# What if an object had enough speed that from another perspective it was enough to form a blackhole? [duplicate]

Suppose a baseball is traveling through a vaccum towards another object extremely fast. If it's travelling fast enough then shouldn't its kinetic energy give it enough mass that the observer thinks it should collapse into a black hole and evaporate as Hawking radiation? How can this be reconciled with the perspective of a second object at rest with the baseball, which would have no reason to see a black hole?

## marked as duplicate by Rob Jeffries, Community♦Nov 1 '15 at 21:54

In reality it is the object's momentum $p$ that is relativistic:
$$p=\frac{mv}{\sqrt{1-\frac{v^2}{c^2}}},$$
where $m$ is mass, $v$ is velocity and $c$ is the speed of light.