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I know this is subjective, but the principle "should be of interest to mathematicians" trumps. (I hope.)

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closed as off topic by S. Carnahan, Scott Morrison Dec 24 '09 at 2:21

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Since this thread continues to interest people, a request: Do people know more jokes that are erudite? That is, jokes that are related to interesting mathematics in some way. (Not necessarily very abstract mathematics.) The Banach-Tarski joke below is a good example, in my opinion. –  Greg Kuperberg Nov 22 '09 at 0:11
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I just voted this -1, and I'd like to see the question closed. People have had over a month to enjoy it, and its continued presence on the front page seems to encourage people to post very soft questions. This takes Math Overflow in what I think is a bad direction. –  Tom Leinster Nov 28 '09 at 12:34
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I disagree with Tom. I think some levity is desirable, and MO shouldn't all be serious business. –  Richard Dore Dec 10 '09 at 21:50
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With respect to the title, "No." –  Harry Gindi Dec 10 '09 at 22:23
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I've decided to finally put this one out of its misery. All that's happening now is people add new, mostly lame, jokes at the the end, which no one ever reads, and as a result the question keeps bouncing back to the front page. It's time to die. Closed. –  Scott Morrison Dec 24 '09 at 2:23

81 Answers 81

Mike's last joke reminded me of this one: a comathematician is a device for turning cotheorems into ffee.

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For a while I've been wondering what mbinatorics would be, if it existed. Presumably it would be useful for mputer science. –  Michael Lugo Oct 25 '09 at 0:53
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AJ Tolland is fond of saying that what we really need is a machine for turning some of those theorems back into coffee. –  Noah Snyder Oct 27 '09 at 22:58
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I disagree. Mputer science would be useful for mbinatorics, not the other way around. –  Boris Bukh Oct 30 '09 at 22:44
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Ribet once told me that he was sent a generic UG textbook by a publisher for free, with the suggestion that he use it in his UG course. He decided not to, and took the book to Black Oak Books (2nd hand book store in Berkeley) and sold it for a few $$. On the walk back to the department he bought some coffee with the money, and then realised to his amusement that he'd done precisely what Noah mentioned above. –  Kevin Buzzard Nov 4 '09 at 11:24
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I think I'm going to have to start referring to "cocoa" as "a". –  Ian Morris Nov 24 '09 at 10:23

Your momma's so fat she's not embeddable in R^3. Oh yeah? Your momma's so fat she contradicts Whitney's theorem.

A topologist is someone who doesn't know the difference between his ass and a hole in the ground but does know the difference between his ass and two holes in the ground.

I went to visit him while he was lying ill at the hospital. I had come in taxi cab number 14 and remarked that it was a rather dull number. "No" he replied, "it is a very interesting number. It's the smallest number expressible as the product of 7 and 2 in two different ways."

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I could not stop laughing after reading the Ramanujan joke. –  Steven Gubkin Nov 6 '09 at 21:30
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As for topology, I prefer the one about a topologist drinking tea. It goes like that. A topologist is drinking tea from a cup when suddenly the handle drops off. The topologist is amazed: the new shape is different but he can still drink tea from it. And so he does until the bottom of the cup drops off. Now he is totally befuddled: the shape is equivalent to the original one but how can he drink his tea now? –  fedja Nov 11 '12 at 4:11

Here's one I came up with a few years ago that I'm quite proud of.

Q: What do you get when you cross a chicken with an elephant?
A: The trivial elephant bundle on a chicken.

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I don't get that one. Explanations? –  Randomblue Nov 26 '09 at 15:05
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The other day I told this one to a physicist friend of mine and we couldn't stop laughing for several minutes! –  Alberto García-Raboso Dec 15 '09 at 1:19
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@Justin: see en.wikipedia.org/wiki/Fiber_bundle#Trivial_bundle . –  Qiaochu Yuan Jun 10 '10 at 12:33
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I heard this from Rob Easton (I think) several years ago, I also found it hilarious. Again, thank you. –  Karl Schwede Oct 29 '10 at 2:35
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What do you get when you cross a citrus fruit with a bull? The trivial lime bundle on a taurus. –  Michael Albanese Jun 10 '13 at 12:28

Here are a few of my own inventions:

Old Macdonald had a form; ei /\ ei = 0

Save the environment: use continuation passing style!

