Gravitational Lensing?

Question

Is Gravitational Lensing the reason light cannot escape a black hole?

If you believe in relativity then you believe that planets or other massive objects influence the shape (or fabric) of space. Then does it follow that since a black hole has infinite gravity it would have infinite warp on the fabric of space, so any light source from within would follow the shape of space that was infinitely warped and just spin in circles around the center of mass? In theory.

Answer 1

Gravitational lensing is actually when light is bent by gravity being extered by objects.

These do not have to be black holes, but they are definately objects that exert large amounts of gravity.

You have a remember that black holes only exhibit infinite (I hate that word) gravity at the event horizon. So light can pass near a black hole and be distorted/lensed unless it crosses the event horizon.

Your question assumes that something at the event horizon is capable of creating light, if there is such an object then light would be subject to gravity which would pull it back towards the singularity at the event horizon as the black hole spins.

Answer 2

First, you assumption that a black hole has infinite gravity is not correct. It has a huge gravity, but not necessarly infinite. A black hole can actually have a releativly small mass (say a solar mass) but still have a strong enough gravity so the escape velocity is greater than the speed of light.

And, that is the crux, if an objects gravity is large enough so that escape velocity is greater than the speed of light, then you have a black hole.

I did the math for a question like this yesterday, and a mass of the sun, with a radius of 3km will have a gravity strong enough so that it would be considered a black hole.

Now, on to gravitational lensing. Any object with mass has a gravational field. That field will warp space, and light, while traveling in a stright line hits that warped section, it will bend, the same way a marble rolling on a level ground will bend it's path if it hits a hole.

This bending can cause the light behind a massive object to bend together and focus on a point. That is gravational lensing.

Answer 3

The same phenomenon causes both gravitational lensing and the fact that light cannot escape a black hole. They are both results of the same thing, one is not the cause of the other.

Gravity causes space to bend. If gravity is bent to to enough mass between the source and observer or light, you will get ghost images and such.

For a black hole, the gravity field is so great that the escape velocity needed to get out is faster than the speed of light, thus not even light can escape - even though it has no mass. The gravitational intensity increases as you get closer.

The distance where the escape velocity equals the speed of light is called the event horizon. The center of the black hole, the point of infinite density, is called the singularity.

Answer 4

When an object is behind another one, preferrably a massive one, the light that normally would travel directly toward the earth is blocked by the massive object. The light that is emitted and is not headed toward the Earth is bent around the massive object and redirected to the Earth. The event horizon of a black hole is a radius from the singularity where no light escapes from. A black hole can be a gravitational lens, but only for light who's path doesn't enter the event horizon. The effect is possible because light has momentum, and therefore has a "travelling mass".

Answer 5

The gravitation of a black hole is not infinite. It depends solely on the mass of the black hole. The event horizon is the radius at which the escape velocity of the black hole exceeds the speed of light; that means that a beam of light or any particle with mass can never escape (aside from Hawking radiation, which allows matter to escape but not information).

Answer 6

Masses moving toward a larger mass,=Gravitational motion,Would follow a curved trajectory.The light going thru the sun"s photosphere will be bent due to the refraction phenomena.
So gravitational bending of light going thru the field would have to travel near a very large mass having a gross density to be affected. This scenerio is what is called gravitational lensing.

However light going thru a glass also is bent to form a picture at the focus. So it must be the configuration of the mass of the grlass that causes this lensing effect.

It is said that light bends because of the warping of space curvature. This proves that space contains a substance that is subject to compression.
If Space was empty that it would make no commonsense to say that it warps and the curvature of emptiness would be emptiness.

Answer 7

That is essentially one way of looking at it, yes.
The black hole lenses all light right back to itself.