Predicting Gravitational Waves
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Flaws in Newton's Theory
As scientists developed better astronomical tools, they noticed slight differences between their measurements and Newton’s predictions. For example, Newton’s prediction of Mercury’s path around the sun was slightly different from what astronomers observed. Newton’s theory also did not give a satisfactory answer to the question:
What would happen if the sun suddenly disappeared?
According to Newton’s theory, the whole universe would know about the sun’s disappearance immediately. This means that all of the planets revolving around the sun would fly out of orbit right away. However, Einstein reasoned that it should take longer for the planets farthest from the sun to find out what happened, so the closet planets should fly out of orbit first.
Image Courtesy of NASA/JPL-Caltech.
The idea that information can travel across the universe instantaneously is called action at a distance. Einstein and many other scientists were troubled by action at a distance because it means that some information can travel faster than light.
Einstein finally solved the action at a distance problem in 1916. He explained that gravity was not an instantaneous force as Newton assumed, but that it took time to travel. This assumption was one reason why some of Newton’s predictions were not quite right. Before we discuss Einstein’s theory of gravity (called the General Theory of Relativity), however, we need to discuss his Special Theory of Relativity.
