The astrophysics version of the joke is funnier, but perhaps only if you're an astrophysicist. "A farmer is having trouble with the milk production of his cows

The astrophysics version of the joke is funnier, but perhaps only if you're an astrophysicist. "A farmer is having trouble with the milk production of his cows, and winds up engaging an astrophysicist to write a report. Three weeks later, he opens the report to find it begins: 'Let us consider a spherically symmetric cow, emitting milk equally in all directions..."