Page 19 - GALIET PHYSICS BLOSSOMS III

Since we are inside this geometry, we cannot visualize it ’from outside’. However we can still test ’from inside’ to see what the geometry is. One way is to look at the path of a ray of light in a vacuum (which defines a straight line in our world).
Describe using diagrams how the theory of Einstein was tested using light propagation past the sun. Explain what would have been seen if Newtonian theory were correct, and what was actually seen.
Einstein’s theory that space is curved was tested simply using gravitational lensing or light bending. The essence of General Relativity is that spacetime curvature affects all things, including light. Succintly, the theory posits that when light comes closest to the Sun, the more it deflects. So the theory was tested with the Sun’s deflection of light. First, we need to look at how the trajectories of light rays move through the universe. Given that light travels always at the same speed, we assume light must travel in the straightest possible path. However, if space is curved, then light trajectories must also be curved.
To test Einstein’s theory in 1919 under Sir Eddington, astronomers travelled to Africa and to Brazil’s Sobral and Principe Islands aspiring to measure the displacement of stars near the Sun during a total solar eclipse. Normally, we cannot see stars close to the Sun; but during a solar eclipse, when the moon blocks the sun’s light, we can observe things more clearly. As a result, during the daytime, the Royal Society’s astronomers measured the angular separation between two stars just at the point when the light from one of the stars passed near the Sun. They discovered that the space’s curvature near the Sun caused the closer-to-the-Sun light beam (Star A) to curve or bend more than the other star light beam (Star B). As a result, they realized that the two stars’ angular separation should appear smaller than their true angular separation.
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