The announcement that the Earth is five millimeters smaller than previously believed was to many people a nonevent—in part, I’m guessing, because five millimeters isn’t very much. Five millimeters is roughly half the width of the pinkie finger (call it one-fifth of an inch for those stouthearted holdouts who have not learned to think metric). It’s an almost inherently negligible distance, five millimeters. Certainly when compared with the mighty Earth, a difference of five millimeters might not have seemed worth getting worked up about.
But to those of us burdened with the privilege of writing humor columns for science magazines, it was very much worth getting worked up about. If ever there was a morning to have a little champagne with breakfast, as opposed to the usual steadying few tumblers of Hennessy, this surely was it. On the one hand you had the Pythonesque absurdity, the sheer Borgesian weirdness of someone measuring the planet and finding it five millimeters too petite. At the same time, inextricably bound up with the humor, were several unimpeachably substantive questions: What did these people mean, the world is five millimeters smaller than they’d thought? How was such precision possible? And the big one: So what?
I headed off to NASA’s Goddard Space Flight Center to investigate in a spirit of uncharacteristic optimism. Either this five-millimeters thing was as ludicrous as it sounded and I could make merciless fun of everyone involved, some of whom, doubtless, would have mustaches. Or, less likely, I’d find there was something serious to it after all, something that really matters.
Well, I’m back. And to my mild surprise, it’s the latter. The Goddard Space Flight Center sits 20 miles south of Baltimore, in the great sprawl of forests, gated communities, and sinister government agencies that billow from Washington, D.C., like the swirled cape of a melodrama villain. Behind chain-link fences and unsmiling checkpoints, the buildings of Goddard have a low and windowless appearance—even those of them that are relatively tall and/or have windows—making it a prime outpost for Serious Thinking.
It should be noted that the new, downsized measurement of our planet was made by one Professor Axel Nothnagel at the University of Bonn in Germany. And yet I am in Maryland. If you find this perplexing, I fear you are betraying your lack of education on two key topics: this correspondent, who doesn’t happen to like Germany, and Very Long Baseline Interferometry, which is the technique Nothnagel relied upon in assessing the Earth with such sidesplitting precision.
I am here to confer with two people who know a great deal indeed about Very Long Baseline Interferometry: Chopo Ma, specialist in extragalactic astrometry at Goddard’s Space Geodesy Laboratory, and Dirk Behrend, the coordinating director of the IVS, which stands for International VLBI Service, the VLBI in which unpacks to (oh, will you look at that) Very Long Baseline Interferometry. In a conference room deep in the bowels of Goddard’s particularly windowless Building 33, these world-class authorities dim the lights, throw a magic-lantern image of the Earth upon a screen, and quickly share with me the finer points of measuring a planet to the nearest millimeter.
The key to it, apparently, is quasars. Quasars are active galaxies—very distant, very active galaxies, the most distant detectable objects, in fact, in all of existence. How far away? So very, very far away, explains Ma rather casually, that if one of them were shooting laterally across the sky at the speed of light, it would, to us, appear motionless. That’s if you could see it, of course, which you wouldn’t be able to because it’s so far away. Hearing it is another matter entirely, however. Quasars turn out to be prodigious broadcasters of radio emissions, issuing faint whispers of smooth jazz and shadow traffic from across the inky vastness of Space.
Herein lies their usefulness. Being so very, very far away, and therefore holding their positions in our sky with what appears to be perfect constancy, quasars allow us to find our bearings here on Earth with near-perfect precision. By gathering the radio signals emitted by any particular quasar at various far-flung points about the globe and measuring the tiny time lag between the signal’s arrival at the different locations, people like Ma and Behrend can tell exactly how far apart those locations are.
Sheepishly, I bring up the issue of Nothnagel’s five millimeters, and Ma replies, in that maddening way scientists tend to do, that things are not so simple. The world “is and it isn’t” five millimeters smaller than previously thought, he says. It depends on collecting information over a long period of time, and thanks to VLBI, we also know that the world is constantly expanding and contracting and wobbling in amounts that make five millimeters look like . . . well, like five millimeters. For one thing, the entire solid Earth bulges some 40 centimeters (16 inches) twice a day, kneaded by the pull of the sun and the moon.
