But a guy who can will himself to shrink down to subatomic sizes? That's a bit more than I think I can roll with.
Hank Pym doesn't use willpower to shrink or grow, he uses a gas or pill containing a type of subatomic particle he discovered and named Pym Particles. They shunt mass to or from another dimension. (In the animated Avengers
series, it's depicted more as an energy field.)
And let's not forget, the Hulk changes size by a factor of two or three and gains mass out of nowhere, which should be impossible. What Ant-Man does is simply a more extreme version of the same process.
Also, we've had movies like The Incredible Shriking Man, Fantastic Voyage
, and Honey, I Shrunk the Kids