Starfleet Jedi

I've noticed a large number of threads on SB.com talking about Avatar, and also some confusion and uncertainty, so let's take a few minutes to get this right. First: The Navi themselves.

I'll start by introducing a basic problem. I'll call it the Goliath problem. Let's say I take a simple human David, and I magnify him by a factor of two with a zoom lense in order to produce Goliath. How much stronger does Goliath have to be than David?

Well, Goliath is eight times the mass, but if I have Goliath jumping and running and swimming and climbing, he's also accelerating twice as fast, jumping twice as high, and climbing twice as fast - because his motions have been scaled up without slowing them down. So his muscles need to supply sixteen times the force. And if Goliath throws a spear or shoots an arrow, he's exerting twice the force over twice the distance for thirty two times the energy. We're talking about kilojoules. If it has a nice point, it will have penetration characteristics comparable to a rifle round.

His muscles need to exert four times the amount of force per unit area, too, indicating a radically different biology, and his bones are similarly getting four times the stresses and strains per unit area. The fact that Navi bones are reinforced with carbon fiber makes perfect sense. They need to be super-strong.

Now, the Navi aren't quite twice as tall - more like 1.7 times as tall. The quoted figure is ten feet. They're not twice as thick, either. Eyeballing it, Navi are probably 3-4 times the volume of a human soldier. If anything, though, they move more than twice as quickly than a typical human on Pandora - meaning that if they have the same overall density, they should be 6-8 times as strong as a fairly athletic human based on how they move, provided Pandora's gravity is only a little less than Earth's.

Pandora is lower gravity. Four times the strength of a human is possible, but pretty close to the lowest possible bound, if we put Pandora's gravity at somewhere around half Earth's. More realistically, Navi need muscles with a much higher performance of force per unit of cross sectional area than humans have. We don't see humans bounding much, so we shouldn't assume Pandora's gravity is much lower than Earth without good reason (the unofficial wiki says 0.8 times Earth gravity; I don't know if that has any official backing in some guide or not, but it seems plausible).

How well the Navi can act in a standard gravity field is going to depend on Pandora's gravity. 8 m/s^2 would mean that it's like jumping around with a human-sized weight on their back, which I doubt would slow them much; 5 m/s^2 would mean it's like having an extra Navi strapped to them, which would cripple their ability to move around quickly.

Elementals are 8-9 feet tall. Space Marines are 7-8 feet tall. Normal humans are generally 5-6 feet tall, but both of these super-engineered humans look like scaled up humans (more or less) in form. An Elemental might actually outmass a Navi, and might have comparable strength, but has less reach and less speed. A Space Marine is at a serious reach disadvantage, and possibly a speed disadvantage, depending on the wildly varying interpretations of Space Marines (the ones seen here, which some SB.com residents seem to think are going very fast, are quite clearly sub-Navi speed).

On the flip side, Navi don't have quite the same superhuman resistance to physical trauma as those two heavily modified human variants. They don't have particularly high technology levels, but their ability to interface with Pandoran wildlife makes them very natural cavalry. They're not just metaphorically in tune with nature and of one mind with their mounts; they have a biological ethernet jack and a good network protocol.

Technological oddities

On the whole, I thought Avatar did a pretty good job on the realism count. Better than we usually see. There are a couple things that seem odd, but we have some explanations for most of them. I'm hesitant to look at the game, because I suspect things will go downhill from the movie.

Arrows vs cockpit glass

You'll see scenes where Navi arrows are bouncing harmlessly off the transparent cockpits of the gunships and minimecha. They barely scratch the glass. And then, there's the scene where the Navi are divebombing the gunships from above, and suddenly, arrows are penetrating the same cockpit glass.

There's actually a good reason for that. The arrows are a high-mass low-velocity projectile - and being fired straight downwards while in a high-speed dive could easily double or triple their velocity. Their kinetic energy is likely increasing by somewhere between half an order of magnitude and a full order of magnitude, and it's much harder to stop. It's perfectly consistent to have the arrows bouncing off when fired from below, and smashing through when fired from above off the back of a divebombing banshee.

Shuttle bomber

Why on earth does the shuttle move at gunship speed? Clearly it could fly faster. This one is a little harder, but I see two reasons.

One is that the bombing mechanism is ad hoc. You're flying with an open cargo bay and having men push giant pallets of explosives out. While the shuttle can reach very high velocities, you don't want to do so with an open cargo bay.

The second reason is that the goal of Quaritch's mission isn't really to destroy the sacred tree. Quaritch's goal is to rout the Navi, and destroying the sacred tree in the middle of blasting their army into smithereens is how he intends to completely smash the morale of the Navi and discourage them from ever returning to this region. So the first priority is actually to destroy the Navi army. The bomber mission really is of secondary importance, and arranging it to look as fearsome as possible is critical.

Ewok adventures

On the whole, human technology works quite well. The Navi throw some surprises at them, true, but down on the ground, the Navi get routed. The AMPs are not comically unstable mecha like AT-STs, they do not walk into log traps, they do not trip, they don't have unsecured top hatches that Wookies can pry open. Nothing short of some serious megafauna takes those down on the ground, and even the regular human troops, armed with automatic weapons, seem to be doing fairly well.

The Navi get routed on the ground; in spite of the shock of their ambush and the success of divebombing with arrows, they simply cannot handle the air war, either. The two heavy human craft - Quaritch's gunship and the shuttle - are both taken out by Jake Sully using human explosives, grenades and a missile pried loose from the ship.

This is not like the comical defeat of stormtroopers by Ewoks. The Navi and their banshees are powerful and fast, their arrows quite a bit heavier and higher velocity, the terrain far more restrictive, and they have quite a bit more help. Not only a gunship of their own (ala Chewie), but human military advisors from the same unit (Trudy and Jake both are able to advise on tactics favored by Marines and Quaritch personally), telepathically linked massive animal companions, and finally all the fauna of the jungle coming out to attack on their behalf.

The Navi demonstrate themselves as certifiably badass (certainly deadlier than Ewoks) but they're still losing with anything short of a (literal) deus ex machina - Eywa, the very real god of the Navi, sending out the animals of the world to stop the attackers. We don't walk out of the movie thinking that the human mercenaries were comically incompetent; we walk out thinking that Jake Sully managed a miracle. Several, really.

Birds vs Planes

It might seem odd that suicidal flying creatures could take down modern military aircraft. Then again, it might not. The banshee's ability to take down the gunships appears to be tied to their ability to smash into them at high velocity. It may seem pretty astonishing, but at the same time, if all the birds of Earth were being controlled by a biological supercomputer, they could take down much of the USAF's current inventory.

The overall tech picture

Most of the technology is really pretty close to modern in the big scheme of things. Compared to Star Trek or Star Wars, it looks completely modern and hyper-realistic, with the exception of the Avatar program itself.

And I know there's always a lot of complaints about mecha, but the ones we see here look downright sensible in comparison to the usual case. They're not that large, and the terrain is ridiculous enough to make conventional vehicles troublesome.