Didn’t I just say this?
If your decorating skills are up to text, I say, go last century with the Schrödinger equation.
It may or may not trigger PTSD in him, though, depending on how the summer went. Just warning…
But until she asks him it won’t be determined whether or not he has actually done anything.
But whether or not he has actually done anything will be in an indeterminate state, until she asks him.
Nor, if he did any thing at all, can it be determined which of many possible things he has done, until observed. Perhaps it can be argued that, at the time of the act of baking the cake (and in particular, the act of creating the pattern in the frosting), the superimposed possibilities of what he has done all summer will collapse and it will become determined.
ETA: If this interpretation is correct, then the topping suggested in Post #2 becomes inadvisable.
Woops… sorry… I didn’t read all the way down. I should’ve done a search for “Manhattan” first.
If he’s been talking about atoms, I would second the use of the Schroedinger equation (or the energy eigenvalue equation). He wouldn’t be using Feynmann diagrams to talk about atoms.
If you want to be genuinely profound, though, you could use the commutator:
[x,p] = ih
(with a little bar through the upright of the h, and the i is traditionally italic).
That puppy is the entire core of quantum mechanics. It is the only genuine and irreduceable distinction from classical mechanics, and it would be recognized as signalling “quantum” by anybody in any of the far-flung suburbs of physics and physical chemistry.
Don’t forget the little hats over the x and the p. Shown here.