Bad and good science in Avatar!

[Clarke]

Except they CANNOT MAKE UNOBTANIUM because they do not know how the elements are bonded together.

Good science is good observation.  

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

If they're not on Earth, (which is stupendously unlikely, since the only potentially stable element that we don't have on Earth in some quantity is E126) then you'll end up synthesizing elements either way, only antimatter will be costing you thousands, if not tens of thousands of times more energy.   E=mc² and all.

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.))

It seems implausible that you'd find enough antimatter in Jovian orbit to fuel a starship in a reasonable timeframe, but I don't know enough to outright say, "Objection!" You win, your encyclopedia-fu is stronger than mine. However, I do know enough to object to a spacecraft powered solely by fusion getting up to 0.7c, which you mostly need to get out of the solar system in a reasonable span of time. (Unless it's acceptable to take 50 years just to get some antimatter?) Fusion power is only 1/10th as efficient as antimatter annihilation, and plugging that into the equation I posted earlier says you've a fuel-to-payload ratio measured in the billions.

[Niwantaw]

Except they CANNOT MAKE UNOBTANIUM because they do not know how the elements are bonded together.

Good science is good observation.  

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

If they're not on Earth, (which is stupendously unlikely, since the only potentially stable element that we don't have on Earth in some quantity is E126) then you'll end up synthesizing elements either way, only antimatter will be costing you thousands, if not tens of thousands of times more energy.   E=mc² and all.

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.))

It seems implausible that you'd find enough antimatter in Jovian orbit to fuel a starship in a reasonable timeframe, but I don't know enough to outright say, "Objection!" You win, your encyclopedia-fu is stronger than mine. However, I do know enough to object to a spacecraft powered solely by fusion getting up to 0.7c, which you mostly need to get out of the solar system in a reasonable span of time. (Unless it's acceptable to take 50 years just to get some antimatter?) Fusion power is only 1/10th as efficient as antimatter annihilation, and plugging that into the equation I posted earlier says you've a fuel-to-payload ratio measured in the billions.

http://en.wikipedia.org/wiki/Bussard_ramjet

and they make a bloody huge space ship that can hold 50 years of accumulated antimatter

[Clarke]

Ramjets would work if the interstellar medium was slightly denser. It's trillions of times less dense than even hydrogen gas, so you're not going to get much fuel out of it.

[archaic]

Umm, three things:

First, given that the tawtute have constructed a laser array, to accelerate and decelerate ISV's at the earth end, why would Hell's Gate not have manufactured a similar array at the Pandora end? It wouldn't even need to provide 100% of the thrust, even 1% would provide a considerable reduction in the fuel requirement.

Second, another possible flaw, is the difference in accelerative and decelerative forces required from the earth end array. Out bound from earth, an ISV is carrying enough fuel to slow the ISV to (effectively) rest from 0.7c, where as an inbound ISV has empty fuel tanks, the difference in mass would be significant and, therefore, the demand on the laser array also.

Third, we know that unobtainium sells for $20 000 000 per kg. It takes 17kg of antimatter for each kg of unobtainium payload to fetch it.
Therefore the cost to the RDA of antimatter, must be less than $1 176 470.59 per kg.

[Irtaviš Ačankif]

Antimatter can be created only with pure energy. However, this is not too expensive as Thomas R may have thought:

First, let's start with 1g of antimatter. Annihilate it with 1g of matter. We get some energy. Then we make that energy into 2g of antimatter, assuming that antimatter does not have negative mass (most physicists believe so). Then we start over, annihilate the antimatter with 2g of matter, and so on.

This would be in effect annihilating matter to turn it into antimatter, since in the end this happens:

X grams of antimatter + X grams of matter = energy = 2X grams of antimatter

If, and this is a BIG if, the RDA has the technology to make energy turn into whatever particle they want, wheter antimatter or not, then antimatter is pretty cheap - just run the thing in a cycle.

