By Davide Castelvecchi
From Science News, March 31st, 2007; Vol.171 #13 (p. 206)
A proposed experiment that would make ancient astronomers proud could end speculation about dark matter.
Scientists have long known that most stars orbit their galaxies so rapidly that gravity wouldn’t be strong enough to keep them from flying away. The mainstream explanation is that some yet-undetected, or dark, matter adds mass to galaxies, increasing their gravitational tug.
Last year, astronomers reported the most dramatic evidence yet for dark matter (SN 8/26/06, p. 131). But a few scientists remain skeptical. In an alternative theory, called modified Newtonian dynamics, or MOND, forces such as gravity would produce small accelerations in addition to that which standard Newtonian physics predicts. MOND would explain the orbits of stars without any need for dark matter.
Alexander Ignatiev of the Theoretical Physics Research Institute in Melbourne, Australia, now proposes to test MOND here on Earth. At particular times and places, he calculates, all the accelerations caused by the motions of Earth and the sun cancel each other out. But if MOND were true, a small effect would remain—and state-of-the-art instruments might detect it. The effect of that anomalous acceleration on a test mass would measure a hundred-billionth that of the normal gravitational acceleration at Earth’s surface.
The trick is to position an instrument within 7 centimeters of a specific latitude and longitude. Only two spots would qualify: one in Antarctica and one in northern Greenland. And just like many ancient rituals, the experiment could take place only during an equinox.
Ignatiev published his proposal in the March 9 Physical Review Letters.