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Recent findings in astrophysics suggest that the observable Universe can be modeled as a sphere of radius R = 13.7 × 109 light-years with an average mass density of about 1 × 10−26 kg/m3, where only about 4% of the Universe’s total mass is due to “ordinary” matter (such as protons, neutrons, and electrons). Use this information to estimate the total mass of ordinary matter in the observable Universe. (1 light-year = 9.46 × 1015 m.)
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