(a)what are black holes?
(b)do they really exist?
(a) A black hole is a region of spacetime from which nothing can escape, even light. To see why this happens, imagine throwing a tennis ball into the air. The harder you throw the tennis ball, the faster it is travelling when it leaves your hand and the higher the ball will go before turning back. If you throw it hard enough it will never return, the gravitational attraction will not be able to pull it back down. The velocity the ball must have to escape is known as the escape velocity and for ...
The expert determines what are black holes and whether they really exist.