Quantum Radiation by Classical Black Holes and Flying Mirrors

In Einstein’s classical general relativity, a black hole is defined as a region in spacetime with a radius that nothing, including photons, can escape from it after entering the radius. This inescapable radius is the so-called black hole horizon. However, by imposing quantum fields on top of the classical black hole spacetime geometry, it turns out that the quantum fields may get excited and lead to particle pair creation due to the interaction with the classical gravity. The study of this semiclassical combination of quantum fields and classical gravity is called quantum field theory in curved spacetime (QFTCS).