The theory suggests that during a brief period—estimated to have lasted between 10^-36 and 10^-32 seconds after the Big Bang—the universe expanded by a factor of at least 10^26. This expansion was driven by a hypothetical energy field called the *inflaton*, which acted as a form of dark energy. As the inflaton decayed, it seeded the universe with particles and radiation, eventually leading to the formation of matter and the structures we observe today.
One of the primary motivations for inflationary theory was the horizon problem, which questioned why different regions of the universe appear to have the same temperature despite being too far apart to have been in causal contact. Inflationary expansion explains this uniformity by stretching these regions beyond the observable horizon before they could equilibrate differently. Additionally, the theory naturally accounts for the universe’s near-critical density (flatness problem) by fine-tuning the expansion rate during inflation.
Evidence supporting inflationary theory includes observations of the cosmic microwave background (CMB) radiation, which reveals tiny temperature fluctuations consistent with quantum perturbations amplified during inflation. These fluctuations later evolved into the large-scale structure of galaxies and galaxy clusters. While direct detection of the inflaton field remains elusive, ongoing experiments, such as those studying gravitational waves or B-mode polarization in the CMB, aim to provide further confirmation.
Despite its success, inflationary theory is not without challenges. Variations of the theory exist, including chaotic inflation, new inflation, and eternal inflation, each proposing different mechanisms for the inflaton field and its behavior. Some models also attempt to reconcile inflation with quantum gravity and string theory, though these remain speculative. Overall, inflationary theory remains the leading framework for explaining the universe’s early evolution and its large-scale properties.