Home > Avatar (2009 film), Clement's Game > SciFi Round Twelve: Pocahontas in SPACE!!!!

SciFi Round Twelve: Pocahontas in SPACE!!!!


Avatar (not the one with the last airbender) is one of the prettiest films I’ve come across.  Beautiful cinematography.  Nice constructed language for the aliens.

Now, it’s time to look for problems with the science and internal consistency.

It’ll be like shooting fish in a barrel, but let’s have a go at it anyway.

***

The blue alien is the alien "avatar" of the dude on the right.  He proceeds to learn how to be more awesome than the real aliens.  Oops.

The blue alien is the alien “avatar” of the dude on the right. He proceeds to learn how to be more awesome than the real aliens. Oops.

A Little Astronomy Goes A Long Way

Somewhere, something has gone horrible wrong.

And I’m not even referring to the outrageousness of naming a substance unobtainium, or the moon you’re visiting Pandora.  I’ll try not to open that box too much.

There is so much wrong here, it’s hard to know where to start.  According to the movie (and the wiki), Pandora is a moon around the gas giant Polyphemus, which in turn is in orbit around Alpha Centauri A.  First off, as I mentioned in an earlier post, there is no such gas giant in the Alpha Cen system.  (Though there’s a much smaller, hot rock orbiting Alpha Cen B.)

The next problem is that Alpha Cen A’s habitable zone is further out than that of Alpha Cen B.  Planets in the habitable zone of the latter may have stable orbits.  There could even be an Earth-like planet, which, while not detected yet, hasn’t been ruled out.  (They’re looking.)  However, planets in the habitable zone of Alpha Cen A are probably not going to be in stable orbits.  They would be further out, and more easily perturbed into unfortunate orbits (or possibly even ejected) by encounters with Alpha Cen B.

Next up: Polyphemus is smaller than Jupiter, but Pandora is about the size of Earth.  This… doesn’t really work.  Jupiter’s largest moon, Ganymede, is bigger than Mercury, but much smaller than Mars… and not really close to Earth-size.  Pandora is too big, or Polyphemus is too small.  Or something.

For bonus points, gas giants and their moons presumably formed outside the “ice line.”  That means, they were cool enough that not many volatile elements were warmed up and vaporized off.  “Volatiles” includes water.  This is why so many of the outer moon are icy, and why comets actually spend most of their time in the outer solar system.  (If they didn’t, they wouldn’t have any ice left for the sun to bake off to make them into comets.)  Pandora should be an iceball or a water-world, not rocky.

There are even more astronomical issues in the wiki details, but I think I’d better stop while I’m ahead.

The Unobtainium

This doesn’t make much sense either, alas.

Supposedly, unobtainium (oh, geez, the name, the name…) is a room-temperature superconductor necessary for the production of maximally high-speed, but sub-light, interstellar travel.  Unobtainium is available on Pandora, but not Earth.  (The first expeditions, without ships using unobtainium, were slower and generally much less awesome.)

Problem one:

The floating rocks.  These are awesome.  They also don’t work.  There’s an issue with stability.  The setup is essentially a mountain sitting on a big unobtainium magnet, which then floats in Pandora’s magnetic field.  You then have to avoid having your magnet flip over and stick itself to the ground with the same amount of force.  So all the mountains have to be bottom-heavy, to avoid flipping.  And too much of a perturbation – like, say, collisions or explosions – could still knock them over.

You can get around that by having a superconductor and an external magnetic field, but those would have to be both very large solid chunks of superconductor and an absurdly powerful magnetic field to hold the mountains up.  A couple of different estimates by me and Michael suggest that for a small-ish mountain made of superconducting material, you’d need at least 5 Tesla of magnetic field to hold it up.

That’s five TESLA.  At least.  Supposedly from Pandora’s magnetic field.  For comparison, Earth’s magnetic field is about 30-60 µT.  Yes, that’s micro-Tesla.  3e-5 T.  Way, way less than 5 T.  Sunspots?  Still only up to a few times 0.1 T.  But there is something on Earth that makes that high a magnetic field.

It’s called an MRI machine.

When they wheel people into one of those things, they have you take off everything made of metal.  Now, rotating in a magnetic field or sitting in a changing magnetic field will induce currents, more easily in better conductors.  Larger currents get produced by larger motions/changes in magnetic field.  Anything made of metal that goes in the machine will conduct a current induced by the magnetic field… and dissipate heat… which can be uncomfortable.  Plus, the same thing can happen for the human body itself, which is part of the reason why they wheel people in slowly.  Another part (as discovered by one of Michael’s cousins) is that neurons have conducting parts, too.  Turn your head too quickly while in a few-Tesla magnetic field, and you see lights, taste metal, and other funny sensory effects.  (Don’t worry, he was fine shortly afterwards.)

Suffice it to say, if Pandora really had a 5 T field on its surface under the Hallelujah Mountains, communications and electronics failures are the small problems.  The presence of the mountains themselves will make the field very nonuniform.  So, you get weird effects on your brain every time you move, and all the metal surfaces of, for instance, your helicopter are getting heated to high temperatures by induced currents.  Ouch.

