Quantum gravity

The quantum gravity is currently in development theory, which is to unite quantum mechanics and general relativity, ie the two great physical theories of the 20th century. While the general theory of relativity describes only one of the four elemental forces of the universe, namely the gravity, the quantum theory treats the other three elemental forces ( electromagnetic interaction, weak interaction and strong interaction ). The union of these two theories is necessary, among other things because of their overlap, but also due to different scientific philosophical consequences.

In general, the general theory of relativity describes the structure of the universe by and large, is practical in large masses and accelerations. Quantum theory, however, describes the interaction between elementary particles in small regions of space. Although gravity is the weakest of the elemental forces, it determines the worldview of physics: it is the only one of the four elemental forces which, according to present knowledge, only evocatively, since there is only one gravitational charge ( mass), and thus not opposite charges can cancel each other out. The other elemental forces, however, are only for microscopic processes of importance - with the exception of the electromagnetic interaction, which reaches quite macroscopic and in the case of interstellar plasma or the magnetic fields of, for example, the sun and earth and cosmic scales. Overlap of both theories occur in some extreme cases:

• The Big Bang is the model of general relativity is a problem, since the curvature of spacetime becomes infinite (so-called singularity ), so that the laws of general relativity are overridden, and assume density and temperature extreme values ​​.
• For black holes, which accompanied bend by their enormous mass, with its small size, the space-time also to the singularity.

Some physicists connect with the still to be formulated unification of gravity with the other elemental powers hoped that occur in such a theory does not formally infinite terms more, and can be extreme cases in which all the elementary forces must be given equal consideration, then calculate. In addition, the quantum gravity is considered a possible candidate for a TOE ( Theory Of Everything).

So far, however, gravity defied persistently attempts by physicists to insert them in the quantum model. This is because all forces are divided into elementary portions, the quantum. The forces can be decomposed as in quantum theory and calculate and explain just exactly there. Gravity, however, is not so easily disassembled and so today theories are developed, which should make this possible.

A candidate for the quantum gravity is string theory, in which all elementary particles are represented by one-dimensional strings. However, this theory can according to current knowledge, only in a 10 -, 11 - or 26 -dimensional universe formulate.

An alternative is to loop quantum gravity (including loop quantum gravity LQG ) in which even space and time are quantized.

These are just the most represented theories, but there are still a number of other explanatory models.