avatar (not airbender)

[Logan Darklighter]

I saw the movie on Monday evening. STILL thinking about it. I want to make a more involved post about it. But I want to think about it some more. Suffice to
say, I have some of the same caveats about the anvilicious nature of the story as others have mentioned, but it still entertained me enormously. I mean - I
don't necessarily buy the whole "Noble savage" bit either, but I still love Dances with Wolves. Anyway.

In addition to the story, I've been thinking a lot about the science of the movie. Over at Ain't it Cool News, one of the regular contributors has an
article on that which I found fascinating. Original link is
here. But I figured I'd reproduce it here. All credit to Copernicus for a great article.

(And I'm happy to say that I guessed right at the time of viewing that the Floating Mountains were laced with Unobtanium.)

Our longtime friend and frequent contributor Copernicus saw AVATAR and wanted to
share some thoughts about the film's science. Copernicus is a quite a scientist himself, so this is a very fascinating read & we really appreciate
his taking the time to put this piece together for us.






Here's Copernicus...











First, a little background: I'm a professor of astrophysics who has


searched for planets, worked on SETI (Search for Extraterrestrial


Intelligence) programs, and taught classes on life in the universe.


Right now, I'm helping to build a global network of telescopes to


search for planets and supernovae.

That is a long-winded way of saying that it is part of my job


description to think about the possibility of life on other worlds.


So when James Cameron makes one of the most expensive movies ever


made, and one that puts us right in the middle of an alien culture... in


3D.... well to say I'm interested doesn't begin to cover it.

Since the movie has already been reviewed to death, I'm going to focus


on something that hasn't been covered yet - the science. But while


this is interesting exercise, for me it is story first, and science


second. I'd put it like this:

Copernicus' Law of Science Fiction: Bending the laws of


physics out of service to the story is fine, doing it out of ignorance


is unconscionable.

I don't mind if the ships in Star Trek can go faster than the speed of


light - otherwise the story would be pretty boring. And I know


there's no sound in space, but I want Star Destroyers to


rumble, and the Millennium Falcon to have that iconic whine. But if a


director casually gets science wrong for no real reason other than


that he is stupid or lazy (see ARMAGEDDON, THE CORE, and THE DAY AFTER


TOMORROW, to name a few), then to hell with him. If the filmmakers


don't respect the intelligence of the audience, I'm not going to


respect the movie.

Fortunately, James Cameron has a knack for science that rivals his


moviemaking skills.






THE SCIENCE OF AVATAR

Historically, movie directors have had their asses kicked by


astronomers as far as taking us to exotic worlds. For the most part,


movie planets look like an extreme form of Earth -- they almost always


have an oxygen atmosphere at an Earthlike pressure and gravity. Movie


planets don't even come close to matching the diversity of worlds in


our solar system: the surface of Io is a mottled, sulfurous


orange-yellow, constantly being repaved by volcanoes shooting hundreds


of miles into the sky. Titan has a thick smog atmosphere that blots


out the sun and rains hydrocarbons. Mars has planet-wide dust storms


and a 17-mile-high volcano that nearly reaches above the atmosphere.


Venus has a crushing, choking sulfur dioxide atmosphere with a


pressure 92 times that of earth, and a temperature that can melt lead.


Enceladus shoots ice geysers into space. And the real Pandora orbits


within the rings of Saturn. These are only a few of the hundreds of


planets, minor planets, and moons in our solar system: we've


discovered hundreds elsewhere in the galaxy, some of which seem even


crazier: super-Earths, nearly boiling puffed-up Jupiters, and objects


that may be free-floating rogue planets without a star.

So I can't think of a better use for 3d and a few hundred million


dollars of effects than filmmakers starting to raise the bar to


finally approach the awesome reality of nature. Due to the limits of


budgets, finances, and creativity, I can't think of another film that


has attempted something near the scale of what Cameron has done here.

I'll address the different aspects of the science in sections.