If not, then antimatter costs at least what it does today: $62.5 trillion per gram. Adjusting for inflation and the high demand for antimatter power, the price would be somewhere near $300 trillion per gram, or $300 quadrillion per kilo. Unobtanium is only $20 million a kilo - quite cheap. By the way, Thomas R meant 72 kilos of antimatter PER KILO OF UNOBTANIUM, not for the entire ship. 72 times 300 quadrillion is 21.6 quintillion. $21.6 quintillion for something worth just $20 million would be just just just SKXAWNG!

It would be like shipping back something worth 2 dollars at a cost of 21 trillion dollars, or an 1 versus 21,000,000,000,000. Stupid RDA...

[Clarke]

1) Bootstrapping problem. You can't have the array there when you make the first trip, and if you can't make the first trip, you can't get the array there, even if it lets you make economical trips later. Besides, where on Earth Pandora is Hell's Gate getting the energy from? We don't see any multi-kilometre solar collectors in the film.

2) The Earth end has to get the fully laden ISV up to speed, so it needs a maximum capacity that can do that. It doesn't really matter how many times it has to do it to the one ship.

3) Where'd you get the 17kg from?  

Then we make that energy into 2g of antimatter...

Sorry, that's impossible. Baryon number is conserved, which means it's impossible to create matter without producing antimatter along with it. Nice plan, though. 

[Niwantaw]

Ramjets would work if the interstellar medium was slightly denser. It's trillions of times less dense than even hydrogen gas, so you're not going to get much fuel out of it.

Since the time of Bussard's original proposal, it has been discovered that the region surrounding the sun has a much lower density of interstellar hydrogen than was believed at that time (see Local Interstellar Cloud). T.A. Heppenheimer analysed Bussard's original suggestion of fusing protons, but found the bremsstrahlung losses from compressing protons to fusion densities was greater than the power that could be produced by a factor of about 1 billion, thus indicating that the proposed version of the Bussard ramjet was infeasible.[2] However Daniel P. Whitmire's 1975 analysis[3] indicates that a ramjet may achieve net power via the CNO cycle, which produces fusion at a much higher rate (~1016 times higher) than the proton-proton chain.

[Clarke]

[The Local Interstellar Cloud] is very tenuous, with 0.1 atoms per cubic centimeter

Hydrogen at standard pressure has a density of 10¹⁹ atoms per cm³, to give you an idea of how thin that is.

[Human No More]

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.

Package deal fallacy.
Interestingly, several pen and paper RPGs with defined tech levels (e.g. level 7 is x level of things possible, y things experimental) have had to redefine theirs because humans have advanced up several tech levels in some fields (primarily medical science and bioengineering) faster than anticipated, and more slowly in others (primarily low level physics and space).
Plus, as I've pointed out to people before, a robotic exoskeleton, especially one that's practical, won't be available to people with no money, now or at any time in the future. In addition, they augment strength based on limb movement - they are useless if you are unable to move your lower body at all.

Saying 'it does' would place Avatar in the same category as bad scifi, the kind where you have swords somehow made of light, or that thinks light years is a measure of time - the fact that JC has researched it all and made it all possible puts it above most - the only scifi I have encountered that you could call 'more realistic' is Stephen Baxter's.

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

What's to say he doesn't prefer a manual... like some people today?
/facepalm

Weaponised lasers are near-useless on Earth due to the power requirements - the only useful ones to get around this are chemical lasers, which require and produce large amounts of hazmat as fuel and waste. A laser on Pandora would not only suffer from magnetic interference, but the thermal blooming would make one on Earth look effective.
An ion cannon is even worse physics, as ions are charged particles - charged particles repel each other - giving it a range of effectively zero (and, as I pointed out earlier, the entire reason the marines are there is because of the limitations on weapons)

Why is antimatter being cheaper impossible? It can easily be produced on a large scale with sufficient energy - an easy solution is to build a Dyson shell, and beam the energy to collectors which use it for production.

