Space is sparse, not empty

The interstellar medium contains gas, dust, charged particles and radiation, but its density varies greatly by location. A common approximate density for gas in the Milky Way’s interstellar medium is about one atom per cubic centimeter—roughly 330,000 atoms in 88 U.S. gallons, not one. Intergalactic space is far more diffuse: at about one atom per cubic meter, that volume would contain roughly a third of an atom on average. The illustration is AI-generated.