The sci-fi movie 'The Wandering Earth 2' has received rave reviews upon its release!

After the explosion of Mars and the explosion of the moon in "Wandering Earth 2", Chinese science fiction movies have risen to a pure level

Although adapted from Liu's original work, in reality, the movie "The Wandering Earth" only borrowed the concept of a novel, and most of the characters and plot are completely transformed. As a sequel and prequel, this movie has no written references at all, so it is not an exaggeration to say that it is an original science fiction movie.

Firstly, the grand proposition

The first part of "The Wandering Earth" mainly tells the story of how humans overcome difficulties and continue to travel after the Earth is forced to wander, while the timeline of the second part takes place at the beginning of the mountain relocation plan.

Because the expansion of the sun is about to engulf the Earth and the entire galaxy, humans have to unite to deal with the disaster. At first, people were debating how to save themselves. Even though the plan to install engines on Earth and push them out of the solar system in search of a suitable environment was later clarified, it still faced opposition from many people due to the uncertainty of its success.

So the difficulty of 'Wandering Earth 2' is more complex than the first installment. It not only needs to face harsh environments and changes at any time, but also guard against destruction and suspicion from within humans.

Meanwhile, due to the uncertainty of the mountain relocation plan, another form of self rescue has emerged, namely digital life, which can detach from the physical body and obtain eternal life through information media. Compared to the possibility of death, this painless method is obviously more likely to win the favor of many people.

At the beginning of the film, the audience is asked a question, which is what is the essence of civilization? Does it need to be carried by humans?

Around this point, in addition to improving the main storyline of the first half of Liu Peiqiang, the film also added lines from Andy Lau's portrayal of Tu Huosheng's daughter. Two lines advance in parallel, intersecting in the crisis of the moon, revealing the answer to the audience through human choices in extreme environments.

There are many things that this movie wants to talk about, such as social inequality, mutual restraint in the face of difficulties caused by human distrust, and standing up for failure. The addition of these elements not only enriches the connotation of the movie, but also makes it more debatable.

Secondly, the ultimate special effects

If 'The Wandering Earth' opens a door for Chinese science fiction movies, the sequel will undoubtedly achieve this goal by going up a staircase.

From the setting of the scenes, the presentation of details, and the adaptability to the plot, this movie is infinitely close to Hollywood's top tier science fiction blockbuster.

As soon as the space elevator opened, it firmly caught the audience's attention. As the tallest building in human history, the space elevator satisfies all the fantasies of science fiction fans about such devices. Whether in appearance, operation mode or function, space elevators are too unique and completely overturn the audience's perception.

When the Earth was attacked by an asteroid that split from the Moon, iconic buildings in major cities were either destroyed or flooded, causing not only an explosion in visual effects but also a temporary sense of panic at the end of the day.

The climax stage uses nuclear weapons to detonate the moon, which is the culmination of the film's special effects. As the lines in the film say: When all nuclear weapons explode together, the scene is indeed beautiful, but this cruel beauty comes at the cost of hundreds of lives. The perfect combination of special effects and plot in movies makes special effects no longer a cold auxiliary tool, but a weapon that can move and warm people's hearts.

Thirdly, eternal emotions

This movie has a strong cast. Except for the stable output of Wu Jing and Andy Lau, the performance of others is not inferior.

Although it is a science fiction commercial blockbuster, the film uses a lot of ink to depict the emotions between humans. Love, family, friendship, those sincere bonds can always blend into the hearts of the audience unintentionally, allowing people to break through the defense line.

Wu Jing's portrayal of Liu Peiqiang is the only "old man" among the main characters in the sequel. Due to the full cast of characters in the previous movie, the sequel is more about adding to their emotional storyline. He and his wife Han Duoduo went through countless hardships and twists and turns from knowing each other to falling in love, especially the life and death test during the fall of the Ark space station, which further brought them closer and prompted them to enter the marriage hall. In one part of the movie, Han Duoduo is diagnosed with a terminal illness, and Liu Peiqiang takes her by plane to see the dilapidated buildings in Shanghai that have been largely submerged by seawater.

Two people cuddled together like this, even though they knew it was death, it was still so warm and romantic.

Andy Lau plays Tu Yuheng, who feels even more guilty about his daughter Yaya's premature death. Because of this obsession, he tried every means possible to promote the continuation of digital life. If Liu Peiqiang is a constant of the Wandering Earth project, Tu Yuheng is undoubtedly a variable of this project. It is this obsession that breaks through life and death, ultimately saving humanity and making the future more possible.

