The Inflationary Universe
The inflationary universe theory was developed by combining ideas in cosmology with findings from another area of study, particle physics. The connection between these two fields at first seems odd, since the goal of cosmology is to understand the largest objects that we know of, while the goal of particle physics is to understand the smallest. Particle physicists study the protons, neutrons, and electrons that combine to make atoms, as well as a host of other particles, such as the quarks that join to form protons and neutrons. The relationship between the two fields, however, arises naturally from the big bang theory, which implies that the early universe was far hotter than any furnace that can be produced on Earth. Our only hope to understand the behavior of matter at these extreme temperatures is to understand the particles from which the matter is made, and the forces by which the particles interact.
The crucial concept from particle physics that makes inflation possible is the predicted existence of a peculiar form of matter, called a false vacuum, that can turn gravity on its head. Gravity is normally an attractive force between any two objects, but a false vacuum produces a gravitational force that repels. A false vacuum was still just a theoretical idea in 1997, as the energy needed to produce it was much larger than anything available. Nonetheless, particle physicists were reasonably sure that this form of matter can exist.