Bad and good science in Avatar!

[Irtaviš Ačankif]

A maser would be quite weak against large hordes of ikranya. Like I said, just use a MASSIVE tsaheylu interference machine to make ALL of the ikranya fall down AT ONCE. 

By the way, what does comparing energy density to mass density converted to energy using E = mc² have to do with Death-Staring Pandora? Sorry, I'm just 13 and learned physics by myself, don't use any calculus except basic integrals and derivatives (no luck with partial differentiation for me!)

[Clarke]

But anyway, I still LOVE Pandora and Avatar!  

Ditto, but I also find Cameron's failure at writing scientific sci-fi amusing. (Time-travelling alien robots from the future? Fine. Aliens with impossibly chemistry? Fine. Interstellar mining? My disbelief goes sproing and I can't take the rest seriously.)

Any equation on measuring the force on a diamagnetic substance like water at a given magnetic field strength? I suppose that some sort of diamagnetic constant would be involved...

Does knowing a water molecule is about 95.87 pm (95.87 x 10^-12 m) across help? As a first try, I'd calculate the force on each end of the water molecule, (at a guess, they've got a charge of 1e) and then double that, and that would be the force attempting to align the molecule to the field. If you know anything about rotational dynamics, imagining the molecule as a rod with a positive end and a negative end and calculating the torque shouldn't be too hard. (Though I haven't tried it.) If you don't know anything about rotational dynamics, just ignore that last sentence.  

A maser would be quite weak against large hordes of ikranya. Like I said, just use a MASSIVE tsaheylu interference machine to make ALL of the ikranya fall down AT ONCE.  

Depends what's aiming it. There'd be no reload time, and no wind drift, so it might be more economical to have a computer aim it instead of a human. I can't remember who said it, but it's true that humans are weak, slow and squishy.

By the way, what does comparing energy density to mass density converted to energy using E = mc² have to do with Death-Staring Pandora? Sorry, I'm just 13 and learned physics by myself, don't use any calculus except basic integrals and derivatives (no luck with partial differentiation for me!)

I didn't know any calculus when I was 13, so you're doing far better than me. And the reason I brought up the energy/mass density is because of what happens when you disturb a magnetic field: the energy that was in the field has to go somewhere. Usually, a magnetic field gets generated by a current going through a wire, so when the field collapses (by say, the current not being there anymore) the energy induces current in the wire. But this flying-mountain field collapsing would be the equivalent of annihilating several kilograms of antimatter, and any current that generated would probably just vaporize the conductor. (Such as, I dunno, Na'vi nervous systems... ) More likely, you'd get a gamma/X-ray radiation burst. Since gamma rays penetrate pretty much everything, and do horrendous damage to living tissue... to quote Aliens, game over, man. Game over.  

(Yes, this would mean that Quaritch's best move is to leave a remote bomb under the mountains, and then detonate it once everyone's off the moon.)

[Irtaviš Ačankif]

I do know a lot about Newtonian rotational dynamics. However, isn't there a simple formula to calculate magnetic forces? It seems so strange since we have Coulomb's Law and Newton's Law of Gravitation but no simple formula for magnets?

It is quite true that humans are weak, slow, and squishy. However, wouldn't the megatesla field totally destroy the maser aimer, not to mention all of the machinery and the Na'vi?

Can you explain a bit about why the mag-field will collapse and release energy?

[Clarke]

The reason there's no formula is because magnetism doesn't actually exist. It's a "side effect" of the electric force, which is why there's no such thing as "magnetic charge." If I remember correctly, both the magnetic and electric fields are proportional to the differential of the other, so you get electromagnetic induction. It's all rather complicated, and AFAIK remains so until you know how to do calculus on arbitrary quantities. (Don't ask me, I don't.  ) Considering we're mucking about and we're not using the results for anything, approximating it with Columb's Law seems fair enough.

And you're completely right; the entire moon would be demolished and reduced to degenerate matter, but I was imagining it somehow worked as shown in the film, so we had something to talk about.  

