"The Wandering Earth 2" movie poster
One thing is to say, "The Wandering Earth 2" is really good, in the face of the epic narrative and Chinese positive energy, Marvel Thanos snapped his fingers that set suddenly seemed too pediatric and boring.
However, like to like, since the good words have been said by you, as a nuclear engineer, it is not interesting for us to add to the cake, so I have to take a magnifying glass and nitpick its "small faults".
Did you find that Da Liu likes nuclear fusion? The main setting of "The Wandering Earth 2" is almost all related to nuclear fusion:
Solar helium flashes are a type of nuclear fusion;
The planetary engine used to push the Earth away also relies on heavy nuclear fusion to produce 150 trillion tons of thrust, so large that only Eurasia and the Americas can withstand it;
Many of the 3,614 nuclear bombs that were later detonated on the moon were hydrogen bombs based on the principle of nuclear fusion;
The point is, these nuclear bombs also triggered fusion in the core of the moon, blowing it up and thus saving humanity!
Nuclear fusion is the process by which multiple lighter nuclei combine into one heavier nucleus.
For example, nuclear fusion on the sun can be loosely thought of as the fusion of four hydrogen nuclei into one helium-4 nucleus (composed of two protons and two neutrons).
Since the mass of the helium-4 nucleus is lighter than the four hydrogen nuclei combined, the lost mass is converted into energy, so the nuclear fusion inside the sun can release huge energy, so that the sun continues to emit light and heat.
As for the later helium flash, three helium-4s fused into a carbon-12 nucleus.
The Sun's energy comes from the fusion | that occurs at the Sun's core Screenshot of the trailer for "The Wandering Earth 2"
What happens in a hydrogen bomb in a nuclear bomb and in a controlled fusion device is deuterium-tritium fusion. Deuterium and tritium are also hydrogen, but the deuterium nucleus is one proton and one neutron, and the tritium nucleus is one proton and two neutrons.
Deuterium-tritium fusion will form a helium-4 and a neutron, which can also release a huge amount of energy, so the hydrogen bomb explosion is particularly powerful, far more powerful than the atomic bomb.
Deuterium-tritium fusion process produces a helium-4 and a neutron and releases energy
In the large-wave nuclear fusion of "The Wandering Earth 2", the most reliable is the more than 3,000 nuclear bombs made by humans, which can really explode, which is real and childless.
And the heavy nuclear fusion of the planetary engine and the more amazing lunar nuclear fusion can be described in one sentence: it is difficult to move God here!
Well, I believe many people will think that my brain is locked by Tomoko (now the "Three-Body Problem" TV series is also very popular), but under the current laws of physics, I can only come to this conclusion.
Planetary engine
Planetary engine | in The Wandering Earth 2 Screenshot of the movie trailer
Let's start with the 12,000 spectacular planetary engines, without which Earth would not be able to set off to wander.
The planetary engine is probably the most powerful engine ever described in science fiction. Da Liu can imagine this thing, the movie can make it convincing, the author is really impressed!
And in terms of scientific principles, planetary engines can basically make sense. Planetary engines are fueled by stone, which accounts for the majority of silicon, which can be fused to form iron nuclei, which release energy.
The inspector asked, why not use deuterium or hydrogen as fuel? These can be extracted from seawater. The reason is that the consumption of planetary engines is too large, and there is not enough seawater on Earth to burn ... Therefore, it is still good to be stone, it is everywhere, inexhaustible, inexhaustible.
The original novel did not elaborate on the structure of the planetary engine, only mentioning that it reached a height of 11 kilometers and a diameter of 50 kilometers at the bottom. Trucks pour stones through the feed ports, and the spouts on top of the engine eject a huge jet of plasma upwards.
The movies "The Wandering Earth" and "The Wandering Earth 2" reproduce these huge engines on the screen, and they are full of details. The author speculates that the planetary engine should be derived from the current magnetic confinement controllable nuclear fusion device, the tokmak.
Planetary engine under construction in The Wandering Earth 2 | Movie poster
Even deuterium-tritium fusion, which has a low threshold, requires harsh conditions. This is because atomic nuclei are positively charged, and to initiate fusion, you need to bring them closer to a distance of 10-15 meters, which is less than one billionth of a hair. As the so-called same-sex repulsion, the charge carried by the nucleus will produce a huge repulsive force at such a short distance.
To overcome this repulsive force, extremely high temperatures are required. To achieve deuterium-tritium fusion on Earth, it would take about 100 million degrees Celsius, even higher than the center of the sun.
