Bad science in fiction Hall of Shame

[monstah]

24 minutes ago, YNM said:

On Armageddon : I think there's a reason why it's so bad.

 

It's an action rip-off of a sci-fi.

Here's the "real" stuff.

Heh, going from 11km to "the size of Texas" is kinda like the jump in size from mother ships in Independence Day and the sequel (which, again, no one mentioned yet. What the hell is up with gravity in that movie? It even forms... vortices??)

[kerbiloid]

4 hours ago, radonek said:

Lasgun-shield interaction is much less predictable and it's usage is more driven by political ramifications then technology.

Iirc, if a lasgun ray touches the force field dome, an explosion happens which kills the shooter, so they avoid the lasgun usage and prefer a melee.
I can't recall any "it may burst" or so, thus I can't see why if shoot from inside the dome, it wouldn't burst.
As for predictability: OK, let's drop two timer-activated lasguns per dome.

Another nice thing - stillsuit.
So, a body produces the sweat, and when it evapourates it dissipates the waste heat cooling the body.
What does the stillsuit do? It holds the sweat inside preventing the heat dissipation.
It would be like crossing a desert in chem suits and masks. Harkonnens would just gather the unconscious freemen lying on sand.

Hooks used by the freemen to rule the worm. So, a worm can scratch through the earth mass but its skin is afraid of two microscopic hook?
If some insect bothers you, then you would probably just scratch against a door and forget about it. I guess, Shai-Hulud would do the same.

Environment  friendly plastic goods being manufactured by the freemen.
Plastic is carbon. Sand is silicon. Not a lot of material for the organics industry.

4 hours ago, radonek said:

Dune is not a space opera at all.  

When Thufir Hawat taught Paul to kill by slashing with blade rather than piercing with tip because piercing lacks artistism (or something like that, as I read these books in translation),
I became sure that the House of Atreides is doomed and it would be better if Paul would be sitting with his back to the door, he'd suffer less.

So, I just prefer to think that Dune is a nice opera, rather than sci-fi with a lot of mistakes. Like SW, etc.

1 hour ago, ARS said:

The movie claims that the asteroid is roughly the size of Texas. Do you know other object the size of Texas?

Afaik, "size of Texas" is an American idiom for "very large", not accurate size.

Upd.
If the shuttles were made of titanium irl, probably Challenger and Columbia would stay alive.

Upd 2.
If they had mini-guns, probably Mir would have armor plates.

Edited February 5, 2018 by kerbiloid

[Canopus]

The Gatling guns in Armageddon were on of the weirdest parts of that movie. They never even try to justify their existence on that mission. I could accept them on the updated shuttles as maybe some Airforce thing analog to Almaz, but why on the Rovers?

Edited February 5, 2018 by Canopus

[Superfluous J]

59 minutes ago, kerbiloid said:

Afaik, "size of Texas" is an American idiom for "very large", not accurate size.

In the movie they also gave the dimensions in numbers. They were comparable to Texas.

[YNM]

25 minutes ago, Canopus said:

The Gatling guns in Armageddon were on of the weirdest parts of that movie. They never even try to justify their existence on that mission.

Apart from being an action movie I guess.

Edited February 5, 2018 by YNM

[radonek]

48 minutes ago, kerbiloid said:

Iirc, if a lasgun ray touches the force field dome, an explosion happens which kills the shooter, so they avoid the lasgun usage and prefer a melee.

Like I said, you got it all wrong. Reason for melee combat is that shield technology is very efficient defense against projectile weapons. As for lasers, I guess that is best explained by Thufir Hawat himself:

Quote

"There is no traitor," she said. "The threat's something else. Perhaps it has to do with the lasguns. Perhaps they'll risk secreting a few lasguns with timing mechanisms aimed at house shields. Perhaps they'll . . . "
    "And who could tell after the blast if the explosion wasn't atomic?" he asked. "No, my Lady. They'll not risk anything that illegal. Radiation lingers. The evidence is hard to erase. No. They'll observe most of the forms. It has to be a traitor." 

