Great website from the University of New South Wales - excellent intro to relativity that doesn't require too much brain power to comprehend. What i don't get is why the speed of light has to be constant in the first place...? (although i understand it is actually slowing down as the universe gets older- aren't we all). I have been mystified by the "constants of nature" since high school physics... what if G, E etc were different? Would we be here to blog about it? The anthropic principle seems to me a bit of a cop out!