Transcript: Black holes can only properly be understood in terms of Einstein’s Theory of General Relativity, but speculation about their existence first occurred over 200 years ago. In 1784 the Reverend John Mitchell, an English amateur astronomer, knew that the escape velocity from an astronomical object increased with density and gravitational field, and he speculated that a sufficiently dense object could have an escape velocity larger than the speed of light. Since light and all other electromagnetic radiation travels at 300,000 kilometers per second, an object with escape velocity larger than this would be dark, a black hole. Black holes are the densest form of matter we can ever know or understand, even denser than a neutron star. If the Sun were shrunk to a radius of three kilometers it would be a black hole.