Captain America and the Hulk's super powers are explained by science in their respective comics, but the real-life explanations aren't so far-fetched either, according to videos published by Standford University.
Stanford biologist Sebastian Alvarado explores the origins of each character by using real-life examples to speculate on how their powers work. In the case of Captain America, included above, Alvarado discusses photo-sensitive carriers of drugs that exist in research today. The films see Cap getting pumped with a special serum and zapped in a chamber. Alvarado draws comparisons to drugs in development that are shot with UV light, which causes them to release and activate whatever they happen to be carrying.
As for the big, green, rage monster known as the Hulk, the answer is a little more tricky. In the comics, the Hulk's transformation is the cause of gamma radiation. Alvarado takes the time to talk about how this would affect Bruce Banner's transformation, why he's green and how he changes from one form to another.
"The only molecular mechanics that I happen to know about that can turn on a gene and turn off a gene is epigenetic modification," Alvarado said. "Now imagine all the genes that correspond to being a normal, mild-mannered scientist like Bruce Banner, and all the genes involved with being rage Hulk, and imagine each of them having a light switch. An epigenetic modification could transition all of the switches that turn Bruce Banner into Bruce Banner and the Hulk into the Hulk. And the nice thing about all of this is that they're very reversible."
There is no answer, however, for how the Hulk's pants stay on. Check out the video below.