What shape of pasta takes the least time to eat? Brachistochroni!

You might be a mathematician if you think fog is a composition.

The Yoda embedding, contravariant it is.

How are Goethe's Faust novels like isomorphisms of sets? Dey're de monic epics.

I'm kind of in two minds about this whole Schroedinger's cat thing...

qwhine, n. self-recrimination

recursive: (λ damn. damn (damn)) (λ damn. damn (damn))

Coeschatology: the study of the beginning of times. The coend is ming!

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The first one is just awesome! Please keep inventing! –  Armin Straub Oct 29 '09 at 15:33
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the yoda joke is great!! –  Martin Brandenburg Jan 17 '10 at 11:58
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@Mike Goethe’s Fausts are not novels, but dramas. –  The User Jul 11 '13 at 19:44
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@Olga Mathematics is culture. –  The User Jul 11 '13 at 19:45

A British mathematician was giving a talk in Grothendieck's seminar in Paris. He started "Let X be a variety...". This caused some talking among the students sitting in the back, who were asking each other "What's a variety?". J.-P. Serre, sitting in the front row, turns around a bit annoyed and says "Integral scheme of finite type over a field".

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I don't get it... –  Kevin H. Lin Dec 10 '09 at 22:35
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It's a dig at an attitude of dealing with abstract concepts without looking at concrete examples first, obviously exaggerated for effect. You need to know some algebraic geometry to understand the punch line. –  Felipe Voloch Dec 11 '09 at 1:21
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That's pretty funny. –  Keenan Kidwell Apr 17 '10 at 23:23
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It is a well-established tradition in France to keep the (scheme-theoretic, what else ?) definition of "algebraic variety" in limbo, just to keep the students from getting bogged down into concreteness :-) –  Simon Pepin Lehalleur Aug 10 '10 at 21:52
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The joke seems to presuppose the distinction between scheme and prescheme. –  Lennart Meier Mar 5 '12 at 10:10

an anecdote about David Hilbert from the wonderful book (for us laymen ;-) Prime Obsession:

Hilbert had a student who one day presented him with a paper purporting to prove the Riemann Hypothesis. Hilbert studied the paper carefully and was really impressed by depth of the argument; but unfortunately he found an error in it which even he could not eliminate. The following year the student died. Hilbert asked the grieving parents if he might be permitted to make a funeral oration. While the student's relatives and friends were weeping beside the grave in the rain, Hilbert came forward. He began by saying what a tragedy it was that such a gifted young man had died before he had had an opportunity to show what he could accomplish. But, he continued, in spite of the fact that this young man's proof of the Riemann Hypothesis contained an error, it was still possible that some day a proof of the famous problem would be obtained along the lines which the deceased had indicated. "In fact," he continued with enthusiasm, standing there in the rain by the dead student's grave, "let us consider a function of a complex variable...."

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Is there a copy of the paper presented to Hilbert? –  SDevalapurkar Mar 26 at 0:52
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@SanathDevalapurkar: no you are not going to prove the Riemann hypothesis –  Wicht Apr 18 at 12:55

I like this one:

A mathematican walks into a bar accompanied by a dog and a cow.
The bartender says, “Hey, no animals are allowed in here!”
The mathematician replies, “These are very special animals.”
“How so?”
“They’re knot theorists.”
The bartender raises his eyebrows and says, “I’ve met a number of knot theorists who I thought were animals, but never an animal that was a knot theorist.”
“Well, I’ll prove it to you. Ask them them anything you like.”
So the bartender asks the dog, “Name a knot invariant.”
“Arf! Arf!” barks the dog.
The bartender scowls and turns to the cow asking, “Name a topological invariant.”
“Mu! Mu!” says the cow.
At this point the bartender turns to the mathematican and says, “Very funny.” With that, he throws the three out of the bar.
Outside, sitting on the curb, the dog turns to the mathematican and asks, “Do you think I should have said the Jones polynomial instead?”

