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"The range of measured densities within our universe is staggeringly large. We find the highest densities within pulsars, where neutrons are so tightly packed that one thumbleful would weigh as much as a herd of 50 million elephants. And when a rabbit disappears into “thin air” at a magic show, nobody tells you the thin air already contains over 10,000,000,000,000,000,000,000,000 (ten septillion) atoms per cubic meter. The best laboratory vacuum chambers can pump down to as few as 10,000,000,000 (ten billion) atoms per cubic meter. Interplanetary space gets down to about 10,000,000 (ten million) atoms per cubic meter, while interstellar space is as low as 500,000 atoms per cubic meter. The award for nothingness, however, must be given to the space between galaxies, where it is difficult to find more than a few atoms for every 10 cubic meters.
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When you leave the galaxy, you leave behind nearly all gas and dust and stars and planets and debris. You enter an unimaginable cosmic void. Let’s talk empty: A cube of intergalactic space, 200,000 kilometers on a side, contains about the same numbers of atoms as the air that fills the usable volume of your refrigerator. Out there, the cosmos not only loves a vacuum, it’s carved from it."