Even though we know that ordinary matter accounts for only about one-twentieth of the universe’s energy and a sixth of the total energy carried by matter (with dark energy constituting the remaining portion), we nonetheless consider ordinary matter to be the truly important constituent. With the exception of cosmologists, almost everyone’s attention is focused on the ordinary matter component, which you might have thought to be largely insignificant according to the energy accounting.
We of course care more about ordinary matter because we are made of the stuff—as is the tangible world in which we live. But we also pay attention because of the richness of its interactions. Ordinary matter interacts through the electromagnetic, the weak, and the strong nuclear forces—helping the visible matter of our world to form complex, dense systems. Not only stars, but also rocks, oceans, plants, and animals owe their very existence to the nongravitational forces of nature through which ordinary matter interacts. Just as a beer’s small-percentage alcohol content affects carousers far more than the rest of the drink, ordinary matter, though carrying a small percentage of the energy density, influences itself and its surroundings much more noticeably than something that just passes through.
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