Nolan’s “time Trilogy” comes down in one continuous line. The transformation of time scale in inception is very common in general relativity. It is estimated that the idea of general relativity is used. Star Trek’s treatment of slowing time near black holes is in line with modern science. (it’s estimated that it’s because of inviting Science Consultant Kip Thorne) < / P > < p > in previous sci-fi films, the setting of returning to the past through time travel also appeared. For example, contact, adapted from Carl Sagan’s novel, is the originator of such films. In such films, the tool of time reversal is often wormholes. < / P > < p > in fact, it is theoretically feasible to go back to the past through wormholes. According to the theory of general relativity, there are some strict solutions of Einstein’s field equation. These exact solutions are called wormholes. The emergence of wormholes also makes the existence of closed time-like curves in space-time, which is equivalent to returning to the past. However, wormholes appear under harsh conditions, which generally require negative energy density, which can only be obtained through quantum effect, so it is not easy to obtain in the real world. So using wormholes to go back to the past is also similar to a science fiction concept. < / P > < p > and in the latest movie creed, Nolan uses another concept – entropy. The basic assumption of this movie is that entropy increases in the same direction as time. From a physical point of view, is it possible to achieve such a time reversal? Now, let’s take a look at some of the physics behind it. Time is an abstract and mysterious concept. Before entering the 20th century, some physicists thought that time had its forward direction, which was consistent with the direction of entropy increase locally. After Clausius and others established the second law of thermodynamics, a trend of thought began to rise in the scientific community. Of course, this trend of thought itself is flawed, because the direction of time discussed here is consistent with the direction of entropy increase, but it does not clearly explain what “time” is. At that time, because Einstein’s theory of relativity had not yet been born, time in people’s mind was similar to “Beijing time”, which was a kind of public time. In other words, people think that the time in New York and Paris is the same and can be unified; the time passing of people on the train is the same as that of people on the plane. Moreover, the time direction of different characters in different places is the same. < / P > < p > with Einstein’s theory of relativity, our understanding of time has undergone a qualitative change: different places have different gravitational field strength, and different people have different speed and direction of time passing. In this sense, it is a fuzzy concept of time before the 20th century to describe the time arrow by the direction of entropy increase without the modification of relativity. At the same time, it must be pointed out that not all systems have one-way increase in entropy, but a large number of self-organized systems have their entropy reduced. For example, when plants absorb sunlight for photosynthesis, the entropy of this process does not necessarily increase. In 1944, Schrodinger, one of the founders of quantum mechanics, directly introduced the special concept of “negative entropy” in what is life. He believed that on the one hand, there is entropy increase in the life system, on the other hand, it constantly obtains negative entropy from the environment. For example, we human beings eat vegetables in order to obtain substances with negative entropy relative to our human beings, so as to maintain our human nature The low entropy state of the body – of course, human feces are high entropy. < p > < p > entropy is a concept in statistical physics. Its essence is characterized by the formula s = klnw on Boltzmann’s tombstone. Where W is the number of microscopic states corresponding to the system. For example, if there are three people standing in a row to take pictures, from the perspective of entropy, there is a “micro state” problem: there are three possibilities for the person standing at position C, and many possibilities for the person standing on both sides. In this way, there are six possibilities (i.e. factorial of 3), corresponding to the microscopic state number W. therefore, the entropy of this photo can be calculated from here. In general, for a closed thermodynamic system, the entropy tends to increase. So, some people interpret it as an arrow of time. However, the direction of entropy increase is equivalent to the arrow of time, which is just a kind of mapping similar to mathematics. Whether this mapping is a real physical law needs further demonstration. < / P > < p > the air conditioning in our home is to change the high entropy state into the low entropy state. (of course, this process consumes energy) so if we think that the time counter current corresponds to the high entropy state to the low entropy state, then air conditioning is also a kind of “time machine” that can make time countercurrent. But obviously, air conditioning can’t help us cross to the Qing Dynasty to meet Empress Dowager Cixi. Based on this, we can draw a conclusion that a machine which can produce a low entropy state from a high entropy state may not cause a time reversal. If you want to travel through time and space, you need to know more about physics. < / P > < p > in the film creed, we can see that the female scientist Laura played by Clemens Posey explains the working principle of “reverse bullet” to the hero who did not understand “time reversal”. The reverse bullet can be seen as an object whose time is countercurrent – note that the time arrows around the bullet point to the future, only the time arrow of the bullet itself points to the past. < / P > < p > point to the future and point to the past, which is the theory of relativity, we need to use the light cone. In flat space-time, there are two light cones at each point in time and space: the tangent vector of the world line in the upper light cone (i.e., the time arrow) points to the future, and the light cone below points to the past. < p > < p > in the presence of gravity, according to Einstein’s theory of relativity, space-time is no longer flat, and the structure of the light cone will be distorted and the difference between the past and the future will become complicated. For example, in Godel space-time, the light cone is slowly tilted by the rotation of space-time, and finally reverses. At this time, the world line can be a closed time-like curve – that is, there are people who can go back to the past in Godel space-time. < / P > < p > so, from a relativistic point of view, it’s better to let gravity help us go back to the past, because gravity can distort space-time. It is unscientific to go back to the past completely depending on entropy reduction. In “Star Trek,” Nolan has photographed the return of gravity to the past, which is scientific. However, some physicists have proposed a new idea to link entropy with gravity. In 2010, e. Verlinde proposed “entropy force”, which uses the direction of entropy increase to explain the direction of gravity (gravity has only one direction, that is, attraction, and gravity will not repel each other). According to Verlinde, there is an imaginary surface between two objects. When the distance between the two objects changes, the entropy on the surface will also change. And the system always tends to increase, so gravity is reflected. Of course, gravity is not a fundamental interaction in this theory. So if Nolan wanted to make the physical logic of the creed clearer, he might have asked Verlinde to be a scientific adviser. < / P > < p > if we consider quantum mechanics, the person who comes out of the revolving door of the creed moves against time, then this “reverse time person” is essentially composed of antimatter. The antiparticles that make up antimatter human beings have not only positrons but also antiprotons. It is theoretically possible to form these antiparticles into a living body. But the question is, what is the behavior of such a time reversal in the real world? The positron was predicted by Dirac when he was very young. This kind of particle has positive energy, but the charge is opposite to that of ordinary electron. Several years later, Feynman, another great physicist, used the “Feynman diagram” to calculate the interaction between photons and electrons. He interpreted positrons as electrons moving against time, which was also recognized by the scientific community. Therefore, in the general sense (space-time is considered flat because of special relativity), the particle moving against time is called antiparticle. < / P > < p > when the positron in the reverse time collides with the electron in the real environment, it will annihilate and become light; while the antiproton in the reverse time collides with the positron in reality, just like the Large Hadron Collider, producing many kinds of particles. Obviously, it is unrealistic for such a reverse time person to survive in the real world. No matter the electrons or air in the environment, they will bombard the antiparticle of human body, and send out huge energy, which will lead to the death of the reverse time person by explosion. This is obviously considered in the film. People need to wear protective clothing when they come out of the revolving door time machine. Of course, the film makes some scientific concessions: when antimatter people come into contact with other people or objects, they just need to wear a mask, and they don’t need to worry about annihilation of positive and negative matter. Therefore, from the current physical theory, it is completely possible to move against time, but the abuse of the concept of entropy needs to be vigilant. The relationship between entropy increase and time is an old physics. Maybe relativity and quantum mechanics will give us more enlightenment. Global Tech