There's a graduate student that I'm sort-of mentoring/working with at Arizona, named Xiaoying Xu (hi Xiao!). She's bright and curious, and she asks some very good questions. She asked me one yesterday that's pretty tough to wrap your head around:
How do I explain to someone why light doesn't age?
Well, here on Earth, time progresses at a certain speed. That is, if I measure how many seconds tick by as the Earth revolves once around the Sun, I'll get 31,556,926 seconds. (31,558,150 if I'm measuring a sidereal year.)
But let's say in the course of that year, I put you on a rocket ship, and…
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