The ILLUSTRATED THEORY OF EVERYTHING: The Origin and Fate of the Universe by Stephen W. Hawking

Author:Stephen W. Hawking [Hawking, Stephen W.]
Language: eng
Format: epub
Tags: Science & Math, Essays & Commentary, Quantum Theory, Professional & Technical, Professional Science, space, Time, Physics, origins, Cosmology, black holes, string theory
Amazon: B001B4374U
Publisher: PHOENIX BOOKS, INC.
Published: 2006-05-02T07:00:00+00:00

By conservation of energy, one of the partners in a virtual particle pair will have positive energy and the other partner will have negative energy.

Since then, the calculations have been repeated in a number of different forms by other people. They all confirm that a black hole ought to emit particles and radiation as if it were a hot body with a temperature that depends only on the black hole’s mass: the higher the mass, the lower the temperature. One can understand this emission in the following way: What we think of as empty space cannot be completely empty because that would mean that all the fields, such as the gravitational field and the electromagnetic field, would have to be exactly zero. However, the value of a field and its rate of change with time are like the position and velocity of a particle. The uncertainty principle implies that the more accurately one knows one of these quantities, the less accurately one can know the other.

So in empty space the field cannot be fixed at exactly zero, because then it would have both a precise value, zero, and a precise rate of change, also zero. Instead, there must be a certain minimum amount of uncertainty, or quantum fluctuations, in the value of a field. One can think of these fluctuations as pairs of particles of light or gravity that appear together at some time, move apart, and then come together again and annihilate each other. These particles are called virtual particles. Unlike real particles, they cannot be observed directly with a particle detector. However, their indirect effects, such as small changes in the energy of electron orbits and atoms, can be measured and agree with the theoretical predictions to a remarkable degree of accuracy.

By conservation of energy, one of the partners in a virtual particle pair will have positive energy and the other partner will have negative energy. The one with negative energy is condemned to be a short-lived virtual particle. This is because real particles always have positive energy in normal situations. It must therefore seek out its partner and annihilate it. However, the gravitational field inside a black hole is so strong that even a real particle can have negative energy there.

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