There's a device called an inductor, which uses a magnetic field to store energy. What happens when you plug in an inductor to a circuit is that, instead of getting a maximum current nearly instantly, the current slowly increases. This is because this new current will change the EM field around itself. This change produces a magnetic field, and this changing magnetic field then goes on to produce a current, but in the opposite direction to the original. It's not quite as strong as the original, though, so some still gets through. As the current stays in the wire longer, the "change" in the local magnetic field gets less and less, and so there's less opposing current. However, while the opposing current exists, you need to put in more energy than you otherwise would need to to get curernt to move. (say, if you did the same thing with a bare piece of wire, it'd take slightly less energy.) That extra energy ends up in the magnetic field around the inductor.

When you remove the power supply, the same thing happens in reverse; the current doesn't drop to zero instantly. It decreases slowly, and the energy you need to provide the extra current comes from the magnetic field. However, the voltage you get out of that depends on the resistance of the circuit. If you move a fully charged, high-energy inductor into a low resistance circuit, (Can we say R=0? ) the magnetic field will lose its energy incredibly quickly, and produce massive voltages. In mundane circuits, these can quite easily be large enough to fry fragile components, like transistors or semiconductors. I'll let you imagine what our 19MT field can do.

[Tsyal Maktoyu]

But anyway, I still LOVE Pandora and Avatar! 

Ditto, but I also find Cameron's failure at writing scientific sci-fi amusing. (Time-travelling alien robots from the future? Fine. Aliens with impossibly chemistry? Fine. Interstellar mining? My disbelief goes sproing and I can't take the rest seriously.)

Well, science isn't economics (it's social science, but not real science ). Using an (realistically designed) antimatter-powered spacecraft to mine an interstellar superconductor might not make economic sense, but it is still scientifically possible. The only really unscientific gimme that JC put in the movie was the mountains. Everything else, even if appearing uneconomical, could still exist. Maybe those damn mountains should have been grounded, because they seem to just taint the believability of everything else.

[Clarke]

Well, science isn't economics (it's social science, but not real science ). Using an (realistically designed) antimatter-powered spacecraft to mine an interstellar superconductor might not make economic sense, but it is still scientifically possible. The only really unscientific gimme that JC put in the movie was the mountains.

...And Jake's wheelchair.   ...I suppose that's not technically unscientific, but c'mon. We can build and maintain an entire, alien, artificial body, (and link it into your nervous system with no apparent problem) but not give the guy an exoskeleton? Which we can almost do, right now, in 2011? (Cyberdyne is shipping them in production in 2015.)

You don't even need to ground the flying mountains. Just don't say they're being held up by magnetism. If you must "explain" them, then say it's "space-wacey."  It's not like RL physics will give you a better explanation.

[Tsyal Maktoyu]

They do have the technology to let Jake walk again (spinal cord repair, likely exoskeletons as well), but Jake can't afford it himself, remember how he cites the economy? The price of hi-tech medical equipment is probably just as artificially inflated as it is today. I guess vets still face the same problems with the healthcare system in 2154 as they do in 2011.

[Clarke]

If you can unseat Mr. Cameron, you can have ours.  (That's David, not Jim.)

[Irtaviš Ačankif]

Umm... at least he can get an electrical wheelchair.

I think that approximation with Coulomb's Law would be rather difficult: 1, because we don't have the right value for Coulomb's Constant, and 2, we don't have anything to plug "q" with.

[Niwantaw]

The Venture Star cannot be fueled by anything other than James Cameron's burning money. The VS is apparently fueled by antimatter; fair enough, that's in the Valkyrie-class design, and theoretically works. What doesn't make any sense is Unobtanium being more expensive than that antimatter. Unless something really bizarre comes up in the next 140 years of physics, (like violation of conservation-of-energy bizarre) Unobtanium must be the most expensive substance to manufacture, since you must put in 100% of its energy content yourself. No normal-matter substance requires that. Even worse, you say that Unobtanium is a compound, which means I don't even have to construct the atoms myself, which gets rid of 99.999% of the energy cost. (Probably more. I could do the math if you want me to.) I only have to arrange existing elements into a specific shape, and that is trivial compared to the production and storage of even anti-hydrogen. Not to mention orders of magnitude less dangerous.

