[Pure physics background knowledge introduction without spoilers]
1. In the past time-travel movies, such as "Predestination", "Edge of Tomorrow", "Source Code" and "Butterfly Effect", they are often "time is a one-way flowing river", and crossing is only a return to the past. The time point, the direction of the passage of time has never changed. But this time, time will flow in the opposite direction: lost things will come back on their own; couples quarrel and break up before falling in love; people are dug out of underground coffins into this world and then stuffed back into their mother's belly to leave ... farther, the world in the movie is a three-dimensional space plus one-dimensional time, you can choose to go forward or backward, a real four-dimensional space.
2. But what determines the direction of the flow of time? I believe everyone who has watched the movie knows that this is related to the second theorem of thermodynamics - entropy is constantly increasing, and the thermodynamic arrow determines the direction of the passage of time. So let's go a step further, why is entropy increasing? This question is actually not so easy to answer, we need to answer first: what is entropy? Of course, from an academic point of view, entropy has many definitions (such as Boltzmann entropy, information entropy), but the core idea refers to the complexity of a system. lower. Here is an example, such as Boltzmann entropy (S=klnΩ), where k is a constant, where Ω represents the number of possible microstates. The greater the number of possible microstates, the greater the entropy of a system. Maybe the theory is too difficult to understand. Let me use an analogy. Suppose you sleep with your boyfriend/girlfriend. At first, you will only lie on your back. At this time, you have only one possible state. Your Ω=1 entropy is 0. . However, after a while, the two of you naturally found out: Huh? It turns out that you can sleep on your side, hug, hug, sleep with your back, and even sleep on top of each other! So, over time, you have more possible states and more entropy - this is the second law of thermodynamics .
3. After answering what entropy is, why does entropy always increase? No problem, quantum mechanics! In fact, there are also some explanation methods from quantum mechanics, but I am afraid that after I finish writing these, there will be no readers of the article. If anyone in the comments wants to see me, I will write again. So today, let's not talk about the theory, let's talk directly from the origin of the universe - if someone asks you why the entropy increases in the future? You answer directly: it is because of the Big Bang. Surely nothing is wrong. The current prevailing theory is that the universe originated from a singularity, when entropy was minimal. Then, after the creation of the universe through the Big Bang, the entropy became larger and larger. If the universe did not have the law of increasing entropy, the Big Bang would not have happened, and there would be no you and me. Then some people will ask: the entropy must have increased at the time of the big bang, but now that the development of the universe is almost mature, is it possible to change from expansion to contraction, and then to decrease in entropy? Well, that's what this movie is about and where it's innovative.
4. The answer is entirely possible. In his short story "Collapse", Liu Cixin directly corresponds the direction of the passage of time to whether the universe is expanding or contracting. Inflating; if the universe begins to shrink one day, the direction in which our time passes will also change. In that world, we cannot understand whether it is human language or way of life (think about the fact that you spit out your food every day) In that world, it is estimated that only other people say "Shanghai tap water comes from the sea". to understand.
5. Redshift and blueshift: In the movie, red represents our normal time direction, and blue represents the opposite direction. In fact, the colors here are not randomly chosen by Nolan, but have a saying. How did humans discover that the universe is expanding? It's actually a "redshift" - the light from stars moving away from us is shifted toward the longer wavelength end of the spectrum (the red direction) (the Doppler effect). Therefore, when the universe is expanding, when we look at distant galaxies, there will be a redshift, so red represents our current time flow. Blueshift is just the opposite. If our universe were shrinking, we would see a shift in the spectrum of distant galaxies toward blue light. This is called a blueshift. That's why blue is set as the color in reverse time. Therefore, the default entropy increase in the movie is related to the expansion of the universe.
6. The grandmother paradox: In fact, the core of this paradox is, can history be changed? In fact, the film only touches on this topic, and does not have a deep discussion on this topic. Because in fact, as it is said in the film: Everything that has happened will happen, and will always have happened. In fact, people in the future already know what happened in the past, and they are just acting on the scene and finishing the drama. Essentially Nothing about changing history. However, there are two popular explanations for whether I can go back in time and kill my parents: one is a parallel universe - I can do it, but I just change this one universe, but In fact, there are many other parallel universes. For example, in the universe I used to live in, my parents didn't die, so I have me. Another explanation is - I can't change what has happened, and even if we can go back in time, we can only watch on the sidelines of things that have an impact on the future and witness them happen. But what I prefer is the third explanation: as depicted in the movie "Arrival", the concept of time itself is only a human fantasy. This world itself has no time. Your whole life, in the eyes of higher-level civilization, is just a painting, and you can see everything at a glance. But some people may ask, if time does not exist, what is the meaning of life in such a world? This question cannot be answered. After all, in this world where time exists, I still don’t know what the meaning of life is. . .
7. Where does the entropy increase end? At present, the more popular sayings are: heat death theory; expansion and contraction theory; if you are interested in this part, please update it later
8. Finally, evaluate the movie itself: In fact, my expectations for the movie "Creed" have always been very high. After all, I heard that Nolan tried this theme again after he became famous for "Memento". However, from the results, I can't say that it can meet my expectations. Compared with comparable films like "Predestination", "Edge of Tomorrow", "Source Code" and "Butterfly Effect", there are actually some shining points of Creed, but they are not as amazing as "Inception" and "Deadly Magic". .
In this period of scarcity of new movies due to the epidemic, it is still worth watching.
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