Tuesday, May 15, 2007

Subtlety

I suppose I should read Walter Isaacson's new biography of Einstein, which sits on top of the NYT Bestseller List, but, lordy, I have read so many biographies of Einstein I'm not sure there is room in my brain for another. My favorite is Abraham Pais's Subtle Is the Lord: The Science and the Life of Albert Einstein (Oxford University Press, 1982)

Einstein said: "The most incomprehensible thing about the world is that it is comprehensible." And when you think about it, it is indeed remarkable that a mass of nerve fibers the size of a softball can comprehend the cosmos -- hundreds of billions of galaxies with a 15 billion year history. Of course, some softball-sized masses of nerve fibers are more remarkable than others. Einstein proposed "laws of nature" so remote from ordinary experience that a generation passed before experiments could be devised to decisively test them.

Let me mention just one experimental confirmation of Einstein's theory of general relativity.

At the end of a star's life, gravity causes the star to collapse upon itself. Stars rather more massive than the sun are squeezed so strongly by gravity that even atoms are collapsed; electrons are squeezed into protons to create neutrons. Such an object will be about as big as the state of Rhode Island, and spinning extremely rapidly for the same reason a ice skater spins more rapidly when she draws in her arms closer to her axis of spin. Radiation from the whirling star is emitted as a beam and observed in pulses, like light from a rotating lighthouse lamp. These collapsed stars are called neutron stars or pulsars. The first pulsar was observed in 1967. Today, thousands of them are known. Their pulses of radiation are as exact as the best atomic clocks on Earth.

One pulsar, called PSR 1913+16, is part of a binary system -- two stars locked in a whirling dance. Einstein's theory predicts that two masses revolving about each other will emit gravitational waves, in the same way that oscillating electric charges emit radio waves. We do not have the technology to detect these gravitational waves, but they should carry energy away from the rotating star system and the flash rate of the pulsar should slow down. Astronomers have been observing the binary pulsar for 30 years, and the slowdown is exactly as predicted by Einstein's theory. The agreement is breathtakingly precise.

A collapsed star thousands of light-years away flashes precisely as predicted by equations dreamed up by Einstein long before pulsars were discovered. Nothing is more incomprehensible than that this should be true.