time goes by.
In these pages, I present a few of the insights which I found helpful, surprising, or just pleasing. I expect most visitors will be to be amateurs, who are studying relativity for fun, just as I am; I found these things useful, so perhaps you will too. Some things here are obscure items or things which most authors just assume you know (which you might not), and some may be things everybody talks about but which I think I have a slightly different slant on. Of course, I have my own view of time dilation and the best "intuitive" way to view it, and I talk about that. And some of the things here are just tricky problems or derivations which I worked out, and which I just wanted to show off somewhere. No doubt most of this material is available (somewhere!) in textbooks and journal articles, but I did not find it there in an accessible form.
I have made little effort to separate "special relativity" and "general relativity". They are cut from the same cloth; the former is just a special case of the latter, and there is not even clear agreement today on where to draw the line between them. Most people seem to treat the "special" theory as dealing with flat spaces and coordinates in which the metric is Minkowski's (either diag(-1,1,1,1) or diag(1,-1-1-1) depending on your taste), and call anything that addresses nonzero curvature or uses a different metric tensor "general relativity". Examples of both cases appear here.
Finally, if you've come this far, don't leave without checking out the links page.
(For general information on conventions used on this website, as well as general advice about learning relativity, please see the About page.)
Write up the Lie derivative of a vector, for which I've finally got a good pictureAnd for an unrelated view of Albert Einstein, here's a quote from Bob Dylan, which I've included solely because I'm amused by it and enjoy the song from which it comes.
Something on parallel-accelerating rods
Translate more of the site into French (including the front page)
Add a page introducing relativity
Reorganize and split up Accelerating Twins page, which is too big
Linear twins, porthole view
The Relativistic Albatross
Brachistochrone and a little on applications of calculus of variations
A discussion of 1-forms and rank 2 tensors from the algebraic POV