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which is the variant of the encient: "Who was the greatest baseball player that ever lived?" "Ruth!" barked the dog. "Okay, that's it!" says the bartender, and physically throws both man and dog out the door and onto the street. Turning to the man, the dogs shrugs and says, "Dimaggio?" –  David Lehavi Oct 22 '09 at 18:38
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You joke is due to Joel Hass, I believe. –  Ryan Budney Nov 6 '09 at 21:09

Here's a legend we have at our institute:

Prof: "Give an example of a vector space."

Student: "V"

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It'd be funny if it weren't true. –  lhf Dec 26 '09 at 0:13
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There's a (true) legend about an exam of linear algebra for engeneering students, in which the professor asked: "How many eigenvalues does an $n\times n$ matrix have?" and the student answered "Well... $n\cdot\sqrt{2}$". –  Qfwfq Dec 5 '12 at 14:30
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I've heard it as "how many elements are there on the diagonal of a $n\times n$ matrix?" "Uhm... $n\sqrt{2}$. –  Federico Poloni Jul 11 '13 at 11:19
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We had (almost) the same example: What examples of vector space did the teacher show you? $\mathbf R^3$? -- No -- Then $\mathbf R^2$? -- Neither. --- So what? --- $K^n$. –  ACL Jul 11 '13 at 17:39

Don't remember where I saw this, but as a woman in mathematics, it tickles me no end:

A poet, a priest, and a mathematician are discussing whether it's better to have a wife or a mistress.

The poet argues that it's better to have a mistress because love should be free and spontaneous.

The priest argues that it's better to have a wife because love should be sanctified by God.

The mathematician says, "I think it's better to have both. That way, when each of them thinks you're with the other, you can do some mathematics."

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and what about the lawyer? :) –  Sándor Kovács Mar 29 '11 at 5:34
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Actually, that reminds me of a joke my mother tells: Q. What's the difference between deer nuts and beer nuts? A. Beer nuts are a dollar fifty, but deer nuts are under a dollar! Maybe it's hereditary. –  Elizabeth Henning Apr 3 '11 at 1:55
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I don't get it. Does she intentionally say "under a dollar" instead of "under a buck", or accidentally? Or does she not get it? –  Keenan Pepper Aug 25 '11 at 23:12

I've always thought that "What's the value of a contour integral around Western Europe?" "Zero. All the Poles are in Eastern Europe." was pretty good, although not laugh-out-loud funny by any means.

Another one I personally like is "What's an anagram of Banach-Tarski?" "Banach-Tarski Banach-Tarski."

It's not really a "joke," (and whether it's "mathematical" is, I suppose, debatable), but Knuth's article on the complexity of songs is pretty great.

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The Banach-Tarski joke is very good. –  Greg Kuperberg Nov 21 '09 at 23:59
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The first joke to me sounds like a debased version of the following joke, which was quite topical in about 2004: "Q: What's the value of the contour integral around the British Isles? A: Zero, because all the Poles are removable". This refers to the fact that at the time the joke was coined, Britain was host to a large number of Polish migrant workers who were in the unusual position of being intra-EU migrants not having indefinite leave to remain in Britain. –  Ian Morris Nov 23 '09 at 13:32
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I would imagine the variant given was around before 2004. –  Sean Tilson Mar 6 '10 at 0:31
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Here is a joke in the same vein as the Banach-Tarksi one. What does the B stand for in Benoit B. Mandelbrot? Benoit B. Mandelbrot. –  Michael Albanese Sep 17 '13 at 5:28

Q: How do you tell an extroverted mathematican from an introverted one?

A: An extroverted mathematician stares at your shoes when talking to you.

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This can be found in Steven Krantz's A Primer of Mathematical Writing, page 159 (footnote). The exact quote from there is: An introverted mathematician is one who looks at his shoes when he talks to you. An extroverted mathematician is one who looks at your shoes when he talks to you. –  KConrad Apr 26 '11 at 0:31

My favourite, from Eilenberg's obituary:

When someone once asked Professor Eilenberg if he could eat Chinese food with three chopsticks, he answered, "Of course," according to Professor Morgan. The questioner asked, "How are you going to do it?" and Professor Eilenberg replied, "I'll take the three chopsticks, I'll put one of them aside on the table, and I'll use the other two."

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Here is the one I heard recently.

Professor: What is a root of $f(z)$ of multiplicity $k$?