FLORA AND FAUNA

From a visual perspective, Avatar's Pandora is breathtaking. While


most movies have only hinted at the exotic nature of their worlds with


an establishing matte painting or two, here Cameron takes us on an


elaborate three-dimensional tour though various habitats, from the


treetops to the forest floor. He's created a whole ecosystem, from


semi-intelligent trees to giant land and air creatures. Most seem


inter-related via symbiotic relationships. In fact, Cameron has taken


the Gaia hypothesis, that the biosphere of the Earth is itself a kind


of living entity, and sexed it up - the biosphere of Pandora is


essentially a god, and it's networked! Creatures can plug into each


other via what amounts to USB hair and fiber optic roots. While some


of these ideas are not without their faults (see below), Cameron gets


points for creativity - this is true science fiction, not space opera.

I do have one minor complaint, that given their networking abilities,


the Na'vi should not be so technologically inferior to the humans. On


Earth, the largest barrier to technological progression was that


information that existed in the brains of primitive humans could not


be easily shared or preserved. As soon as writing was developed,


suddenly it was possible to store information outside of the brain,


and record and build upon knowledge. The knowledge available to a


human or tribe went from one brain's worth (and a minimal amount of


oral tradition), to thousands, and ultimately billions of brains'


worth. The result was a technological and social explosion. Hominids


have had technology like spears for about half a million years, but


only 7,000 years after the development of writing we had left the


planet. And the sharing of knowledge is still undergoing a revolution


with the development of the internet. Now we have instantaneous


access to the combined knowledge of the entire history of humanity.

Since the Na'vi have had the ability to download information and share


it in a massive network for long periods of time (evolutionary


timescales), they should be way ahead of us in terms of technological


development. Still, I have to give Cameron a pass here. It is


thematically necessary that the Na'vi are technologically primitive,


and their root-network is necessary to the plot. Maybe you could say


that they could have evolved more technology, but they don't need it


or want it. Still, that reeks of the "Noble savage" idea, and I have


to agree with Stephen Pinker that that is a bunch of
hoo-ha.

But my major complaint from an evolutionary standpoint is that there


is no way in hell that life on Pandora would evolve to look so similar


to Earth life: there are humanoids, space horseys, hammerhead


rhinoceri, and pseudo-pterodactyl beasties. And to make it worse,


they have DNA, and the DNA is close enough to our own that Na'vi and


human DNA can be combined! Again, I have to give Cameron a pass.


First, it is easier for the audience to relate to familiar things.


And more than that there is a significant plot point that I won't


spoil towards the end of the film that hinges on humans and Na'vi


having similar DNA.

One way out of both my evolutionary nitpicks is the panspermia


hypothesis -- that life in the galaxy was seeded in multiple places by


an advanced civilization. But even then the odds against evolution


producing such similar animals on different planets is astronomical.


Since we have a clear record of evolution on Earth, some civilization


would have had to keep taking specimens from earth, first


pterodactyls, and ultimately humans (after they evolved), and then


would have had to deliver them to Pandora, possibly modified via


genetic engineering. That would be an interesting sequel: humans and


Na'vi come together to confront their godlike humanoid ancestors!

Grade on astrobiology: A for the scale of the ecosystem, C for being


too much like Earth - call it a B overall.




WORLD AND STAR SYSTEM

Pandora is a moon of Polyphemus, a fictional gas giant orbiting Alpha


Centauri A. I've always wanted to know what the view would be from


the moon of a gas giant. Can you imagine a quarter of the sky being


taken up by a massive cloud-covered planet visible night or day? We


get to see it in Avatar, and since Jupiter is the king of the gods,


maybe majestic is an appropriate word to describe it. I wonder if


Cameron's choice to set this on the moon of a gas giant wasn't a slap


in the face to Lucas, as if to say "this is RETURN OF THE JEDI done


right." (I know it is ambiguous in the Star Wars universe whether or


not Endor orbits a gas giant.)

But what had me really geeking out is the choice of the star system.


Alpha Centauri A is perfect. First, as the closest star system to the


sun (4.37 light years), it may well be the first star we travel to.


