The question of ultimate constituents of the physical universe was one of the first questions at the dawn of the Western tradition of philosophy. At present, the most successful answers to this question are offered by the fundamental theories of elementary particle physics, which are formulated within the broader conceptual and mathematical apparatus of quantum field theory. The aim of this paper is to explain in an accessible manner the fundamental changes brought about by the transition from particle to field understanding of the universe in contemporary physics. The brief account of Newton’s ontological view of the world serves both as an introduction and as a background to what follows. The paper also intends to address and encourage philosophers interested in ontological problems to study the latest physical theories despite their mathematical complexity and apparent inaccessibility.