Video: Perhaps you've noticed all the fuss this week over Albert Einstein and his famous general theory of relativity, which turned 100 years old. Who better to give you a glimpse into what the theory is all about than a Time Lord -- the Tenth Doctor himself?
In this charming animation, David Tennant gives you a whirlwind tour of the key concepts of general relativity: objects with mass curve space-time, and this gives rise to what we feel as gravity. And since space and time are unified, if space can warp, so can time: the bigger the curvature, the slower time flows. In theory, at least, space-time can warp so much that wormholes can form, creating a shortcut connecting two otherwise distant parts of the universe. (The good Doctor knows all about that.)
What's nice about this particular video is that it doesn't stop there. General relativity might need a few tweaks in light of the 1998 discovery that not only is our universe expanding, it's expanding at an ever-increasing rate. That's why physicists today invoke dark energy and dark matter as a possible explanation consistent with the GR's predictions.
As Tennant notes, physicists have been putting general relativity to the test for a century now, and a new crop of experiments will put the theory to the test yet again, hopefully with definitive results. "If it succeeds again, physicists will party. If they find its limits and it finally fails, they will party too. Physicists are funny like that."
Bonus: In his annual Thanksgiving post, Caltech physicist Sean Carroll gives thanks for the mathematical basis for curved space-time: Riemannian Geometry. Since we're celebrating the 100th anniversary of general relativity, he reasons, "it makes sense to honour the epochal advance in mathematics that directly enabled Einstein's epochal advance in our understanding of space-time."