2013-10-30
Explanation
The Joke
A parent tells their partner: "I plan to use reverse psychology to make my kid a physicist." In the next beat, the parent says to the child: "Girl! There's only one cross product you should care about, and that's JESUS!"
The Humor
The joke operates on two levels. First, the parent is employing "reverse psychology" -- by loudly insisting the child focus on religion (specifically Jesus and "the cross") rather than physics, the parent hopes the child will rebel and become interested in physics instead. Second, there is a clever double meaning in "cross product": in mathematics and physics, the cross product is a vector operation fundamental to physics (used in electromagnetism, mechanics, etc.), while "the cross" is the central symbol of Christianity (the crucifix). By telling the child the only "cross product" that matters is Jesus, the parent is banking on the child's natural rebelliousness to drive them toward the mathematical cross product -- and thus toward physics.
References
- Cross product: A binary operation on two vectors in three-dimensional space, producing a vector perpendicular to both. It is fundamental in physics, particularly in electromagnetism (e.g., the Lorentz force law).
- Reverse psychology: A persuasion technique involving advocating the opposite of what you actually want, in hopes that the target will rebel and do what you truly desire.