Quantum gravity is a castle in the air

When you spend some time digging into the history of physics, you find yourself uncovering the foundations of physics, and then you come to appreciate a few things. You come to appreciate how gravity works, and why an electron falls down. It isn’t because gravitons are flying back and forth: Graviton image by Julie Peasley, see http://www.particlezoo.net/ You also come to appreciate that light interacts with light to form electrons and positrons in gamma-gamma pair production. You come to appreciate that the electron is not a…