Man’s size in terms of fundamental constants

Abstract

Why are we the size we are, instead of some very different size? Simple physical scaling laws and three ’’requirements’’ dictate that our size be of order (h/2/mee2)(e2/Gmp 2)1/4. They also ’’predict’’ the mass and radius of the Earth. The three requirements are: (i) We are made of complicated molecules; (ii) we breathe an evolved planetary atmosphere; (iii) we are about as big as we can be without breaking.