Here are a few sites with some VERY nice multimedia demonstrations and explanations of this sort of thing:
- Einstein Light - multimedia modules that present the main ideas of relativity, with background info about mechanics and Galilean relativity; electricity, magnetism and relativity (Maxwell); the principle of Special Relativity; relativistic mechanics leads to E = mc2 ; how relativity implies time dilation, and more.
- The Elegant Universe - a fascinating and thought-provoking journey through the mysteries of space, time, and matter. Brian Greene's excellent 3-hour visual feast, with outstanding graphical animations explaining string theory (alias "the theory of everything").
- Superstring Theory >> Cosmology >> Take a trip through the Big Bang >> Black Holes
I really like the explanations given by physicist Joseph Wolfe of the University of New South Wales (in Australia) at the Einstein's Light website. For example, at www.phys.unsw.edu.au/einsteinlight/jw/module4_time_dilation.htm (in the section called Is time dilation true? How big are the effects?) there's this interesting example:
You'll have to read the rest of the article to see this in context, but it's a sobering thought all the same."Some particles striking the Earth's upper atmosphere have energies that exceed 2*1020 eV. If such particles are protons (with mass of about 1 GeV), their speeds would be 0.999 999 999 999 999 999 999 995 c. For them, g is 1011. Now the age of the universe is about 13 billion years for us, but for such particles, the age of the universe would be about (13 billion years/1011), ie about a month. Such a particle could cross the visible universe in a matter of months (their time)."