Simplify the following text for a Grade 12 native English-speaking person.
Original: John Stewart Bell ( 28 June 1928 â `` 1 October 1990 ) was an Irish physicist who made great contributions to quantum physics , and especially to the question of what Heisenberg 's uncertainty principle really tells us about the world .
Simplified: John Stewart Bell ( 28 June 1928 -- 1 October 1990 ) was an Irish physicist , and the originator of Bell 's Theorem , one of the most important theorems in quantum physics .