By your logic, oil is unrealistic because it can't be economically synthesised today. /facepalm
'Building from base elements' and producing xenon fluorides are the equivalents of reaching Andromeda vs low Earth orbit. Saying 'It's unrealistic because there isn't something I wanted to see' is quite possibly the very worst logic I have ever seen applied to Avatar, and I honestly do not say that lightly at all.

Antimatter can be created only with pure energy.

There is no such thing as pure energy. Stop watching bad scifi
Energy is the capacity for work to be done. Not a substance. Claims otherwise are based on a total misunderstanding of matter-energy equivalence. 'Pure energy' makes as much sense as 'pure velocity' or 'pure weight'.

Again, read my email I posted previously. Quoting a current-day antimatter price is like quoting a 1942 plutonium price (actually, that analogy is insufficient, since it is a far larger discrepancy).

1. Build Dyson shell and/or lunar He-3 mines (not to mention the numerous other sources in the system, or even electrolytically produced deuterium).
2. Produce antimatter with modern, non-2000s processes.

Either source would provide abundant and cheap power in sufficient quantity.

[Human No More]

1) Bootstrapping problem. You can't have the array there when you make the first trip, and if you can't make the first trip, you can't get the array there, even if it lets you make economical trips later. Besides, where on Earth Pandora is Hell's Gate getting the energy from? We don't see any multi-kilometre solar collectors in the film.

2) The Earth end has to get the fully laden ISV up to speed, so it needs a maximum capacity that can do that. It doesn't really matter how many times it has to do it to the one ship.

3) Where'd you get the 17kg from?  

Then we make that energy into 2g of antimatter...

Sorry, that's impossible. Baryon number is conserved, which means it's impossible to create matter without producing antimatter along with it. Nice plan, though. 

1. The first ISV has been retired. It was much larger, due to needing better cooling systems and carrying more antimatter and larger engines. Also, hydrogen from Polyphemus - read the background.

2. Read the above post.

[Irtaviš Ačankif]

If you build a Dyson shell why use it to produce antimatter? Why don't just charge up big batteries with it? It would be a much safer method of energy storage than converting the energy to antimatter via E=mc².

Why would building from base elements be harder than making xenon flouride? Isn't xenon and flouride two BASE ELEMENTS which don't bond together in nature? Okay, it might be more expensive than a trip to Pandora, but it is always possible.

Oil can be synthesized. Umm, at least in some way. You can synthesize petroleum very easily with hydrocarbons, but it would be more expensive than a trip to an oil rig. However, unobtanium is farther than an oil rig - quite farther in fact.

When I said pure energy, I did not think of energy as a thing. I just meant that you need energy, and lots of them. It is not like giving some activation energy to a chemical reaction - you have to produce everything from nothing with nothing but energy. You'll need God-like energy to produce stuff the way God probably did.

And if you want really serious and not-bad scifi, go watch 2001: A Space Odyssey. Its physics are just terrificly realistic.

[Clarke]

Package deal fallacy.
Interestingly, several pen and paper RPGs with defined tech levels (e.g. level 7 is x level of things possible, y things experimental) have had to redefine theirs because humans have advanced up several tech levels in some fields (primarily medical science and bioengineering) faster than anticipated, and more slowly in others (primarily low level physics and space).

Well, yes. It turns out space travel at human timescales is hard, because space is big. Very big. You might think it's a long way down the street to the chemist's, but that's peanuts compared to space. Listen...
...Oops, now you've got me quoting H2G2.  

Plus, as I've pointed out to people before, a robotic exoskeleton, especially one that's practical, won't be available to people with no money, now or at any time in the future. In addition, they augment strength based on limb movement - they are useless if you are unable to move your lower body at all.

It's "soft" sci-fi to assume that economics work the same way 140 years from now as they do today. Exhibit A. Also, it's mentioned in P880, if not the other BG material, that Jake's wheelchair is made of carbon fibre. That's not cheap either.

