Using the formula $F=G\frac{m_1m_2}{d^2}$ where $m_1$and $m_2$ are the masses of two objects, $G$ is the gravitational constant, and $d$ is the distance between the objects, it is possible to calculate the force of the gravitational attraction between the objects in Newtons. However, since light is affected by black holes, the property required to interact gravitationally is energy, not mass.

How can I calculate the gravitational attraction between objects using their energies instead of their masses?


1 Answer 1


The harsh answer is, "by solving Einstein's field equations". That is an extremely more difficult problem than using Newton's law -- the equations take up at least a page when you write them out.

However for the case of light near a black hole, you can treat the black hole as unaffected by the light, and instead solve the null geodesic equation. This is still harder than Newton's law, but it's at least tractable, compared to Einstein's field equations. For Schwarschild black holes, the Wikipedia article has much information.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.