test involved measuring the bending of light as it passed around the sun. Both Newton's and Einstein's theories predicted that light would be deflected by gravitation. But the amount of deflection predicted by the two theories differed. The light to be measured in such a test originates in distant stars. However, under ordinary conditions the sun's brightness prevents scientists from observing the light from these stars. This problem disappears during an eclipse, when the moon blocks the sun's light. In 1919 a special British expedition took photographs during an eclipse. Scientists measured the deflection of starlight as it passed by the sun and arrived at numbers that agreed with Einstein's prediction. Subsequent eclipse observations also have confirmed Einstein's theory.Other physicists have proposed relativistic theories of gravitation to compete with Einstein's. In these competing theories, almost all of which are geometrical like Einstein's, gravitational effects move at the speed c. They differ mostly in the mathematical details. Even using the technology of the late 20th century, scientists still find it very difficult to test these theories with experiments and observations. But Einstein's theory has passed all tests that have been made so far. B. Applications of Einstein's Theory Print section Einstein's general relativity theory predicts special gravitational conditions. The Big Bang theory, which describes the origin and early expansion of the universe, is one conclusion based on Einstein's theory that has been verified in several independent ways.Another conclusion suggested by general relativity, as well as other relativistic theories of gravitation, is that gravitational effects move in waves. Astronomers have observed a loss of energy in a pair of neutron stars (stars composed of densely packed neutrons) that are orbiting each other. The astronomers theorize that energy-carrying gravitational waves are radiating from the...
