would be much smaller? In essence, if we could travel on a beam of light, would we be able to pretty much go anywhere a limitless amount of times because, from our perspective on the light beam, time essentially slowed to a halt? Sorry if these questions got too convoluted or in-depth; I have just been doing a lot of research lately and my brain is fumbling for some semblance of an explanation to things I'm having trouble grasping. Thanks.