Making waves Einstein's way.

• Author: Braffman-Miller, Judith
• Position: Science & Technology

IMAGINE A PUDDLE lingering on the street after a heavy summer thunderstorm. Now, imagine a small child walking along the damp sidewalk, picking up a small stone, and tossing it playfully into the puddle. Ripples form in the shallow water left over from the rain, and then propagate outward through the puddle. Gravitational waves propagating though spacetime are similar to the ripples propagating though that puddle of water.

According to Albert Einstein's General Theory of Relativity (1915), gravity causes spacetime to curve under the influence of mass--the more mass contained within a particular region of space, the greater the curvature will be at the boundary of that particular region. As celestial bodies roam around through the universe, the curvature of spacetime changes in accordance to the movement and location of those bodies--and, under certain special circumstances, accelerating objects will cause alterations in this curvature that propagate outward through spacetime at the speed of light in a wavy way. These ripples in the curvature of spacetime are termed gravitational waves, and these are generated in certain gravitational interactions. These ripples in the fabric of spacetime then travel outward from their place of origin.

In 1916, Einstein predicted that, on the basis of General Relativity, gravitational waves carry energy in the form of gravitational radiation, a manifestation of radiant energy comparable to electromagnetic radiation. Gravitational wave astronomy is an emerging field that uses gravitational waves in order to obtain precious observational information concerning bodies (such as neutron stars and black holes), supemovae blasts, and cosmological processes that include many of the myriad mysteries of the primordial universe soon after its inflationary Big Bang beginning almost 14,000,000,000 years ago.

A team of astronomers recently announced their observations of these gravitational ripples in the fabric of spacetime that have, at long last, reached Earth from their distant origin--an ancient catastrophic event in a remote region of the universe. In astronomy, long ago is the same as far away. The more distant an object is in space, the more ancient it is in time. The speed of light sets something of a universal speed limit. This is because no known signal in the universe can travel faster than light in a vacuum, and so the more remote a shining object is in space, the longer it has taken for its traveling light to reach Earth. This first detection of the previously elusive gravitational waves confirmed this major prediction of General Relativity.

Gravitational waves carry a treasure trove of information about their generally spectacular origins--and about the nature of gravity itself. This information cannot be obtained in...