Second, it is familiar in that you can see it with the naked eye if


you live in the southern hemisphere - it is the brightest star in


Centaurus. Actually, what appears to be a single star can be resolved


as a binary system if you use a telescope. It is Alpha Centauri A, a


bit more massive than the sun (1.1 solar masses), and Alpha Centauri


B, a bit less massive than the sun (0.9 solar masses). The choice of


G-type stars near the mass of the sun is great - they last for


billions of years - plenty of time for life to evolve. They are in an


elliptical orbit around a common center of mass, which means they come


together and drift apart over the course of one 80 year orbit. The


two stars get as close as 11 astronomical units (an AU is the average


Earth-Sun distance; 11 AU is about the distance to Saturn), and get as


far apart as 36 AU (about the distance to Pluto).

Would you see the companion star (Alpha Cen B) in the sky from


Pandora? That depends on where it is in its orbit. At the farthest


distance it would be a few hundred times the brightness of the full


Moon as seen from Earth. But your eyes are logarithmic detectors, so


it would actually only seem a few times brighter than we perceive the


Moon. At its closest approach, Alpha Cen B would be a few thousand


times as bright as we see our Moon. This is not all that bright - in


comparison, on Earth the Sun is about half a million times brighter


than the Moon. So on Pandora, if Alpha Cen B is up in the daytime


then you might not even notice it, depending on how far away it is in


the sky from Alpha Cen A. But if it is up at night (as it would be


for half the year), it would never get completely dark - the sky would


just be kind of dark blue.

Technically, there is a third star in the system, Proxima Centauri,


but it is a tiny red dwarf a huge distance, about 12,000 AU, away - it


is not even clear it is bound to the system. At any rate, it would


not be prominent in the sky as seen from Pandora. Incidentally, my


first job as a graduate student was to help calibrate the fine


guidance sensors on the Hubble Space Telescope to help my advisor look


for planets around Proxima Centauri. Sadly, we didn't find any.

It is an interesting question as to whether planets around either


Alpha Cen A or B could exist in stable orbits that would last for


billions of years. You might think they couldn't because the gravity


of the other star would perturb any forming planet.


However, simulations show that at least at Earth-like distances,


stable planets can form in that system.

Grade for astronomy: for the choice of star system, setting in on a


moon, and around a gas giant, Cameron gets an A+.




THE STAR'S EFFECT ON LIFE

Electromagnetic radiation comes in many forms, gamma rays, x-rays,


ultraviolet, visual, infrared, and radio. Our eyes evolved to see in


the narrow range that the sun has its peak output -- the visual band


-- and the flora and fauna of Earth evolved pigments and colors that


work at these wavelengths. But this isn't universal -- some animals


can see a narrower region of the spectrum than us, and others see


farther into the ultraviolet or infrared. Our cornea blocks most UV


light, but bees, for example, don't have one and can see farther into


the UV. They can see patterns in flowers that we can't.

In fact, colors are really something manufactured in our brain -


physically colors are just different wavelengths of light ranging


uniformly from short wavelengths (violet) to long (red). What we see


as blue or green or red helps us differentiate sky from grass from


blood, but to a creature from another world, all these things might


appear as the same color. In fact, you could imagine that bats might


use echolocation to "see" rough surfaces as one color and smooth


surfaces as another. So since colors are something created by our


brains and not intrinsic to the universe (only wavelengths of light


are), it is virtually certain Pandorans would see color differently


than we do.

Alpha Cen A has almost the same temperature as the Sun, but it is just


a bit hotter. As a result, the star puts out most of its light at


visual wavelengths just like the Sun. But the star's output is only


part of the story - the oxygen and ozone in our atmosphere block much


of the ultraviolet light from the Sun, and water vapor blocks some of


the infrared light. Pandora doesn't have an oxygen atmosphere (if the


movie mentioned what gasses it contains, I didn't catch it), so we


might expect more of the ultraviolet light to reach the surface. The


creatures there might be able to see farther into the ultraviolet.


There might be all kinds of patterns that the inhabitants of Pandora


can see that just look blue to us. Maybe that's which there are so


many blue colors in the film. To take this a step farther, I would


have loved to see a scene where a character sees beautiful colors or


patterns as an Avatar, only to have this beauty evaporate into a


uniform sea of blue when he sees the same vista with human eyes.

Another feature of Pandora adding to the ubiquitous shades of blue is


that bioluminescence seems to be a staple of the ecosystem. As


Massawyrm points out, this makes sense for a world that may spend days at a time


shrouded in darkness. Remember that a day occurs when Pandora rotates


on its axis. But it might take a month or so to orbit its gas giant,


which we know looms large in the sky, and could blot out the sun for


days.

