Everyone can guess the worst way to load passengers on to a plane is to do it front to back. People would have to wait at every row or squeeze awkwardly past. It would stand to reason, then, that the way airlines usually do it—back to front—would be the best way. But according to Fermilab physicist Jason Steffen, that's not the case. As it turns out, it's far from the best: it's the second worst.