Spider-Math and Bat-Physics: Science in a Superhero World
Toward the end of “The Amazing Spider-Man”, Peter Parker saves a small child trapped in a car as the car is tossed from New York City’s Williamsburg Bridge by the movie’s villain, the Lizard. He does this by shooting a web of spider silk from a gadget on his wrist, catching the car mid-air and eventually, using the spider silk to reel the child back to safety.
To work, this technique relies on the strength of spider silk. And in mass quantities, spider silk is extraordinarily strong, stretchier than nylon and, pound for pound, stronger than steel cable. In other words, produced in mass quantities, it could, plausibly, dangle a car and child from a New York City bridge. That’s according to Jim Kakalios, physics professor at the University of Minnesota and a science consultant for the film, which was released July 2012.
It’s the elasticity of spider silk that makes this scene even more plausible, said Skip Garibaldi, professor of mathematics at Emory University. Elasticity means there’s less “jerk” on the cars and the passengers trapped inside when they come to a stop. Of course, this all depends on Spider-Man bringing enough silk for the job.
“He needs a backpack of silk to do it,” Garibaldi said.
When it comes to the science behind the fantasy, some superhero scenes fall shorter than others. Batman’s cape, for example, lacks the wingspan to set the Dark Knight gently on the ground after leaping off a Gotham skyscraper. His hang glider cape would in reality shatter his knees, Kakalios said.
Sure, comic book superheroes have powers that transcend science. That’s part of the fantasy. But Kakalios is committed to bringing science fiction closer to science fact. He volunteers through a program run by the National Academy of Sciences called the Science and Entertainment Exchange. The program helps match filmmakers with scientists on an as-needed basis. In July 2012, the group celebrated its 500th consult.
Some consultants are tapped for quick fact checks; others are part of the creative process from the beginning, like Kakalios and Spider-Man. Kakalios, for example, wrote the “Decay Rate Algorithm” equation for the filmmakers, who needed an identifiable formula to explain the research of scientist-turned-giant lizard Dr. Connors in the movie.
Kakalios has also turned his love of comic books into an introductory physics course called the Physics of Superheroes and has written two books on the subject. Watch Hari Sreenivasan’s interview with him in the video above.
In the 1960’s, writers began weaving more science into the story lines of comic books, after comics were accused of being too violent and lacking educational value.
When the Flash from the 1960’s comic of the same name catches a bullet, he is operating under Einstein’s Special Theory of Relativity, for example. Namely, by running the same speed in the same direction as the bullet, the flying bullet appears stationary to him, and he is thus able to grab it.
Superheroes get their facts wrong more often than right, Kakalios said. In “The Amazing Spider-Man” No. 9, Spider-Man calculates his centripetal forces correctly when swinging from building to building. But in the same comic, his understanding of physics lapses when he throws metal chairs into the air to “attract” the lightning produced by the villain of that comic, Electro. While metal is a good conductor, that doesn’t mean it attracts electricity.
“That’s as ridiculous as saying that water is attracted to drains,” Kakalios said.
Here are some examples from Kakalios’ book of other superheroes who got their science right, or close to it:
How the Invisible Woman Disappears
After a brush with cosmic rays, The Fantastic Four’s Sue Storm develops the ability to turn transparent at will. Molecules in most of our cells absorb and re-emit light in the visible end of the spectrum. But there are cells in our bodies that are transparent to visible light, such as the lens of our eyes. Sunlight also contains light at shorter wavelengths, like ultra violet rays, that our eyes can’t see. So the idea is that if Storm can change her cells so they absorb and reflect ultra-violet light while letting visible light pass through them, she would appear invisible to the naked eye, while she would still be able to see in the ultraviolet region of the spectrum.
Superman Knows His Electrical Currents
Superman didn’t always have to fly or use his superhuman strength to intimidate his enemies. In his very first appearance in “Action Comics” No. 1, Superman attempts to scare information out of a crooked lobbyist by slinging the man over his shoulder and running across a telephone line and hopping over the grounded poles. The lobbyist protests that Superman will electrocute them both, but Superman knows that as long as he avoids making a connection to the ground, that they are in no more danger than the birds resting on the same wire. In order for an electrical current to move through the wires it needs to flow to a place with lower voltage — like the ground. If Superman was touching the wire and the pole simultaneously, he and the lobbyist would complete the electrical circuit and all that current would certainly kill the lobbyist, if not the Man of Steel as well.
Catching Bullets is Easy if You’re the Flash
The Flash can catch a speeding bullet by moving at the bullet’s speed, Kakalios said. By increasing his velocity to match that of the oncoming bullet, it’s reasonable that he could snatch it out of the air. It’s the same reason you can pick up a ginger ale that’s moving at 500 miles per hour — when it’s on an airplane. The relative velocity between the airline passenger and the beverage is zero, making pouring easy.
The Conservation of Momentum Kills Spider-Man’s Girlfriend
In “The Amazing Spider-Man” No. 121, the Green Goblin knocks Spider-Man’s girlfriend Gwen Stacy off of a bridge. Spider-Man catches her mid-fall with his web, but when he pulls her to safety she is dead. Kakalios says her death was the result of the conservation of momentum. When she is thrown from the bridge, her velocity increases due to gravity. By the time Spider-Man catches her 300 feet down, Kakalios estimates she is traveling at 95 miles per hour. That velocity goes from 95 miles per hour to 0 in the short time the webbing catches Stacy, creating the same results as a high-speed car crash — too much force is needed to bring the 110-pound girl to a stop. If Spider-Man had slowed her deceleration gradually, the way a car’s airbag slows you down over several milliseconds during a crash, she might have survived.