No need to call an expert for a simple equation that I first learned in high school physics when I was 17. Surely there is no one in here who couldn't understand high school physics.
It's called the inverse square law and I'm including a link to a wikipedia discussion of how it works. Our problem with microwave energy can be exampled in the section dealing with
Electrostatics:
"Electrostatics
The force of attraction or repulsion between two electrically charged particles, in addition to being directly proportional to the product of the electric charges, is inversely proportional to the square of the distance between them; this is known as
Coulomb's law. The deviation of the exponent from 2 is less than one part in 1015.
F = kq1q2/r2"
https://en.wikipedia.org/wiki/Inverse-square_law