329
See also: Gravitational theory 66–73 ■ The theory of relativity 146–53
decades-long search had revealed
the gravitational equivalent of
tsunamis created by two black
holes spiraling around each
other and then colliding.
It is hoped that the discovery
of gravitational waves will provide
a new way of observing the
universe. Instead of using light
or other electromagnetic radiation,
astronomers are hoping to map
the universe by the gravitational
effects of its contents. While
radiation is obscured in many ways,
including by the opaque plasma
of the early universe up to 380,000
years after the Big Bang, gravitational
waves pass through everything.
This means that gravitational
astronomy could see back to the
very beginning of time, a trillionth
of a second after the Big Bang.
Wave behaviors
LIGO stands for Laser Interferometer
Gravitational-Wave Observatory.
It is a remarkable set of instruments
for measuring expansions and
contractions in space itself. This
is no easy task. A ruler cannot do it
because, as space changes in size,
so does the ruler, so the observer
measures no change at all. LIGO
succeeded using the benchmark
that remains constant whatever
space is doing: the speed of light.
Light behaves like a wave, but it
does not require a medium through
which to travel. Instead, light
(and any kind of electromagnetic
radiation) is an oscillation of an
electromagnetic field: in other
words, light is a disturbance in
a field permeating all of space.
Gravitational waves can be
understood as disturbances in the
gravitational field that permeates
the universe. Einstein described
how these disturbances are causedTHE TRIUMPH OF TECHNOLOGY
Relativity reveals that gravity is
the warping of spacetime by mass.Moving objects create ripples through
spacetime, or gravitational waves.Gravitational waves
let astronomers see
farther into space
than ever before.Gravitational waves can
be detected by measuring
the expansion and
compression of spacetime.Within a period of 20 milliseconds,
the two black holes LIGO had detected
increased their orbital speed from
30 times a second to 250 times a
second before colliding.by the mass of objects curving
the space around them. What is
understood as the “pull of gravity”
is a small mass appearing to alter
its motion and “fall” toward a larger
mass as it encounters a region of
warped space.
All masses are in motion—
planets, stars, even galaxies—and
as they move, they leave a trail of
gravitational disturbances in their
wake. Gravity waves propagate in
a comparable way to sound waves,
by distorting the medium through
which they travel. In the case
of sound waves, that medium is
made of molecules, which are made
to oscillate. In the case of gravity,
the medium is spacetime, the very
fabric of the universe. Einstein
predicted that the speed of gravity ❯❯