Simplify the following text for a Grade 12 native English-speaking person.
Original: Experts in another field called quantum mechanics , say , in addition , at high speed the creation and annihilation of particles becomes possible , so , it is not possible to keep the number of particles constant .
Simplified: In quantum field theory , at high speed , the creation and annihilation of particles becomes possible , so , it is not possible to keep the number of particles constant .