The critical mass density needed to just halt the expansion, Ask an Expert

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The critical mass density needed to just halt the expansion of the universe is approximately 10^-26 kg / m³.

(a) Convert this to eV / c² ⋅ m³.

(b) Find the number of neutrinos per cubic meter needed to close the universe if their average mass is 7 eV / c² and they have negligible kinetic energies.

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