Schrödinger's cat is a famous paradox in the field of quantum mechanics: a cat, some radioactive elements and a bottle of poison gas are enclosed together in a box.Within one hour, the probability of decay of radioactive elements is 50%. If it decays, a hammer connected to the Geiger counter will trigger and break the bottle, release the poison gas and kill the cat. Because of the equal probability of this happening, Schrödinger supposes that the cat in the box is considered dead and alive before the box is opened.

We generally think that when no one was watching, the particles in Schrödinger's box had either decayed or not decayed—there must be one of the two. However, this does not meet the requirements of quantum mechanics. If there must be one, quantum mechanics can not explain the double-slit interference experiment and cannot explain the wave-particle duality of particles. Quantum mechanics believes that the particles in the box are in the superposition state of the decay and no decay states.

The fact that we cannot understand quantum mechanics means that it cannot meet the criterion of truth of logical unity. Fortunately, this standard is not the fundamental standard of truth, but an alternative standard. The fundamental criterion of truth is practicality. The role of theory is to improve people's practical ability. When the formula of quantum mechanics can help people solve practical problems, we can believe it is true.

The alternative standards for truth include prediction, stability, simpleness and logical unified. The fact that quantum mechanics can accurately predict many experimental results shows that it satisfies the predictive criterion, the fact that it can use simple formulas means that it satisfies the criterion of simplicity, and it can withstand practical tests for a long time shows that it satisfies stability criterion. So in the five standards of truth, quantum mechanics meets four, only one is not satisfied, and we cannot find a better theory than quantum mechanics. So no matter whether we understand it, we have to accept quantum mechanics. Problems that it cannot be understood can only be solved by other methods.

In the history of science, in addition to quantum mechanics, many theories were once unfathomable, and most of them were later understood. The unfathomable state is the opposition state of contradiction. It turns to unification when it is understood. The unification is achieved through some certain concrete ways. What is the concrete way to unify the contradictions? For example, when cars go through the crossroad, the north and the south cannot go when east and west go. This is a contradiction. However, the contradiction is unified on repairing an overpass, the overpass is a concrete way to achieve the unification of contradictions. If some people has never seen an overpass in the past, when you tell them that cars can go north, south, east and west at the same time, they would think it impossible. Human imagination can develop with intelligence and practice. If we do not have enough imagination, it is difficult to find these concrete ways. Now we cannot understand the contradiction of quantum mechanics, probably because we still lack imagination. Einstein believes that quantum randomness, like all other types of randomness in physics, is the result of some deeper processes behind it.