A Niche in the Library of Babel

In one of those Hollywood coincidences, two recent movies, “Avatar” and “Surrogates” made use of the idea of remote-controlled bodies.   In “Surrogates”, people had robot bodies that were so much better than real ones that no one went out in public in the flesh any more.  Their robots were so much stronger and better-looking than they were  (E.g. Bruce Willis once again has hair!) that people preferred them.   They would lie on couches at home plugged into some kind of neural control system and walk their perfect selves around.

Bruce Willis zoning out in “Surrogates”

In “Avatar”, people use vat-grown bodies to walk around on an alien world.  The air is poisonous and the natives are hostile, so this is the only way to move about freely.   There too people lie on a couch to control their remote bodies.

The ideas are similar but the usages are not.  “Surrogates” uses its robots to make literal the behavioral masks that people wear in society.   Instead of having to learn to smile and make small talk, you let your robot be your persona.   That’s intriguing, but they didn’t do much with it.  The robots are mainly used to jump over cars and get shot in big chase scenes.  The surrogates are ultimately considered to be evil for some reason and are all destroyed.   Personally, I think it would be great to not have to risk your one and only body in some risky occupation like Willis’s policeman, but movies are much more conservative than SF fans.

In “Avatar”, the bodies are a way to literally see through another’s eyes, to empathize with people who are completely foreign.   They don’t live or think the way we do, and unfortunately they have something we want.  It becomes all the more important, then, to understand their perspective before they get steamrolled by modernity.

Anyway, these two movies got me wondering what would actually be involved in these neural controllers.   They would have to interface to our nervous systems somehow.  How much data would actually have to be sent and received?  What’s the bandwidth of the human IO system?

It turns out that no one knows.   That is, I was unable to find any reference that listed basic things like how many nerve fibers run from the spinal cord to the muscles and sensory organs.    The best I was able to find was this paper, “Measurements and mapping of 282,420 nerve fibers in the S1–5 nerve roots” from 2009, that described the nerves that run from the 5 sacral vertebrae, the ones at the very end.  The researchers had dissected several cadavers, taken pictures of the spinal cords, and counted them.   By hand!  They found ~280,000 nerve fibers total, of which the majority were sensory, followed by motor, and then “parasympathetic”, which control organs.

There are 31 pairs of spinal cord nerves total, one for each vertebra.

The other spinal nerves are unlikely to have similar numbers (E.g. the hands are likely to have far more nerves than the legs and feet), but I can’t find any references for them.  If they also had ~60K fibers/nerve, the whole spinal cord would have ~1.7M fibers.

The nerves that run directly from the brain to various parts of the skull are better understood, and are listed here.  There are 12 pairs of cranial nerves, of which the optic is by far the largest, with 1.2 million fibers to each eye.  The auditory only has 30,000, 40X fewer.   A high-quality video stream, such as the one from a Blu-ray player, needs 20 Mbits/sec (compressed, not raw pixels), while a high-quality compressed audio stream needs 200 to 500 Kbits/sec, so the 40X about jibes.

So let’s call it 1.2 * 2 + something ~= 3M fibers for cranial nerves.  With another 1.7M for the spine, we’ll round it up to 5M nerve fibers total that connect you to the outside world.  At what bit rate do these nerves run?  This study from U Penn in 2006 looked at the data rate in guinea pig optical nerves, and found that they averaged ~10 bits/second.   If that’s true for all fibers, that would mean that your total bandwidth is only ~50 Mbits/sec.  That’s about what a good wireless link can do.

So if you were floating in a tank inside the Matrix (and who’s to say you aren’t?), it would only take a medium-speed Ethernet to fool you into thinking you were in the real world.   The evil Matrix robots would have to spread that Ethernet into 5M fibers, most of which are only a micron across, but we’ll wave our hands vigorously and say “micro-machined silicon neural interface chips” and “superconducting quantum interference device magnetometers”, and leave it at that.

Of course, there are easier ways to take you out of your body.  Movies do it all the time.  You forget about the taste of the stale popcorn and the way your feet stick to the floor, and are lost in the story.   Digital cinema data rates are about 100 Mbits/second (again, that’s compressed with JPEG 2000, not raw), so that’s not far off of what it take to simulate everything.   The latest films double the data rate again for 3D, although it’s possible to share info between the two views.   That’s not easy, but it’s worth it if it lets theaters raise the price a couple of bucks, and so raise their margins from almost zero to something respectable.

However, there is a way to leave your body at a far lower data rate.  The technique takes a lot of practice, and usually has to be learned in childhood.   Many people, maybe even most, never got comfortable with it.  It can be physically damaging if done to excess, but it’s crucial for certain professions.

I’m referring, of course, to reading.   A typical novel contains about 100K words  (10 Mbit) of text, and takes maybe 3 hours (10K seconds) to read, for a data rate of 1000 bits/second.   Once immersed in it your own brain will create all the other sensations.   Your memory will provide smells, touches, sights, and sounds.   Your predictive and pattern-matching faculties (OK, call it your imagination) will invent the feeling of sailing with Long John Silver or playing quidditch.   It turns the brain against the body and disconnects it from the world.    No wonder some think it’s dangerous!

