It’s that time of year again.  The week when I attempt to explain Einstein’s special theory of relativity.  It’s one of those days when, if I don’t get the correct proportion of caffeine into my system, the synapses fail and I find myself staring into my own powerpoint presentation and speaking in tongues.  If you’ve ever taught this concept, as I do every Fall in my twentieth century science class, you’ve probably experienced this.  As the story goes, astrophysicist Arthur Eddington was once told by an interviewer that supposedly there were only three people in the world who properly understood Einstein’s theories of relativity, and Eddington was one.  To which Eddington reportedly responded, who’s number three?

The moment of brain strain usually occurs about the time that I have to explain that the speed of light does not change, but that measurements of mass, time, and space differ from one observer to the next.  It’s a challenging concept that gets even more tricky when confronted by the twin paradox.  You know the one: two twins, one on earth and one in a spaceship traveling near the speed of light.  The traveling twin returns to find his twin much older than him.  Students invariably ask, if these measurements are relative, why wouldn’t the earth-bound twin be the one to be younger?  The answer, which a physicist could explain better, has to do with physical acceleration of the rocket ship (when it turns around) interfering with the effects of time dilation.  French physicist Paul Langevin put forth one such explanation back in 1911.  Side note: yes, Langevin did have some actual ideas and should be remembered for more than his having an extramarital affair with Marie Curie.

Anyway, if anyone would like to see a nicely done animation of these concepts, I’d recommend the following short one, which is done very well. Enjoy the brain melt!