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