Grade for the astrophysics: For the fact that this world doesn't have


an oxygen atmosphere, and the plausible use of color, A.






PHYSICS

Since Pandora is a moon and is presumably smaller than the Earth, the


gravity would be lower. This is alluded to in the film, and creatures


do grow larger and survive falls from greater heights than you could


on Earth. I wonder if Cameron dialed in a different gravity to the


physics engine rendering everything. To my eye, for at least the


human scenes, the gravity looked just like Earth gravity, but then


again if the gravity is close the differences can be subtle.


Virtually all science fiction movies feature planets with gravity at


1g, since, of course, until now, filming has always been done on


Earth. Since here so much of the world was created inside the


computer, I would have liked to see this aspect pushed a bit farther.

In one of my biggest pet peeves regarding the science of Avatar, there


is one scene where the gas giant, Polyphemus, can clearly be seen to


be rotating in the span of about a second or two. Let's say it


rotates about a degree out of 360 degrees in those 2 seconds. That


means it makes one rotation in 720 seconds, or 12 minutes! Jupiter


takes about 10 hours to rotate. So the gas giant in Avatar rotates


about 50 times faster than Jupiter. Winds on Jupiter can exceed 100


meters per second, so the winds on Polyphemus would have to exceed


5000 m/s - this is supersonic and clearly implausible. Here's one


case where Cameron opted for visual effect over realism, but to me the


bargain isn't worth it. It looks unrealistic and takes me right out


of the movie. But I do like the look of the clouds on Polyphemus -


they look like a cross between Neptune and Jupiter. The highlight is


a giant storm resembling Jupiter's Great Red Spot. That is


particularly appropriate for Polyphemus, named after a mythological


cyclops.

But my biggest beef in Cameron's trading physics for visuals is those


goddamn floating mountains. Seriously, floating mountains? How the


hell do they stay up there? This is such an egregious flouting of the


laws of physics that surely there is some reasoning behind it.

Between the fact that Pandora seems to be sort-of at 1g, the


impossible rotation of Polyphemus, and the floating mountains, physics


is one one area AVATAR gets a marginal fail on Copernicus' Law of


Science Fiction. But on all the other aspects of science, Cameron


gets either a pass or passes with flying colors.

The dream of interstellar travel will only become a reality far beyond


our lifetimes. But I love the fact that today I can be deeply


immersed in not just a plausible, but a compelling alien world just by


putting on a pair of 3D glasses and visiting my local theater. Even


if I have to drive 100 miles to see it in IMAX, that is nothing


compared to interstellar distances! And I love that there is a


filmmaker that plays more than lip service to the science in his


films, stimulating discussion and thought about distant worlds among


geeks everywhere. I was inspired to do astronomy after seeing STAR


WARS as a kid. I'm willing to bet that a fair fraction of tomorrow's


astronomers will have decided to devote their life to the discovery of


new worlds because of AVATAR.




Mail Copernicus

-- Copernicus

Thanks for the enthusiastic response to the article. Thanks for all


the emails, and it is nice to see some interesting discussion in the


talkbacks (who knew?). A few updates:

People have sent links to several sources that explain many of the


questions I had. One is the pandorapedia. Another is A


Confidential Report on the Biological and Social History of


Pandora. And people sent the script treatment. I have not read


the entirety of that last one yet, but the first two are interesting


reading.

Levitating mountains: As dozens of people have pointed out, the


mountains supposedly contain unobtainium, a room-temperature


superconductor. Superconductors expel magnetic field lines, and as a


result magnets can levitate above a superconductor. Here


superconducting mountains are apparently levitating over the strong


magnetic field of the moon or planet, or both. I had thought about


some kind of mechanism like that but dismissed it for two reasons:


(1) how could mountains form, stay in place, be weathered and shaped,


etc. (2) if there is unobtanium in the floating mountains, why not get


it there so as not disrupt the Na'vi. But I think I was just


short-sighted. In the case of (1), the intention is that the


mountains started out attached, but broke off and floated upwards at a


certain point, and now they sort of float around. I buy that, at


least enough for a cool movie scene. And for (2), maybe the


unobtanium in the mountains isn't the right kind, or isn't pure, or is


hard to mine. Interestingly, a geologist emailed me with another


sighting indicating the strong magnetic field of the planet: the stone


arches seen at the climax seem to be from mineral growth along


magnetic field lines. Awesome.

