The Height of a Giraffe

TL;DR

This paper revises the estimated height of the tallest running organism on a habitable planet using a modified theoretical approach, resulting in a significantly larger estimate of about 3.6 meters.

Contribution

It introduces a new theoretical estimate of organism height based on physical constants, improving upon previous models by Press and Lightman.

Findings

Estimated height of tallest organism: ~3.6 meters

Number of atoms in the organism: approximately 3 x 10^32

Revised model yields larger height estimate than previous work

Abstract

A minor modification of the arguments of Press and Lightman leads to an estimate of the height of the tallest running, breathing organism on a habitable planet as the Bohr radius multiplied by the three-tenths power of the ratio of the electrical to gravitational forces between two protons (rather than the one-quarter power that Press got for the largest animal that would not break in falling over, after making an assumption of unreasonable brittleness). My new estimate gives a height of about 3.6 meters rather than Press's original estimate of about 2.6 cm. It also implies that the number of atoms in the tallest runner is very roughly of the order of the nine-tenths power of the ratio of the electrical to gravitational forces between two protons, which is about 3 x 10^32.