String Theory: Variations of the Inflation Model
Some variations and alternatives to the inflation model are posed by string theorists and other physicists. Two creators of inflation theory, Andreas Albrecht and Paul J. Steinhart, have worked on alternative theories as well.
In 1980, astrophysicist Alan Guth proposed the inflation theory to solve the horizon and flatness problems (although later refinements by Andrei Linde, Andreas Albrecht, Paul Steinhardt, and others were required to get it to work). In this model, the early universal expansion accelerated at a rate much faster than we see today.
It turns out that the inflationary theory solves both the flatness problem and horizon problem (at least to the satisfaction of most cosmologists and astrophysicists). The horizon problem is solved because the different regions we see used to be close enough to communicate, but during inflation, space expanded so rapidly that these close regions were spread out to cover all of the visible universe.
The flatness problem is resolved because the act of inflation actually flattens the universe. Picture an uninflated balloon, which can have all kinds of wrinkles and other abnormalities. As the balloon expands, though, the surface smoothes out. According to inflation theory, this happens to the fabric of the universe as well.
In addition to solving the horizon and flatness problems, inflation also provides the seeds for the structure that we see in our universe today. Tiny energy variations during inflation, due simply to quantum uncertainty, become the sources for matter to clump together, eventually becoming galaxies and clusters of galaxies.
One issue with the inflationary theory is that the exact mechanism that would cause — and then turn off — the inflationary period isn’t known. Many technical aspects of inflationary theory remain unanswered, though the models include a scalar field called an inflaton field and a corresponding theoretical particle called an inflaton. Most cosmologists today believe that some form of inflation likely took place in the early universe.