Se o Universo que podemos ver já é tão grande...

By making accurate measurements of the cosmic microwave background fluctuations, WMAP is able to measure the basic parameters of the Big Bang model including the density and composition of the universe. (...)

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WMAP determined that the universe is flat, from which it follows that the mean energy density in the universe is equal to the critical density (within a 2% margin of error). Of this total density, we now know the breakdown to be:
4% Atoms, 23% Cold Dark Matter, 73% Dark Energy.

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Thus 96% of the energy density in the universe is in a form that has never been directly detected in the laboratory. The actual density of atoms is equivalent to roughly 1 proton per 4 cubic meters.