It does not matter how smart device you devise (and it can be quite simple as shown) - if your opponent goes kaboom, you are implicitly suspect of violating the Convention and can end up on receiving end of nuclear exchange. No science in this, its politics.  Which is why this book, unlike space operas, never gets old.

[mikegarrison]

6 hours ago, radonek said:

You got it completely, utterly wrong. Shields work different from what you think. Lasgun-shield interaction is much less predictable and it's usage is more driven by political ramifications then technology. Much like everything else in the book. Because, and here you made biggest mistake, Dune is not a space opera at all.  

Again, this was basically all driven by author desire. He wanted a world where spaceships carried whole armies between planets but then they fought knife fights once they got there. It was all about the pseudo-medieval culture he wanted to describe. So he invented the personal shields to make projectile and laser weapons ineffective.

[Superfluous J]

38 minutes ago, radonek said:

Which is why this book, unlike space operas, never gets old

Space operas never get old. And space operas have more to do with the (in)accuracy of science than politics.

Calling Dune a space opera isn't to disparage it, but to explain why for it the dodgy science isn't as important as it is for Gravity.

[DAL59]

In the ender's game series, there is relativity, and also instantaneous communication.  If you have both, you can violate causality.  

[kerbiloid]

1 hour ago, radonek said:

It does not matter how smart device you devise (and it can be quite simple as shown) - if your opponent goes kaboom, you are implicitly suspect of violating the Convention and can end up on receiving end of nuclear exchange. No science in this, its politics.  Which is why this book, unlike space operas, never gets old.

That's even better. Shoot a timered lasgun inside a force field dome of your opponent's enemy/creditor/lender and accuse your opponent.

24 minutes ago, 5thHorseman said:

Calling Dune a space opera isn't to disparage it, but to explain why for it the dodgy science isn't as important as it is for Gravity.

Exactly. Just different genres.

Edited February 5, 2018 by kerbiloid

[Mitchz95]

4 hours ago, ARS said:

10. The movie said that the asteroid is knocked by comet out of asteroid belt and now headed to earth. First off, assuming it's around 900 km in diameter and made of iron (like what they claimed many times in the movie), it would have the total mass roughly 9 x 10^24 grams. That's a lot, you can ram it with comet for years and not move it much, never mind that the probability of a comet hitting an asteroid is incredibly low.

12. The idea to bury the bomb makes sense when it comes to maximizing effect of bomb's explosion. However, on the asteroid with 900 km diameter, why the heck you only drill 800 feet!? That's around 1/5000th of half the diameter of the asteroid! Also, if they only have limited time to do it, then why they drill on 45 degree angle!? It adds an extra 300 feet to their drilling.

To be perfectly fair to Armageddon...

10. The asteroid is the comet, and the asteroids it dislodged are the ones raining down on Shanghai and Paris. That's still bad, but at least it kinda-sorta justifies why nobody's discovered that Texas-size asteroid yet: it's a rogue comet from outside the solar system.

12. They mention that they're drilling onto a fault line, which would presumably have carried the effect of the detonation to the core. Still bad, again, but not quite as bad as it's made out to be.

[kerbiloid]

Spoiler

2 hours ago, 5thHorseman said:

In the movie they also gave the dimensions in numbers. They were comparable to Texas.

Got it. The astronomer had heard "size of Texas" and was translating this into numbers. Bruce Willis heard the numbers and reverse translated this into "size of Texas", lol.

 

[mikegarrison]

1 hour ago, DAL59 said:

In the ender's game series, there is relativity, and also instantaneous communication.  If you have both, you can violate causality.  

Annnnnd, they do, in Xenocide.

[monstah]

2 hours ago, kerbiloid said:

Shoot a timered lasgun inside a force field dome of your opponent's enemy/creditor/lender

So, do the equivalent of a nuke on an unsuspecting bystander, who might have sided up with you?

[sevenperforce]

2 hours ago, Mitchz95 said:

To be perfectly fair to Armageddon...

10. The asteroid is the comet, and the asteroids it dislodged are the ones raining down on Shanghai and Paris. That's still bad, but at least it kinda-sorta justifies why nobody's discovered that Texas-size asteroid yet: it's a rogue comet from outside the solar system.

