Q. Consider the following statements:

  1. Light is affected by gravity.
  2. The Universe is constantly expanding.
  3. Matter warps its surrounding space-time.

Which of the above is/are the prediction/predictions of Albert Einstein’s General Theory of Relativity, often discussed in media?

  • 1 and 2 only
  • 3 only
  • 1 and 3 only
  • 1, 2 and 3

Answer: (d) 1, 2 and 3

Notes
  • The bending of light by gravity can lead to the phenomenon of gravitational lensing, in which multiple images of the same distant astronomical object are visible in the sky. Albert Einstein predicted the existence of gravitational waves in 1916 in his general theory of relativity. Gravity, Einstein asserted, is caused by a warping of space and time. Gravity is the curvature of spacetime caused by massive objects.
  • In 1917, Einstein applied the general theory of relativity to the structure of the universe as a whole. He found that the general field equations predicted a universe that was dynamic, either contracting or expanding. Since observational evidence for a dynamic universe was not known at the time, Einstein introduced a new term, the cosmological constant, for the field equations to allow him to predict a static universe. In these years the modified field equations predicted a stable universe of closed curvature according to Einstein’s understanding of Mach’s principle. This model is known as Einstein’s world or Einstein’s stable universe.
  • 2010: International Team of Astronomers confirmed Albert Einstein’s theory of general relativity and that the expansion of the universe is accelerating after looking at data from the Hubble Space Telescope… there is an unknown source of energy in the universe which is causing the cosmic expansion to speed up.;
  • 2016: Japanese researchers’ study finds that the expansion of the universe could be explained by a cosmological constant, as proposed by Einstein in his theory of general relativity.
  • 2018: Hubble Space Telescope captured image of a phenomenon called Einstein Ring.
Gravitational Waves
  • Gravitational waves are waves of the intensity of gravity that are generated by the accelerated masses of binary stars and other motions of gravitating masses, and propagate as waves outward from their source at the speed of light.
  • Albert Einstein predicted their existence in his general theory of Relativity in 1916.
  • Einstein’s mathematics showed that massive accelerating objects (things like neutron stars or black holes orbiting each other) would disrupt space-time in such a way that ‘waves’ of undulating space-time would propagate in all directions away from the source. These cosmic ripples would travel at the speed of light, carrying with them information about their origins, as well as clues to the nature of gravity itself.
  • The strongest gravitational waves are produced by cataclysmic events such as colliding black holes, supernovae (massive stars exploding at the end of their lifetimes), and colliding neutron stars. Other gravitational waves are predicted to be caused by the rotation of neutron stars that are not perfect spheres, and possibly even the remnants of gravitational radiation created by the Big Bang.
  • Gravitational waves transport energy as gravitational radiation, a form of radiant energy similar to electromagnetic radiation.
  • Newton’s law of universal gravitation, part of classical mechanics, does not provide for their existence, since that law is predicated on the assumption that physical interactions propagate instantaneously (at infinite speed) – showing one of the ways the methods of Newtonian physics are unable to explain phenomena associated with relativity.
Gravitational Lensing
  • Gravitational lensing occurs when a massive celestial body – such as a galaxy cluster – causes a sufficient curvature of spacetime for the path of light around it to be visibly bent, as if by a lens. The body causing the light to curve is accordingly called a gravitational lens.
  • According to Einstein’s general theory of relativity, time and space are fused together in a quantity known as spacetime. Within this theory, massive objects cause spacetime to curve, and gravity is simply the curvature of spacetime. As light travels through spacetime, the theory predicts that the path taken by the light will also be curved by an object’s mass.
  • Extremely massive celestial bodies such as galaxy clusters cause spacetime to be significantly curved. In other words, they act as gravitational lenses. When light from a more distant light source passes by a gravitational lens, the path of the light is curved, and a distorted image of the distant object – maybe a ring or halo of light around the gravitational lens – can be observed.
Gravitational Lensing
Gravitational Lensing