Shortly after the Big Bang, the universe experienced an incredibly fast and dramatic expansion known as cosmic inflation. This occurred within a fraction of a second—from about 10⁻³⁶ to 10⁻³² seconds after the universe began.
During inflation, the universe expanded exponentially, growing much faster than the speed of light (this does not violate relativity because space itself was expanding, not objects moving through space). This rapid stretching smoothed out any irregularities and made the universe appear homogeneous and isotropic on large scales, which matches what we observe today through the cosmic microwave background radiation.
Cosmic inflation also helps explain several puzzling features of the universe, including:
- The Horizon Problem: Why distant regions of the universe have the same temperature despite not being in contact.
- The Flatness Problem: Why the universe appears to have a very flat geometry.
- The Structure Problem: How tiny quantum fluctuations during inflation seeded the formation of galaxies.