Student: It is a number $a$ such that if you plug it into $f$, you get $0$; if you plug it in again, you again get $0$, and so $k$ times. But if you plug it into $f$ for the $k+1$-st time, you do not get $0$.

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Actually, I kind of like this in a serious way :) –  David Corwin Dec 28 '12 at 5:37
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If you differentiate the function each time in between plugging it in, then this is correct! –  Toby Bartels Jan 26 at 6:56
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...or divide by $(z-a)$ in between... –  Jonas Meyer Jul 9 at 19:36

There's a mathematician whose non-mathematician friends are constantly ribbing him because his field is just so abstract and seems to have no relevance to the real world. One day, it gets to him, and he resolves to arm himself with some practical applications of research mathematics for the next encounter. He realizes that his own specialty (mathematical logic) is probably too far beyond them to be of any use there, so he goes to the department bulletin board to find an upcoming talk about something practical. Luckily, a talk is scheduled that afternoon on "the theory of gears." "Perfect!" he says. Nothing could be more practical, more down-to-earth. Finally, he'll be able to prove to his friends that mathematics is relevant to the real world. That afternoon, he's so excited that he goes to the talk five minutes early and sits in the first row of seats. Then, at the scheduled time, the speaker stands up and begins: "While the theory of gears with real numbers of teeth is well understood...."

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This is pretty awesome. The best (worst?) part is, I would actually like to hear that talk. –  DoubleJay Apr 19 '10 at 8:58
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I just told this joke at a conference, except I flubbed it and said it was about gears with uncountably many teeth. Five minutes later, I found two of the listeners arguing about slippage in an explicit construction they had come up with. –  Neil Toronto Nov 21 '13 at 20:25

I have a few that I've heard and liked.

(1) The Mobius strippers always show their backside.

(2) Apparently, a quote of Paul Erdos, but it's funny nonetheless : Another roof, another proof.

(3) An experimental physicist meets a mathematician in a bar and they start talking. The physicict asks, "What kind of math do you do?" to which the mathematician replies, "Knot theory." The physicist says, "Me neither!"

(4) The primary reason Bourbaki stopped writing books was the realization that Lang was one single person.

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My college roommate and I inadvertently acted out a variation of (3) when I was in a knot theory seminar. It was a rare Abbott-and-Costello-esque moment. –  Darsh Ranjan Nov 21 '09 at 9:19
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+1 for (4) ... heh :) –  Andrew Critch Dec 1 '09 at 10:45

Based on the answers above, no.

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My favorite one-liner:

Why did the mathematician name his dog "Cauchy"? Because he left a residue at every pole.

My favorite anecdote:

An engineer, a physicist, and a mathematician find themselves in an anecdote, indeed an anecdote quite similar to many that you have no doubt already heard. After some observations and rough calculations the engineer realizes the situation and starts laughing. A few minutes later the physicist understands too and chuckles to himself happily, as he now has enough experimental evidence to publish a paper. This leaves the mathematician somewhat perplexed, as he had observed right away that he was the subject of an anecdote and deduced quite rapidly the presence of humor from similar anecdotes, but considers this anecdote to be too trivial a corollary to be significant, let alone funny.

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+1 for the one-liner. –  Włodzimierz Holsztyński Oct 11 '13 at 1:23

jose's post reminds me of one I heard Michael Hutchings tell during an undergraduate calculus lecture:

$e^x$ was walking down the street one day and met a polynomial running in the opposite direction.

"Wait, why are you running?" asked $e^x$. The polynomial said:

"There's a differential operator over there! It could differentiate me and turn me into zero!" And the polynomial continued running in fright.

"Ha ha," $e^x$ said to himself. "I'm $e^x$! Let them differentiate me as many times as they want, it makes no difference to me!" So $e^x$ walked on and reached the differential operator. He confidently introduced himself: "Hi, I'm $e^x$!" The reply:

"Hi, I'm $\partial/\partial y$!"

