General relativity and spacetime curvature

Summary

General relativity describes gravity not as a force acting instantaneously across space, but as the curvature of spacetime caused by mass and energy. Massive objects alter the geometry of spacetime, and freely falling bodies follow paths determined by this curved geometry. When massive objects move in an asymmetric way, their changing curvature can propagate outward as gravitational waves at the speed of light. Gravitational waves are ripples in spacetime curvature that transport energy and change the relative separation of freely falling objects. They are produced by powerful astrophysical events such as merging black holes and neutron stars, and their effects are extremely small by the time they reach Earth. The observation of gravitational waves, first indirectly through binary pulsars and directly by LIGO in 2015, provides strong evidence for general relativity and opens a new way to study the universe.

Key Points

• 1

  In general relativity, gravity results from the curvature of spacetime produced by mass and energy.

• 2

  Changes in spacetime curvature caused by accelerating, nonspherically moving masses can propagate as gravitational waves.

• 3

  Gravitational waves travel at the speed of light and carry energy away from their sources.

• 4

  A passing gravitational wave produces tiny, alternating changes in the separation of freely falling objects.

• 5

  Observations of binary pulsars and black-hole mergers have confirmed predictions of general relativity.