The IDFA wanted to find a way to make cows produce more milk. So they decided to consult with the foremost biologists to find ways to improve production. After five years of research, 20 million dollars spent, hundreds of protests by Greenpeace and PETA, they came back with a New and Improved Cow. It had a milk production improvement of 5% over the original.
The IFDA was somewhat disappointed by these results. They decided to try again, so this time they engaged the greatest chemists in the world. After two years, 10 million dollars spent, and the accidental poisoning of a small town in Colorado, they got a 3% improvement in milk output.
The IFDA was again underwhelmed by this success, but undaunted they decided to try hiring the greatest physicists available. The physicists tried for a year, and after spending 5 million dollars on radiation therapy and centrifugal distillation of cattle forage, they got a 0.1% improvement in output.
In desperation the IFDA turned to the mathematicians. Upon hearing the problem, the foremost mathematician of our time offered to solve their problem for a marginal fee. He told the delegation that they could come back the next morning and he would have the solution for them. The next morning they returned, flushed with anticipation, and he handed them a piece of paper with the computations for a 300% increase in milk production.
The paper began: "Consider a perfectly spherical cow, radiating milk isotropically".
This joke has appeared in many different forms, generally mocking the profession of either the mathematician or the physicist. Variations include jokes calling for a 'perfectly spherical racehorse', 'perfectly spherical chicken, or even the ever humorous 'perfectly spherical Jesus'. (No, I'm not going to post the Jesus joke. It's a little too derivative.)
Q: How many theoretical physicists does it take to change a lightbulb?
A: Just one, but he can only do it if it's a perfectly spherical lightbulb.
The reason that this is 'funny' is that many calculations work much better of you can assume that a star, volume, or cow is a perfect sphere
. Mathematicians and physicists realize that this is not always practical, and have taken up the phrase "perfectly spherical cow" as a sort of self-mocking mantra. When talking about a highly simplified hypothetical model of reality you will often hear a joking reference along the lines of "...of course, that assumes perfectly spherical cows".
A biologist, a chemist and a physicist are shown a cow, and asked to describe what they see. The biologist goes first, and says "Well it's a Bos bovis part of the Bovidae family, in the mamalia class, etc."
The chemist goes next, stating "I see a complex assembly of organic molecules, assembled into proteins to form a self-sustaining and replicating system..." And on he goes, describing the wonderous chemical interactions in front of him.
When he's finally finished, the physicist says "Well, in a first-order approximation, it's a sphere."
You might well wonder how this joke could possibly have so many forms? Surely one is enough? Well, there aren't nearly as many math jokes as you might expect, so the ones that exist get stretched a little thin. These three jokes are an excellent indicator of how nerdy you are. If you laughed at the first one, you can get along with a nerd. If you laughed at the second one, you are a nerd. If you were still laughing at the third one, it's time to step away from the computer and get a life.
Now if you'll excuse me, it appears that I need to go get a life.