Saying 'it does' would place Avatar in the same category as bad scifi, the kind where you have swords somehow made of light, or that thinks light years is a measure of time - the fact that JC has researched it all and made it all possible puts it above most - the only scifi I have encountered that you could call 'more realistic' is Stephen Baxter's.

No, bad sci-fi would be, as Cameron accidentally demonstrated, inventing science to hold up your point with. If you just never mention it, or make some reference to to Jake hearing the unknown explanation and not understanding it, that's fine. After all, there's no explanation whatsoever given to the Avatars themselves, and we're fine with those! (Despite possibly unrealistic oddities in how they work.) However, trying science and getting it wrong just throws a wrench in the disbelief of anyone who's understood you've got it wrong.

What's to say he doesn't prefer a manual... like some people today?
/facepalm

Fair point. Also, there's a more important reason: electric wheelchairs are usually several times heavier than manuals. Considering the fuel ratios involved on the ISV, this is really really important.

Weaponised lasers are near-useless on Earth due to the power requirements - the only useful ones to get around this are chemical lasers, which require and produce large amounts of hazmat as fuel and waste. A laser on Pandora would not only suffer from magnetic interference, but the thermal blooming would make one on Earth look effective.
An ion cannon is even worse physics, as ions are charged particles - charged particles repel each other - giving it a range of effectively zero (and, as I pointed out earlier, the entire reason the marines are there is because of the limitations on weapons)

Supercapacitor technology would probably let you squeeze a reasonable amount of power into a laser.
...Magnetic interference? In my laser? If that happens, thanators are the last of your problems!   (But I don't think anyone mentioned ion cannons)

Why is antimatter being cheaper impossible? It can easily be produced on a large scale with sufficient energy - an easy solution is to build a Dyson shell, and beam the energy to collectors which use it for production.

Oh, come on. If we've got the material engineering to disassemble the Solar System into a Dyson sphere, then we can just disassemble Pandora as well! And why it's impossible I'll demonstrate in a sec.

By your logic, oil is unrealistic because it can't be economically synthesised today. /facepalm
'Building from base elements' and producing xenon fluorides are the equivalents of reaching Andromeda vs low Earth orbit. Saying 'It's unrealistic because there isn't something I wanted to see' is quite possibly the very worst logic I have ever seen applied to Avatar, and I honestly do not say that lightly at all.

Let's look at the "build Unobtanium from base elements" option. Since I obviously don't know anything about Unobtanium's composition, I'll substitute the most energetic chemical reaction I can find: stripping all 9 electrons from Fluorine, the most "clingy" of all elements. According to this page, the ionisation energies go up massively each time, with the total being 262,040 kiloJoules/mol. This is equivalent to 2715.86 eV per atom.

Now, the alternative: building antimatter. Just to show up the problem, I'll assume we need the lightest (and thus cheapest) possible element, anti-hydrogen. To build this, we need one anti-proton and one anti-electron, which have the same masses as conventional protons and electrons. Because of that, it's really easy to calculate the energy we need. You read that correctly: 938.89MeV. 938,890,000eV per atom.

Antimatter requires, at minimum, (we've been working with 100% efficient machines till now!  ) 345,000 times more energy than assembling even the most uncooperative of chemical reactions. We can't assume that 1kg of antihydrogen translates into 1kg of unobtanium!  It's more like 8.5kg of antimatter for 1 of unobtanium, assuming you're not taking anyone back to Earth!

Where's your antimatter construction process that's in excess of 1 million times more efficient than your chemistry?  

Antimatter can be created only with pure energy.

There is no such thing as pure energy. Stop watching bad scifi
Energy is the capacity for work to be done. Not a substance. Claims otherwise are based on a total misunderstanding of matter-energy equivalence. 'Pure energy' makes as much sense as 'pure velocity' or 'pure weight'.

Pure energy usually refers to EM energy, like laser beams.   (Or, in particle accelerates, E_k) I know there's a lot of misconceptions about the term, but it does have a use.

