# Non-linear Curvature

*Most recent answer: 12/28/2009*

Q:

Hello,
According to QED, EM force is mediated by virtual photons. Therefore, near black holes - where gravity is very intense - the virtual photons would not be able to travel a large distance and hence the range of EM force would be restricted.
Moreover, according to general relativity, curvature of spacetime is caused by energy density. However, does the curvature of spacetime curve spacetime?

- Majid Hasan (age 22)

Lahore, Punjab, Pakistan

- Majid Hasan (age 22)

Lahore, Punjab, Pakistan

A:

Those are great questions.

The first one is over my head, though I know that the answer is that static fields do extend out from black holes. Of course, before the black hole forms the charge and its field are already there, so the field doesn't really have to propagate, just stay put. If we get a better answer, we'll update.

On the second question, the answer is yes. That makes the General Relativity equations fundamentally non-linear, which leads to their weird behavior. On the other hand, in some ways it leads to more boring behavior. Imagine two big stars in strongly elliptical orbit around their center of mass. As they move closer together, gravitational potential energy is lost and kinetic energy is gained. If only one of those two counted as a source term from gravity, the effective mass as measured from the distant gravity would oscillate up and down. Since it doesn't, they most both in effect count.

Mike W.

The first one is over my head, though I know that the answer is that static fields do extend out from black holes. Of course, before the black hole forms the charge and its field are already there, so the field doesn't really have to propagate, just stay put. If we get a better answer, we'll update.

On the second question, the answer is yes. That makes the General Relativity equations fundamentally non-linear, which leads to their weird behavior. On the other hand, in some ways it leads to more boring behavior. Imagine two big stars in strongly elliptical orbit around their center of mass. As they move closer together, gravitational potential energy is lost and kinetic energy is gained. If only one of those two counted as a source term from gravity, the effective mass as measured from the distant gravity would oscillate up and down. Since it doesn't, they most both in effect count.

Mike W.

*(published on 12/28/2009)*