Li's portrayal of Zhou Zhezhi is the soul figure of the entire "Wandering Earth" project. He always stabilizes the morale of the army at critical moments and drives the course of human history with his unparalleled personal charm. His speech in the film is very infectious, completely enhancing the theme expression of the film. Compared with mainstream trends abroad, the "Wandering Earth" project has distinct Chinese characteristics. Essentially, the entire plan is like the ancient legend of 'fools moving mountains'. Doing something that seems completely impossible to succeed takes 2500 years and 100 generations. Perhaps only the Chinese understand its meaning.

Sha Yi played Zhang Peng in several scenes, but he shed the two most important tears in the film. Firstly, when someone has to sacrifice to detonate a nuclear bomb, he takes the initiative to let pilots over 50 stand out, which is to exchange his own sacrifice for the peace and stability of the next generation. On the other hand, when the nuclear bomb exploded, he told the Earth how beautiful he was, his obsession with life, and his feelings for his hometown and mother, which completely overflowed the screen and made people feel heartbroken.

Fourth, philosophical thinking

Compared to the first part, which focuses on showcasing humanity's heroic spirit and perseverance in the face of disasters, the second part is obviously bigger, making humanity truly a community of shared destiny for the first time and jointly promoting the resolution of disasters.

The greater significance of this movie lies in proposing the ultimate direction of life progress. The film uses a large number of shots to showcase the intelligent system Moss' observation of humans, laying a bigger foreshadowing at the end of the Easter egg. All the choices made by Moss ultimately stem from its completely different understanding of life from traditional concepts, as Ma Zhao said in the film: 'Without human civilization, there is no meaning'. However, how to define 'human' is debatable.

At present, human cognition and thought must rely on the body, but in higher stages of civilization, thought may also be detached from the body. Moss hoped that humanity could evolve in this direction, but this clearly posed a serious conflict with current beliefs, leading to the emergence of various crises.

Just like digital life, it's difficult to judge whether it's good or bad. This relationship is like Copernicus and the Pope. When the final result is inconclusive, no one can prove whether he is Copernicus or the Pope. This discussion, in the second part, only superficially touched upon and did not delve deeper. If there is a third part in this film, it may become an important background setting for the story.

What does it feel like for physics majors to watch "The Wandering Earth 2"?

Happy New Year. If there is anything worth celebrating on the first day of this year's Chinese New Year, I believe physics enthusiasts will blurt it out - "The Wandering Earth 2" has been released. I just came out of the cinema. It's really a great science fiction film.

Here is a setting for readers who are not familiar with the story background. According to the storyline shown in the movie production notes and trailers, as early as 1977, astronomers speculated on the accelerated fusion of the Sun's core based on historical records of solar activity; In 2026, a solar storm exceeding G5 broke out, and the international community began to pay attention to the helium flash crisis, gradually forming the spaceship faction that escaped by spaceship and the earth faction that wandered with the earth; In 2030, the Earth School Plan was adopted, and the construction of Earth's planetary engines began. In 2039, during the era of braking, the Earth's rotation will be stopped by engines; Starting the plan on a monthly basis in 2042; In 2044, the space elevator crisis; In 2058, the lunar crisis; In 2065, the Earth comes to a halt and the propulsion engine ignites, entering the era of acceleration; In 2075, Jupiter's gravitational crisis; In 2078, there will be a solar helium flash crisis.

First, let's talk about the motivation behind the entire story, which is the rapid expansion and aging of the sun, also known as helium flashes.

1. Helium flash: Why does the sun age?

Our sun is in its prime, known as the main sequence star stage in astronomy. It is approximately three-quarters hydrogen, one-quarter helium, and contains small amounts of oxygen, carbon, neon, and iron. The main source of energy for the sun's luminescence and heat generation is the fusion of hydrogen inside, where every four hydrogen atoms (protons) converge into a helium nucleus, known as a proton proton chain reaction.

The inner layer of the sun is high temperature and pressure, which can fuse to produce helium, while the external environment does not have high temperature and pressure enough for hydrogen fusion. Due to the mass of the Sun, helium produced in the inner layer is captured by gravity, while hydrogen from the outer layer does not enter the interior. Therefore, when the hydrogen in the inner layer of the Sun is depleted and all becomes helium, the heat generated by the fusion of the inner layer cannot resist gravity and collapses.