Again, read my email I posted previously. Quoting a current-day antimatter price is like quoting a 1942 plutonium price (actually, that analogy is insufficient, since it is a far larger discrepancy).

1. Build Dyson shell and/or lunar He-3 mines (not to mention the numerous other sources in the system, or even electrolytically produced deuterium).
2. Produce antimatter with modern, non-2000s processes.

Either source would provide abundant and cheap power in sufficient quantity.

Did I ever quote modern day prices?
(And 2 is not actually an option, if the intention is getting around the limits a couple of paragraphs back. All the maths I've posted assumed 100% efficient machines. You cannae break the laws o' physics, Cap'm. Or Colonel, as it might be.)

1. The first ISV has been retired. It was much larger, due to needing better cooling systems and carrying more antimatter and larger engines. Also, hydrogen from Polyphemus - read the background.

A larger/less efficient ISV would require even more fuel! Also, decelerating from 0.7c requires multiple 100-gigawatt lasers, regardless of what's powering them. That's not an easy undertaking.

And with the combination of unobtanium and working nuclear fusion, I'm really surprised that Earth is crapsack as it is, considering power should be too cheap to meter!  

If you build a Dyson shell why use it to produce antimatter? Why don't just charge up big batteries with it? It would be a much safer method of energy storage than converting the energy to antimatter via E=mc².

Energy density. You can't get c^2 J/kg with a battery.  

And if you want really serious and not-bad scifi, go watch 2001: A Space Odyssey. Its physics are just terrificly realistic.

Well, it started realistic, certainly. It falls apart slightly in the sequels, but it's still very very good.

[Human No More]

If you build a Dyson shell why use it to produce antimatter? Why don't just charge up big batteries with it? It would be a much safer method of energy storage than converting the energy to antimatter via E=mc².

Because you need to store it, meaning the ISV would be composed almost entirely of batteries in that case, and because ion drives are extremely slow and the only practical use for electrical power for spacecraft propulsion. If it can be contained, antimatter is a storage and reaction medium all in one.

Why would building from base elements be harder than making xenon flouride? Isn't xenon and flouride two BASE ELEMENTS which don't bond together in nature? Okay, it might be more expensive than a trip to Pandora, but it is always possible.

They do form naturally - xenon fluorides are not assembled via machines or anything. They are subjected to extreme conditions that do not naturally occur on Earth to create the compound, certainly (but could feasibly exist elsewhere - there is no manual intervention past subjecting them to the conditions), but a simple compound of two elements and a crystalline metallic structure comopsed of multiple heavy elements and with a strucutre that extends into 4 dimensions are entirely different things.

Oil can be synthesized. Umm, at least in some way. You can synthesize petroleum very easily with hydrocarbons, but it would be more expensive than a trip to an oil rig. However, unobtanium is farther than an oil rig - quite farther in fact.

Yes, but synthetic oil is not even energy-neutral, and hence effectively useless. As it is, humans can still not synthesise proteins even, which would be a step up in complexity but still pale in comparison to something line unobtainium.

When I said pure energy, I did not think of energy as a thing. I just meant that you need energy, and lots of them.

...then say 'large amounts of energy'.

[Clarke]

....with a strucutre that extends into 4 dimensions....

[Human No More]

Plus, as I've pointed out to people before, a robotic exoskeleton, especially one that's practical, won't be available to people with no money, now or at any time in the future. In addition, they augment strength based on limb movement - they are useless if you are unable to move your lower body at all.

It's "soft" sci-fi to assume that economics work the same way 140 years from now as they do today. Exhibit A. Also, it's mentioned in P880, if not the other BG material, that Jake's wheelchair is made of carbon fibre. That's not cheap either.

Things haven't changed so much in the last 140 years, economically. Not as much as you'd like to believe, anyway.

Why is antimatter being cheaper impossible? It can easily be produced on a large scale with sufficient energy - an easy solution is to build a Dyson shell, and beam the energy to collectors which use it for production.

