Enrico Fermi was one of the greatest physicists of all time. Take a look at the history of any branch of physics, and he was there, helping things along. Take a look at his most famous portrait and he made a boneheaded mistake. Maybe on purpose.
You know that thing called quantum theory? Enrico Fermi helped develop that. You know those things called the nuclear reactor and the atom bomb? Enrico Fermi helped develop those. He gave the world insights into radioactivity, gas laws, and even that old chestnut, the conservation of energy. How did he do this? By being very smart, and very precise. His colleagues called him "The Pope," because he was less likely than any of them to make a mistake.
Guess what he did in the most famous photo ever taken of him?
Fermi's most famous photo shows him in front of a blackboard full of equations. He taught at the University of Chicago after fleeing Italy in the 1930s, and here he is posed to look like he's giving a lecture. On the blackboard directly above his head is the equation for the fine structure constant, a dimensionless value meant to signify the strength of an electromagnetic interaction. Fermi was a master at physics, and knew the subject backwards and forwards, but the equation is wrong. Fermi has transposed the ħ and the e. Fermi's greatest enemy could hardly make hay out of such an innocuous error. But the mistake is just a bit regrettable, because the picture has become famous — it ended up on the US stamp commemorating the hundredth anniversary of Fermi's birth. Italy, sentimental over their homegrown genius, also issued a stamp honoring Fermi. Guess which picture they used.
In recent years, a little controversy has kicked up over the famous photo. Technically, this isn't the photo used on the stamp. There are several pictures of Fermi, clearly in the same place wearing the same clothes. This was part of an extended photo session, and Fermi would probably have set up the board himself. While serious about his work, he had a sense of humor, and some say that he deliberately wrote the equation wrong to have a little giggle with his friends. If so, there's no record of it. Was one of the great geniuses of physics pranking us?
Mistake Image: Smithsonian Institution