Physicists tell us that there is no such thing as empty space. Imagine that you have removed every atom from a small box to try to make a perfect vacuum inside. That would be difficult but not impossible. There would still be a gravitational field inside, and perhaps some electric or magnetic fields (or electromagnetic waves). But if you took it to the cold of space and let it fall freely those could be eliminated. Not practical, but experiments that we can imagine, without actually doing them, are called “thought experiments.”
Einstein often did these, as when he imagined trying to overtake a light ray. Would it stop, or go backward? No, he concluded that would be impossible and it led him to the Theory of Relativity. Do not call that “just a theory,” it is a thoroughly tested description of very fast-moving objects – such as electrons and protons in particle accelerators, and satellites used by your smartphone with GPS.
Another theory was developed nearly 60 years ago to explain how fundamental particles such as electrons have mass. Photons are particles of light; they have zero mass and can never be brought to rest. A high energy photon can turn into an electron and its antimatter partner, a positron, when it passes by an atomic nucleus. The newly created electron and positron have exactly the same mass and – here’s the puzzle – it is the same mass no matter where in the universe this “pair creation” happens.
How do they “know” what mass to have? Of course, electrons do not have brains or know anything, but it is as if something in the vacuum determines their mass. Theorists thought a new field may fill space. Unlike familiar gravity and electromagnetic fields, this field has no direction, just a value, and is everywhere the same. This field prevents particles like electrons (and quarks) from zipping through space at the speed of light, no matter how much energy you give them. In other words, it gives them mass. Without that, atoms would not exist – no atoms, no you!
Professor Higgs said that if such a field exists, it should have a particle going with it; like the photon is a particle of the electromagnetic field, but this one should have mass. It is called the “Higgs boson,” and its discovery was announced ten years ago (July 4, 2012) at CERN, the European Laboratory for Particle Physics in Geneva, confirming that theory. So far!