Question

3. Describe two real (not thought) experiments or observations that have critically tested new gravity effects predicted by Einstein’s ideas about relativity. Note: The mass-independence of free fall is not a new effect - it has been known about for centuries.

Answer 1

1. The most striking prediction of general relativity is that of gravitational waves. Electromagnetic waves are caused by accelerated electrical charges and are detected when they put other charges into motion. Similarly, gravitational waves would be caused by masses in motion and are detected when they initiate motion in other masses. However, gravity is very weak compared with electromagnetism. Only a huge cosmic event, such as the collision of two stars, can generate detectable gravitational waves. .
2. Since almost two centuries earlier astronomers had been aware of a small flaw in Mercury's orbit around the Sun, as predicted by Newton's laws. As the closest planet to the Sun, Mercury orbits a region in the solar system where spacetime is disturbed by t he Sun's mass. Mercury's elliptical path around the Sun shifts slightly with each orbit such that its closest point to the Sun (or "perihelion") shifts forward with each pass. Newton's theory had predicted an advance only half as large as the one actually observed. Einstein's predictions exactly matched the observation.