In the first fraction of a second after the Big Bang, the universe is thought to have experienced a period of extremely rapid expansion, growing by a factor of 10⁷⁸ — an unimaginably large number — in an incredibly short time. This idea, known as cosmic inflation, was first proposed by physicist Alan Guth in 1980 to solve two major issues with the traditional Big Bang model. These issues, known as the horizon problem and the flatness problem, involved inconsistencies in how the universe appeared to be both extremely uniform and geometrically flat, despite the expected chaos of a rapidly expanding cosmos. The horizon problem refers to the observation that the cosmic microwave background (CMB), a form of ancient light emitted about 380,000 years after the Big Bang, shows a nearly uniform temperature across the entire observable universe. However, if the universe had only expanded in the usual way, regions that are now far apart would not have had enough time to interact or reach thermal equilibrium. The flatness problem involves the universe's geometry, as calculations suggest that the universe's density must have been extremely close to a critical value — too much and it would have collapsed, too little and it would have expanded too quickly. Inflation provides a solution by explaining how the universe could have started in a very small, uniform region that expanded rapidly, stretching this uniformity across the cosmos. According to Guth's theory, this rapid expansion would have stretched the universe from a tiny, hot zone into a vast, uniform space. This process explains why the CMB is so uniform and why the universe appears flat. Observations of the CMB, made by satellites like the Planck mission, confirm this uniformity, with temperature differences of only about 0.001% across the sky. These small variations, however, are not random — they are the seeds of future galaxies, created by quantum fluctuations that were magnified during inflation. Cosmic inflation also raises intriguing possibilities about the nature of the universe itself. It suggests that the observable universe, vast as it seems, is only a tiny part of a much larger structure. In some models, this larger structure could contain other regions with different physical laws, leading to the concept of a multiverse. In this view, our universe might be just one of many "bubbles," each created by its own inflationary event, existing side by side in a vast cosmic expanse.