The central temperature of the sun is only about 15 million °C, and it can achieve fusion because the pressure of the core is particularly high, and the mass is particularly large, even if the probability of fusion is low due to low temperature, but its huge mass makes the total power of fusion still very large.
At a high temperature of 100 million °C, no substance can remain solid, all become plasma, and no container made of any material can hold these plasmas, so it is necessary to use a magnetic field to constrain and prevent the plasma from directly contacting the container wall.
The Tokmak device confines the plasma to fusion in an annular vacuum chamber. The International Thermonuclear Test Reactor (ITER), which is currently under construction, is a tokmak that can produce 10 times the energy input from fusion, but no controlled fusion device can achieve continuous output of fusion energy.
International Thermonuclear Test Reactor under construction | ITER
If the planetary engine achieves continuous and controlled silicon fusion, a major problem needs to be overcome, that is, how to convert energy into momentum of plasma jets.
The fuel density in the vacuum chamber of the current Tokmak device is very low, even if the temperature reaches hundreds of millions of degrees, the pressure is not high, and the current maximum pressure is only 2.05 atmospheres. With this pressure, it is impossible to produce high-speed jets like planetary engines.
Therefore, the planetary engine must achieve nuclear fusion at great density and extreme pressure, and to control such high-density plasma, it requires an unimaginably strong magnetic field, and the feed and jet cannot destroy the stability of the plasma. This difficulty, with the existing scientific and technological capabilities, is unimaginable, maybe future human beings can do it.
But can this silicon core fusion really be achieved on Earth?
Heavy nuclear fusion
Considering that the planetary engine burns stone, that is, the fusion of silicon nuclei, this heavier nuclear fusion is more demanding than the conditions of deuterium-tritium fusion, because the larger the atomic number, the greater the charge carried, and the stronger the repulsion.
Hydrogen fusion can occur at 15 million °C inside the sun, or even lower, but to occur helium flashes, that is, from three helium 4 fusion into one carbon 12, it takes 100 million ~ 200 million °C, and it is necessary to accumulate a large amount of helium 4 like the old age of the star.
For the real sun, this condition will take at least billions of years to achieve, so don't worry about ushering in the solar helium flash crisis within 100 years like the setting of "The Wandering Earth".
For the fusion of two silicon nuclei (14 protons + 14 neutrons) to occur, the repulsion between the charges is much greater than helium fusion, and you can imagine how difficult it would be.
Direct fusion of two oxygen nuclei (8 protons + 8 neutrons) much smaller than the atomic number of silicon requires a high temperature of 1.5 billion °C and a high density of 10 million tons per cubic meter.
There is little literature on how high conditions are required to achieve the fusion of two silicon nuclei, and some articles say that 3 billion °C is required, which is a reasonable speculation.
Therefore, even in the interior of the star, fusion from silicon nuclei to heavier nuclei is not simply to add up two silicon nuclei, but to continuously absorb helium 4 nuclei, each absorption increases 2 atomic numbers, a total of 7 additions, in order to fuse to nickel 56 nuclei. This nucleus is very unstable and will quickly decay into cobalt-56 and then into stable iron-56 (26 protons + 30 neutrons).
The process by which the internal fusion of massive stars forms iron 56
But such a process cannot be achieved by our sun, and it takes a star with more than 8 times the mass of the sun to eventually produce iron 56.
In other words, the planetary engine in the wandering earth needs to simulate the internal environment of massive stars several times larger than the sun, so that it is possible to burn "stones" and achieve silicon fusion. But the problem is that there is not so much helium on Earth, and helium resources have always been scarce, not as easy to find as stones.
Therefore, the planetary engine must achieve a high temperature of 1.5 billion ~ 3 billion °C and unimaginable high density, so that the silicon nucleus and oxygen, magnesium, or itself to fuse.
Do you think this condition can be achieved on Earth?
Even if it is assumed that it can be realized, there will be a basin of cold water next, that is, from silicon fusion to iron, it does not release a lot of energy!
This is because the specific binding energy of the nuclei is different.
Specific binding energy is the energy required to completely disassemble an atomic nucleus into nucleons, averaging the energy required by each nucleon. The higher the specific binding energy, the more stable the nucleus.
Specific binding energies of different nuclei
The fusion from hydrogen or deuterium to helium 4 increases very quickly than the binding energy, so the energy released is very large, but from helium 4 and all the way up to iron 56, the specific binding energy grows very slowly and the energy released is very limited.
