For centuries there was a debate about the basic structure of matter. Was it atomic or composed of broader, more diffuse elements (eg: earth, wind, fire and water)? The argument rumbled on right up until the start of the 20th Century when Einstein's analysis of Brownian Motion was used to decide the issue in favour of the Atomists. Case closed.
But is that what really happened? My problem with it is as follows:
The original concept of the atom came not out of any empirical observations (much less out of any experimental findings); it was an entity that seemed logically necessary if matter was to be given a secure foundation.
The argument ran like this: objects we encounter in the world are (or seem to be) composite. They are made up of groups of smaller objects. And those smaller objects are themselves composite. But this analysis of reality into smaller and smaller bits cannot go on forever - sooner or later you have to reach a utterly simple object: the basic building block out of which everything more complex is constructed. Without such a simple object it is difficult to see how "reality" really is real. Therefore (the argument ran) a commitment to the reality of the external world entails a commitment to the existence of fundamentally simple objects.
Of course, ancient Greek and Indian philosophers had never seen such an object and had no idea how to go about looking for one. But one thing it seemed they did know: this object must be indivisible, because if it could be divided then it was composite and therefore didn't provide the necessary ultimate foundation. Hence they named it the "atom".
Fast forward to the early 20th Century and science claims to have finally discovered this mysterious foundational object. Except, of course, that what science calls "the atom" in no way fits the logically necessary job description laid out by the ancient Greeks. It is both divisible and composite. It may well be a fascinating and important thing, but it's not an atom.
So where does this leave the philosophical theory of the atomic structure of matter? Are we any closer to proving it? Are there any other contenders? How, for example, does String Theory fit in with such a claim?