Michael C. LaBarbera, professor in Organismal Biology & Anatomy & Geophysical Sciences at the College of the University of Chicago, has written an unbelievably interesting piece about the science behind horror movies like The Incredible Shrinking Man, Dr. Cyclops, Fantastic Voyage and more. This is a definite must read!
In The Incredible Shrinking Man (1957), the hero is exposed to radioactive toxic waste and finds himself growing smaller and smaller. He is lost to family and friends while fending off the household cat and must make his own way in a world grown monstrously large. He forages food from crumbs and drinks from puddles of condensation. In one famous scene, he defends himself against a house spider by using an abandoned sewing needle, which he has to struggle to lift.
Stop the projector! Time for a little analysis.
When the Incredible Shrinking Man stops shrinking, he is about an inch tall, down by a factor of about 70 in linear dimensions. Thus, the surface area of his body, through which he loses heat, has decreased by a factor of 70 x 70 or about 5,000 times, but the mass of his body, which generates the heat, has decreased by 70 x 70 x 70 or 350,000 times. He’s clearly going to have a hard time maintaining his body temperature (even though his clothes are now conveniently shrinking with him) unless his metabolic rate increases drastically.
Luckily, his lung area has only decreased by 5,000-fold, so he can get the relatively larger supply of oxygen he needs, but he’s going to have to supply his body with much more fuel; like a shrew, he’ll probably have to eat his own weight daily just to stay alive. He’ll also have to give up sleeping and eat 24 hours a day or risk starving before he wakes up in the morning (unless he can learn the trick used by hummingbirds of lowering their body temperatures while they sleep).
Because of these relatively larger surface areas, he’ll be losing water at a proportionally larger rate, so he’ll have to drink a lot, too. We see him drink once in the movie–he dips his hand into a puddle and sips from his cupped palm. The image is unremarkable and natural, but unfortunately wrong for his dimensions: at his size surface tension becomes a force comparable to gravity. More likely, he’d immerse his hand in the pool and withdraw it coated with a drop of water the size of his head. When he put his lips to the drop, the surface tension would force the drop down his throat whether or not he chooses to swallow.
As for the contest with the spider, the battle is indeed biased, but not the way the movie would have you believe. Certainly the spider has a wicked set of poison fangs and some advantage because it wears its skeleton on the outside, where it can function as armor. But our hero, because of his increased metabolic rate, will be bouncing around like a mouse on amphetamines. He wouldn’t struggle to lift the sewing needle–he’d wield it like a rapier because his relative strength has increased about 70 fold. The forces that a muscle can produce are proportional to its cross-sectional area (length squared), while body mass is proportional to volume (length cubed). The ratio of an animal’s ability to generate force to its body mass scales approximately as 1/length; smaller animals are proportionally stronger. This geometric truth explains why an ant can famously life 50 times its body weight, while we can barely get the groceries up the stairs; were we the size of ants, we could lift 50 times our body weight, too. As for the Shrinking Man, pity the poor spider.
. . .”You can drop a mouse down a thousand-yard mine shaft; and, on arriving on the bottom, it gets a slight shock and walks away….A rat is killed, a man broken, a horse splashes.” Haldane was being quite literal. . .