The

**hoop conjecture ** is a theory proposed by Kip Thorne in 1972 to

predict whether or not any given object of

*any* given shape will

collapse to form a

black hole. A tricky problem, as the collapse of highly non-

spherical objects may, or may not form a black hole, depending on their exact

geometry and

mass.

It works like this: For the object in question, measure its mass, and then take a hoop with a circumference equal to the object's *critical circumference*. If the object can be placed in the hoop, and the hoop rotated around it so that the object and hoop *never* touch, then it **must collapse to form a black hole.**

This conjecture hasn't been finally proved yet, but every simulation of implosions of non-spherical objects has formed a black hole exactly when predicted, according to the conjecture.