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# Physics Behind James Cameron's Avatar Movie

Undoubtedly, Avatar, a film by James Cameron, was a groundbreaking film. Without getting into a discussion about whether or not it is a good movie, I am personally of the opinion that it is. We will attempt a fictional space travel mission into the Pandora satellite in order to study its physics and observe some aspects of it. In the film, they give us a lot of information and some numerical data that can be used to estimate some of the interesting properties, but we will also use the physical characteristics. A good science fiction movie can serve as a great tool to help us learn more about physics.

## Space travel and the location of Pandora

In this story, the fictional moon Pandora is located in the Alpha Centauri system, made up of Alpha Centauri A, Alpha Centauri B, and Proxima Centauri. There is still debate about whether this system is double or triple, but this does not matter too much to us. We are more interested in knowing that it is at a distance of about 4.36 light-years away since in the film they give us the data of the duration of the trip: 5 years 9 months and 22 days. This makes for a very considerable average speed of 75% the speed of light. However, the ship is not going to leave directly with that speed, but there must be an acceleration time and a deceleration time. Therefore, the cruising speed must be even higher.

In the wiki, they give us a value for this cruising speed of 87% of the speed of light and they also tell us that the ISV Venture Starship never exceeds 5 g's when accelerating or braking. This is enough information to fiddle with the numbers and the result is that the ship takes at least 2 months to accelerate to 0.87 c and another two months to break once it reaches its destination. The rest of the time it would be a trip at a comfortable cruising speed, but ... surprise! At this speed, the ship would not take almost 6 years, if not the trip would last less than 5! It seems that we have a little contradiction, but it can be fixed by giving a cruising speed somewhat lower than those 0.87 c, taking more time to accelerate, or doing it at fewer g's. I leave it to you to fight with the light speeds of calculations

So far, all the calculated times are taken for an observer on Earth, since for the colonists traveling in the spacecraft the journey would have a shorter duration due to the effects of time dilation due to special relativity. To be exact, for the settlers the trip would barely last 2 years and 10 months. And despite the fact that they are in a state of cryosleep (something like sleeping in cryopreservation ) this decrease in time is useful since it is not necessary to load the ship with extra weight for food, medicine, etc. You only take what you need, something essential in space travel due to the high price of putting an extra kilo in orbit.

### What life is like on Pandora

We know from the wiki that Pandora is a satellite of a giant gas planet called Polyphemus(Polyphemus in Spanish) that orbits around Alpha Centauri A, a star very similar to our Sun. Polyphemus is similar in aspect to Jupiter, being smaller and denser than Saturn; while Pandora is slightly smaller than Earth. Its gravity is 80% terrestrial, its atmospheric density 20% higher, while the pressure at sea level is 10% lower. From these data, we can deduce, for example, that it will cost less effort for birds to fly than on Earth. The reason is obvious. A higher density of the air provides greater thrust to the bird, just as when we submerge ourselves in water, it offers greater thrust than air and we "weigh" less. In addition, gravity and air pressure are lower, factors that also help. Nothing is said about the temperature of the satellite, but it appears to be similar to a temperate terrestrial climate. However, it is striking that attention is not paid to the strange day-night cycles that they should have on Pandora due to the long-duration eclipses that Polyphemus will cause and having two suns in the sky (the light from the little Proxima Centauri would be negligible).

Now let's look at some of the scenes in the movie. The Na'vi , the humanoids that inhabit Pandora, is significantly older than humans - perhaps twice as tall. And the same happens with the rest of the animals and plants. The reason you will have already deduced: the lower gravity of the satellite means that living beings can develop and grow more. And as if this were not enough, the bones of the Na'vi skeletons are reinforced with carbon fiber. That makes them more resistant. If you have seen the movie you will remember the scene in which the protagonist, Jake Sully, controlling his avatar, throws himself from the top of a tree and uses the branches of the lower trees to slow down his fall. His teacher Neytiri does it without a problem, but he falls crashingly. And still, nothing happens to him! The explanation is not only its greater resistance or less gravity, but there is also influence (although negligible in this case) of the lower limit speed that can be reached in Pandora. And it is that assuming the viscosity of its atmosphere equal to that of the Earth, in Pandora, the limit speed is 20% lower than in our planet.

On gravity, more scenes are seen in the film such as when Colonel Quaritch is in his office lifting a weight with a multitude of disks that seem quite heavy. They do not give any value, but the colonel does comment on the need to work hard so as not to lose strength in a weaker gravity. And as for the content of the atmosphere, this is not mentioned either, but it is said that humans can only breathe it for 20 seconds before losing consciousness, causing death after being exposed for four minutes. The reasons can be three: a very low oxygen concentration, the presence of gases that are easier to absorb than oxygen (such as carbon monoxide), or both. I do not have it very clear, It takes a lot for him to get the phosphorus to burn. You know, if there is no oxygen there is no combustion. Even so, after several attempts, he succeeds and the torch that is manufactured shines with great force, which surprised me in the cinema and continues to surprise me now. Is it a license from the writers or is it that Jake did not know how to light a match? Namely.

The most surprising aspect of life on Pandora is that all living beings are united, they are like one great and unique planetary living being. According to Dr. Grace, trees are the basis of everything because their roots are the electrochemical communication network that links all of Pandora. Exactly it says that each tree has 10 thousand connections with the trees that surround it and that in Pandora there are nothing more and nothing less than a billion (10 12) trees. This value may seem exaggerated at first, but it is not. Assuming that the water surface in Pandora is identical to the terrestrial one: 71% of the total surface; and assuming that the forest area is 80% of the solid surface, we arrive at the result that we could place 6-meter diameter trees at a distance of about 4 meters from their neighbors. This I think is consistent with what is seen in the film, except for the gigantic Mother Tree, of course.

### Pandora's Magic

The humans did not invade Pandora for tourism, they invaded it looking for a mineral that can only be found there: unobtanium. It is a superconducting material at room temperature that is sold on Earth at a not inconsiderable amount of 20 million per kilogram. Its trade and the infinite applications that can be made with it are saved to the inhabitants of a battered Earth in the middle of the XXII century.

The Hallelujah Mountains are the place in Pandora where it appears most spectacularly. This formation is found levitating in the sky of the satellite since it is in an area that humans call the "vortex of the flow". This vortex is about the magnetic poles of the satellite, where the magnetic field lines are greatest. In this area, the Hallelujah Mountains, being formed by unobtanium, suffer an effect known as the Meissner Effect, whereby a superconductor below its critical temperature (temperature below which the material is superconducting) acquires diamagnetic properties. Which makes it repel magnetic fields. In Pandora, we have the magnetic field of the satellite and unobtanium as a superconductor; and it appears that at the poles, the flow of the field is strong enough to lift these flying islands loaded with valuable materials. However, on the rest of the planet, there is also a magnetic field, which, although less intense, should produce unobtanium uprisings over the entire surface, something that is not appreciated in the film.

Obviously, there are many aspects to the film that can be discussed, but I will leave them to you. Also, if you want to continue talking about Avatar, not only from a physics point of view but also from a more general scientific point of view, I invite you to visit this HomoScience forum thread created for it. Please feel free to share your ideas about how Pandora works, or about life on the planet, by leaving a comment here.