Physics attaches great importance to experiments, and the original physical theories are summarized from experiments. After any physical theory is established, it needs to be verified repeatedly through experiments. One hundred years after Einstein's theory of relativity was put forward, it is still being tested by a series of rigorous experiments.

But some experiments are difficult to realize in reality, so physicists put forward thought experiments, and many great physicists, including Einstein and Newton, put forward thought experiments. Although it is only an ideological experiment, it is thought-provoking and promotes the development of physics. In these thinking experiments, four names are related to animals. They are called physics? Four beasts? .

(1) Tortoise in Zhi Nuo

This is the earliest? God beast? , proposed by the ancient Greek philosopher Zhi Nuo 2480 years ago, is also known as Zeno paradox. Imagine a person running at a speed of 10 m/s and a tortoise crawling at a speed of 1 m/s. At first, the tortoise was ahead of the man 100 m. So, when can humans catch up with the tortoise?

This problem seems to be a simple catch-up problem. As long as a person's running distance is equal to the tortoise's leading distance plus the tortoise's crawling distance, it can be calculated that this person is11.1after starting. (100/9) seconds to catch up with the tortoise.

However, if you look at it from another angle, the result is completely different. 1 sec, man running 10 m, tortoise leading by 9 1 m; In the fifth second, the man ran 50 meters, and the tortoise was 55 meters ahead of the man. At the first 10 second, the man ran 100m, and the tortoise took the lead 10m. 1 1 sec, men running 1 10 m, turtles leading 1 m; 1 1. 1 sec, the man ran11m, and the tortoise was 0. 1 m ahead.

If the space can be divided infinitely, then the distance between the tortoise and human beings contains infinite points. Therefore, the tortoise can always be in front of people, although only a little ahead. So, does this mean that people will never walk an infinite number of points to catch up with the tortoise?

Actually, it is not. At first, the tortoise leads 100m, and the time required for people to finish 100m is:

100/10s = 10/0s.

During this period of 10 second, the crawling distance of the tortoise is:

10? 1m = 10m

This is the distance after the tortoise leads the human 10 second, and the time required for the human to catch up with this 10 meter is:

10/ 10 sec = 1 sec

During this period of 1 sec, the crawling distance of the tortoise is:

1? 1m = 1m

This is the distance after the tortoise is ahead of human 1 sec. The time required for human to catch up with this 1 m is:

110 sec =0. 1 sec

So infinitely repeated, the time for people to catch up with the tortoise is:

10+ 1+0. 1+0.0 1+0.00 1+0.000 1+? Seconds =11.11? Seconds, that is, 100/9 seconds, so people can catch up with the tortoise in a limited time.

(2) Schrodinger's cat

According to the Copenhagen interpretation of quantum mechanics, when there is no observation, the quantum system is in an uncertain superposition state. Once observed, the wave function collapses and the uncertainty disappears, and the quantum system will become a certain state. This description is quite different from our common sense and will also affect the macro world.

So Schrodinger, one of the founders of quantum mechanics, put forward such a thought experiment. In a closed box, there is a radioactive substance. If it decays, the generated particles will trigger the Geiger meter to discharge and release the hammer through the relay. The hammer will fall and break the poison bottle, causing the cat in the box to die. If the radioactive material hadn't decayed, the cat in the box might still be alive.

According to Copenhagen's explanation, when the box is not opened for observation, the decay of radioactive materials is uncertain and in a superposition state, which will lead to the uncertainty of the cat in the box? Dead and alive? State. This is the famous Schrodinger's cat.

In this regard, the multi-world explanation or parallel universe theory has been put forward. The cat in the box is actually alive and dead, which will lead to two unrelated parallel universes, and the observer in each timeline will observe a certain state.

(3) Maxwell demon

The law of entropy increase shows that the order degree of isolated systems will only get lower and lower, and the chaos degree will only get higher and higher, which is an irreversible process. For example, after water and ethanol are mixed, pure water and ethanol cannot be separated spontaneously. Because the whole universe is considered as an isolated system, it means that the universe is destined to reach a state of thermal silence with the maximum entropy in the future, and then the universe will fall into complete silence.

But according to the famous physicist Maxwell, the universe may still be saved, which requires Maxwell's demon. Maxwell's demon can control the movement of each particle. What does this mean? God beast? With the ability of inverse entropy, the mixed water and ethanol molecules can be separated, and other particles in the universe can be made more orderly, thus reversing the hot end of the universe.

(4) Laplace demon

This one? God beast? Originally proposed by physicist and mathematician Laplace. Microscopically, everything in the universe is particles, and the operation of the universe is the result of the same movement of all particles. Laplace knows the momentum and position of all particles in the universe, so everything that happens in the universe is doomed and can be calculated.

But with the development of quantum mechanics, physicists realize that the micro-world is dominated by uncertainty, and it is impossible for us to accurately measure the momentum and position of a particle at the same time. In addition, according to chaos theory, when we try to calculate the future of particles, our calculation behavior will affect the motion of particles, and this difference will be gradually amplified, which will lead to unpredictable results.

Finally, who do you think will win if the four beasts of physics fight each other?