The Boston Globe has a short profile of James Kakalios, a physicist at the University of Minnesota, who has examined the physics of comic books:

Surprisingly enough, according to Kakalios, comic books get their physics right more often than you'd think. In a telephone interview from his home in Edina, Minn., he fielded one skeptical query after another. For example, could the Flash really pluck bullets out of the air? ''Granting the 'miracle exception' of the Flash's super-speed in the first place, the answer is yes," said Kakalios. ''All he has to do is match his speed to that of a bullet, so that the relative speed between him and the bullet is zero. That's consistent with Newton's laws of motion-we do the same every time we pour a cup of coffee on an airplane traveling 600 miles an hour."

Fair enough. But isn't Thor's trick of flinging himself through the air by throwing his hammer at high speed then grabbing onto it again, a violation of the principle of conservation of momentum? ''I thought so at first, but in hallway conversations with my colleagues we realized that when a track athlete loses his footing during a hammer throw, he's pulled behind the hammer," said Kakalios. ''So when Thor twirls Mjolnir, his mighty hammer, he's coupling his body's center of mass to the Earth's by planting his feet firmly-and when he's ready to fly, all he has to do is jump a little to break his connection with the Earth."

Now what we really need is a biological analysis of the Teenage Mutant Ninja Turtles. Could two different species be genetically combined using only a glowing green ooze poured from on high? I say no, but then, science has never failed to surprise...