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Meson Cloud Model: At any given instant, the proton might really be a neutron (ddu) plus a positively charged pion (ud‾ud‾ud- ud-)—or another proton (uud) plus a neutral pion (an equal superposition of uu‾uu‾ and dd‾dd‾). This violates energy conservation but it is allowed, for a fleeting moment, by the Heisenberg uncertainty principle. By adding up the contributions from all the possible channels, the theorists can model the composition of the sea.
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