Sky & Telescope October 2000 [antikvár]

Gravity Matters o you play lotto or some other get-rich-quick rip-off? Do you plop down a buck and happily accept odds of tens of millions to one? Let's turn the game around. Plop down hundreds of millions of dollars (or even enough billions to make Hubble blush) and claim the odds of winning are one to one. That's what the builders of LIGO and other gravitational-wave detectors are gambling on. The bet hinges on two leaps of faith — that Einstein is right once again and that gravitational waves can be detected directly. We think we've already seen their effect on the neutron-star binary PSR 1913-hl6, so maybe LIGO and its siblings have a sure bet after all! The last half century has been remarkable in that we've opened wide the electromagnetic spectrum, our vision of the universe. We know the least energetic creatures that live there: atoms that shiver at essentially absolute zero deep within dense clouds of gas. But we are still far away, I suspect, from meeting the most energetic ones, the universe's true superstars. That's the real promise of gravitational-wave physics: to discover the unimagined. Even space-time ripples woven into the fabric of the universe by the Big Bang itself await capture. And, since ripples have wavelength, we can anticipate new harmonies, new symphonies. That's why we've devoted this month's suite of features to gravitational waves and the machines that search for them. What if LIGO sees nothing? The standard debate will begin: we need more sensitivity (more money), the design is flawed (previous naysayers), Einstein is wrong (the fringe). Well, the Viking landers didn't find life on Mars, but we kept looking. Now success may be close at hand. From the time Einstein proposed his general theory of relativity in 1915 only a handful of astronomers thought about gravity in a relativistic sense — until 1963. That's the year quasars were recognized as something special — so special that something other than thermonuclear fusion had to power them. This was a stage-call for enormously gravid black holes, with millions or billions of solar masses, to account for the quasars' astounding energy output. And, with the discovery of Cygnus X-1 — a ponderous ghost doing a Dumbo-tango with an equally ponderous but visible partner — we realized that black holes come in much smaller sizes too. For two millenniums astronomers were restricted to measuring the locations of things on the sky. Only during the last century or so — as terrestrial physics was hammered onto celestial bodies — have we begun to understand how pieces of the universe actually work. Now, ironically, the cutting edge has returned to measuring — but this time of the shape of space itself.