For this limited energy to achieve the extreme conditions at the core of a massive star, even if it can be done, I am afraid it will not be worth the loss.
Nuclear explosion of the moon
After talking about the planetary engine that "burns stones", let's talk about the blow-up moon in "The Wandering Earth 2".
This brain hole is really big, people have to admire the imagination of the screenwriter, after all, in the original novel, only the moon was pushed away without blowing it up.
But to blow up the moon, 3614 nuclear bombs alone are clearly not enough. The movie also mentions that the energy produced by the explosion of these nuclear bombs is only 1 billionth of the energy needed to destroy the moon. Because the Moon, although much smaller than Earth, is still large, reaching a diameter of 3476 kilometers. Even if there are tens of thousands of nuclear bombs, it is only tickling and stirring up a cloud of dust for the moon.
So the setting in the movie is to arrange these nuclear bombs in a huge crater to form an array, and by accurately detonating the nuclear bomb array, trigger the fusion of the lunar core, and then blow up the moon.
Detonate the lunar | Screenshot of the trailer for "The Wandering Earth 2"
These bombs only act as a "trigger" or "fuse", somewhat like the principle of hydrogen bombs: an atomic bomb is used as a fuse to trigger the fusion of deuterium and tritium.
However, during the detonation of the hydrogen bomb, the atomic bomb does not directly rely on high temperature to initiate fusion, but uses the X-rays generated during the explosion to compress and heat the fusion fuel to achieve nuclear fusion conditions.
The lunar crust is also mainly composed of stone, which is not conducive to the propagation of X-rays, so the author speculates that it may be to use the shock wave generated by the nuclear explosion to achieve instantaneous compression of the central point of the moon to trigger lunar nuclear fusion.
Reasoning here, everything is reasonable, but then it is outrageous. Because the Moon, like the Earth, has an iron core, that is, the main component of the lunar core is iron 56.
As mentioned earlier, the volume of the moon is not small, larger than Pluto, so its interior will diverge from elements. In the early days of the moon, the internal matter was in a molten state, so the heavy material continued to sink and the light material continued to rise. Because metals such as iron are heavier, they gradually "sink" towards the center to form metal cores, mainly iron, and a small amount of sulfur and nickel.
Interior structure of the Moon
Iron-56 is extremely famous in the universe, with the highest specific binding energy and a more stable structure than any other nucleus (except hydrogen). Fusion from iron 56 upwards does not release energy anymore, but instead needs to absorb energy and requires unimaginably extreme conditions — for example, when the massive star's shell collapses inward and hits the core at the moment of a supernova explosion, or when two neutron stars merge.
Most of the elements on Earth with a higher atomic number than iron, such as gold, silver, uranium, etc., are formed under such extreme conditions.
Schematic diagram of the moment of neutron star merger | University of Warwick/Mark Garlick
With more than 3,000 nuclear bombs, can such conditions be formed? Apparently not!
Even if it is really a mistake, with a particularly small probability, a drop of iron 56 at a certain point has fused, because this fusion is an energy-absorbing reaction, it will not produce a violent explosion, and the energy of the nuclear explosion shock wave will be directly absorbed.
Some say that lunar fusion can also be seen as a supernova explosion, because supernova explosions also have iron cores. This thinking is profoundly wrong.
Supernovae are a big explosion at the end of the life of massive stars, the reason for the explosion is not because of iron core fusion, it is precisely because the massive star burns everything that can be fused, the remaining iron core does not fuse, loses the power to resist gravitational collapse, under the action of huge gravity, the star shell crashed down on the iron core inside, which caused the big bang.
Schematic diagram of a supernova explosion
Therefore, the energy source of the supernova explosion is the gravitational potential energy of the star itself, not the fusion of iron cores. A planet as small as the moon does not need to rely on fusion to resist gravitational contraction, and supernova explosions are impossible.
So, want to blow up the moon? Even if he handed over these more than 3,000 nuclear bombs to God, he could only spread his hands: he really couldn't do it!
Then again, "The Wandering Earth 2", as a science fiction movie, requires a large imagination, and some unreasonable things in science are inevitable. As long as it can meet the needs of the plot and promote the development of the plot, it makes logical sense!
It's like the author, although I picked so many faults, I was still full of interest when watching movies in the cinema, and I was still unfinished after watching it, which is definitely the pinnacle of science fiction movies.
Without further ado, this is the second brush!
Author: Sagittarius A
Edited by Steed
Cover image source: "The Wandering Earth 2" movie stills
An AI