Oh, come on. If we've got the material engineering to disassemble the Solar System into a Dyson sphere, then we can just disassemble Pandora as well! And why it's impossible I'll demonstrate in a sec.

I said a Dyson shell, not sphere. Read up on the difference. The point of one is it is nonsolid and can be expanded as needed - it is basically just a network of power satellites.

By your logic, oil is unrealistic because it can't be economically synthesised today. /facepalm
'Building from base elements' and producing xenon fluorides are the equivalents of reaching Andromeda vs low Earth orbit. Saying 'It's unrealistic because there isn't something I wanted to see' is quite possibly the very worst logic I have ever seen applied to Avatar, and I honestly do not say that lightly at all.

Let's look at the "build Unobtanium from base elements" option. Since I obviously don't know anything about Unobtanium's composition, I'll substitute the most energetic chemical reaction I can find: stripping all 9 electrons from Fluorine, the most "clingy" of all elements. According to this page, the ionisation energies go up massively each time, with the total being 262,040 kiloJoules/mol. This is equivalent to 2715.86 eV per atom.

Now, the alternative: building antimatter. Just to show up the problem, I'll assume we need the lightest (and thus cheapest) possible element, anti-hydrogen. To build this, we need one anti-proton and one anti-electron, which have the same masses as conventional protons and electrons. Because of that, it's really easy to calculate the energy we need. You read that correctly: 938.89MeV. 938,890,000eV per atom.

Antimatter requires, at minimum, (we've been working with 100% efficient machines till now!  ) 345,000 times more energy than assembling even the most uncooperative of chemical reactions. We can't assume that 1kg of antihydrogen translates into 1kg of unobtanium!  It's more like 8.5kg of antimatter for 1 of unobtanium, assuming you're not taking anyone back to Earth!

With that logic, computers should be capable of performing 250PFLOPS today simply because the energy is available. Complexity and technological limitations are the real limiting factors - power generation may be more widespread, but in the early 20th century, a modern microprocessor was just as possible to make as today, except people lacked the technology base then.

Where's your antimatter construction process that's in excess of 1 million times more efficient than your chemistry?  

Why does it need to be? It is stated in the background material that energy production is no longer any problem at all due to its abundance, but it simply caused more exploitation of natural resources, which is the main real problem.

Pure energy usually refers to EM energy, like laser beams.   (Or, in particle accelerates, E_k) I know there's a lot of misconceptions about the term, but it does have a use.

That doesn't make it correct - it is like calling water a mixture. It's a possible misconception only.

As for antimatter production, non-2000s processes refers mainly to efficiency - collecting antimatter in quantities greater than a few nuclei at a time.

A larger/less efficient ISV would require even more fuel! Also, decelerating from 0.7c requires multiple 100-gigawatt lasers, regardless of what's powering them. That's not an easy undertaking.

That's why it was retired - I was pointing out the flaw in your 'there is nothing at Pandora so they couldn't get there' argument.

And with the combination of unobtanium and working nuclear fusion, I'm really surprised that Earth is crapsack as it is, considering power should be too cheap to meter!  

It is stated in the background material that energy production is no longer any problem at all due to its abundance, but it simply caused more exploitation of natural resources, which is the main real problem.

[Irtaviš Ačankif]

If you build a Dyson shell why use it to produce antimatter? Why don't just charge up big batteries with it? It would be a much safer method of energy storage than converting the energy to antimatter via E=mc².

Because you need to store it, meaning the ISV would be composed almost entirely of batteries in that case, and because ion drives are extremely slow and the only practical use for electrical power for spacecraft propulsion. If it can be contained, antimatter is a storage and reaction medium all in one.

If you use antimatter as propulsion how do you use it except to power ion drives? Heat steam turbines with antimatter? It wouldn't work in the vaccuum of space. Annihilate antimatter and use the gamma rays for propulsion? Then you need heavy stuff to annihilate the antimatter with and there is also the problem of the radiation. Spew it out of openings? Too much of a waste! You use antimatter to power ion drives! Additionally, VASIMR ion drives can produce pretty high thrust, enough to make an airplane fly.