It does say that they can't manufacture unobtainium because of the fact they can't replicate the conditions caused during pandora's formation that forced the elements to bond. Ergo you saying it's uneconomical do this is in fact not the case.

that doesn't mean they can't manufacture it full stop it  just means the can't manufacture it at the time of the film.


EDIT: and as for weapons to use instead of conventional firearms either railguns as they are efficient, long ranged,accurate and munitions are relatively cheap or my personal favorite:

Spoiler

also if masers suffer from the same flaw as conventional lasers they are unlikely to be very useful ever for combat due to being incredibly INCREDIBLY short ranged.
Cool though.

[Clarke]

Umm... at least he can get an electrical wheelchair.

Considering how good we seem to be at neurology, I'm surprised he doesn't have a mind-controlled one.  Cyborgism FTW!  

I think that approximation with Coulomb's Law would be rather difficult: 1, because we don't have the right value for Coulomb's Constant, and 2, we don't have anything to plug "q" with.

We don't? I thought Coulomb's Constant was 1/(4πe₀), which can be rewritten in by-definition values if you really want to. As for the other q, not sure. I suppose you could either calculate the electric (rather than magnetic) force holding up the mountains, and that'll give you a nice distance->force function you can do differentials and stuff on, or you could use the Lorentz force:



where the velocity is... er... in hydrogen the electron's energy is -13.6 eV and the electron mass is 500keV/c^2, then the velocity is 0.007303c = 2189.4 km/s. And the electron's charge is -9.11e-19C.

It does say that they can't manufacture unobtainium because of the fact they can't replicate the conditions caused during pandora's formation that forced the elements to bond. Ergo you saying it's uneconomical do this is in fact not the case.

that doesn't mean they can't manufacture it full stop it  just means the can't manufacture it at the time of the film.

Well, if they can't manufacture it, they can't have it. It's theoretically impossible for multiple kilograms of antimatter to be cheaper than one of unobtanium. Also, we've had noble gas compounds for decades, though I'd be surprised if Cameron knew that.

EDIT: and as for weapons to use instead of conventional firearms either railguns as they are efficient, long ranged,accurate and munitions are relatively cheap or my personal favorite:

Spoiler

also if masers suffer from the same flaw as conventional lasers they are unlikely to be very useful ever for combat due to being incredibly INCREDIBLY short ranged.
Cool though.

So what if they ionize the atmosphere rather than the target? That just means you need MOAR POWAH!   (And I was thinking handheld weapons. LOICs means there's no plot.)

[Niwantaw]

It does say that they can't manufacture unobtainium because of the fact they can't replicate the conditions caused during pandora's formation that forced the elements to bond. Ergo you saying it's uneconomical do this is in fact not the case.

that doesn't mean they can't manufacture it full stop it  just means the can't manufacture it at the time of the film.

Well, if they can't manufacture it, they can't have it. It's theoretically impossible for multiple kilograms of antimatter to be cheaper than one of unobtanium. Also, we've had noble gas compounds for decades, though I'd be surprised if Cameron knew that.

Why will antimatter cost more than a substance that can't be created whereas antimatter can as we can manufacture it now (albeit very slowly in small amounts) what is to say they aren't going to refine the technique of manufacturing antimatter? We (as a species) aren't exactly masters of
the universe we don't even nearly know everything about antimatter. Heck what's to say the ISV even needs that much fuel?

EDIT: and as for weapons to use instead of conventional firearms either railguns as they are efficient, long ranged,accurate and munitions are relatively cheap or my personal favorite:

Spoiler

also if masers suffer from the same flaw as conventional lasers they are unlikely to be very useful ever for combat due to being incredibly INCREDIBLY short ranged.
Cool though.

