Hi MarkM! Great to see you on the chain.
It must be admitted that the LoF is over my head. As to physics seeing size in protons and neutrons, it occurred to me to ask Chat-GPT. It replied the following which it is hoped may be helpful.
Yes, physics does consider protons and neutrons to have a size, although defining that size can be somewhat complex due to their nature as composite particles.
Size of Protons and Neutrons
Protons
Radius: The proton radius is typically measured to be around 0.84 femtometers (fm), or 8.4 x 10^-16 meters. Recent experiments and measurements, particularly involving muonic hydrogen, have suggested that the proton might be even smaller, leading to ongoing debates in the physics community.
Neutrons
Radius: The neutron radius is roughly similar to that of the proton, also estimated to be about 0.8 to 0.9 femtometers. Like protons, neutrons are considered to be composite particles made up of quarks and gluons, which complicates the definition of their size.
Composite Nature
Both protons and neutrons are made of three quarks held together by gluons. The size attributed to them is a measure of the distribution of these quarks and the associated field strengths within the particle.
Measurement Challenges
Due to their composite nature and the methods used to measure their size, the reported values can vary, leading to different interpretations and ongoing research in particle physics.
Summary
While protons and neutrons have sizes measured in femtometers, the exact definitions can be nuanced due to their complex structures and the ongoing developments in experimental physics.
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