Many of nature's deepest mysteries come in threes. Why does space have three spatial dimensions (ones that we can see, anyway)? Why are there three fundamental dimensions in physics (mass M, length L and time T)? Why three fundamental constants in nature (Newton's gravitational constant G, the speed of light c and Planck's constant h)? Why three generations of fundamental particles in the standard model (e.g. the up/down, charm/strange and top/bottom quarks)? Why do black holes have only three properties—mass, charge and spin? Nobody knows the answers to these questions, nor how or whether they may be connected. But some have sought for clues in the last-named of these properties: spin.It's pretty heavy reading after the first paragraph but covers some amazing territory, relating gravity and electromagnetism, and explaining frame dragging. Here's something interesting to consider: If you look up at the sky and spin around, you'll see the stars trace circles around your field of vision, and your arms will swing out away from your sides. Are you spinning around in the universe or is it spinning around you? According to relativity, it doesn't make any difference. Either way, there's still a frame-dragging effect between your frame of reference and that of the universe, warping space between your body and the cosmos, so that your arms fall away from your body.
Monday, May 12, 2008
Spacetime and Spin
Here's a really cool article up at stanford.edu's spacetime collection.