the theory that minute, discrete, finite, and indivisible elements are the ultimate constituents of all matter.

Answer: Atomism

Explanation:

In a strict sense, atomism states that atoms are qualitatively identical, combinable only by juxtaposition, and indivisible. however, some forms of atomism are less strict on these features. Nuclear reactions show atoms that are no longer viewed as indivisible because more fundamental particles emerge in the explanations of nuclear reactions.