In what way or ways would the physical universe be different if protons were negatively charged and electrons were positively charged?
Gravity would be a repulsive force instead of an attractive one.
The value of the Coulomb constant k would change.
Like charges would attract, and opposite charges would repel.
Since protons are more massive, the universe would acquire a net negative charge.
Atoms would consist of protons orbiting a nucleus composed of electrons and neutrons.
There would be no difference other than the sign on the charged particles.