# Special Relativity

Yesterday's post on a variation of the "Twin Paradox" with both twins accelerating was very successful-- 337 people voted in the first poll question, as of a little before 9am, and the comments to the original post are full of lively discussion. That's awesome. I wish I could take credit for it, but the problem posed is not original to me. It comes from a 1989 paper in the American Journal of Physics, which also includes the following illustration setting up the situation: The article contains a full explanation, and also the following figure illustrating the result: The correct answer is…

### Book giveaway: Einstein for Beginners

Today's free book is "Einstein for Beginners" a comic style introduction to Einstein's life and work by Joseph Schwartz and Michael McGuiness To claim the book, be the first commenter to assiduously affirm that you will read and review the book in less than 6 months and then send me your snail mail address to science dot woman @ google's mail service.

### Why doesnât Light Age?

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…

### Faster-than-light travel: is it possible?

Apparently, this is becoming a good place for people to get their questions answered! My friend Brian, recently wanted to know what the possibilities were for faster-than-light travel. Specifically, he was interested in it because he wants humans to do it. Brian: but otherwise how will we ever have a civilization like that in Star Trek? Presumably, Brian's goal is to be able to travel nearly instantaneously between any two points in the galaxy. The problem is that there are physical laws we have to obey; we don't have a choice. One of them is special relativity, which tells us that the…