# Physics humor for a Friday morning ...

By **
joe
**

From xkcd
Heh …
If you don’t know what a complex conjugate is, read this. Basically, if I have a function Ψ(x) which has a “real” part ψr(x) and an imaginary part ψi(x), with the ψ’s being real valued functions, so Ψ(x) = ψr(x) +*i**ψi(x)), then multiplying Ψ(x) by its complex conjugate (Ψ*(x) = ψr(x) - *i**ψi(x) , where *i* =√(-1) ) yields:

(ψr(x) + *i**ψi(x)) * (ψr(x) - *i**ψi(x))

which (using basic algebra’s FOIL method) ψr2(x) + ψi2(x) Which is real valued, as the ψ’s are real valued. This is the basis for the ‘joke’. And its funny … really …