So what if they ionize the atmosphere rather than the target? That just means you need MOAR POWAH!  (And I was thinking handheld weapons. LOICs means there's no plot.)

Meh C&C renagade has hand held ion cannons. but it's more fun to nuke the site from orbit. with a "clean" WMD. also Na'vi in space sabotaging the iion cannon. that

[Clarke]

Imagine you're building a house. You've got two starting points:
1. You have an empty plot of land, and umpteen tons of stone, wood, ceremic, metal, etc. You have to build the entire house yourself, with no prefabrications, from the foundations being poured up to the roof shingles being cast. The furniture and fittings are also built by you, from your pile of raw materials.
2. You have an completed but unfurnished building, with structurally sound floors, ceilings and walls. The plumbing, electrical cabling and gas pipes are fitted. You can also buy from IKEA.  

In the Avatar-verse, somehow completing the house with the first option several times over (possibly >10 times over) is cheaper than the second option.

About, "not needing that much fuel", you do not want to quote the maths. It ends only slightly better than the flying mountain magnetar.  

[Niwantaw]

Imagine you're building a house. You've got two starting points:
1. You have an empty plot of land, and umpteen tons of stone, wood, ceremic, metal, etc. You have to build the entire house yourself, with no prefabrications, from the foundations being poured up to the roof shingles being cast. The furniture and fittings are also built by you, from your pile of raw materials.
2. You have an completed but unfurnished building, with structurally sound floors, ceilings and walls. The plumbing, electrical cabling and gas pipes are fitted. You can also buy from IKEA.  

In the Avatar-verse, somehow completing the house with the first option several times over (possibly >10 times over) is cheaper than the second option.

Just going to point out a slight flaw in your analogy.
The first one is free whereas the second one you have to buy from IKEA

And if you are going to insist that no one on earth will ever produce enough antimatter to fuel star ships effectively think of it in a much more simple manner. Using unobtaniun means that you can more efficiently use antimatter. it also makes storing it much easier. Funnily enough if antimatter was expensive then unobtanium is going to be in great demand as it would reduce the amount of antimatter needed and as there is only one source of it that requires antimatter to be spent in moderate to large quantities then unobtanium is going to be very expensive. also another reason for unobtanium being expensive is going to stem from the fact that while there may be dozens of companies that create antimatter. (Which judging by the fact that the main source of energy on earth is matter-antimatter reactors it is quite probable that there are more than a few) There is only one company that is able to mine and distribute unobtanium which as its a miracle substance needed for a lot of important things the RDA can charge as much as they damn please.

another thing to consider is that a single ISV will carry more than a few kilos of unobtanium a trip. It would probably be carrying a few hundred tons if not more unobtanium on each return trip making it somewhat profitable.

About, "not needing that much fuel", you do not want to quote the maths. It ends only slightly better than the flying mountain magnetar.  

Unless I'm very much mistaken NO ONE has the maths for the fuel efficiency as all I can find on the matter says nothing more than the ISV using beamed energy for the outbound acceleration phase from earth and it then using the matter-antimatter engines for the acceleration on arrival at Pandora and the inverse on the return trip.

[Clarke]

Just going to point out a slight flaw in your analogy.
The first one is free whereas the second one you have to buy from IKEA

I meant in terms of effort needed, not money.

And if you are going to insist that no one on earth will ever produce enough antimatter to fuel star ships effectively think of it in a much more simple manner. Using unobtaniun means that you can more efficiently use antimatter. it also makes storing it much easier. Funnily enough if antimatter was expensive then unobtanium is going to be in great demand as it would reduce the amount of antimatter needed and as there is only one source of it that requires antimatter to be spent in moderate to large quantities then unobtanium is going to be very expensive. also another reason for unobtanium being expensive is going to stem from the fact that while there may be dozens of companies that create antimatter. (Which judging by the fact that the main source of energy on earth is matter-antimatter reactors it is quite probable that there are more than a few) There is only one company that is able to mine and distribute unobtanium which as its a miracle substance needed for a lot of important things the RDA can charge as much as they damn please.

