Question

State Einstein’s principle of equivalence. How does this relate to bending of light by stars?

Answer 1

In the theory of general relativity, the equivalence principle is the equivalence of gravitational and inertial mass, and Albert Einstein's observation that the gravitational force as experienced locally while standing on a massive body (such as the Earth) is the same as the pseudo-force experienced by an observer in a non-inertial (accelerated) frame of reference.

Einstein’s theory of general relativity, the presence of a mass curves the surrounding space in a way that is similar to the “bending of space toward the light”. The resulting angle of deflection for light passing close to the Sun is exactly twice as large as in the Newtonian case – with the equivalence principle and the curvature of space each responsible for half of that value.

Now the equivalence principle provides a powerful argument that light is influenced by gravity. In fact, it was through such reasoning that Einstein first thought about the deflection of light as he was working on general relativity. However, if we want to be certain whether or not there is large-scale light deflection, we need to go beyond the equivalence principle, and take into account the geometry of space. In general, light gets bend while passing from a massive object due to gravity.

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