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Does gravitational force of black hole attract the light? Or is it something else?

ACuriousMind
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user21891
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  • Gravity effects anything with energy. While light doesn't have rest-mass, it still has energy thus effected by gravity. Check It. http://physics.stackexchange.com/questions/34352/how-is-light-affected-by-gravity. – Shuvo Habib Oct 15 '15 at 11:19

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According to general relativity(GR), gravity can be described as the curvature of spacetime. In GR there is thus no gravitational force. There only appears to be a force.

For example, a bullet shot in outer space will travel along a straight line. When a bullet is shot nearby a planet, due the local curvature of spacetime, the bullet will seem to be attracted by the gravitational force of the planet. However, according to GR, the bullet actually follows a straight line through a curved part of spacetime.

Because in this picture gravity is a purely geometrical effect it applies to all objects. It is for this reason that the observed gravitational acceleration is the same for all objects, independent of their mass (if you ignore air resistance, feathers fall just as fast as rocks) This even holds if the mass is zero, as for light.

In the special case of a black hole, the space is so strongly curved that close to the black holes there are no straight lines which point away from the black hole. It is therefore impossible for anything, including light, to leave the black hole.

Crimson
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  • Note that where I use the term straight line, the technical term is a geodesic – Crimson Oct 15 '15 at 11:51
  • Re There only appears to be a force. Where an object's world-line in spacetime is a geodesic we say that the object is "falling". The only thing that can stop an object from falling is a force. There is no force that causes satellites to orbit their planets---satellites "fall" in elliptical orbits---but there is a very real force pushing upward on the soles of your feet that stops you from falling in to the center of the Earth. – Solomon Slow Oct 15 '15 at 13:21