"Schrödinger's cat is a thought experiment proposed by physicist erwin schrödinger, according to his vision, a cat is put into a box completely isolated from the outside world, this box contains a device that can release toxic substances, and a particle with a 50% probability of decay, once this particle decays, then the device in the box will immediately release the toxic substance, causing the cat in the box to die.

The copenhagen interpretation of quantum mechanics states that a quantum system is in an indeterminate superposition state when it is not observed, and once that quantum system is observed, its superposition state collapses and its state is determined.

Schrödinger pointed out that if the theory is correct, then the particles in the box are in a superposition state that "Decays and does not decay", and since the decay of the particles has a definite relationship with the life and death of the cat, it is a strange conclusion that until the box is opened, the cat in the box is in a superposition state that superposition of "Dead and alive" States.

It is clear that this "Dead and alive" Cat is unacceptable, and in fact, schrödinger wanted to use this thought experiment to show people how outrageous the so-called superposition state is. The cat has become the "Face of quantum mechanics".

Schrödinger's cat is also known as one of the 'sacred beasts' of physics, but it is not the only one to have received this title.

In fact, apart from schrödinger's cat, the other three great beasts are the laplace demon, the zeno tortoise and the maxwell demon. Here we will learn more about each of them.

Lapras demon

The "Laplace demon" Was proposed by the physicist and mathematician pierre simon laplace, who believed that the universe follows the law of cause and effect, and that the present universe is in fact the "Cause" Of the future universe, and the "Effect" Of the past universe. Fruit" Of the past.

In this case, if a "Divine beast" Had access to all the information about all the forces of natural motion and all the objects of natural composition in the present universe, and could analyse them, it would know everything about the universe, from the smallest particles to the largest structures, both in the past and in the future. It is clear and unambiguous.

This "Beast", which could see everything, became known as the laplace demon, and if it existed, it would mean that everything in the universe was already predetermined, which, it must be said, was unacceptable. Fortunately, the subsequent emergence of "Chaos theory" Essentially negated the possibility of a predictable universe, and the uncertainty of the microscopic world described in quantum mechanics made the existence of the laplace demon a remote possibility.

Zeno's turtle

"The zeno tortoise was coined by the ancient greek mathematician and philosopher zeno. The special feature of this 'beast' is that although it moves much slower than you, if you let it run first, you will never catch up with it.

As shown in the diagram above, suppose you are faster than the zeno turtle and you let the zeno turtle run first and you start chasing it when it reaches position b. Then when you reach position b, then the zeno turtle "Now you keep chasing, and when you get to position c, the zeno turtle runs to position d, and when you get to position d, the zeno turtle runs to position e. ......

Zeno points out that because the zeno turtle is constantly moving forward, each time you catch up to the zeno turtle at its last position, its actual position will always be a little ahead of that position, so that although the distance between you and the thus, although the distance between you and the zeno turtle keeps getting shorter, you can never catch up with it.

As you can see, the "Zeno tortoise" Is a paradox, after all, in the real world, it simply cannot happen, but nevertheless it is difficult to disprove it. "It was not until the advent of calculus that it was possible to prove theoretically and rigorously that the zeno turtle did not exist.

Maxwell's demon

"Maxwell's demon" Comes from a thought experiment proposed by the physicist james clark, the founder of classical electrodynamics, and before understanding this "Beast", it is necessary to briefly introduce "Temperature before we get to know this beast, we need to briefly explain what this physical quantity "Temperature" Is all about.

In microscopic terms, temperature refers to the intensity of the thermal motion of the microscopic particles inside an object; the higher the speed of the thermal motion of the microscopic particles, the higher the temperature.

It is important to note that temperature is actually a collective expression of a large number of microscopic particles and is statistically significant, so when we say the temperature of a mass of air, we are actually referring to the average speed of thermal motion of the air molecules in that mass, whereas for the individual air molecules in that mass, they do not move at the same speed, as shown by the fact that some are fast and some are slow (as shown in the figure below).

Maxwell's idea is to assume that there is a closed container filled with air, now divide this container into two regions, a and b, and set up a channel between these two regions that can be switched on and off, this channel is very small and only allows one air molecule to pass at a time, by a "Fast" And "Slow" That can identify the thermal motion of a single air molecule this channel is so small that only one air molecule is allowed to pass at a time and is controlled by a creature that can recognise the "Fast" And "Slow" Thermal movement of individual air molecules.

What this creature does is that when an air molecule in area a approaches the passage, if the air molecule is faster then it opens the passage and allows it to move to area b. If the air molecule is slower then it closes the passage and does not allow it to move to area b. For air molecules in area b the reverse is true, i.e. If the air molecule is slower then it is allowed to pass and if it is faster then it is not allowed to pass. Faster then it is not allowed to pass.

This creature is known as the "Maxwell demon" And it can be seen that under its control, the faster air molecules in region a will continue to gather in region b. At the same time, the slower air molecules in region b will also continue to move to region a. As this process continues, it will eventually create a as this process continues, the result is a "Low temperature in region a and a high temperature in region b".

Maxwell argues that the energy consumed by the 'maxwell demon' control channel could theoretically be so small as to be negligible compared to the kinetic energy of individual air molecules, and if this were the case, then the process would be considered to be in violation of the second law of thermodynamics.

If the second law of thermodynamics could be violated, it would mean that a second type of perpetual motion machine would be possible, so it is generally accepted in the scientific community that the maxwell demon could not exist. Nevertheless, there are some researchers who are very interested and have tried to create an artificial maxwell demon in their experiments, but so far, no such experiments have been successful.

The 'four great beasts' of physics have only existed in thought experiments, and their creation has contributed to the development and improvement of related theories.