Classical physics defines the vacuum as a state of absence :a vacuum is said to exist in a
One might expect that the vacuum would always be the state of lowest possible energy for a given region of space. If an area is initially empty and a real particle is put into it, the total energy, it seems, should be raised by at least the energy equivalent of the mass of the added particle. A surprising result of some recent theoretical investigations is that this assumption is not invariably tree. There are conditions under which the introduction of a real particle of finite mass into an empty region of space can reduce the total energy. If the reduction in energy is great enough, an electron and a positron will be instantly created. Under these conditions the electron and positron are not a result of vacuum fluctuations but are real particles, which exist indefinitely and can be detected. In other words, under these conditions the vacuum is an unstable state and can decay(衰)into a state of lower energy; that is one in which real particles are created.
The necessary condition for the decay of the vacuum is the presence of an intense electric field. As a result of the decay of the vacuum, the space permeated by such a field can be said to obtain an electric charge, and it can be called a charged vacuum. The particles that materialize in the space make the charge vacuum is likely to be found in only one place: in the immediate vicinity of a super heavy atomic nucleus(原子核) ,one with about twice as many protons as the heaviest natural nuclei known. A nucleus that large cannot be stable, but it might be possible to assemble one next to a vacuum for long enough to observe the decay of the vacuum. Experiments attempting to achieve this are now under way.
Which of the following titles best describes the passage as a whole?
A.The Vacuum: Its Fluctuations and Decay.
B.The Vacuum: Its Creation and Instability.
C.The Vacuum: A state of Absence.
D.Particles That materialize in the Vacuum.