Studying the interrelations between General Relativity and Quantum Mechanics, Hawking understands that the two theories are irreconcilable to the microscopic scale. General Relativity describes the phenomena on a cosmic scale and quantum studies the interactions there occur at levels of atoms and particles. The contrast between the two theories occurs when they are examined the characteristics of space: relativity theorises a smooth and continuous space like a piece of paper, while quantum claims that the microscopic-scale Universe is grainy, subdivided into infinitely small "lumps", the quanta.
According to quantum theory, space is not empty, but formed by pairs of particles, ordinary matter and antimatter which has a charge opposite to the first. The quantum fluctuations of the vacuum cause birth of particle-antiparticle pairs near the horizon of the events of the black hole. One particle of the couple falls into the black hole, while the other succeeds to escape into the outer universe. To respect the principle of conservation of the overall energy, the particle that has precipitated into the black hole must have negative energy
(compared to an observer who is far from the black hole).
Press Release: Violent Acceleration and the Event Horizon
Theory and history: Hawking and the paradox of black holes
Black holes
MAQ/April 2018/20