Sunday, May 6, 2012

On the physics of Avengers

Obviously, this is going to be a spoiler-ridden analysis of the physics of the film. I can't imagine how I could cover this without spoilers, so you have been warned...


Hugo Weaving in Captain America
holding the tesseract.
The Avengers is a superhero movie, and as such, there's a lot of physics that we throw out the window in the name of the genre. The Hulk becomes massive, absorbing that mass from ... where? Is that an endothermic or exothermic process? We don't worry about it, because it's just a convention of the genre.

However, there is a long tradition of nit-picking aspects of the story in comics when the author makes a point of trying to use the science as the justification for plot elements. So, to move on to that...


Dark energy is a consistent theme in the movie. At the start, we see that the tesseract (or Cosmic Cube as it's called in the comics) being experimented on in a remote complex whose sign indicates that it is intended for the study of "dark energy". At first, I assumed that this had nothing to do with the cube, since the label slapped on a secret research facility run by S.H.I.E.L.D. is almost certainly not going to be helpful. However, later in the film, Loki asks Thor something along the lines of, "how much dark energy did father have to use to get you here?"

I'm not a big fan of assuming that Joss Whedon is engaging in casual coincidence; it usually ends up with my being quite wrong. In this case, I think it's safe to say that those two mentions of dark energy were not a mistake.

So, what is dark energy? The simplest answer is: there's no such thing. "Dark energy" isn't a real form of energy. Instead, it's a placeholder term which astrophysicists use for whatever is causing strange errors in our measurements of distant galaxies. Dark matter, a similar, but much more specific concept, relates to measurements of galaxies which show that they have more mass than we can see. When we talk about dark matter, we can be pretty precise because we can measure roughly where the excess of matter lies based on its interactions with surrounding matter. Dark energy, on the other hand, arises as a concept from the fact that we observe galaxies moving uniformly apart from each other at a rate which is increasing, not slowing as we would expect. Dozens of theories have been proposed to explain these measurements, and all of those theories are loosely referred to as, "dark energy." It's important to understand that dark energy could turn out to be a simple misunderstanding of the basic laws of physics, rather than an actual force. However, if it is a force, then it is a force so powerful that it dwarfs the measured energy of the rest of the universe! Obviously, this is a rich source for science fiction and fantasy story telling.

So, back to The Avengers. Loki hints that dark energy is a power source that Asgard can draw on. So we can assume that in The Avengers' universe, dark energy is a real force and not just a miscalculation or miscalibration in our understanding of the basic rules of the universe. We can also assume that its vast potential can be tapped by the beings of Asgard. If we assume that, then it makes sense to assume that the  tesseract is also utilizing this same power source and that the reason for the dark energy lab's selection was precisely that they had the people available to properly understand the fundamentals of the power source the cube was drawing on.

There's still some odd questions. Why does Loki call it "dark energy"? That's our name, and it's just a placeholder at that. Wouldn't the Asgardians have their own name? Also, if dark energy is a placeholder term for something that we've never been able to identify, how would we know that the power driving the cube had anything to do with it?

The Hulk from The Avengers.
There are lots of problems with the simple Newtonian physics of the movie, of course. Lots of them are the usual sorts of superhero problems. For example, The Hulk stops a very large half ship / half monster by punching it. Of course, physics being what it is, The Hulk should have been ripped away from the pavement he was standing on, and thrown back a few blocks by the impact. There  are several times that Iron Man should have been pulped inside of his suit due to the high-speed impacts that it took.

One thing I did like was the scene where Thor strikes Captain America's shield with his hammer. The Shield, as you may know if you've read the comics, is made of vibranium, a fictional metal that can absorb kinetic energy and convert it to sound waves. This is how bullets bounce of the shield. However, when Thor hits the shield, he unwittingly destroys all of the surrounding trees by blasting them with sound from the shield: his own strength, converted to sound. Nice effect.

Update: I thought of something cool this morning and Jeff pointed out a really neat item as well:

We actually see a nuke go off in space and it's not one of those cheesy plasma-ring effects that was (as far as I know) first used in Star Trek VI, but everyone will remember from the revamped FX in Star Wars IV. Instead, it's an orange ball of plasma which is entirely reasonable. The only problem I have with that is that it should probably have faded around the edges very rapidly. In an atmosphere the "fireball" is mostly super-heated air that has turned to plasma. In space, the vaporized material of the bomb itself and whatever it was blowing up will serve the same purpose, but around the fringes of the fireball, where there was no initial material, you'll only have the plasma that was spread there by the bomb itself, and that's rapidly dissipating in vacuum... Still, the effect was excellent and much better than I expect of a superhero movie.

What Jeff pointed out was that the ships that are coming in through the portal are initially buffeted by contact with the atmosphere. A nice touch that I didn't notice. Also, the point is made that one of their weaknesses is the fact that they don't bank terribly well. Of course, for craft that are mostly designed for space and only partially for atmosphere, this makes perfect sense. Again a detail I don't expect in a superhero movie...