 
Goals | Einstein & Beyond | Echoes From Big Bang | Binaries | Black Holes
Ripples in space-time are waves of gravity emitted by the movement of massive bodies, such as black holes or binary systems, in space. The movement of these massive bodies disturbs the "fabric of space-time" around them, sending ripples of gravitational waves radiating outward. These waves are predicted by Einstein's Theory of General Relativity, but have yet to be directly detected. The new generation of gravitational wave detectors, such as the Laser Interferometer Space Antenna (LISA), a space-based detector, and the Laser Interferometer Gravitational-Wave Observatory (LIGO), and other ground-based detectors, are designed to study these waves. These detectors will enable us to learn more about gravity, how gravitational waves propagate, and the sources that emit them.
Much of what we now know about gravity comes from our experiments within our Solar System. These experiments confirm that gravity is a universal force connecting all forms of mass and energy. This means that gravity should act in the same way wherever you are in the Universe. However, there are still unanswered questions, leftover from theories developed by Einstein and others (see the Einstein and Beyond section). Some of these questions may be answered by the new kinds of low-frequency observations that scientists expect LISA to provide.
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What LISA will see.
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The most predictable and most powerful sources of gravitational waves emit their radiation at very low frequencies (below 10 millihertz), although some sources will be detectable at higher frequency bands. Binary systems in our own Galaxy are the most predictable sources and supermassive black hole mergers in distant galaxies are the most powerful sources. LISA will study thousands of compact (small and dense) binaries in our own Galaxy, merging supermassive black holes in distant galaxies, and the spiral descent of dying stars into black holes. LISA will also search for gravitational wave emission from the early Universe, probing the energy content at about one second after the Big Bang.
LISA will be able to test the predictions of Einstein's theories and determine if they are correct. This will be accomplished by studying the varying signals coming from a compact star spiraling into a black hole and mapping the structure of space and time around the black hole. Additionally, the arrival times of light and gravitational waves emitted by the same source will be compared, to test Einstein's prediction that gravitational waves and light waves should travel at the same speed. LISA's observations, complemented by those of ground-based detectors like LIGO, will extend and enhance our understanding of the Universe.
On to About Einstein & Beyond I
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