Complex sentence: The universe is mostly empty space, close to a vacuum, and considering only ordinary matter, the density of the Universe is 9.9 x 10 − 30 g/cm 3 which is equivalent to only 6 protons in one cubic meter of emptiness.
Split into simpler sentences: The universe is mostly empty space, close to a vacuum. Considering only ordinary matter, the density of the Universe is 9.9 x 10 − 30 g/cm 3, equivalent to only 6 protons in one cubic meter of emptiness.