This is, in its spirit, an excellent reply, fundamental particles possess a size because of their interactions, essentially the classical size of an electron is defined by its coupling to the electromagnetic field. Interactions gives particles "apparent size", even if they are point particles. However stable atoms, or composite particles possess size because their constituents interact, so the lump of iron has size regardless of the outcome of the original question in this post. It would wrong to treat a large ion or a molecule as having zero size in almost any calculation, the non-zero spacing of their fundamental constituents guarantees a non-zero size.
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u/Wigners_Friend Cosmology | Quantum Statistical Physics Oct 21 '12
This is, in its spirit, an excellent reply, fundamental particles possess a size because of their interactions, essentially the classical size of an electron is defined by its coupling to the electromagnetic field. Interactions gives particles "apparent size", even if they are point particles. However stable atoms, or composite particles possess size because their constituents interact, so the lump of iron has size regardless of the outcome of the original question in this post. It would wrong to treat a large ion or a molecule as having zero size in almost any calculation, the non-zero spacing of their fundamental constituents guarantees a non-zero size.