TERM PAPER: Science Fact or Cinematic Fiction?

Density

Movies cannot seem to grasp the concept of density. Gold in particular is commonly shown as much lighter than it is. It is shiny and valuable, and is the number one material choice for old civilizations making weird things to leave behind, but the scene where the hero casually picks it up and tosses it around is a mistake. One gold brick weighs almost 30 pounds. In movies, the issue of the density of gold in rarely addressed, and people regularly carry very large amounts of gold with little to no inconveniences. 

In Raiders of the Lost Arc, Indiana Jones has to steel a golden idol from a temple. He carefully walks up to it, eyeballs the weight, and then lightens his bag of sand. He then attempts to make an equal weight replacement, hoping to fool the weight pad. The idol weighed more than sand, but Indy thinks this is a good comparison and when he picks it up it seems quite light. Judging by his hand and guessing small, the idol is about 19 by 9 by 8 centimeter. That would be 1539 cubic cm. 23.5 cubic cm gold is 1 lb. Therefor, if the idol were solid gold it would be 65 lb. He casually tosses it to his friend in the next scene, and neither of them react to the idol as if it were any significant weight.

Another option is if it was not 24 k gold, which it probably wasn’t. Other metals in the mixture are less dense, and could make it lighter. 9K gold is on the very low end of the scale. It costs $14.26 for one gram as of the writing of this. In contrast, one gram of 24 K gold is $38.03. The value of Indy's prize would become much less impressive. 11 grams per cubic cm is about the specific gravity of 9 K gold. Even assuming all that, the idol would still weigh would still be 16,929 grams, or 37 lb gold. A significant price, but also still a significant weight.

The most likely explanation is that the idol is either hollow or gold plated. I've heard that the idol is supposed to be 3 lbs. Going off of that, we can work backwards to see how that could be possible. For comparison, 3 lb of solid 24 k gold would be about 70 cubic cm about a 4 by 4 cube. If the idol was supposedly 3 lbs, or 1360.78 grams, the specific gravity would be 0.188. Considering how thin the layer of could could me, I will not factor that in, and instead look for a material that has a specific gravity close to that. A good match is balsa wood, a very soft wood. The specific gravity of balsa wood is about 0.13. Going off of these measurements, it is probable that the idol is merely a gold plated wood carving.

While there was a probable explanation in Raiders of the Lost Arc, In Night at Museum We see the formation of the solid gold tablet. The golden tablet of the Pharaoh Akhmenrah is even larger than the idol. However, not only do they carry and hold it out no problem, but even a kid runs around with it without hindrance. It looks to be about 30 by 20 by 3 cm, or 1,800 cubic cm. A solid gold tablet of this size would weigh about 76.5 lb. There is no way they were all able to hold that thing up Simba style.

There are other ways Hollywood has issues with density. Another common one is lava. Lava has a density of 3100 kg/m3, in addition to being quite viscous. In Lord of the Rings the finale has gollum sink into the lava, however unless we assume his bony is much more dense than an average human, this is unlikely. The average human density is about 1010 kg/ m3. Lava is often shown as red, glowing water, but water has a density of 1000 kg/m3. We can float in water, with some effort, and we would absolutely float in a substance 3 times as dense. Another way to check this is too look at the specific gravity of lava, which is 3.1. Since this is just the density of lava over the density of water, we know that that means is is 3 times as dense. Although less theatrical, Sam would probably have gotten a kick watching gollum writhe in agony as he burned up on the top of the lava.

Lastly, Independence Day has a particularity horrible physics fail. Where the alien ships are approaching, we hear this:

COMMANDING OFFICER

               “We estimate it has a diameter of
                over five hundred and fifty
                kilometers and a mass roughly one

fourth the size of our moon.”

This sounds very impressive and intimidating. Those are both huge numbers. One thing we fail to realize, is the sheer scale of planetary bodies. The moon may be smaller than the earth, but it is still enormous. The ship is only 15 miles in diameter, and mostly hollow. It is even flattened, not a true sphere. The moon has a diameter of 3500 km, over six times the size of the ship. Its mass is 8 x 10¹⁹ tons. When taking into account the diameter, we can calculate that the specific gravity would be 3.34 (which matches with the previous topic of lava being 3, since lava is essentially heated rock). A fourth the mass of the moon would be 2 x 10¹⁹ tons. Trying to fit that in 550 km would result in a density of (2 x 10¹⁹) /50 km, or 1.81436947999999992e+26 grams/5e+6 cm, which is 212 g/cubic cm. ( I used a separate source to find the final density, since the numbers got so big.) In contrast, the earth's density is about 5.5 g/cubic cm, and we hold our own atmosphere. The densest metal know to man is Osmium, which is only 22.59 g/ cubic cm. Factoring in that the ship was mostly hallow, it would be even more dense than these calculations,. If we believe the movie, the aliens must have built Some crazy super dense substance, possibly to be a shield against equally intense power blasts from the enemy. I shudder to think how strong their weapons must be.

 Hollywood can be lazy sometimes, and phone in the science. Thankfully, it almost always results in some funny realizations when you think it out. Like crazy intense alien arms races, and Indianna Jones risking his life for a wooden statue.