The inner and outer layers of the sun

But this does not mean that the sun will shrink, as the collapsed inner layer will become hotter, heating up the hydrogen in the outer layer and igniting fusion reactions, which will cause the sun to expand thousands of times and even reach the position of Venus' orbit on the surface. At this point, the sun enters the red giant phase. Red giants typically last for 1 billion years. At the end of the red giant stage, the temperature of the Sun's core can reach up to 100 million degrees, enough to ignite the nuclear reaction of helium aggregation into carbon and oxygen. This is called helium flash.

So according to current stellar theory, even before helium flashes, the Sun would expand into a red giant, baking life on Earth.

According to current theory, the Sun lasted for 11 billion years in the main sequence stage, and now the Sun is only 5 billion years old, so there is no need to worry about its expansion and aging.

2. Planetary Engine: Is Heavy Nuclear Fusion Feasible?

In order to advance the Earth, 12000 planetary engines were built, of which 10000 were built in the northern hemisphere for propulsion and 2000 were built near the equator for steering. These engines are over 10000 meters high and cover an area of approximately 1000 square kilometers, which is very large.

Steering engine and propulsion engine

As die hard science fiction fans, six months ago, we estimated the first step in Earth's wandering - how to stop spinning (how to make the sun rise from the west). We assume that the engine adopts the working fluid propulsion scheme commonly used in old aerospace, and the engine can spray working fluid at a second cosmic velocity of 11.2 km/s, and then calculate how much power is needed.

According to the plan in the movie production manual, it took 26 years for people to complete the brakes, while in the original novel it took 42 years. Here we use the time of the novel. According to calculations [2], the total amount of working fluid that 2000 servos need to spray per second is 73.36 billion tons, with an average power of 4.6 × 10 ^ 21W

You may not know this number. For example, it is equivalent to consuming 45 times the global electricity generation in 2021 in one second. Compared to current engineering technology, this is the installed capacity of the 200 billion Three Gorges Dam, or 575 billion nuclear fission power plant units (measured in units of the largest installed capacity at present). But for the sun, this is only one percent of its radiated power.

Converted, the total thrust of the engine should reach 8.21 × 10 ^ 17N, so the thrust of a single engine should reach 41 billion tons. But both the original work and the movie set the thrust of an engine at 15 billion tons. For safety reasons, I suggest doubling this setting again.

When the engine starts, it generates huge heat, so at the beginning of the plan, the surface temperature will rise to 70-80 degrees Celsius, polar glaciers will melt, and some coastal cities will be submerged due to tides caused by the cessation of rotation.

Submerged Shanghai and massive planetary engines

Where does such tremendous thrust come from? The wandering Earth imagined a highly technological nuclear fusion, also known as a 'burning stone'. First, let's talk about what a nuclear reaction is.

The atomic nucleus is composed of protons and neutrons, collectively known as nucleons. Nucleons combine to form atomic nuclei, releasing energy. In the process of nuclear reaction, the binding mode of nucleons will change, and the recombination process of this binding mode is accompanied by changes in energy. If the nuclear reaction absorbs energy, it indicates that the initial state is lower than the final state; if the nuclear reaction releases energy, it indicates that the initial state is higher than the final state.

Due to the conservation of the number of nucleons in nuclear reactions, we define the average binding energy of nucleons in a nucleus by dividing the energy released when the nucleus binds by its number of nucleons. The higher the average binding energy, the lower the energy of the nucleus and the poorer the reactivity. The smaller the average binding energy, the higher the energy of the nucleus, and the more likely a nuclear reaction is to occur.

Specific binding energies of different atomic nuclei

From the graph, it can be seen that the average binding energy is the smallest (because it only has one proton and is not bound), while the average binding energy of Fe ^ 56 is the largest. Any atomic nucleus with an average binding energy less than Fe-56 can approach and release energy towards Fe-56 through nuclear reactions. The nucleus on the left side of Fe 56 can be transformed into Fe 56 through fusion, while the nucleus on the right side can be transformed into Fe 56 through fission.

We just talked about hydrogen fusion in the sun. From the figure, it can be seen that helium nuclei can continue to polymerize into carbon, nitrogen, oxygen, etc., but subsequent reactions require higher pressure and temperature.

