If photons have no mass, how are black-holes able to suck in light?

Question

If photons have no mass, how are black-holes able to suck in light?

In: Physics

Answer 1

Gravity as mass attracts mass is the model in Newtonian mechanics.In general relativity, gravity is the curvature of space-time caused by mass deforming it.

We know that general relativity explains our observation of the universe better than Newtonian mechanics. The bending of light because of gravity is in fact one way that special relativity was tested. The [https://en.wikipedia.org/wiki/Eddington_experiment](https://en.wikipedia.org/wiki/Eddington_experiment) is an observation during a total solar eclipse in 1919. They observed a star that was close to the edge of the sun observed that their position had changed because the gravity of the sun bent the light. You had to do it during an eclipse else the glare of the sun would make an observation of a star close to it impossible. The result is an observation that Newtonian mechanics can’t explain but general relativity

This was front-page news on most major newspapers around the world, it made Einstein and his theory of general relativity world-famous.

We still use Newtonian mechanics in most situations. Is a lot simpler to use and the result is almost identical on the human scale and the solar system scale.

On the solar system scale, the [Precession of the perihelion of Mercury](https://aether.lbl.gov/www/classes/p10/gr/PrecessionperihelionMercury.htm) is the change in position in the obit is it farthest from the sun. The difference between the two explanations is 0.012 degrees per century. This is the most significant difference for obits in our solar system.

You can observe the effects on earth too if you set up very accurate experiments. But for everyday usage the difference is negligible.

So Newtonian mechanics is used most of the time because it is simpler and the difference will be less the uncertainty of any other measurement. In some situations like you need to use general relativity. Blackholes or just light passing close to our sun are examples of where it is needed.

We also know that general relativity can’t explain everything because on a small scale quantum mechanics and general relativity do not match up. There is a lot of recharges that tires to combine them.