# Length Contraction and Black Holes

*Most recent answer: 07/01/2015*

- Jack

New Jersey

That's a very thoughtful question. You'd think that between the inertial mass increase and the length contraction that an object has when viewed in a frame in which it's moving that it would form a black hole. Yet that doesn't make sense because in it's own frame light can escape easily. There must be some mistake.

Without really knowing General Relativity, I do know that its gravitational source term must include not just energy (inertial mass) but the full relativistic four-vector, for which the other three components are the vector momentum. So the source of gravity is very different for that moving object with its momentum than it would be for something with that same energy but no momentum. I guess that makes the solutions of the GR equations come out with no black hole, unlike for the zero-momentum object.

Mike W.

*(published on 07/01/2015)*