Some researchers seem to have measured the proton as being 4% smaller than previously thought: http://www.nature.com/news/shrunken-proton-baffles-scientists-1.12289 What is the reason for this? This is the second time the experiment has been conducted. If it is carried out yet again, and yields the same strange result, then what are we to make of it? Is there any speculation on what is going on here? Is it possible that muons have some previously unknown interaction with the proton? Otherwise, what else could it be?