Superman's ability to fly is even more problematic.
"You need a source of thrust and lift," Dennin said. "There's no way around that."
"In the early [comic books] he could jump and be an unguided missile," the University of Minnesota's Kakalios said.
"But he's [now] able to change direction at will, so he's gained some ability over gravity that would baffle scientists."
Not that this stops the Man of Tomorrow's fans from speculating.
Hal Sparks, an actor and comic book fan, holds forth in The Science of Superman, a National Geographic Channel television special premiering in the U.S. on Thursday, June 29, at 9 p.m. ET/PT. (National Geographic News is part of the National Geographic Society, which is part owner of the National Geographic Channel.)
"This is my theory: [His] flying is based on the magnetic content of his body and the Earth's polarity, so he can push himself away and pull himself toward it," Sparks said.
Science writer Mark Wolverton, another guest on the show, suggests that Superman might be able to generate hypothetical subatomic particles called gravitons.
"If Superman has a way of generating gravitons I would say he would be flying by essentially riding the waves of gravity that are in his immediate environment."
Similarly, magnetic fields have been used to levitate trains. And in the laboratory, frogs have been elevated when a very strong magnetic field is applied to the water in their bodies. (Watch video of a levitating frog.)
But it's hard to see how Superman could draw enough power from the Earth's magnetic field.
As for gravitons, Minnesota's Kakalios points out that they're particles that haven't yet been observed and that repulsion would presumably require the even-more-theoretical antigravitons.
"If you're going to make up particles, you might as well just make up that he flies," Kakalios said.
(Related: "The Science of Superheroes: Beyond The Incredibles" [November 12, 2004].)
Could Superman's other superpowers be easier to explain?
"Maybe he 'superheals,'" Kakalios suggests. Perhaps "it looks like he's invulnerable because no matter what harmed him, his cells instantly regenerate"a sort of supercharged version of the signature power of the X-men comic book and movie character Wolverine.
Strictly speaking, this power would require Superman's eyes to somehow emit x-rays, which would penetrate what he's looking at and then bounce back at him.
But, the University of California's Dennin says, x-rays don't bounce. Even if they did, that doesn't explain how his vision allows him to "peel away" obstructing layers one at a time, like a medical CT scanner.
For this reason, Frank Frisch, a biology professor from Chapman University, will present an entirely new theory in The Science of Superman: Maybe Superman doesn't really have x-ray vision.
Instead, he may use sound waves for a sonarlike mapping power that doesn't need x-raysmuch as doctors use sound to create sonograms of unborn babies.
To melt things with laserlike beams from his eyes, Superman would need "a very large power source," Dennin sayswhich brings us to
Heat vision isn't the only superskill that requires a lot of power. One explanation is that Superman converts light from our yellow sunwhich is presumably more intense than the red sun of Kryptoninto energy that he then stores like a humanoid battery.
Unfortunately, our sunlight isn't really all that different from the light of other stars.
Todd Barber, a propulsion engineer for NASA's Jet Propulsion Laboratory in Pasadena, California, has calculated the amount of energy needed for some of Superman's feats.
It turns out that, even assuming he goes into space, where the sunlight is more intense, he'd have to spend a lot of time recharging his batteries between superdeeds.
The Man of Steel's superacute hearing would seem to be one of his more mundane talents. But it's actually rather inexplicable, says Minnesota's Kakalios. Not because it's so acute, but because there have been instances where he's heard the crack of a gun and flown all the way across his home city of Metropolis in time to stop the speeding bullet.
The problem is thatthe speed of sound being what it isby the time the noise got to him, the bullet would have long since found its mark.
Perhaps a more believable talent is the ability to blow very, very hardhard enough to push away thunderstorms or freeze nearby objects.
Assuming his superlungs can drastically compress air, the freezing effect might actually work, Barber says. That's because gas cools as it expandsan effect that Superman facilitates by pursing his lips so that the air blasts out like rocket exhaust through a nozzle.
Survival in Space
The same superbreath may be what allows him to survive in space without a space suit. To blow so hard, he would have to be able to inhale large quantities of air. And if he can do that, he may be able to hold his breath and "dive" into space for long periods of time.
Bottom line: For his powers to work, Superman would require more than one "miracle exemption." But after 68 years, perhaps he's earned them.
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