The cycle of carbon, nitrogen, and oxygen in stars heavier than the Sun

The Burning Stone is also similar. The oxygen and silicon mainly contained in stones can melt and approach iron at extremely high temperatures and pressures. But currently, people have not even mastered photo nuclear fusion. There are three generations of fusion technology being studied today. The first generation mainly involved deuterium tritium fusion, which required relatively low temperatures and pressures. The second generation is deuterium and helium-3 fusion, and the third generation is two helium-3 fusion. The reaction conditions of these two generations are more stringent.

3. Monthly plan: Roche limit? Ignite the lunar nucleus?

The gravitational force between the sun and the moon is approximately 2 × 10 ^ 20N, and all engines operating at full power cannot directly counteract this force. In order to eliminate this uncontrollable factor, "Wandering Earth" has developed a monthly plan.

The three highlights on the moon are the three lunar engines.

But from the trailer, we can know that the lunar crisis broke out in 2058, and the moon was unexpectedly not pushed out, but collided with Earth.

This painting is very interesting. The red circle represents the Roche limit of the Moon relative to Earth. What is Roche limit? Let's take the first movie as an example.

In the first movie, as Earth grows with the help of Jupiter's gravitational slingshot, it unexpectedly loses control of its trajectory and is about to fall into the Roche limit. If you don't try to escape with greater thrust, it will be torn apart by Jupiter's gravity and become part of Jupiter's rings.

This tearing force comes from the non-uniformity of gravity. Jupiter's gravity on Earth is uneven. The part away from Jupiter has less gravity, while the part closer to Jupiter has more gravity. This difference in gravity will form tidal forces. Yes, the reason why it is called this name is because the tides on Earth are generated by the tidal force of the moon on Earth, and the rise and fall of the moon leads to the rise and fall of tides.

The tidal force will increase as the distance between two celestial bodies decreases. When the distance decreases to the Roche limit, tidal forces will exceed the gravitational force of the Earth itself, thereby disintegrating the Earth. For rigid bodies and fluids, the Roche limit has the following formulas:

But there is a bug in the movie. The average density of Earth is 5.514 g/cm, while the average density of Jupiter as a gas planet is 1.326 g/cm, so the calculated Roche limit is smaller than Jupiter's radius. That is to say, there was no Roche limit before Earth collided with Jupiter. Of course, if we consider fluids on Earth, such as the Earth's atmosphere, it will indeed be torn apart by Jupiter's gravity before a collision occurs.

The Earth's atmosphere and Jupiter's atmosphere pull each other apart.

Returning to the second movie, the average density of the moon is 3.340 g/cm, and its rigid Roche limit can be calculated to be 1.49 times the radius of the Earth. So in the movie, the moon falls on Earth and before it touches the Earth, it will be torn apart by tidal forces.

The monthly plan finally succeeded with difficulty. People first installed thousands of nuclear bombs on the surface of the moon and detonated them through phased array, concentrating the shock wave onto the lunar nucleus and triggering lunar nuclear fusion. Although director Guo Fan admits that disintegrating the moon is a crazy idea, directly destroying the moon would require at least 1 billion times the current nuclear weapons stockpile. But this plot indicates that in the face of a global crisis, countries ultimately "let go of their obsession with history, present, and future" and choose a rational way of cooperation.

Today's people do not see the ancient moon, but this month once shone upon the ancients. From then on, the earth embarked on a lonely journey of wandering.

4. Mountain Relocation Plan: Pushing Earth Out of the Solar System?

Now everything is ready, it's time to leave the solar system. So where should the engine spray?

Intuitively, if you want to avoid the sun, of course you have to spray towards it. But the problem is, according to our estimation in the second section, the thrust of ten thousand propulsion engines is only 4.1 × 10 ^ 18N, which can only provide an acceleration of 0.7 micrometers per second for the Earth. In contrast, the gravitational force between the Sun and the Earth is about 3.5 × 10n, which is like a mayfly shaking a tree. So waiting for a period of time to directly push away from Earth is not feasible.

A more practical solution is to align the acceleration direction with the speed direction of the Earth's revolution, which can maximize kinetic energy. There are two points here. Firstly, to break free from the constraints of gravity, there is no need for speed to spin away from the gravitational source. As long as the kinetic energy is large enough to exceed the gravitational potential energy, as long as the direction of velocity is not straight, the object can escape gravity when it reaches the gravitational source in a while. Secondly, under the same engine power, the momentum increment obtained by reverse injection is the same, which can be approximately understood as the constant velocity increment of the Earth. When the direction of velocity increment is consistent with the original velocity direction, the increase in kinetic energy is maximum.