I just saw the bold. What? What source said that?! Conservation of energy does not work that way!  

another thing to consider is that a single ISV will carry more than a few kilos of unobtanium a trip. It would probably be carrying a few hundred tons if not more unobtanium on each return trip making it somewhat profitable.

And allow me to point out a fundamental fact about rocketry: fuel mass for a given speed increase is proportional to payload mass. You shipping back multiple tons of Unobtanium? You need a lot more fuel.  

Unless I'm very much mistaken NO ONE has the maths for the fuel efficiency as all I can find on the matter says nothing more than the ISV using beamed energy for the outbound acceleration phase from earth and it then using the matter-antimatter engines for the acceleration on arrival at Pandora and the inverse on the return trip.

I have math for the deceleration phase, since I know the delta-v (0.7c) the fuel's energy density (100% ) and I can guess the specific impulse of antimatter. (Let's be generous and say 10,000,000 seconds.)

I also have Tsiolkovsky's rocket equation:

(m₀ is the total mass, m₁ is the payload mass. )
Plugging all the numbers in, eventually I get that m₀/m₁ = 8.5.
IOW, if you want 1kg of Unobtanium, you need to burn 8.5kg of antimatter. Wait, no we don't; because this is only one burn of two! (Assuming we have the lasers to decelerate us while returning to Earth.) That means our 8.5kg of antimatter has to be treated as payload for another burn, and since we already have the ratio of total-to-payload, we just apply it again, so we need 72.25kg of antimatter for every kilogram of unobtanium we want to bring back!

BTW, 72kg of antimatter is equivalent to roughly 0.62 × total energy from the sun that hits earth in one minute.

[Niwantaw]

Just going to point out a slight flaw in your analogy.
The first one is free whereas the second one you have to buy from IKEA

I meant in terms of effort needed, not money.

money comes first in this case. not effort.

And if you are going to insist that no one on earth will ever produce enough antimatter to fuel star ships effectively think of it in a much more simple manner. Using unobtaniun means that you can more efficiently use antimatter. it also makes storing it much easier. Funnily enough if antimatter was expensive then unobtanium is going to be in great demand as it would reduce the amount of antimatter needed and as there is only one source of it that requires antimatter to be spent in moderate to large quantities then unobtanium is going to be very expensive. also another reason for unobtanium being expensive is going to stem from the fact that while there may be dozens of companies that create antimatter. (Which judging by the fact that the main source of energy on earth is matter-antimatter reactors it is quite probable that there are more than a few) There is only one company that is able to mine and distribute unobtanium which as its a miracle substance needed for a lot of important things the RDA can charge as much as they damn please.

I just saw the bold. What? What source said that?! Conservation of energy does not work that way!   

Matter-Antimatter reaction

Function: Energy source to power cities on Earth and interstellar spaceships
Pg. 154

"The development of matter-antimatter power reactors was initially seen as the solution to Earth's energy shortage and pollution problems. But the abundant, cheap energy they produce only encourage the construction of new factories. this in turn created even more drain on Earth's dwindling resources"  pg 155 ASG

While the ASG isn't exactly the most accurate thing in the world it's correct until proven wrong due to there being no other source.

2/3ds of the early matter-Antimatter reactors were incredibly inefficient cooling units meaning that unobtanium is needed for the reactors so when it comes down to it it doesn't really matter how much it costs to get it they would still gather it and if the costs of gathering it and refining it are high the final sell price will be higher meaning that if we go back to the original argument antimatter is cheaper than unobtanium.

[Clarke]

money comes first in this case. not effort.

You can't bribe energy to move around, is my point. You have to expend a gigantic amount of energy, with no shortcuts allowed, to build antimatter, and in comparison, building Unobtanium from base elements lets you take almost every shortcut in the book on top of having to use less than 1% of the energy antimatter would need. It doesn't really matter if you have to invent molecule-assembling nanotechnology to do it because nothing else works; it will probably still be cheaper than producing the antimatter you'd need to ship it from Pandora.