A rogue planet, perhaps...something akin to ʻOumuamua, but dwarf-planet-sized? Sure. But we would have seen it coming a LONG time earlier. Not a rogue comet.

2 hours ago, Mitchz95 said:

12. They mention that they're drilling onto a fault line, which would presumably have carried the effect of the detonation to the core. Still bad, again, but not quite as bad as it's made out to be.

Wouldn't have mattered. Even if the nuclear shockwave propagated along the magical fault line (wait, why would a comet/asteroid have a fault line??!!), it's not going to split a dwarf planet in half, because the dwarf planet still has gravity holding it together.

[DAL59]

1 hour ago, mikegarrison said:

Annnnnd, they do, in Xenocide.

Umm... when do they time travel?

[mikegarrison]

1 hour ago, DAL59 said:

Umm... when do they time travel?

You didn't say "time travel", you said "violate causality". They essentially go outside the causal universe and create a cure for the descolada just by visualizing it. Also, Ender recreates  a young Peter and Valentine out his imagination.

[magnemoe]

5 hours ago, mikegarrison said:

Again, this was basically all driven by author desire. He wanted a world where spaceships carried whole armies between planets but then they fought knife fights once they got there. It was all about the pseudo-medieval culture he wanted to describe. So he invented the personal shields to make projectile and laser weapons ineffective.

This, now poison gas, flame throwers and probably explosives who entered you shield slowly would work. 
You would want stormtrooper armor below the shield, it would give very good chemical protection, decent fragment protection and good defense against bladed weapons as in plate mail. 
Best tool would probably be an sharped charge on an stick, think war axe but an charge, head penetrate shield as pretty slow you hit armor and this trigger the charge, this kills or disables the enemy, unless he block. In that chase the charge will not trigger. 
 

[Superfluous J]

4 hours ago, kerbiloid said:

  Hide contents

Got it. The astronomer had heard "size of Texas" and was translating this into numbers. Bruce Willis heard the numbers and reverse translated this into "size of Texas", lol.

 

Unsure why you felt the need to spoiler that, but no that's not how it went.

The astronomer was giving the numbers to the President of the US, who is a good ole boy and don't like no numbers and just wants it all plain-like. So the astronomer responded, if I recall, "It's the size of Texas, sir."

Edited February 6, 2018 by 5thHorseman

[ARS]

Avatar. Ah, such an eye-candy-filled movie that astonished us with mind-boggling scenery porn. Unfortunately, when it comes to physics, well... To list some:

1. The movie takes place in 2154 on Pandora moon orbiting a gas giant Polyphemus, which orbits Alpha Centauri, 4.37 light years away from Earth. Currently, there's no evidence of gas giant orbiting Alpha Centauri, let alone habitable moon.

2. Would someone please explain how the hell The Pandora, being literally covered by jungle, rainforest, full of green vegetation has so little oxygen in the atmosphere that it's mandatory for humans to wear a mask to breathe?

3. The movie indicates that the trip from Earth to Pandora takes 6 years. To keep the acceleration of the craft within tolerable limit, we assume it requires 6 months to accelerate, and 6 months to decelerate in order to maintain a manageable acceleration of 1.5G (1.5 times acceleration due to Earth's gravity), and the cruising speed would be approximately 80% speed of light. Mass increases as velocity approaches speed of light, a 1 kg mass would become 1.6 kg at 80% speed of light. This means a significant increase in energy requirement to travel to Pandora. At 6 years travel time, the significant increase in energy becomes unavoidable. Normal chemical propellant won't do the job. According to the film material, the spacecraft uses antimatter/ fusion reactor hybrid for propulsion. Antimatter has already present today, albeit in very small amount, and we already created a fusion reaction in hydrogen bomb. However, antimatter is very difficult to make, has short shelf life and incredibly expensive with a price tag of $60 billion/ microgram, not to mention the difficulty in storing it. With the depiction of spaceship in the movie around a mile long, the required antimatter would be on the order of thousands of tons. Even if antimatter becomes cheap enough to beat the cost of fossil fuel by the factor of 1000, it still cost millions of dollars to transport a single kilogram of stuff into Pandora.

