TITLE: Anecdotes about famous mathematicians or physicists
QUESTION [96 upvotes]: I'm not sure whether this question suits this website, however, I don't know where else I could ask it. It is no mathematical problem or something similar, still I hope it won't be closed.
A few weeks ago, our assistant professor in physics told us a story about Maxwell when we came to speak about Maxwell's equations. He said rumour has it that once in an exam, Maxwell faced a differential equation or integral - at that time thought unsolvable - and solved it.
I wonder whether there are more famous rumours or anecdotes about mathematicians or physicists (and which of them are true and which not). I believe everyone knows the story of how Gauss computed
$$\sum_{n=1}^{100} n$$
an exercise his teacher gave to his class to keep it busy. Or a more famous example: Everyone knows how Newton discovered gravity (is that one actually true?). Or how Archimedes found Archimedes' principle. So, to put it into a single line:
Do you know any other noteworthy anecdotes about famous mathematicians or physicists?
EDIT: In case you provide an answer, please also state whether the anecdote is true or not, if possible. Thanks a lot for the hitherto existing answers!

REPLY [9 votes]: I have always enjoyed this anecdote concerning an encounter between Harvey Friedman, whose finite form the Kruskal's Tree Theorem gives rise to the Tree sequence of undescribably large numbers, and the ultrafinitist Russian mathematician, Alexander Yessenin-Volpin. For Yessenin-Volpin, even numbers such as $2^{100}$ are out the reach of the human mind, and therefore of doubtful validity, let alone monsters such as Friedman's.
The question is : If $2$ is accepted, but $2^{100}$ is not, where does one draw the line?  Friedman tells the story of when the two men, whose ideologies could hardly be more different, met :

I raised this objection with the (extreme) untrafinitist Yessenin-Volpin during a lecture of his.  He asked me to be more specific.  I then proceeded to ask to start with $2^1$ and asked him whether this is "real" or something to that effect.  He virtually immediately said yes.  Then I asked about $2^2$, and again he said yes, but with a perceptible delay.  Then $2^3$, and yes, but with more delay.  This continued a couple more times, till it was obvious how he was handling this objection.  Sure, he was prepared to always answer yes, but he was going to take $2^{100}$ times as long to answer yes to $2^{100}$ than he would to answer $2^1$.  There is no way I could get very far with this.


Another concerns Paul Erdos.  In his late years he suffered from terrible vision problems which made it extremely difficult for him to read.  Colleagues arranged for him to have a corrective procedure at the local hospital.  He was taken to meet the surgeon, who began to explain the procedure to Erdos, however Erdos declared he was not interested in details of the operation and simply wished to know "will I be able to read?".  "Yes" was the surgeon's reply, noting that correcting his vision was the point of the procedure.
Some weeks later, on the day the procedure was scheduled, Erdos arrive at the hospital with his colleagues. After going through the necessary preparations, Erdos was wheeled into the operating theatre to the waiting surgical team.  As they began to dim the lights to start the procedure, Erdos sat up and demanded to know what was going on.  "We are dimming the lights to begin the procedure", was the reply.  "But you said I could read!" was Erdos' innocent response.