Chapter 25 Data Thirteen

There are two cornerstones of 20th century physics: quantum mechanics and relativity.Quantum mechanics deals with phenomena in the microscopic world. Under this framework, elementary particles are point particles with no size. The main forces between them are electromagnetic force, weak force and strong force. The structure of quantum mechanics is sufficient to describe the effects of these three forces.As for gravity, it needs to be described by the theory of relativity. Space-time is dynamic and will be bent by the influence of matter. Einstein's equations indicate the relationship between the distribution of matter and the curvature of space-time.

So far, physical phenomena can basically be accommodated in the above two theoretical frameworks, but there are also profound contradictions between the two. Briefly speaking, general relativity violates the uncertainty principle of quantum theory (the so-called God does not play dice) .Therefore, the two have to be revised to make it a unified quantum theory of gravity. The most promising quantum theory of gravity is string theory.Its basic assumption is: all elementary particles are actually a piece of string-like objects, strings have various vibration modes, and each mode represents a particle that transmits force, and electromagnetic force, strong force, and weak force can all be included Among them, the most important thing is that the gravitons that can form gravitational waves are also one of the vibration modes.

Developments in recent years have shown that it is indeed a quantum theory of gravity without inherent contradictions.However, since it cannot be verified experimentally, string theory must calculate everything in the universe if it is to be successful.However, there are some places that are not widely accepted by the public. For example, it requires that the space-time dimension of the universe must be 10 dimensions, otherwise there will be an insurmountable mathematical contradiction, but where are the extra 6 dimensions?String theory has not yet made this point convincingly.