What Causes Gravitational Force?

For a long time, no one knew what caused gravitational force, but Albert Einstein changed that. This idea is known as the General Theory of Relativity. His idea states that the way we view space may not be how it really is. For example, some used to think the world is flat because if feels flat to us. Einstein's theory shows that the reason the planets orbit the sun is because the sun's mass pulls the planets in a circular motion. The other theory of gravity says that two massive objects tend to exchange tiny particles called gravitons. This theory has never been proved as gravitons have never been observed. One of the reasons that some people believe this is because all the other forces are explained by particle exchange. 


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