Cubum autem in duos cubos, aut quadratoquadratum in duos quadratoquadratos, et generaliter nullam in infinitum ultra quadratum potestatem in duos eiusdem nominis fas est dividere cuius rei demonstrationem mirabilem sane detexi. Hanc marginis exiguitas non caperet.
("It is impossible for a cube to be the sum of two cubes, a fourth power to be the sum of two fourth powers, or in general for any number that is a power greater than the second to be the sum of two like powers. I have discovered a truly marvelous demonstration of this proposition that this margin is too narrow to contain.")
^{note }In Layman's Terms, take this equation: x^n plus y^n equals z^n. The Last Theorem says that if n is a number above 2, then x, y, and z can't all be whole numbers (2, 3, 4, etc.).
— Pierre de Fermat
Fermat, a prominent 17th-century amateur mathematician, wrote the above note in his copy of a number theory textbook. By the time he died, the textbook was full of such teasing notes; his son published a new annotated edition of the book containing all of these notes in their proper places.
For nearly all the notes, it didn't take long for other mathematicians to figure out what Fermat was talking about. The quoted one was the exception. As such, it became known as Fermat's last theorem—"last" not in the sense that it was the last mathematics he ever did (he almost certainly wrote the note fairly early in his life) but in the sense that it was the last claim he made to remain unproven. It took until nearly 350 years after Fermat's death until mathematicians Andrew Wiles and Richard Taylor released a proof in 1994.
In fact, it's almost certain that Fermat himself didn't really have a proof. Wiles' proof certainly would have been inaccessible to Fermat; it relies on mathematical concepts which weren't developed until after the Second World War. Romantically, one might imagine that Fermat had come up with some simple proof that has since eluded everyone else. In reality it's far more likely that he was mistaken, especially since later in life he went to the effort of working out a proof for a certain special case (that no fourth power can be written as the sum of two fourth powers)
^{note }Though he could still have had a general proof for all odd numbers or odd primes, since proving the case for all odd numbers/primes and 4 would prove Fermat's last theorem for all cases. In fact, 19th-century mathematician Gabriel Lamé had a flawed proof attempt that could have been much like Fermat's — the idea is just about practicable for a brilliant 17th century mathematician, whereas the flaw in it is a rather subtle technical matter that escaped just about everyone even in the 19th century.
There's often this idea in fiction that Wiles' proof is somehow incomplete or not good enough (mostly for being utterly
inelegant—note, however, that
mathematics is full of theorems whose best-known proof is massively more difficult and complex than the statement of the theorem itself; Fermat's last theorem is by no means unique in this regard). No
currently unsolved problem in mathematics has a story behind it that's nearly as good as Fermat's mysterious margin note, so it can be useful to pretend that Fermat's last theorem remains unsolved.
Not to be confused with Fermat's
Little Theorem, which can be proved convincingly on the back of a postcard.
Instances of Fermat's last theorem in fiction:
- In Arthur Porges' short story "The Devil and Simon Flagg", a mathematician bets his soul that the Devil cannot prove Fermat's last theorem in twenty-four hours. He wins.
- This causes some Fridge Logic along the way though, as this Devil is master of space and time among other things. Yet he didn't even try go back in time and ask Fermat himself.
- Not at all, if we assume that Fermat himself was in error when noting he had a proof. Which is probably the case.
- A problem that might be substituted for Fermat's Last Theorem if reusing this plot would be to ask for Ramsey numbers. Extra bonus for them being associated with an Alien Invasion anecdote.
- Even better would be one of the Millennium Prize problems, 7 math problems of which 6 remain unsolved.
- Star Trek:
- In Star Trek: The Next Generation, Picard spends some time trying to prove Fermat's last theorem. He says he finds it humbling that an 800-year-old problem, first posed by a French mathematician without a computer, still eludes solution. (The episode in question was broadcast five years before Wiles' proof was released.)
- In Star Trek: Deep Space Nine, Jadzia says that one of Dax's earlier hosts had the most original approach to Fermat's last theorem "since Wiles 300 years ago". This may be an attempted Hand Wave for the TNG example, by showing that people are still working on the problem in the Star Trek universe even though it's been solved.
- In the Doctor Who episode "The Eleventh Hour", the Doctor uses Fermat's original proof of Fermat's last theorem^{note }(along with an explanation of why electrons have mass and a description of an FTL drive) to get a team of scientists to take him seriously after hacking into their videoconference. He also admits that the unfinished stuff was his fault as he "slept in".
- In the Doctor Who Missing Adventures novel Millennial Rites, it's mentioned in passing that the Corrupt Corporate Executive villain has an algebraic proof of the Theorem that he's keeping secret.
- Arthur C. Clarke's The Last Theorem is about a Sri Lankan mathematician who discovers a new proof of the Theorem that is not only considerably more concise than Wiles' version but doesn't rely on any mathematics that post-date Fermat, and thus might be Fermat's own proof.
- The Irish band BATS have a song about Andrew Wiles and the theorem.
- Irregular Webcomic! posits that Fermat was a time traveler.
- "Prove Fermat's last theorem" occurs as a problem in an Only Smart People May Pass setup in Gash Bell. It's posed to the dumbest member of the party, and the rest force the guardian to give a simpler question by making him admit that he doesn't know the answer.
- Shows up in Arcadia; as a joke Septimus assigns the Teen Genius Thomasina to solve it. She eventually comes to the conclusion that Fermat was Trolling. Interestingly, Arcadia was published mere months before Wiles' proof.
- In The Millennium Trilogy, Lisbeth spends most of the second book puzzling over the Theorem. At the end of the book, she understands what he meant, but after the ending of the book, forgets it.
- Appears briefly on a blackboard in the 2000 remake of Bedazzled (2000). Satan (Elizabeth Hurley as a Hot Teacher) erases it from the list of homework assignments while commenting, "You'll never use this stuff."
- In Get Backers, Lucky, the genius dog, is given a problem like this to solve. The dog answers that it's unsolveable (x = "nothing"), which is what really clues Ban in to the fact that the whole "genius dog" thing isn't a parlor trick... the dog's actually been infected with the same virus that caused apes to mutate into humans, the so-called "Missing Link Virus." It... doesn't make sense in context, but there is an explanation.
- The Musical Fermat's Last Tango is a No Celebrities Were Harmed version of a modern mathematician using computers to find the proof, while taunted by Fermat's ghost, returned from the afterlife (a specific one for mathematicians, called the After Math). (Was originally to be called Proof, but premiered at the same time as Proof.)
- Tom Lehrer's "That's Mathematics" mentions Wiles' proof of "what Fermat jotted down in that margin, which could've used some enlargin'", though he makes it sound a lot simpler than it is.
- In the Dutch comic Storm: De Kronieken van Pandarve ^{note }Storm: The Chronicles of Pandarve, the planetary intelligence Pandarve tries to solve Fermat's theorem to pass the time. When Storm needs her full attention to deal with an incoming meteor, he reveals that the theorem was solved, and that he knew that all the time but never told her. Pandarve gets quite enraged at this, partially because a mere human proved smarter than her, but mostly because she is now bored. She calms down when Storm tells her about another unsolved problem, Goldbach's conjecture.
- The theorem is mentioned in an episode of Yu-Gi-Oh! ARC-V, in which Yuya is challenged to prove it during a Quiz Duel. Given that he's terrible at math, he declines to answer... But really, given that the quiz only gives you five seconds to respond, it's doubtful anyone would have been able to prove the theorem in time.