In the universe, everything needs to follow any of the three symmetries-C symmetry and charge symmetry; P symmetry, parity symmetry (mirror symmetry); T symmetry, time symmetry. Cosmic symmetry has always been regarded as the axiom of the universe, but with the development of physics, scientists have found that there are exceptions to every symmetry, but all objects follow at least one symmetry. At present, no phenomenon can violate all three symmetries at the same time.

At present, all symmetry is the study of objects, basic forces and physical fields in the universe. Based on symmetry, physicists put forward a new theory, which extends symmetry to the whole "stage", that is, cosmic symmetry.

Symmetric universe can easily explain antimatter: we live in a universe that is expanding and time is advancing, and there are also very rich particles in our universe. If symmetry is extended to the universe, then we can get a mirror universe. In the mirror universe, the whole universe is collapsing and time is going backwards.

Scientists generally believe that at the moment of the Big Bang, the universe should produce symmetric positive matter and antimatter, so as to realize the conservation of charge, but in fact, antimatter has never been found in the universe, and all antimatter comes from artificial experiments.

The whereabouts of antimatter has always been a mystery, but the existence of mirror universe allows antimatter to have its own universe. The matter that reflects the universe consists of antiparticles, which have the same mass but opposite charges.

The mirror universe has a completely opposite passage of time, and the material composition is mainly antimatter, which can explain the special phenomenon that the cosmic charge is not conserved and antimatter does not exist in nature.

When the Big Bang happened, it not only produced an expanding universe, but also produced a collapsing universe. Due to the different physical properties, the positive and negative particles born in the Big Bang quickly moved to different universes, thus avoiding the extinction of the positive and negative particles.

In the mirror universe, dark matter is neutrino: the existence of dark matter also makes more and more scientists support the mirror universe theory. In the mirror universe theory, dark matter is neutrino.

Neutrinos are "invisible particles" in the universe, with very light mass, moving at a speed close to the speed of light, and the interaction with other substances is very inconspicuous, so it is difficult to be found. Neutrinos have been predicted and discovered for more than 20 years. The Antarctic particle detector captured neutrinos outside the solar system, which made many people believe in the existence of mirror universe.

Among neutrinos, there are electron neutrinos, μ neutrinos and τ neutrinos. Strangely, all known neutrinos are left-handed particles. Except neutrinos, all other particles are left-handed and right-handed. Scientists have been looking for right-handed neutrinos, but they can't find them.

According to the symmetry principle and the mirror universe theory, right-handed neutrinos are probably dark matter in the mirror universe.

Neutrinos are difficult to be captured, which is consistent with the characteristics of dark matter, but there are still many unknowns in dark matter. Whether dark matter only contains neutrinos is still unknown.

Summary: The theory of symmetry makes many scientists do their best to maintain the correctness of symmetry, but in our universe, all three symmetries can be broken, but not at the same time.

If there is a mirror universe in our universe that goes back in time, we can explain the phenomenon that antimatter cannot be found in the universe, and we can also use neutrinos to explain dark matter.

After BIGBANG, if there is still a "twin" mirror universe in our universe, then human beings need to find this mysterious mirror universe if they want to use antimatter energy and go back in time.