4. What's the reason humans go to Pandora? To mining Unobtainium! The same term (but not the same stuff) used in The Core! The film material stated that Unobtainium is a room-temperature superconductor, and it sells for $20 million per kilogram. Sounds profitable, but the economic principle teached us that high price means tiny market, making the profitability of mining it seems rather iffy. If it was indeed a lucrative bussiness, then sooner or later, someone would figure out how to synthesize it, because come on, a culture that can go to moon on the another planet on another star system surely could figure out how to sythesize it.

5. As explained above, the energy requirements of transporting stuff from Earth to Pandora is immense, and the cost is very expensive. Shipping heavy equipment, such as mining excavator, trucks, aircraft, ect. directly from earth is not cost effective. A single truck could cost billions to send to Pandora, so they had to be manufactured on site, and they need to build a lot of infrastructures. Weapons and ammunition must be locally produced, otherwise, the quote of "...It costs four hundred thousand dollars to fire this weapon for twelve seconds." becomes literal. Also, why sending workers from earth? It would be cheaper to just send some colonist there, grow population and treat pandora as their home instead of having to spend money for regularly transporting workers to and from Pandora.

6. It's hard to believe that human militia seems awfully under-equipped compared by today's conventional military. No drones, no automated robots, no super-abnormal ammo like incendiary or guided bullets. In the future, the kill rate of individual bullets will likely be much higher than today's so it's not necessary to literally spraying forest with lead to kill a single Navi.

7. The heavy robotic suit (AMP suit) in the movie shares the same problem of structural integrity and energy requirement as in most giant monsters/ robots movie, thanks to the square/cube law.

8. What's the point of linking a human into a body of Navi? The movie claimed they created that to learn/ observe/ communicate with Navi in order to gain information or negotiate. Why would you communicate with them if you gonna get rid of them entirely anyway? Using drones to spy on them is much more cheaper and cost-effective than creating a Navi body and controlling it wirelessly from afar.

9. Although they were visually stunning the floating mountains were arguably the most ridiculous features in the entire movie. They were gigantic chunks of real-estate floating in the sky apparently suspended  by some form of magnetic field. We surmised this from the fact that electronic instruments on all aircraft in the vicinity are driven crazy by the area's "high flux level", presumably a high magnetic flux level. Magnetic fields are also about the only available explanation. Other possibilities such as buoyancy, wind, and electrostatic forces are even more easily ruled out. Unfortunately, the magnetic field strength needed to levitate mountains would have numerous disastrous side effects on the movie's story line, that is if the movie stuck to real physics. First such a field would rip magnetic materials out of aircraft if they flew into it, but that's just the beginning. Even if the aircraft had no magnetic materials in them, moving a conductive material of any type--magnetic or otherwise--through the field would create a large voltage difference across it. All electronic systems or controls, not just the navigation systems would be seriously disrupted. It's doubtful that an aircraft could fly in such conditions. Since both the human brain and heart are conductive, both would have voltage differences generated across them by the motion of riding in an aircraft. Any variation in direction or magnitude of the magnetic field, even subtle changes from vibrations or body movements would induce random currents in the brain with an endless list of possible results including memory loss, hallucinations, psychotic events, and seizures. Randomly induced currents in the heart could result in fibrillation and death.

10. The movie claims that Pandora's gravity is slightly lower than Earth, which helps justify the tall figure of the Navi, and their ability to jump higher. But apparently, that reduced gravity doesn't apply to humans since we don't see them gaining any increased mobility.

11. For some reason, while preparing to blow up the tree of life, Humans also to decides mount a land assault. The Navi meet the ground force head-on with a cavalry charge, a well known form of suicide since at least 1914. And guess what? They get butchered. Meanwhile other blue guys mounted atop flying critters swoop down on the aircraft from above. Aircraft designed for ground assaults could indeed be vulnerable from above. These aircraft used high speed counter-rotating propellers contained in large circular shaped pods. Shooting one of the Navi's spear-like arrows or dropping big rocks into the rotor blades should have been more than enough to severely damaged them and disabled the aircraft, they don't have to jump on the aircraft and throw grenades into the propellers. In addition to performing such attacks from the flying critters, in at least some places, the Navi could have hidden archers atop the floating mountains and rained arrows down on the aircraft attempting to pass between them.

