## March 18th, 2018

)</lj-cut

### Seventeen Equations that Changed the World, by Ian Stewart

Second paragraph of third chapter:
During those two years, an obscure and unassuming undergraduate at Trinity College, Cambridge, completed his studies. Hoping to avoid the plague, he returned to the house of his birth, from which his mother managed a farm. His father had died shortly before he was born, and he had been brought up by his maternal grandmother. Perhaps inspired by rural peace and quiet, or lacking anything better to do with his time, the young man thought about science and mathematics. Later he wrote: 'In those days I was in the prime of my life for invention, and minded mathematics and [natural] philosophy more than at any other time since.' His researches led him to understand the importance of the inverse square law of gravity, an idea that had been hanging around ineffectually for at least 50 years. He worked out a practical method for solving problems in calculus, another concept that was in the air but had not been formulated in any generality. And he discovered that white sunlight is composed of many different colours — all the colours of the rainbow.
One of my colleagues saw me reading this, and commented that while he recognised Pythagoras a2 + b2 = c2, and also Einstein's E = mc2, the third equation on the front cover was unknown to him. It is:
 ∂2u = c2 ∂2u ∂t2 ∂x2
I guess the wave equation isn't as visible in popular culture as the other two. Be that as it may, this is a breezy popular science book, by an author well known in Pratchett fandom, looking at a succession of well known scientific equations and the concepts and consequences that have flowed from each one. He finishes with the Black-Scholes equation regarding the price of financial derivatives:
 ½ σ2S2 ∂2V +  rS ∂V + ∂V -  rV = 0 ∂S2 ∂S ∂t
However, it's not actually clear that Black-Scholes is correct, or that it is helpful (which may not be the same thing). A nice popularising book for the advanced reader; get it here.

This was my top unread book acquired in 2012; next on that list is Something Like Normal, by Trish Doller.