Two equations, each sweet and short, run along the arms of Adam Simpson, who works at the US National Centre for Computational Sciences. One appeared in Newton’s Principia Mathematica in 1687. In three letters, it describes how any object moves through the universe, driven by a push, a fall, a spark. The other appeared 218 years later, in a paper by a young patent clerk named Albert Einstein. An object did not just have energy from its movement, Einstein declared, but had energy hidden away in its own mass. 'I got the tattoos because it’s amazing to me how just a few characters can impact the world so much, and I want others to know that,' Simpson saysPhotograph: Courtesy of Carl Zimmer