Physics of Societal Issues: Calculations on National Security, Environment, and Energy

If there is one characteristic that distinguishes us, as physicists, from the rest of humanity, it is the supreme confidence we have that we can make order-of-magnitude estimates. All we need is the back of an envelope or a cocktail napkin.

For example, we might consider Earth in its early days, when it was a molten sphere, and wonder what the period $τ$ would be of oscillations between oblate and prolate shapes. We immediately note that the period could only depend on Earth’s density $ρ$⁠, its radius $r$⁠, and the gravitational constant $G$⁠. Dimensional analysis then reveals the remarkable result that $τ2$ must be of order $1∕ρG$⁠, and not depend on $r$ at all. If we cannot remember the numerical value of $G$⁠, then we work in terms of the more familiar $g$⁠, the...