alkuräjähdykseksi

Alkuräjähdykseksi, often translated as the Big Bang, is the prevailing cosmological model for the universe's earliest known periods. It describes how the universe expanded from an extremely hot, dense state. The theory is not an explanation of the origin of the universe itself, but rather a description of its evolution from that initial state. Observational evidence supporting the Big Bang theory includes the cosmic microwave background radiation, the abundance of light elements like hydrogen and helium, and the observed expansion of the universe.

The concept of the Big Bang originated from observations of galactic redshift, which indicated that galaxies are generally moving away from each other. This led to the inference that the universe was once much smaller and denser. The term "Big Bang" was coined by astronomer Fred Hoyle in 1949, though he was a proponent of a competing steady-state model at the time. Over time, accumulating evidence has strongly favored the Big Bang model.

Key tenets of the Big Bang theory include the idea that the universe has been expanding and cooling for billions of years. The initial moments of the universe are thought to have involved rapid inflation, followed by the formation of subatomic particles, then atoms. Gravity then played a crucial role in the formation of stars and galaxies from these primordial elements. While the Big Bang model provides a robust framework for understanding cosmic history, ongoing research continues to refine our understanding of the very earliest moments and the fundamental forces at play.