I am impressed with the science in “The Avengers.”
This is not something I ever thought I’d say, considering that in “Iron Man 2″ Robert Downey Jr. BUILDS A PARTICLE ACCELERATOR IN HIS LIVING ROOM. And then manages to synthesize an entirely new element. Which is stable for longer than nanoseconds. And non-radioactive. And manages to magically cure the “palladium poisoning” that was turning his veins into a game of Tron.
And it’s not to say I go see comic book movies for realism. There’s a willing suspension of disbelief that has to be associated with Scarlett Johansson’s form-fitting yet functional leather jumpsuit. But it’s nice to see the writers cared enough to try to get the science (vaguely) right.
Case in point: The scene where Downey Jr.’s genius/billionaire/playboy/engineer Tony Stark and Mark Ruffalo’s genius/derelict/rage monster/physicist Bruce Banner geek out about using thermonuclear fusion to open a wormhole while Captain America thinks about monkeys. The conversation goes something like this:
Banner: Dr. Selvig would have to heat the cube to 120 million Kelvin just to break through the Coulomb barrier.
Stark: Unless he’s figured out how to stabilize the quantum tunneling effect.
Banner: Well, if he could do that he could achieve heavy ion fusion at any reactor on the planet.
You hear that? SCIENCE! And while when the banter gets flying this just sounds like nerdy buzzwords that Joss Whedon remembered hearing in some TED talk once and decided to pepper his script with, he’s closer to the truth than you might think. Let’s break it down.
Fusion. Nuclear fusion is process of combining two light elements into one heavier one. Generally, the two light atoms together have more mass than the heavier atom they combine to form, and the excess mass is released as energy (E, after all, equals mc2). How much energy? Well, the only really successful manmade fusion device to date are bombs — the first of which, codenamed Ivy Mike, erupted in a fireball more than three miles in diameter and vaporized an entire island. So yeah, why not, fusion could create enough energy to make a wormhole.
The Coulomb barrier. It takes a lot of energy to get a fusion reaction started, though — the only way a fusion bomb works is by setting off a traditional nuclear fission bomb (think Hiroshima) and using it to start the fusion process. A large part of the reason for this is, in fact, what’s called the Coulomb barrier. Atomic nuclei can be thought of as a lump of positively charged protons and neutral neutrons — and if you remember your high school physics, two positively charged things don’t like to be brought close to each other (maybe a more intuitive example is two magnetic north poles; this is analogous enough). The strength of the repulsive force between two charges is known as Coulomb’s law, and it states:
Where F is the resultant force, q is the strength of each charge, k is Coulomb’s constant, and r is the distance between the center of the two nuclei. This is an example of what we call an “inverse-square” law in physics, because it is inversely proportional to the square of the distance between two objects — and they crop up everywhere (gravity, power radiation, sound, etc.). The key characteristic of an inverse-square law is that the left side of the equals sign rises dramatically as the distance decreases, e.g. it’s really hard to push together two atoms because eventually the Coulomb force becomes massive. As you might have guessed, atoms need to be really, really close for fusion to occur.
So how do we add energy to the atoms? Well, one way would be to heat them up. Temperature (described here, as any good physicist should, in Kelvin) is just a measure of how fast, on average, the atoms in a gas/liquid/solid are moving. And 120 million Kelvin is hot. Like, really hot. Like, the corona of the sun is just one million Kelvin. For hydrogen gas, 120 million Kelvin clocks the hydrogen atoms at almost four million miles per hour. So you can see why HULK SKEPTICAL OF PUNY HUMAN’S ABILITY TO IMPART MASSIVE QUANTITIES OF ENERGY TO SYSTEM.
Quantum tunneling. But, once again, quantum mechanics to the rescue. One of the coolest (read: weirdest) aspects of quantum mechanics, tunneling is the tendency for particles to overcome potential barriers they classically could never climb — essentially, a spontaneous decrease in the energy required to accomplish something. Here’s a useful analogy: imagine a ball sitting in a valley. If you want to roll the ball into the next valley, you have to kick it with enough energy to get it up and over the hill between the two.
What tunneling is saying is that sometimes, when you kick this ball with only enough energy to make it halfway, or a third of the way, or a quarter of the way up the hill, it will still show up on the other side. Effectively, it has “tunneled” through the potential energy barrier (a barrier, in this analogy, courtesy of gravity). Weird, right?
And what Stark is saying is that, if you could ensure tunneling at high probabilities, the overall energy you’d need to initiate the fusion process — the temperature you’d need — drops substantially. A little hand-wavey, but that’s pretty solid science.
Not that Whedon has figured how to initiate fusion or anything… but not bad for a movie where a flying Norse god shoots lightning bolts out of a hammer at invading extradimensional aliens riding hover jet skis through Manhattan, huh?
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EDIT 5/16/12: This is a relevant find from “Iron Man 2.” While I applaud the guy in charge of props for this assiduous attention to detail (seriously impressive), I stand by my statement that the science in the movie still blows. And now they’ve gone and marginalized physicist Johannes Stark by attributing his Nobel-prize winning discovery to a fictional scientist.
Although the real Stark was kind of a dick (“dick” here is a polite euphemism for “asshat Nazi doucherocket”), so nice job prop department?