In quantum mechanics, vacuum does not mean that there is no field, particle or energy. Quantum vacuum is a state with the lowest energy, which is called "vacuum". In fact, there is no state of zero energy.
The vacuum is not empty.
The uncertainty principle of time and energy explains why the vacuum is not empty. Because of the equivalence of mass and energy, the fluctuation of energy in vacuum can lead to the formation of elementary particles. In 1928, paul dirac found that every elementary particle has a corresponding antiparticle, which has the same mass and other symmetric "mirror image" properties. When they meet, they will annihilate each other and transform mass into energy. Therefore, a particle and its antiparticle represent twice the energy of its rest mass. Conversely, a certain energy can also be regarded as a pair of antiparticles. As a result, the quantum vacuum stirred by energy fluctuation becomes the so-called Dirac Sea, which is full of positive and negative particle pairs that spontaneously appear and quickly disappear. In a quantum vacuum without any force, particle pairs are constantly produced and destroyed, so on average, no particles or antiparticles are really produced or destroyed. Because these particles exist instantaneously and cannot be directly observed, they are called virtual particles (virtual photons, virtual electrons, virtual protons, etc. In fact, there is no essential difference between virtual particles and real particles, but virtual particles do not have enough energy and exist for a very short time. If it can get energy from the outside, it can exist long enough to upgrade to a real particle. Imagine an electric field acting on a vacuum. When a pair of positive and negative electrons appear in the sky, they will be separated into opposite directions by the electric field. If the electric field is strong enough, they will be far enough away and can no longer collide and annihilate each other. At this time, the virtual particles become real particles, and the vacuum at this time is said to be polarized.
However, vacuum is not easy to polarize and requires high energy density to separate virtual particles from real particles. The form of energy required to produce polarization is not important, they can be electric energy, magnetic energy, thermal energy, gravitational energy and so on.
Problems encountered
The uncertainty principle tells us that the vacuum is full of oceans of virtual particles. This intense quantum behavior of the virtual particle ocean also appears in the space around the event horizon of the black hole.
The uncertainty theorem shows that if the position of a particle is determined, its velocity will become uncertain. If a particle falls into a black hole, its position has been determined (at the singularity), so its speed is uncertain, even exceeding the speed of light, and it escapes from the horizon.
Since all forms of energy are equal to mass, we naturally think that gravitational energy will also be spontaneously transformed into particles. Hawking found that for micro black holes, the quantum vacuum will be polarized by the strong gravitational field around it (which is very important). In Dirac Sea, virtual particle pairs are constantly produced and disappeared, and a particle and its antiparticle will be separated for a short time, so there are four possibilities: two partners meet again and annihilate each other (process I); Antiparticles are captured by black holes, while positive particles appear in the outside world (process 2); Positive particles are captured and antiparticles escape (process III); Both fall into black holes (process 4). Hawking calculated the probability of these processes and found that process II was the most common. Due to the tendency to capture antiparticles, black holes will spontaneously lose energy, that is, lose mass. Because the scale of micro-black holes is similar to that of elementary particles, the "transition" of energy may be enough to make particles move a distance greater than the radius of the horizon, and the result is that particles escape. To an outside observer, the black hole is evaporating, that is, emitting a stream of particles. In fact, the particles did not really jump over the "wall" of the horizon, but passed through a "tunnel" briefly opened by the uncertainty principle. This process occurs repeatedly around the event horizon of the black hole, thus forming a continuous radiation flow and the black hole emits light.
Hawking calculation
Hawking's calculation shows that the evaporation radiation of a black hole has all the characteristics of a blackbody. It gives the black hole a real temperature, which is the same throughout the horizon, and is directly determined by the strength of the gravitational field at the horizon.
For Schwarzschild black holes, the temperature is inversely proportional to the mass. The temperature of a black hole with the same mass as the sun can be ignored, which is MINUS seven Kelvin (that is, above absolute zero). Not zero, but pitifully small; Black holes are not all black, but they are not bright at all. Unfortunately, such low-temperature radiation is too weak to be detected in the laboratory.
Hawking's calculation has another important discovery: the smaller the mass of a black hole, the higher the temperature and the stronger the radiation. Obviously, evaporation only has a special effect on miniature black holes, and the temperature of miniature black holes is very high. In a black hole, the greater the mass, the lower the temperature and the slower the evaporation. The smaller the mass of the black hole, the higher the temperature and the faster the evaporation.
For micro black holes, the temperature is very high, which can reach tens of millions or even hundreds of millions. With the intensification of evaporation, the mass will be lost rapidly and the temperature will rise rapidly. With the acceleration of temperature rise, the mass loss will be more intense, and the process will evolve in a crazy form. Finally, the black hole will be destroyed, ending with a violent explosion, and all particles will be pardoned (for giant black holes, the process of particle emission is very slow, equivalent to evaporation; For micro black holes, the process of emitting particles is very fast, which is equivalent to an explosion.
For the giant black hole in the center of the Milky Way, its evaporation process will far exceed the age of the universe. Assuming that the universe has a long life and does not shrink, such a black hole will eventually evaporate. But at present, this black hole is still accretion far greater than evaporation, mainly accretion. Only when the temperature of the universe drops below the temperature of such black holes in the later period, do they begin to evaporate preferentially. However, this process is too slow. When they start to evaporate, they will be far beyond the age of the universe, and it will take about ten to ninety-nine years to evaporate.