Season 17, Episode 54: Galileo Proved That King Kong Would Struggle to Stand

Hey StarTalkians! Episode 54 of season 17 was a “Thing You Thought You Knew” edition, where Neil gave Chuck a crash course in sidereal days, impact craters and “the size of life.”

Why Craters Are Round, Size of Life, The Real Length of Day – TYTYK -…

(From 32:20)

The discussion on the scaling of strength and mass for animals hearkens back Galileo – and likely earlier – and leads to one unusual conclusion. Galileo proved that King Kong wouldn’t work about 300 years before the iconic monster appeared on-screen.

From Galileo to On Being the Right Size

Galileo probably came up with his idea because of a mistake he made when giving a lecture about Dante’s Inferno and the huge structure it implies. His mistake is a pretty intuitive one: if you take a structure and scale everything up equally, you’d naively expect it to still hold up just fine.

But Galileo realized there’s a problem. Imagine a chandelier hanging from a small rope that can just about hold it up. If you double every dimension of the chandelier, the volume – and mass – increases by 2 × 2 × 2 = 8 times. But the rope’s strength only comes from its cross-sectional area, i.e. the number of strands it contains. If you double every dimension of the rope, the length is useless and the strength only increases by 2 × 2 = 4 times.

The chandelier got heavier quicker than the rope got stronger, and it would come crashing down.

A famous essay by polymath J. B. S. Haldane addresses “being the right size,” and wraps Galileo’s conclusions up in a quirky-yet-informative package. He discusses some fictional giants that were ten times a human’s size in each dimension. This means 1,000 times the mass. But their legs – like the rope above – only get 100 times stronger. This means each leg would need to be working 10 times harder in a proportionally-scaled giant.  

Why King Kong is (Probably) Impossible

King Kong’s size varies in different movies, but 50 ft is an oft-used figure. This makes Kong 8.33 times bigger than a normal gorilla. This means his legs would be about 69 times stronger, but he’d weigh about 578 times more. Based on a 150 kg gorilla, Kong would weigh almost 87,000 kg, in the range of the largest sauropod dinosaurs, which had proportionally much wider legs. Even if he could stand, he certainly wouldn’t be climbing any skyscrapers.