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Computer
illustration from a simulation of the collision of two neutron
stars.
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When
Albert Einstein formulated his general theory of relativity in 1916,
he noted that the theory predicts the existence of an entirely new
form of cosmic radiation. Gravitational radiation, unlike the electromagnetic
radiation we know as visible light, radio,and other now-familiar
types, consists of ripples in the fabric of space itself, produced
by the motion of large amounts of matter. When
a star explodes, or when two black holes collide and merge, these
episodes of cosmic violence shake the vacuum of space around them.
This shaking generates waves that travel outward in all directions
through space at the speed of light. When this gravitational radiation
encounters another object, its waves distort it. But they do so
in ways that challenge our ability to detect the distortion, because
they stretch and shrink space (and any objects within it) by amounts
that span only a tiny fraction of the size of a single atom!
Astronomers
and physicists have long known that the detection of gravitational
radiation will allow us to probe deeply into the violent events
that produce it. Because this type of radiation interacts only weakly
with matter, its waves will emerge relatively unaffected from the
heart of catastrophic events in the cosmos. In contrast, light waves
and other forms of electromagnetic radiation must slowly leak through
masses of material blocking their passage. They inevitably lose
much of the information that they originally carried in this passage.
Observation
of gravitational radiation requires isolating precisely manufactured
objects so that they remain as free as possible from all outside
influences. Monitoring with extreme accuracy the shape or the separation
of pairs of these objects then allows us to detect the nearly infinitesimal
movements that arise from the shaking of space-time by the radiation
as it passes by. If we can detect them, the waves of gravitational
radiation offer a new, clear view of some of the most exciting events
in the cosmos, some of which are otherwise unobservable.
Future
generations of detectors may offer the earliest view of the universe
from a time just after the Big Bang and well before the first possible
moment from which we can see electromagnetic radiation.
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