Question

Explain General Relativity. Give examples.

Answer 1

General relativity is a theory of space and time. The theory was published by Albert Einstein in 1915.[1] The central idea of general relativity is that space and time are two aspects of spacetime. Spacetime is curved when there is gravity, matter, energy, and momentum. The links between these forces are shown in the Einstein field equations.

A central idea in general relativity is the "principle of equivalence." An example is that two people, one in an elevator sitting on the surface of the earth, and the other in an elevator in outer space accelerating at 9.8 m/s2, will each observe the same behavior of an object they drop from their hand. The object will accelerate to the floor at 9.8 m/s2in either case, making it impossible for either to distinguish whether or not they are at rest in a gravitational field or accelerating upward at one g. Other versions of this type of "thought experiment" were used to show that light would curve in an accelerating frame of reference. There are several forms of the equivalence principle. These include: Newton's equivalence principle, the weak equivalence principle, the gravitational weak equivalence principle, Einstein's equivalence principle and the strong equivalence principle.

Following phenomenon can be seen as examples of it.

• As light gets closer to the sun, it bends towards the sun twice as much as classical physics (the system used before general relativity) predicts. This was seen in an experiment led by Arthur Eddington in 1919.[3] When scientists saw his experiment, they started to take general relativity seriously.
• The perihelion of the planet Mercury rotates along its orbit more than is expected under Newtonian physics. General relativity accounts for the difference between what is seen and what is expected without it.
• Redshift from gravity. When light moves away from an object with gravity (moving away from the center of the valley), it is stretched into longer wavelengths. This was confirmed by the Pound-Rebka experiment.
• The Shapiro delay. Light appears to slow down when it passes close to a massive object. This was first seen in the 1960s by space probes headed towards the planet Venus.