Avatar is a sci-fi movie that while it's beautiful and has little to no technobabble about the technology, still bears the implausibility and impracticality in terms of technology, practical appliation and physics if viewed thoroughly and carefully examining every detail it provides from dialogue and background materials.

[wumpus]

6 hours ago, 5thHorseman said:

Space operas never get old. And space operas have more to do with the (in)accuracy of science than politics.

Calling Dune a space opera isn't to disparage it, but to explain why for it the dodgy science isn't as important as it is for Gravity.

That isn't quite accurate.  *Ecology* is pretty critical in Dune and I doubt it was all that inaccurate in the 1960s (and probably isn't even detailed enough be shown wrong now, just enough to describe the effects of extremely limited moisture on an ecology).  Physics was only touched on enough to establish the setting (remember, space and time are warped by the psychic effects of guild navigators.  Absolutely no attempt at hard SF in the hard sciences is ever attempted).

Swords in space isn't exactly limited to Space Opera, I think one of the last battles in Forever War involved pre-gunpowder tactics.  I'm blanking on the rest.

Cavalry charges in late history:
Crimean war (1854) Light Brigade Charges for completely unclear reasons.  It does not go well.
US civil war(1860s) at least one cavalry vs. cavalry battle takes place with one side using sabres and the other using carbines.  This likely marks the end of sabre use in said war.
Russo-Japanese war (1904-1905) I wouldn't put it past the Czars to field classic cavalry.  At least one high ranking supply officer wasn't worried about the distinct lack of gunpowder going into the Great War as "it will decided, as always, by lance and sabre".

[YNM]

1 hour ago, ARS said:

Avatar. Ah, such an eye-candy-filled movie that astonished us with mind-boggling scenery porn.

It's a fantasy.

Here's a better-fitting-to-its-genre Avatar.

[Bill Phil]

57 minutes ago, ARS said:

1. The movie takes place in 2154 on Pandora moon orbiting a gas giant Polyphemus, which orbits Alpha Centauri, 4.37 light years away from Earth. Currently, there's no evidence of gas giant orbiting Alpha Centauri, let alone habitable moon.

No, that's astronomy, not physics.

Quote

2. Would someone please explain how the hell The Pandora, being literally covered by jungle, rainforest, full of green vegetation has so little oxygen in the atmosphere that it's mandatory for humans to wear a mask to breathe?

If I recall, it wasn't necessarily lack of oxygen, but the presence of dangerous gases. Even a few percent of CO2 could prove problematic. According to the "Avatar wiki", CO2 percentage is almost 20. That is deadly.

Quote

3. The movie indicates that the trip from Earth to Pandora takes 6 years. To keep the acceleration of the craft within tolerable limit, we assume it requires 6 months to accelerate, and 6 months to decelerate in order to maintain a manageable acceleration of 1.5G (1.5 times acceleration due to Earth's gravity), and the cruising speed would be approximately 80% speed of light. Mass increases as velocity approaches speed of light, a 1 kg mass would become 1.6 kg at 80% speed of light. This means a significant increase in energy requirement to travel to Pandora. At 6 years travel time, the significant increase in energy becomes unavoidable. Normal chemical propellant won't do the job. According to the film material, the spacecraft uses antimatter/ fusion reactor hybrid for propulsion. Antimatter has already present today, albeit in very small amount, and we already created a fusion reaction in hydrogen bomb. However, antimatter is very difficult to make, has short shelf life and incredibly expensive with a price tag of $60 billion/ microgram, not to mention the difficulty in storing it. With the depiction of spaceship in the movie around a mile long, the required antimatter would be on the order of thousands of tons. Even if antimatter becomes cheap enough to beat the cost of fossil fuel by the factor of 1000, it still cost millions of dollars to transport a single kilogram of stuff into Pandora.

