Saturday, 20 July 2013

Is light affected by Gravity?

By visualizing experiments in accelerating reference frames and using the principle of equivalence to transpose them to gravitational situations, Einstein postulated that light is bent in Gravitational field. Light is a type of electromagnetic radiations (Refer Types of Radiations), it consists of a bosonic particle called Photons. Photons are mass-less particle, i.e its mass is 0. According to Newtonian gravity, every object with mass exert Gravitational force and is effected in Gravitational field. Since light is mass-less it must not be effected in Gravitational field and followed a straight path in a Strong gravitational field. This, however, was not that happened.

An experiment with light

Take an example of a sealed box with a torch attached to on of its side. Now suppose the torch is turned on and the box is accelerated in open space. When the box was at rest and not under any influence of gravity, the light followed a straight path, but when the box is accelerated, light could no longer follow the same straight path. It has to follow a curved path. If Gravity is too an accelerated motion then Light, despite having no mass, must follow a curved path in a Gravitational field. This effect could be well observed in a Strong Gravitational field such as block hole from where light cannot escape.

Einstein used such experiments to show that light is influenced by gravity, having no evidence his postulate was not accepted. In 1919 a major astronomical observation proved that it was true.

What caused light to bend?

Developing the idea further Einstein theorized that Gravity causes local distortion in Space Time. As already discussed Space time is a 3-Dimensional location of an object with respect to time (See SpaceTime). Einstein explained that Mass causes dent in Space Time which forces the light to bent and not follow a straight path.

This also means that what position of stars and other celestial bodies we see is not their actual position bu apparent position. The bent light enters the telescope to give us and apparent position but not an actual position.

Apparent positions of stars

<- Previous Chapter                                                                                                                 Next Chapter ->