Plenty of people have asked where the water comes from for the


waterfalls in the floating mountains. To me, it is just like a normal


mountain, with the bottom missing. Where does the water come form in


normal mountains with waterfalls: rain and snow. Yes there was tons


of water, but have you ever been to Yosemite in the spring? When the


snow melts it all comes down at once, and it is an impressive sight.

And this is a little out of the purview of this article, but plenty of


people have also asked why the humans didn't nuke the planet from


orbit. (A) maybe they didn't bring any -- the proverbial "somebody's


gotta go back and get a shitload of dimes" problem, and (B) you people


scare me! Why doesn't the US just nuke countries we don't like? That


is not cool, man.

Planet rotation: Someone affiliated with the film who asked me not to


name them (but who ought to know) says the planet rotation scene was


intended to be time lapse. Brilliant. I'll have to see it again to


confirm that, but I'd buy it, because I think there were other shots


where the planet didn't seem to be rotating quickly.

Oxygen atmosphere: I said that Pandora doesn't have an oxygen


atmosphere, but I was wrong about that -- it does, but it has other


gasses that are poisonous to humans. Clearly Cameron, a fellow diving


and deep sea enthusiast, thought of this, because the people only need


simple gas masks to breathe, and not huge oxygen tanks.

DNA: The Pandorapedia says the Avatars don't have DNA, just something


analogous so that you can map to it. Great! Although, from my


memory, the movie implies they do have DNA. I'd need to see it again


to be sure. Maybe the character explaining it knows as much about DNA


as most people do and just got it wrong. If I had a nickel for every


time I was at a partly and someone told me that they heard that "they"


(meaning scientists) have broken the speed of light, teleported


something, etc.

Interstellar travel: From the pandorapedia: "Mission Profile: 0.46


year initial acceleration @ 1.5 g to reach 0.7 c; 5.83 years cruise @


0.7 c; 0.46 year deceleration; 1 year loiter in orbit around Pandora;


Mission Duration: 6.75 + 1.0 + 6.75 = 14.5 Earth years. However,


relativistic effects shorten the time onboard ship to slightly less


than 6 years each way."

Hmm, I don't think that calculation is quite right, but it is close


enough. To see, let's take the special relativistic part, the


cruising speed. If ET is Earth Time, ST is Ship Time, v is velocity,


and c is the speed of light, then ET=ST/SQRT(1-v^2/c^2). So


ST=5.83*SQRT(1-0.7^2)=4.1 years for the cruising. Even if you assume


there is no time dilation on the accelerating and decelerating parts,


then the trip is only 5 years, not 6. Maybe they are including the


hanging out on Pandora time. To do the calculation correctly I'd have


to drop some GR on you bitches, and I'm too lazy and you'd be bored.


70% of the speed of light is a good figure though -- it is almost


plausible! From what I've read of the ship technologies, they sound


very well thought out too.

Eyes: One of those sources mentioned that some of the creatures have


two pairs of eyes -- one visual, and one that sees in the IR for


nighttime hunting. Sweet! This is not without precedent. We have


two separately evolved "circuits" for vision in our brains -- one


primitive automatic one and another one for conscious sight. Look up


"blindsight," where people with damage to the latter circuit can't


consciously see, but can catch a ball. And of course we have two


types of cells for day / night vision in our eyes: cones that allow


you to see color when there is plenty of light, and rods that allow


you to see black and white only, but give you night vision. Try this:


put an eye patch on while you are inside for about 30 minutes, then


go out where it is dark and blink between your dark and light adapted


eyes. You can really see the color difference. It is awesome.

Wow, it appears that many of my nitpicks about the science were


actually taken into account by the filmmakers and there are answers.


I'm impressed! Hats off to Cameron and company for getting all this


right. I can't wait to use this film in my introductory astronomy


classes.

-Copernicus