Alkuräjähdysperiaate

Alkuräjähdysperiaate, known in English as the Big Bang theory, is the prevailing cosmological model for the observable universe from the earliest known periods through its subsequent large-scale evolution. The theory describes how the universe expanded from a very hot, dense point billions of years ago. It does not describe the initial singularity itself, but rather the evolution of the universe from a very early, hot, and dense state.

Evidence supporting the Big Bang theory includes the observed expansion of the universe, the abundance of light elements (hydrogen and helium) in the universe, and the existence of the cosmic microwave background radiation. The expansion of the universe is evidenced by the redshift of light from distant galaxies, which indicates they are moving away from us. The relative amounts of hydrogen and helium observed today align with predictions made by the Big Bang model for nucleosynthesis in the early universe. The cosmic microwave background radiation is interpreted as the residual heat from the Big Bang, a uniform glow of radiation permeating all of space.

While the Big Bang theory is widely accepted, it does not explain what caused the initial expansion or what existed before it. Ongoing research in cosmology continues to refine and expand upon the Big Bang model, exploring concepts like inflation and dark energy to better understand the universe's origins and evolution. The theory is a cornerstone of modern astronomy and cosmology.