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Can't stop laughing –  DamienC Jun 9 '11 at 20:50

"Finite Simple Group (of Order Two)" by the Klein Four a cappella group at Northwestern University (lyrics by Matt Salomone):

The path of love is never smooth
But mine's continuous for you
You're the upper bound in the chains of my heart
You're my Axiom of Choice, you know it's true

But lately our relation's not so well-defined
And I just can't function without you
I'll prove my proposition and I'm sure you'll find
We're a finite simple group of order two

I'm losing my identity
I'm getting tensor every day
And without loss of generality
I will assume that you feel the same way

Since every time I see you, you just quotient out
The faithful image that I map into
But when we're one-to-one you'll see what I'm about
'Cause we're a finite simple group of order two

Our equivalence was stable,
A principal love bundle sitting deep inside
But then you drove a wedge between our two-forms
Now everything is so complexified

When we first met, we simply connected
My heart was open but too dense
Our system was already directed
To have a finite limit, in some sense

I'm living in the kernel of a rank-one map
From my domain, its image looks so blue,
'Cause all I see are zeroes, it's a cruel trap
But we're a finite simple group of order two

I'm not the smoothest operator in my class,
But we're a mirror pair, me and you,
So let's apply forgetful functors to the past
And be a finite simple group, a finite simple group,
Let's be a finite simple group of order two
(Oughter: "Why not three?")

I've proved my proposition now, as you can see,
So let's both be associative and free
And by corollary, this shows you and I to be
Purely inseparable. Q.E.D.

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This is so amazing! –  SDevalapurkar Mar 26 at 0:37

Q: What is non-orientable and lives in the ocean?
A: Möbius Dick...


A mathematician organizes a raffle in which the prize is an infinite amount of money paid over an infinite amount of time. Of course, with the promise of such a prize, his tickets sell like hot cake.

When the winning ticket is drawn, and the jubilant winner comes to claim his prize, the mathematician explains the mode of payment: "1 dollar now, 1/2 dollar next week, 1/3 dollar the week after that..."


"The number you have dialed is imaginary. Please, rotate your phone by 90 degrees and try again..."


From a former prof. - http://www.math.ualberta.ca/~runde/jokes.html

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Too much time spent on the internets makses the "Möbius Dick" joke close to incomprehensible... –  darij grinberg Jan 11 '11 at 22:00
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The linked page doesn't seem to exist anymore. –  Jonas Meyer Jul 9 at 19:44

Theorem: There are infinitely many composite numbers.

Proof: Suppose there are only finitely many, and multiply them together.

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What if you do this in the ring of integers mod 6? –  Ilya Grigoriev Dec 14 '09 at 22:07
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It's crucial in the proof that you multiply the numbers together and do not add one! :) –  Somnath Basu Feb 28 '10 at 7:16
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What if there is only one composite number? –  Douglas S. Stones Mar 6 '10 at 11:45
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@ Douglas: There is also a long tradition, beginning with Euclid, of giving Euclid's proof without checking the set of primes is non empty. –  roy smith Jan 17 '11 at 17:00
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Roy, it's no problem: in that case, per Jérôme's observation, the trick “multiply them all and add 1” gives 2. –  L Spice Apr 27 '11 at 18:33

(From the unpublished manuscript "Mathematics in a nutshell":)

A coconut is just a nut

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On a related note, a comathematician is a device for turning cotheorems into ffee. –  Michael Lugo Dec 15 '09 at 3:07
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you're talking of finite dimensional nuts, ofcourse. –  Pietro Majer Jun 14 '11 at 10:08
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and cocoa is just 'a' (stolen from a comment on another thread) –  David Corwin Dec 28 '12 at 6:21

"Why did the chicken cross the Mobius band?"

The question isn't whether good math jokes exist, but whether they can be classified. The example above works because it plays on ones expectation of the "chicken crossing the road" jokes. Another one in the same vein, known as the shortest math joke:

"Let epsilon<0."

Another one, which I actually heard in class:

"Take a positive integer N. No wait, N is too big; take a positive integer k."

Here is a non-exhaustive classification of math jokes:

  • Puns on mathematical terminology
  • Mathematical reasoning in non-mathematical setting
  • Twists on expectations
  • Meta-jokes approached in a mathematical mode of enquiry

A joke can belong to more than one classification. For example, the "Dog and cow knot theorists" has both puns and a twist on expectations.

By the way, I would exclude jokes which are purely made on stereotypes, like the above joke on extrovert mathematician, because I don't find it funny.