"The development of matter-antimatter power reactors was initially seen as the solution to Earth's energy shortage and pollution problems."

Antimatter cannot be used as a power source unless you can harvest it from somewhere. You can't harvest it from anywhere inside the Solar System; it would be destroyed by the solar wind or collide with something. You can't harvest it from outside the Solar System either, because your relativistic starships are powered by... yeah. You can only build it from raw energy, and to do that you need to provide 100% of its energy content, which is roughly 50% of the solar energy hitting Earth in a second, per kilogram. ...Actually, Cameron's missed a spectacle: I want to see the planet-sized solar power station that runs all this!  

I'm not missing the point entirely by assuming they haven't managed to harvest it from somewhere, am I?

(Incidentally, the calculations in my last post are assuming a 100% efficient engine. The laws of physics do not let you refine it from there.)

[Technowraith]

Whatever happened to hamster wheel power generators? I mean come on- low pollution, 85% energy recovery/production ratio. Just gotta keep the generator alive. ^.^ 

On a more serious note, the sun would provide the energy needs of the entire planet for a period of months within just 2 hours, if we had a way to harness and capture that energy. That's the problem. We don't have the technological means to generate or store vast amounts of energy. If we tried to even capture just 1 tenth of 1 percent of the energy the sun emits in just 1 minute, we'd overload the entire US power grid.

Matter/anti-matter energy generation almost seems like an oxy-moron because anti-matter when it touches matters annihilates whatever it touches while releasing energy. So in the long run, would you eventually "run out of anti-matter"? Maybe I'm looking at this wrong... lol.

[Clarke]

(I want a hamster-powered ISV!  )

We've thought about that. And you're right, though the sun doesn't provide the needs of the entire planet; it provides the power needs of 70 trillion planets, the issue is catching it all.  

And yes, it's a complete oxymoron. Antimatter does indeed go BANG! and it's gone. You run out of it, and the only way to generate it is with gigantic particle accelerators.

[Niwantaw]

money comes first in this case. not effort.

You can't bribe energy to move around, is my point. You have to expend a gigantic amount of energy, with no shortcuts allowed, to build antimatter, and in comparison, building Unobtanium from base elements lets you take almost every shortcut in the book on top of having to use less than 1% of the energy antimatter would need. It doesn't really matter if you have to invent molecule-assembling nanotechnology to do it because nothing else works; it will probably still be cheaper than producing the antimatter you'd need to ship it from Pandora.

Except they CANNOT MAKE UNOBTANIUM because they do not know how the elements are bonded together. We don't even know what elements make it up (for all we know it could be made from elements not found on earth or in the solar system) That makes it cheaper to mine it and ship it in that to create the required elements from scratch (if that is at all possible) then bond them into unobtanium

"The development of matter-antimatter power reactors was initially seen as the solution to Earth's energy shortage and pollution problems."

Antimatter cannot be used as a power source unless you can harvest it from somewhere. You can't harvest it from anywhere inside the Solar System; it would be destroyed by the solar wind or collide with something. You can't harvest it from outside the Solar System either, because your relativistic starships are powered by... yeah. You can only build it from raw energy, and to do that you need to provide 100% of its energy content, which is roughly 50% of the solar energy hitting Earth in a second, per kilogram. ...Actually, Cameron's missed a spectacle: I want to see the planet-sized solar power station that runs all this!  
[/quote]
from wikipedia:

Several NASA Institute for Advanced Concepts-funded studies are exploring whether it might be possible to use magnetic scoops to collect the antimatter that occurs naturally in the Van Allen belt of the Earth, and ultimately, the belts of gas giants like Jupiter, hopefully at a lower cost per gram.

Evidently the assumption in avatar is that those magnetic scoops work. Thus meaning that not all antimatter would have to be manufactured. also it could be gathered from outside of the solar system through use of fusion powered spacecraft (as fusion power is mentioned several times as a reality in the book (the ISV for example uses fusion powered engines for planetary maneuvering.))