Gravitational lensing



Einstein's Cross- example of lensing.

 Einstein's Relativity theory allows for certain effects that would not be possible according to the Newtonian theory. Because Gravity does not involve a force, massless objects can be affected. A straight beam of light, passing by a dent in space-time caused by a object of mass, will be bent to follow that geodesic path. The implication of this is a phenomena called gravitational lensing.

The main idea of Gravitational Lensing is if a massive object is in front of a star, or other bright object, the rays from the star will be bent around the massive object, appearing to the observer to be two or more distinct objects.

This is far from being just an interesting effect. Using geometry, one can derive the approximate distance of the object. Also Astronomers are using gravitational lensing to predict the placement and size of pockets of dark matter, as it also bends light.
Sincerely,
Space Cadet