I leave with one of my favorite meta-jokes:

"How many members of a certain demographic group does it take to perform a specified task? A finite number: one to perform the task and the remainder to act in a manner stereotypical of the group in question."

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The epsilon joke isn't funny. It would be funny if it read "epsilon <= 0". –  Loop Space Oct 26 '09 at 7:23
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Still don't get the epsilon joke, with or without =. –  mathreader Dec 7 '09 at 4:24
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The joke is that epsilon almost always stands for a small positive real constant, e.g. in the epsilon-delta definition of continuity. –  Qiaochu Yuan Jun 10 '10 at 12:31
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The classification provided by the meta-joke is quite precise :) –  Irene Adler Jul 16 '10 at 14:51

The spectral sequence is like the mini-skirt; it shows what is interesting while hiding the essential.

This saying is attributed to someone from Bourbaki in Bourbaki's Art of Memory.

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From an issue of How to Gamit (the MIT student manual) from the 1980s: a paper should be like a miniskirt: short enough to be interesting and long enough to cover the subject. –  José Figueroa-O'Farrill Oct 27 '09 at 10:21
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Just wondering: if you were wearing a skirt in the same room that somebody was saying one of these, how would you feel? The attributions to these jokes suggest that they are decades old, and it shows. In my opinion, these jokes should be left in those decades. –  anon Apr 18 '11 at 0:08
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@anon: I would feel like any other random person in the room. What is so inappropriate here? The indirect reference to one's genitalia or is it commenting on other people's garments? :) Or to turn it the other way round, how would you feel if you were a sexually frustrated heterosexual male whose class would be attended by attractive females in miniskirts? Is it appropriate to wear them but inappropriate to joke about these issues? Of course, every joke requires certain amount of tact, but on what grounds exactly are you condemning this one to times past? –  Vít Tuček Jan 6 at 16:28

I received today this comment about a paper:

3 lines before section 2.1: A few typos: corresponds, 5-isogeny (I guess a 5-isogenie grants you five wishes?)

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a 5-isogenie grants you 5 identical wishes. –  Michael Lugo Oct 19 '09 at 0:48

Q: How many mathematicians does it take to change a light bulb?

A: One: she gives it to three physicists, thus reducing it to a problem that has already been solved.

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Here are some of my favorites that were invented by friends of mine:

Q: What kind of maps should you take with you on car trips?

A: Automorphisms.

Q: What do you call it when you're trying to prove that a map is injective, but you just can't do it?

A: Monic fail.

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I couldn't, for the life of me, figure out how automorphisms were supposed to be useful on car trips. After all, it doesn't really help to show that the landscape outside your window is non-trivially equivalent to itself; what you're really interested in is showing that it's equivalent to some smaller object you have within your vehicle. Then I realized it's a pun. –  Tanner Swett Jan 12 '11 at 13:05

An engineer, a physicist and a mathematician are driving through the high country in Scotland. Atop a hill, they see a black sheep.

The engineer says: "All sheep are black!" The physicist says: "No, no, some sheep are black." The mathematician: "At least one sheep is black on at least one side."

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If I remember correctly someone told me that this really happened:

A famous mathematician gave a talk (maybe about mathematical physics), after which an as famous physicist sitting in the first row got up, and loudly declared: "That's all nice, but without mathematics, research in physics would be maybe a week behind the state it is now!"

The famous mathematician responded: "Yes, the week god needed to create the world."

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<< The great probabilist Mark Kac (1914-1984) once gave a lecture at Caltech, with Feynman in the audience. When Kac finished, Feynman stood up and loudly proclaimed, "If all mathematics disappeared, it would set physics back precisely one week." To that outrageous comment, Kac shot back with that yes, he knew of that week; it was "Precisely the week in which God created the world." >> –  Cristi Stoica Sep 13 '13 at 16:54

A biologist, a physicist and a mathematician were all drinking coffee and tea and observing a house across the street from them. They notice that two people walk into the house and then an hour later, three people walk out.

Physicist: An experimental error. Our first measurement was incorrect.

Biologist: No, they've obviously reproduced.

Mathematician: No, now when a one person enters the house, it'll be empty again.

http://www.physicsforums.com/archive/index.php/t-4409.html

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