The last post noted how Avatar’s director and writer, James Cameron, left off a key piece of info that would have explained a lot of mysteries in the movie – that unobtanium was a room-temperature superconductor.  We’re still left with a fairly straightforward and somewhat old-fashioned story, at least compared to what literary SF has been doing.  Io9.com noted how much Avatar resembles Poul Anderson’s novella “Call Me Joe”, and that dates from 1957.

So how can we bring “Avatar” into the 21st century in SFnal terms?  Another commenter on io9 (sorry, can’t find reference) noted how oddly human the Na’vi are:

Surprisingly sexy, maybe sinisterly sexy, for a creature from an utterly different evolutionary path.

All the other life on Pandora appears to have 6 limbs, but the Na’vi only have 4.   The others have vents in the their chests for breathing; the Na’vi have mouths.  The others have two neural links on their skulls, and they look like fronds; they have one and it looks like braided hair.  They’re sentient, but don’t appear to have fire or domesticated animals.

So they look human, too human.  By the time of the movie, the world-brain of Pandora, Eywa, has had hundreds of years to watch TV broadcasts emitted from Earth.  It could see that homo sapiens was headed its way, and would have been readying its response.  The Na’vi were lemurs swinging through the forest two hundred years ago, but now they’re humanoid tool users, just like the approaching enemy.  They’re suspiciously attractive, as if Eywa was trying to make creatures that would appeal to and maybe seduce the invaders.

After all, the galaxy is old.  Technological alien races could have swung through the Alpha Centauri system every few million years.  Eywa would have seen their like before.   As in Bruce Sterling’s seminal story, “Swarm”, Eywa could have evolved the Na’vi as a counter-measure to this familiar threat.

It seemed to work.  All the humans who worked closely with the Na’vi loved them, even though they were blood-thirsty xenophobes with the cultural sophistication of a second grade playground.  Several betrayed their own species for the sake of the Na’vi.   They actually let themselves be scanned by Eywa, thinking that they would become Na’vi.  Now it has access to everything that the marine Jake and the scientist Dr. Augustine knows.  Talk of an espionage coup!  Mata Hari had nothing on Neytiri.

By the end of the movie the humans have abandoned their planet-side base.  The remaining humans will be quickly scanned, and then Na’vi will set to work reverse-engineering all the human weaponry.  The human ships in orbit won’t be safe for long.

Will the Na’vi start building their own fleet of matter-antimatter starships to attack Earth?  They live near a gas giant – they have immense energy resources at their disposal.  Will the AI who is the actual power behind Evil Corp find a way to counter Eywa’s plan?  The scale of these movies could expand a lot.

One of the bizarre things about the “Avatar” movie was that no explanation was ever given for why Evil Corp wanted to plunder the Edenic moon Pandora.  They were supposed to be after some mineral with a joke name, unobtanium, but they never said what it was.

The sleazoid exec going on about this mysterious rock

Even more bizarrely, this didn’t seem to bother anyone in the audience, or at least didn’t bother them enough for them to tell their friends to avoid a movie with a huge plot hole in the middle.   Maybe people have gotten so used to MacGuffins in action movies that they don’t care any more.   Let’s just get to the spectacle as quickly as possible before these 3D glasses give us migraines.

It turns out, though, that there actually is an interesting back-story around unobtanium – it’s supposed to be a room-temperature superconductor.  This would in fact be hugely valuable stuff (although nothing is valuable enough to ship across interstellar space).  Not only can you build perfect power lines with it, but you can build perfect magnets, magnets strong enough to run fusion reactors.   In the movie backgrounder site, Pandorapedia, they claim that it’s critical to building  the matter-antimatter starship drives that allow human beings to get to Pandora in the first place.

It also explains Pandora’s floating mountains.   If a magnet is placed above a superconductor, any motion in it will induce a current in the superconductor that exactly repels the magnet:

A magnet floating above a disk of liquid-nitrogen cooled superconductor

It’s called the Meissner Effect, and is one of those places where quantum effects show their bizarre nature at a macroscopic scale.

So if Pandora’s mountains contained iron ore, they could conceivably float above a crust that was a superconductor.   The electromagnetic effects of this would be wild, and would explain the disruption of radio in the “Flux Vortex”.

It might even explain another plot problem in the movie.  The Na’vi can see that humans are powerful and dangerous, yet refuse to consider moving away from their Home Tree habitat.  Why didn’t they just cut a deal?  Evil Corp would be happy to pay them off with the Pandoran equivalents of whiskey and guns.   That’s how most of the encounters between the West and aborigines turned out – they traded instead of fought.

But the whole ecosystem of Pandora was supposed to be linked into a vast nervous system.  Superconductors would make fine nerve fibers.  It wouldn’t be an accident that there was a lot of unobtanium under the Home Tree – that was the tree’s brain.  The Na’vi couldn’t move because mining unobtanium would kill a piece of their god.

This kind of background information is actually pretty cool.   I had no idea that any of it was in there, and it would have improved the movie, at least for me.  The only reference to superconductivity was a floating magnet on the desk of the Evil Corp manager, and  I thought that was just an office tchotchke.    It wouldn’t have taken much to drop it in – just a couple of lines here and there, and it apparently was in an early version of the script.

Still, Cameron decided to drop it, and two hundred million movie-goers didn’t seem to miss it.  Maybe he’ll put it into the upcoming DVD release.