Problem two:

According to the backstory, unobtainium was produced on Pandora by the impact of a Mars-sized object onto Pandora early in its formation.  Unobtainium (whatever weird crystal it actually is) was produced by the high pressure and temperature, and interaction with Polyphemus’s magnetic field.  And this is why it’s not found on Earth, and can’t be manufactured.

That’s happened on Earth.  It’s called the moon-forming impact.  A hypothesized Mars-sized object called Theia smacked the Earth about four-and-a-half billion years ago.  The material that blew off of Earth into orbit eventually coalesced into the moon.

For bonus points, such high temperatures and pressures as in that kind of impact… can be produced in a lab.  (You should use either an impact gun or a diamond anvil cell.)  So, if what they say about the production of unobtainium is correct, we could make the stuff.  It’d take some work to scale it up for industrial purposes, but hey, given how expensive the stuff is, it may well be worth it.  Speaking of money…

Unobtainable Economics

The economy here is impossible, too.  Supposedly, unobtainium is worth $20,000,000/kg, unrefined.  For comparison, platinum, an important catalyst on Earth in the real world, is worth about $55,000/kg, as an essentially pure metal.  And according to my old CRC manual from 2005, plutonium is worth about $5/mg, or $5,000,000/kg.  In other words, unobtainium is four times as valuable as plutonium.  (I’m assuming that inflation must have flatlined somewhere, to make the dollar costs for things in the far future equivalent to now.)

Now, in the future, unobtainium is supposedly powering both the starships used to obtain unobtainium, as well as handling Earth’s power needs.  So, if somebody running a power plant can get at least 4 times the energy with the same amount of unobtainium as plutonium, plus it has less trouble with radiation and toxicity, well, win.

But what about our sellers?  In other words — what are the shipping costs for unobtainium from Pandora to Earth?  The description of their interstellar craft apparently includes both a solar sail and a pair of matter-antimatter engines.  (What? Antimatter?  Where are they getting that?  … never mind.  I’d better stop asking questions.)

Nonetheless, let’s assume that the ship going back has minimal weight, other than fuel and unobtainium.  It travels at 0.7 c, and is powered by matter-antimatter annihilation.  So, for the rocket equation, let’s assume that our exhaust is traveling at the speed of light.  Lots of gamma-rays out the back end.  In the end, you get a ratio of initial mass (fuel plus payload) to final mass of m_0/m_1=exp(arctanh(0.7))=2.4 to accelerate to 0.7 c.  Then you have to spend just as much of your current mass to slow back down again.  So, for every kg of unobtainium you send to Earth, you must expend a minimum of 4.7 kg of fuel, half of which is antimatter.

At present, antimatter is only fleetingly produced in particle accelerators.  Via Wikipedia — current world production of antimatter is less than 10 ng/year.  At a cost of about $10,000,000,000,000,000,000/kg.  That’s $10^19.  $10 quintillion dollars.  Give or take some.  But we need the total cost of antimatter to be less than about $8 million/kg, and also industrial scale production, or else this won’t work.  Especially given that there will be inefficiencies in production, and the ship isn’t a big lump of pure ore.  You need things like space for the crew… containment for the antimatter…

In other words, you need antimatter to be way cheaper than unobtainium to make the operation worth it.  This is a problem.

Of course, all this is for naught once some clever person decides to get rich by making the stuff at home.

Pandoran Ecology

Pandora really has the Gaia thing going.  Now, coevolution is a real thing.  Certain hummingbirds with hugely long beaks that can only drink from, and thus pollinate, certain kinds of flowers are an example.  They develop a unique connection because each is dependent on the other, and a change in one will tend to promote a reasonable change in the other to maintain the beneficial relationship.

The world-tree connection to what seems like every large animal on the planet, and which allows connections between those animals… is a bit much.  Earth has no examples of such strong symbiosis among so many complex species by a related mechanism.  I can’t think of any such tight, mutually beneficial tie between anything more than pairs of species.  Especially since… some of them also prey on each other.  Food webs?  Sure, those happen, but the fundamental bond between the animals on Pandora is quite different.  Plus, the bonds are only ever made between the forest or the Na’vi and the animals.  Bonds between animals are never shown.

I might have bought it if it was just the trees having an emergent consciousness.  With everything so directly connected by the brain-wire-worm-things, yet lacking stronger evidence, I can only strongly suspect that the Pandoran forest and ecosystem are artificially constructed to a large degree.

The Plot

I have no words.

Okay, I lied.  I have a few.  In short:

If I can accurately summarize your plot as Pocahontas in SPACE, and your villains are all stereotypically narrow-minded corporate tools, you should consider changing your plot.

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  1. michaelbusch
    2013/02/09 at 6:40 pm

    One other note re. antimatter:

    At current energy prices, it is _impossible_ for the manufacturing cost/value of the stuff to be less than perhaps 6 billion USD/kg. That’s the mass-energy equivalence for making 2 kg of material (1 kg antimatter + 1 kg matter). So the human society in Avatar would have to have energy prices one-one-thousandth of what they are right now. But if they had that, their economy would be even more different from that portrayed in the movie.

  1. 2013/02/10 at 10:07 pm
  2. 2013/04/03 at 4:46 am
  3. 2013/10/30 at 4:32 am
  4. 2014/03/11 at 8:26 am
  5. 2015/10/17 at 1:53 pm

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