In the theory of the Big Bang, it proved difficult to include particles that had mass, so some theorists looked to see what would happen if all particles had zero mass. The theory worked. Wow! But it didn't represent reality.
Then Peter Higgs and his colleagues came up with a fascinating way to handle it: what if electrons, quarks, and all the elementary particles were indeed massless? Maybe they are! But that contradicts reality. We can measure the mass of an electron.
They knew that the apparent mass of the electron changes when it moves through a crystal, like silicon or quartz. So maybe the mass of the electron is an illusion. Electrons behave as if they have mass, but they don't really. It's just that they are moving through a crystal-like substance. This crystal-like substance was eventually was called the Higgs field. It fills all of space, which is why particles behave as if they have mass.
What about the early universe? Theorists had already speculated about the creation of new fields, and the Higgs field fit right into their theories. In the early universe, the Higgs field was zero; it was everywhere. Then there was a phase transition in which through spontaneous symmetry breaking the Higgs field would rapidly grow and reach a constant value - the value it has now. So from that time onward, all particles would have an apparent mass.
Can this theory be tested? Yes! In quantum physics, any field will have particle properties. That means that we should be able to create a Higgs particle in the laboratory. It would have well-defined properties. The critical one would be that it would decay primarily into very heavy particles, which would then also decay.
The "discovery" of the Higgs boson verified this prediction. Below is a photo (actually a computer-generated depiction) of a Higgs event, taken by the team at the laboratory near Geneva. This photo also appears in my book, Now: The Physics of Time. (My book talks about more than just time, of course.)
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