Matthew Broderick
Richard Feynman

Patricia Arquette
Arline Greenbaum

Peter Riegert
Mel Feynman

Jeffrey Force
Young Richard

David Drew Gallagher
Harold

Raffi Di Blasio
Robert

Josh Keaton
David

James Hong
Abacus Adder

Melissa DeLizia
Young Joan

Peter Michael Goetz
Dr. Gell-Mann

Kelly Wolf
Nurse Kate

Mary Pat Gleason
County Nurse #2

Joyce Van Patten
Aunt Ruth

James Le Gros
John Wheeler

Zeljko Ivanek
Bill Price

Joshua Malina
Calculator Kid #3

Matt Mulhern
Gate Guard