Cosmic horizons represent fundamental boundaries in our observable universe, created by the interplay between light's finite speed and the universe's expansion history. These invisible barriers determine the maximum distance from which light or information can reach us, essentially defining the edge of everything we can potentially observe.</p><p>The most important is the **particle horizon**, located approximately 46.5 billion light-years away—our cosmic horizon of observability. Though the universe is only 13.8 billion years old, space itself has expanded during light's journey to us, stretching this boundary far beyond 13.8 billion light-years. When we observe the Cosmic Microwave Background radiation, we're seeing this horizon as it existed 380,000 years after the Big Bang, when the universe first became transparent.</p><p>The **event horizon** represents an even more sobering boundary—the farthest distance from which light emitted today could ever reach us, given accelerating cosmic expansion driven by dark energy. Currently about 16 billion light-years away, this horizon is actually shrinking, meaning galaxies beyond it are disappearing from our potential future view forever.</p><p>These concepts emerged from Einstein's relativity and were refined through observations by Edwin Hubble and modern cosmologists. Cosmic horizons remind us that our observable universe, vast as it seems, represents only a finite portion of a potentially infinite cosmos.