According to the most accurate scientific theory ever created and generally known as the standard model, all of space is filled with a mysterious stuff called “the Higgs field”. Unlike magnetic or gravitational fields, which vary from place to place (as, for instance, the fact that things weigh more on Earth than on the surface of the Moon), the Higgs field is exactly the same everywhere. What varies is how the different fundamental particles interact with it. That interaction, the theory goes, is what gives particles mass. In other words, the Higgs field is what makes some particles, such as protons and neutrons, relatively heavy, others (like electrons) subatomic lightweights, and still others (like photons) utterly massless. If photons weren’t so light, a person would be shredded by a photon hailstorm every time he or she was exposed to a sunbeam. Then again, if protons and neutrons weren’t so heavy, one wouldn’t dare to go outside to sunbathe anyway. So without mass and its affinity for gravity, there would be no galaxies, no stars, and no us.