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 4 years ago  

Let me try to empahsise my example. Who knows, it may help ;)

In the Standard Model, the masses of the particles arise from the Higgs field. This field has the particularity that it cannot be turned off (today), so that particles are massive no matter what.

In the early universe, there is a moment at which the Higgs field is actually turned. All the particle dynamics was different at that time (massive objects vs. massless ones).