It's cruising speed is about 70% lightspeed. And mass doesn't increase all that much until you hit higher fractions of C. Yes, there is an increase, although it really isn't relevant to how a rocket works. What matters is mass ratio, if the propellant is increasing in mass and the vehicle is increasing in mass, then, if both are increasing in mass by the same amount, the mass ratio should be identical.

Chemical rockets wouldn't even get you to .7c with or without the increase in mass. They're puny.

Current costs of antimatter are irrelevant to future costs. For example, the cost of certain metals just 150 years ago was prohibitive. Now, many of those metals are ubiquitous (aluminum being a good example, it used to cost more than gold, and then, its price dropped dramatically after new methods were discovered of extracting it; over a four year period its price dropped by an order of magnitude from 1855 to 1859). They may have large solar arrays in low solar orbit connected to antimatter factories or something. 

My main gripe here is that they still haven't built a laser array at Alpha Centauri. That's how they depart and brake from/into the Solar System, but they brake with antimatter. Presumably they have the means to set up a large mining operation, which means that it shouldn't be impossible to save on antimatter by using another laser array at Alpha Centauri.

Quote

4. What's the reason humans go to Pandora? To mining Unobtainium! The same term (but not the same stuff) used in The Core! The film material stated that Unobtainium is a room-temperature superconductor, and it sells for $20 million per kilogram. Sounds profitable, but the economic principle teached us that high price means tiny market, making the profitability of mining it seems rather iffy. If it was indeed a lucrative bussiness, then sooner or later, someone would figure out how to synthesize it, because come on, a culture that can go to moon on the another planet on another star system surely could figure out how to sythesize it.

Yeah. High price means small market. Provided that it's an unnecessary utility. In the Avatar universe, unobtainium isn't something they just want to have, they need to have it. Mainly to solve energy issues, apparently. Also, presumably the economy has grown considerably (it's large enough to support a fleet of STL starships), so 20 million may not be as much as you'd think in that economy (another factor to consider is inflation). 

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5. As explained above, the energy requirements of transporting stuff from Earth to Pandora is immense, and the cost is very expensive. Shipping heavy equipment, such as mining excavator, trucks, aircraft, ect. directly from earth is not cost effective. A single truck could cost billions to send to Pandora, so they had to be manufactured on site, and they need to build a lot of infrastructures. Weapons and ammunition must be locally produced, otherwise, the quote of "...It costs four hundred thousand dollars to fire this weapon for twelve seconds." becomes literal. Also, why sending workers from earth? It would be cheaper to just send some colonist there, grow population and treat pandora as their home instead of having to spend money for regularly transporting workers to and from Pandora.

Pandora is too hazardous to truly colonize. For one thing, despite there being greenery, the atmosphere is dangerous. Another issue would be the sheer distance and difficulty of supporting the colony. A small mining base is much cheaper, paradoxically... they don't need that many people. It's mostly automated. Although there is presumably a few reasons for keeping people around.

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6. It's hard to believe that human militia seems awfully under-equipped compared by today's conventional military. No drones, no automated robots, no super-abnormal ammo like incendiary or guided bullets. In the future, the kill rate of individual bullets will likely be much higher than today's so it's not necessary to literally spraying forest with lead to kill a single Navi.

They're not an actual military, and, like you said earlier, it's expensive to bring all that stuff from Earth. Perhaps there is no local manufacturing to speak of.

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7. The heavy robotic suit (AMP suit) in the movie shares the same problem of structural integrity and energy requirement as in most giant monsters/ robots movie, thanks to the square/cube law.

The square cube law is kind of over-rated. While it does apply in general, it ignores things like actual material strength and simply refers to the ratios. We likely have the materials required to build something like it, although not the required joint tech or power source, which is the real issue. I could see its usefulness, considering the forests of Pandora. But without a good power source, it's not going to be useful.