[Clarke]

Annihilate antimatter and use the gamma rays for propulsion? Then you need heavy stuff to annihilate the antimatter with and there is also the problem of the radiation.

You'd want to do this, wouldn't you? Lighter ship => more acceleration. (And ideally all the radiation is passing out of the ship's exhaust. That's the point, after all.)

[Irtaviš Ačankif]

But wouldn't it be the same as hooking up batteries to flashlights pointing backwards? With enough energy to produce antimatter for the trip to Pandora you can also power enough flashlights to accelerate you to 0.8C.

[Clarke]

But wouldn't it be the same as hooking up batteries to flashlights pointing backwards? With enough energy to produce antimatter for the trip to Pandora you can also power enough flashlights to accelerate you to 0.8C.

Yeah, but antimatter annihilation doesn't produce pure gamma radiation, AFAIK. It also produces a bunch of massive particles, which you can spit out your exhaust.
(You could have flashlights that get you up to 0.8c, though. Their power output is measured in terawatts.  )

Things haven't changed so much in the last 140 years, economically. Not as much as you'd like to believe, anyway.

Apart from the entire concept of globalization. And the entire industry of electronics manufacturing, and everything that's led to. Did I mention the computing industry?

I said a Dyson shell, not sphere. Read up on the difference. The point of one is it is nonsolid and can be expanded as needed - it is basically just a network of power satellites.

Sorry, they're usually similar. You could build a Dyson swarm with non-astronomical resources, but it doesn't make a difference to the antimatter vs. unobtanium economics.

With that logic, computers should be capable of performing 250PFLOPS today simply because the energy is available. Complexity and technological limitations are the real limiting factors - power generation may be more widespread, but in the early 20th century, a modern microprocessor was just as possible to make as today, except people lacked the technology base then

.
No, the logic is more like, "It's completely impossible to build a computer can perform at 250PFLOPS by [date]." The numbers in that post were the absolute best under known physics. No future technology will let you get around the fact that antimatter is multiple hundreds of thousands of times harder to build than Fluorine is to ionise. (And there are very few things that will react more energetically than a F⁹⁺ ion.)

Why does it need to be? It is stated in the background material that energy production is no longer any problem at all due to its abundance, but it simply caused more exploitation of natural resources, which is the main real problem.

Otherwise it's not economical to burn antimatter as Venture Star fuel.  
(And what natural resources? Why not just use your magical synthesis machines to build everything?  )

As for antimatter production, non-2000s processes refers mainly to efficiency - collecting antimatter in quantities greater than a few nuclei at a time.

You still need to put in c² J/kg in, regardless of how you gather it. (Unless you're harvesting it from somewhere.)

That's why it was retired - I was pointing out the flaw in your 'there is nothing at Pandora so they couldn't get there' argument.

But it has to be able to get there and back at least once, to get unobtanium to us. That's... infeasible when your fuel-to-payload ratio is >5.

[Irtaviš Ačankif]

The whole unrealistic thing about Avatar was the crappy Earth. I mean, look at all that chatter! Why not run fusion and antimatter power stations? No pollution at all! Greenhouse gases? Bye-bye. Even if you destroy all of the trees on Earth perfectly clean power will still produce a decent Earth. And why exploit natural resources? What do you need? Deuterium? Just pump it from the oceans. Oil? No, that is outdated by fusion power and antimatter. Wood? Why not use plastic?

I hate to say this, but JC seems to be a die-hard anti-technology-ist even if he used pretty advanced technology for the movie. He kinda believes that we need to be Na'vi-ish hunter-gatherers in order to be in harmony with nature.

By the way, is the Extended Collectors' Edition shots canon? If not we can make up our own Earth which can be a bit more realistically clean.