the cross and turned away; the spacecraft was in the heavens where it belonged. Perfectly aligned with its guide star, it has been in orbit ever since.

CATCHING WAVES

Another critical test of general relativity doesn’t involve space probes; it is taking place right here on Earth. The LIGO (Laser Interferometer Gravitational-Wave Observatory) project is attempting to detect gravitational waves, the elusive ripples in the space-time fabric first predicted by Einstein in 1916. A joint project of scientists from Caltech and MIT, the observatory’s detectors began operation in 2001 and have scanned for signals ever since.

Researchers believe cosmic catastrophes, such as supernova explosions or collisions between black holes, generate volleys of gravitational waves. These shock waves are thought to fan out in all directions from such disturbances, rattling any massive objects lying in their paths—in the same way that shops rumble when an elevated train passes overhead. Although they’ve yet to be found directly, astronomers Joseph Taylor and Russell Hulse have used binary pulsars (pairs of rapidly spinning neutron stars) to show that they are likely to exist. For this work they received the 1993 Nobel Prize for Physics.

The LIGO project was proposed by physicist Rainer (Rai) Weiss of MIT, along with Kip Thorne, Ronald Drever, Rochus Vogt, and other researchers at Caltech. Born in Berlin in 1932 to a politically active family, Weiss emigrated with them at a young age to the United States to escape the terrors of the Nazi regime. Like Everitt, he was not originally trained in general relativity but rather in another branch of physics. Weiss received his Ph.D. at MIT, in the field of atomic physics under the supervision of Jerrold Zacharias.

Zacharias had dedicated himself to building high-precision time-pieces based on the predictable rhythms of atoms, an extraordinarily important endeavor with broad implications for a variety of scien-



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