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8. What's the point of linking a human into a body of Navi? The movie claimed they created that to learn/ observe/ communicate with Navi in order to gain information or negotiate. Why would you communicate with them if you gonna get rid of them entirely anyway? Using drones to spy on them is much more cheaper and cost-effective than creating a Navi body and controlling it wirelessly from afar.

Because it's probably cheaper to try to negotiate than replace all the military hardware they might lose in the ensuing battle (if not actual vehicles, certainly some lives would be lost along with quite a bit of other resources). Again, very expensive to replace. Might be a bit cheaper to just send a few "cloned" bodies there and put human minds into them than actually engage the Navi.

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9. Although they were visually stunning the floating mountains were arguably the most ridiculous features in the entire movie. They were gigantic chunks of real-estate floating in the sky apparently suspended  by some form of magnetic field. We surmised this from the fact that electronic instruments on all aircraft in the vicinity are driven crazy by the area's "high flux level", presumably a high magnetic flux level. Magnetic fields are also about the only available explanation. Other possibilities such as buoyancy, wind, and electrostatic forces are even more easily ruled out. Unfortunately, the magnetic field strength needed to levitate mountains would have numerous disastrous side effects on the movie's story line, that is if the movie stuck to real physics. First such a field would rip magnetic materials out of aircraft if they flew into it, but that's just the beginning. Even if the aircraft had no magnetic materials in them, moving a conductive material of any type--magnetic or otherwise--through the field would create a large voltage difference across it. All electronic systems or controls, not just the navigation systems would be seriously disrupted. It's doubtful that an aircraft could fly in such conditions. Since both the human brain and heart are conductive, both would have voltage differences generated across them by the motion of riding in an aircraft. Any variation in direction or magnitude of the magnetic field, even subtle changes from vibrations or body movements would induce random currents in the brain with an endless list of possible results including memory loss, hallucinations, psychotic events, and seizures. Randomly induced currents in the heart could result in fibrillation and death.

Yeah, the floating mountains where kind of ridiculous. I was under the impression that they had high concentrations of unobtainium, which, in the movie's world, induces floating. I don't think that would happen in real life, but, whatever.

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10. The movie claims that Pandora's gravity is slightly lower than Earth, which helps justify the tall figure of the Navi, and their ability to jump higher. But apparently, that reduced gravity doesn't apply to humans since we don't see them gaining any increased mobility.

Lower gravity doesn't imply greater mobility for humans. Just less resistance when doing things. Maybe most of the characters' muscles have adapted to the slightly lower gravity.

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11. For some reason, while preparing to blow up the tree of life, Humans also to decides mount a land assault. The Navi meet the ground force head-on with a cavalry charge, a well known form of suicide since at least 1914. And guess what? They get butchered. Meanwhile other blue guys mounted atop flying critters swoop down on the aircraft from above. Aircraft designed for ground assaults could indeed be vulnerable from above. These aircraft used high speed counter-rotating propellers contained in large circular shaped pods. Shooting one of the Navi's spear-like arrows or dropping big rocks into the rotor blades should have been more than enough to severely damaged them and disabled the aircraft, they don't have to jump on the aircraft and throw grenades into the propellers. In addition to performing such attacks from the flying critters, in at least some places, the Navi could have hidden archers atop the floating mountains and rained arrows down on the aircraft attempting to pass between them.

Yeah, that was just kind of dumb. Although it's not really a science issue, since it can be assumed that the Navi probably aren't very good at taking down helicopters.

[KG3]

Avatar, for some reason folks in the theater got upset because I cheered when the space marines blew up the giant tree that the Navi lived in.  What can I say?  I guess I'm more of a lawn and garden guy than a tree and shrub guy.

[KG3]

  One science fiction question I have is about doors.  The use of sliding doors in spaceships seems rather ubiquitous both on TV and in movies.  I've seen them slide horizontally, vertically, diagonally, both for interior doors and air locks.   It seems to me that the only sliding doors I've ever seen in real life have been at the supermarket or in houses going out to the patio.  Does anybody know if a sliding door has ever been used in or proposed for an actual spacecraft?  I'm sure it looks cool on screen and it must make things easier for the set designers and such but could/would they work in a pressurized vessel?