The current space technology also uses this acceleration direction to achieve ascent from low orbit to high orbit. In most cases, this is the most fuel-efficient way of maneuvering, also known as Hohmann maneuver.

Hohmann transfer orbit 

I imagined the process of the Earth ascending into the orbit of Jupiter. If the engine thrust is calculated according to the second section, this process will take at least one hundred years. In order to catch up with the movie timeline, let's not consider the engine thrust for now. Assuming that each ignition at perihelion can generate a growth rate of 3km/s for the Earth, we only need three orbit changes to complete it.

The reason why it only ignites at perihelion is because here the Earth has the highest speed, and the same speed increment increases the mechanical energy the most, and also lifts the apogee the most. In the original work, because we don't know when the helium flash will erupt, people become nervous every time they pass perihelion, which is compared to the "Russian roulette wheel in the universe".

The acceleration effect of Jupiter's gravitational slingshot (for example, not igniting at perihelion).

When the Earth approaches Jupiter, it will produce a slingshot effect with Jupiter's gravity, gaining some momentum from Jupiter and accelerating. This process is actually like swinging a racket when you play ball. If the quality of the ball is very small compared to the racket, the maximum growth rate of the ball can reach twice the speed of the racket.

The mass of Earth is only three thousandths that of Jupiter, so it can be considered as a photosphere hit by Jupiter, which can result in significant velocity gains from gravitational slingshots.

5. Wandering destination: Triple Galaxy?

Through Jupiter's gravitational slingshot, Earth officially breaks free from the gravitational constraints of the solar system and moves towards a new sun. In "Wandering Earth," people take Proxima Centauri, which is 4.2 light-years away from the Sun, as their new home.

This idea is beautiful, but there is a tricky problem: Proxima Centauri, Alpha Centauri A (South 2A), and Alpha Centauri B (South 2B) together form a three star system. This alpha Samsung Centaurus is the location of the Three Body civilization set in the science fiction novel "The Three Body Problem". The reason why Trisolarans invaded Earth is because their ternary star system undergoes random motion under the influence of gravity. We once introduced it in 'Helping Three Body Find a Stable Solution Before Broadcasting'. Of course, currently Proxima Centauri is relatively far away from the binary system of Nanmen AB, and according to today's orbital parameters, it is still in the epoch of perpetuity.

Alpha Samsung Centaurus

But there's a joke:

On the way to wandering Earth, people encountered the Trisolaran Fleet.

Earthlings: Our sun is rapidly aging, and we must move to a neighboring galaxy.

Trisolarans: Our star system is unstable, we must transfer to the solar system.

The Earthlings and Trisolarans looked at each other in confusion.

Science fiction movie "Wandering Earth 2" still photo 20

The nearest star systems to the Sun

Considering that 'The Wandering Earth' was written earlier than 'The Three Body Problem', Liu himself probably didn't expect it to be so coincidental. So is there a better option? The second closest star to Earth currently is Barnard's Star, located 6 light-years away from Earth. Like Proxima Centauri, it is also a red dwarf with a mass of approximately 0.144 M ⊙ and a surface temperature of approximately 3000K K

In November 2018, it was discovered through the Doppler shift method that Barnard's Star also has a planet named Barnard's Star B. Its mass is more than three times that of Earth, and its surface temperature is about -170 ℃.

Barnard's Star

If the Earth were to stop in the orbit of Barnard's Star B, it should also be able to obtain a good living environment. This can avoid the chaotic operation mode of the three star system, but it requires wandering for 1.8 light-years, which is about 400 years.

Looking at the entire plan for the Wandering Earth, it takes 500 years to accelerate to 0.5% of the speed of light, 1300 years to complete two-thirds of the journey, and 700 years to slow down and enter the gravitational field of Proxima Centauri, in order to adjust the Earth's course and anchor it on a stable orbit. The entire process took 2500 years and spanned 100 generations.

Some people in the movie question whether it can be completed. Teacher Li Xue Jian replied, "I believe my child will believe, and their child will also believe. The spirit of fools moving mountains is not only a gene engraved in traditional culture, but also a precious spiritual wealth in our real life.