# Hawking Radiation & Black Holes

Black holes do actually radiate, this radiation is dubbed hawking radiation after its discoverer Stephen Hawking. The Hawking radiation was discovered when you incorporate the ideas of quantum mechanics into how a black hole would work. To understand hawking radiation, you must first understand two things:

## 1. Quantum Vacuum Fluctuations

Vacuum is normally described as something completely empty, with no particles what so ever in it. But In quantum mechanics, there’s the heisenbergs uncertainty principal which says that at particle small levels you can’t know every thing to a 100%, the more you know about one thing the less you can know about another thing. This apply for example to energy and time. If you want to know the energy level better you have to measure it under a longer time. The vacuum, which isn’t supposed to have any energy, has particles constantly being created and destroyed. This is because of the above mentioned uncertainty principal. According to it, energy may fluctuate and the higher the energy level of the fluctuations have, the less time they can exist. This makes it possible for a virtual particle/anti-particle pair to be created, move around a bit and then meet and annihilate each other so that the energy borrowed in the creation is returned. The particles created in these fluctuations are said to be virtual, because you can’t detect them directly but you can measure their effect on other things such as the energy levels in atoms. But the virtual particles can become real, detectable, particles if they are able to take some energy from a field of some kind. the problem is that under their short life time they simply haven’t got enough time to become real particles.

## 2. Tidal Gravity

The longer away you get from earth the weaker its gravitational pull will be, e.g. you’ll fell the pull of gravity stronger on the surface of earth then if you where out in the atmosphere. This is called tidal gravity. For a black holes the tidal gravity near the horizon can be incredibly strong, there may be an immense difference between the pull on your feet then the pull on your head, if your feets are closer to the horizon then your head. But as it turns out for a bigger black hole the difference in tidal gravity is far less then a small black hole. We’ll talk about this later.

If a virtual particle/anti-particle pair is created near the event horizon of a black hole, the tidal gravity can be so strong that the pair gets separated for a long enough time so that the gravitational field give the particles energy and then they can become real particles. Then one of the particles might be sucked into the hole so that it can’t annihilate the other. While the other one escapes and moves away from the hole. So now the hole will have lost half the energy it put into making the two virtual particles real particles.