What did Dr. Pym discover that allowed him to change size?

The correct answer to this question isPym Particles. Dr. Pym is a fictional character created by Stan Lee, Jack Kirby, and Larry Leiber. He appears in the Marvel comics, making his first appearance in 1962 in Tales to Astonish #27. Dr. Pym is a scientist and the original Ant-Man.

He could also mutate into Yellowjacket and a Wasp. Dr. Pym is apart of many teams, including the Avengers, West Coast Avengers, Illuminati, and Avengers Academy. Along with appearances in comics and film, Dr. Pym has been featured in the video and arcade games, TV shows, and has action figures.