This question seems very unreasonable. The world outside the mirror is certainly the same. What happens outside the mirror will happen inside the mirror. There is no difference between the two except the direction. But don't jump to conclusions. Our first feeling is that the world outside the mirror should be the same, which is based on our understanding of the laws of nature. Indeed, symmetry and conservation are the basic laws of this world, at least until Yang Zhenning put forward parity non-conservation.

Symmetry and conservation are the basic laws of the universe, and they always appear in pairs. If there is symmetry, there must be corresponding conservation. For example, time translation symmetry, simply put, is that we kick a ball at 5 o'clock and then kick a ball at 8 o'clock, with the same strength and angle. The final positions of the two balls should be exactly the same, and will not change with the change of time, which corresponds to the conservation of energy.

In addition to time translation symmetry, there is also space translation symmetry. For example, if we kick a ball in China and then go to Pakistan to kick a ball with the same strength and angle, the distance and orientation of the two balls should be exactly the same as the position where we kick, which in turn corresponds to the conservation of momentum.

Time translation symmetry and space translation symmetry are just two examples, in addition to space rotation symmetry and so on. In a word, symmetry and conservation are the foundation of the world. Now we can get back to the point and talk about things outside the mirror. The world inside and outside the mirror is exactly the same, following the same physical laws, except in the opposite direction. This is called "mirror symmetry", and each symmetry has a corresponding conservation. So what conservation law does mirror symmetry correspond to? Parity conservation.

What is parity conservation? Explaining this need involves some mathematical problems. Based on the principle of not complicating the problem, we simply know that parity conservation is the conservation of microscopic particle wave functions.

For most particles, parity conservation is no problem, but there are always two difficult students in a class, θ particle and τ particle are these two problem students. Theta particle and τ particle are a particle anyway, because they are the same in quality and charge. The only difference is that their decomposed products are different. Not only the decay products are different, but also the parity of their two decay products is different.

A group can have several problem members, but the laws of physics cannot. The existence of special cases means that there is a problem. Is there a problem with parity conservation? The problem is obviously not that simple.

There are four basic forces in our world, gravity, electromagnetic force, strong interaction force and weak interaction force.

Under the action of gravity, electromagnetic force and strong interaction force, there is sufficient experimental evidence to prove parity conservation, and the only one without evidence is parity conservation under weak interaction, so Yang Zhenning and Li Zhengdao began to doubt parity conservation under weak interaction.

Their doubts were not accepted from the beginning, because questioning the conservation means questioning the basic laws of the universe, so in order to prove this, they must produce sufficient evidence, so they designed an experiment: let one radioactive nucleus spin, and then try to control another same radioactive nucleus to spin in the opposite direction, which is equivalent to creating a world and a corresponding mirror world. If parity is conserved, then the two worlds should be exactly the same, that is to say, the beta rays emitted by two radioactive nuclei in all directions during the decay process should be exactly the same. The so-called beta rays are electrons produced by radioactive atoms in the process of decay.

Although Yang Zhenning and Li Zhengdao designed this experiment, they didn't have the experimental conditions, so they found Ms. Wu Jianxiong, the later chairman of american physical society, who was a Chinese physicist. She helped them to do this experiment in the National Standard Cryogenic Physics Laboratory of the United States, when the radioactive element cobalt 60 was used.

The final experimental results show that the electrons emitted by cobalt 60 in the same direction are different in the two worlds, and the difference is great, which proves that the world in the mirror and the world outside the mirror are different under weak interaction, that is to say, parity is not conserved. The experimental results of Yang Zhenning and Li Zhengdao caused an uproar, but when the experimental results just came out, they were hardly accepted in the scientific community. Scientists agree that this experiment is wrong. The scientist Bloch even vowed that "if parity is not conserved, I will eat my hat". As a result, the hat became very embarrassing, because a large number of scientists confirmed the correctness of Yang Zhenning and Li Zhengdao's theory after repeated experiments. Therefore, the two men won the Nobel Prize in the second year after the theory was put forward.