“When we think about the present, we veer wildly between the belief in chance and the evidence in favour of determinism. When we think about the past, however, it seems obvious that everything happened in the way that it was intended.” -Michel Houellebecq
If you take anything in the Universe and want to know what its size is, you simply take something whose length is known and compare. On microscopic scales, it isn’t much different: take something of a known wavelength — like light or another matter particle — and compare. If your wavelength is too big, you’ll pass right through; if your wavelength is the right size or smaller, you’ll interact.
This concept of deep inelastic scattering has been successful at measuring the sizes of molecules atoms, atomic nuclei, and individual protons and neutrons. It’s discovered what we consider to be truly fundamental particles: the particles of the Standard Model. But are they truly fundamental? Are they truly point-like? Or is there an actual size to them, after all?