Transcript: There are two fundamentally different types of matter in the universe. Baryons is the term that refers to normal matter: the stuff that we’re made of; our world, the Earth, the Sun, most of the universe we’re familiar with. It’s the normal material of matter, protons, neutrons, and electrons, although electrons being nearly two thousand times lighter than protons or neutrons do not weigh much in the census. The baryon density is the cosmic density of all this material. To calculate it, astronomers sum up the matter contained in all the galaxies in the universe including their stars, their gas, and their dust, that’s ten to the power twenty galaxies, a hundred billion, billion galaxies, also the material in the intergalactic medium which at early epochs was a majority of the material which has since flowed into galaxies. The sum of the census is ten to the power eighty baryons or microscopic particles. As huge as this number is, it’s only 0.3 percent of the critical density. If there was nothing more than baryonic matter in the universe, it would not nearly be sufficient to close the universe.