The Physics of Star Trek

The Physics of Star Trek by, Lawrence M. Krauss
I just finished this audio book. I have to say it was absolutely fascinating. Although I have disagreements with some, popular physics theories, which are talked about in the book. (I don't know why they invent stuff, e.g. dark matter, to explain the unknown. It reminds me of the aether blunder in physics. Perhaps a fifth dimension beyond space-time would answer some the need for dark matter like it does for gravity. Oh, but you can't observe this fifth dimension so it must not exist, you can't test for dark matter and that is ok?)
How old is the Universe? My questions in response are; whose clock do you use, how fast are you traveling, how fast is the universe expanding, from what vantage point and is the speed of light constant?