Democritus's Unverified Assumption

All of science is a direct manifestation of physics, but physics cannot account for all of reality; the necessary truths of logic are more foundational than scientific facts (not that any ways matter behaves can truly be known, for all we have in this regard are perceptions), and the very space required to hold matter must be outside of physical substance, or else matter would have nowhere to exist.  Then there is time, without which events in a material world could never occur.  Scientific endeavors and information hinge on purely immaterial things that still have a necessary relationship with the physical world.  Only a fool pretends this does not reflect reality.

Physics nonetheless deals not with the nature of reason, space, or time, even if there are important philosophical facts about the connection between these things and matter, but with physical objects, no matter how large or small they are, and how they behave.  According to contemporary scientific paradigms of particle physics, all matter consists of atoms, particles too small to be seen macroscopically but that themselves break down into smaller particles.  The initial philosophy of "atomism" actually held that atoms are the smallest unit of matter possible and move in an otherwise empty "void" of space.  Democritus was among the first historically recorded philosophers to propose that all physical things reduce down to atoms.

Democritus, if he thought all that exists reduces down to matter and space, was not only wholly mistaken, but he could have quickly disproven his own mistake by rationalistically analyzing the immateriality of logic, consciousness, and time.  However, this issue of broader metaphysics is beyond the scope of most comments made about him and his atomic theory.  Beyond this, however, there is still plenty to dispute about atomic theory itself.  If atoms do exist, how would one truly know?  Whether or not atoms are the smallest physical particles in existence, how could one know that there is such a thing as a "fundamental" particle in the first place?

Even though some of the scientific ramifications of atomism, such as the idea that atoms actually exist, have found empirical support in recent centuries, not even the currently supported ideas about atoms can be philosophically proven.  If the senses cannot directly perceive atoms, as any "atomist" like Democritus would have likely admitted openly, there can only be indirect evidence for their existence; if the senses can perceive atoms, their existence is still up in the air, for the senses largely establish that one is having sensory perceptions.  The actual existence of units of matter smaller than can be perceived is unverifiable.  It is ultimately up in the air in a way that most people would find puzzling.

Atoms cannot be proven to exist like logic, consciousness, or even some some sort of material world can be, but it is not impossible to gather evidence in favor of them.  This only puts atoms in the same epistemological category as something like other minds--a category holding ideas that may or may not correspond to things that actually exist regardless of what seems to be true.  Thus, atoms are by no means special in having their existence fall into unverifiable territory!  This still leaves open the very real possibility of gathering empirical support for the existence of atoms.  It is just that imperceptible atoms cannot be proven to exist when directly even looking at another person cannot prove that they exist.