There is a Cosmic Background Radiation uniformely distributed throughout the Universe. This is relevant the Big Bang Theory predicted that the universe's beginning was unfathomably hot, and the universe filled with radiation as space expanded, leaving behind just such a footprint.1, 2
The hot big bang model successfully predicted the early abundance of helium-4, deuterium, helium-3, and lithium-7.1 This is relevant because it is highly improbable that these specific abundances would be predicted accurately by chance.
The Friedman solutions to Albert Einstein’s field equations for the General Theory of Relativity predicts a past time extremity to the universe known as the Big Bang “singularity.”1 This is relevant because the General Theory of Relativity is true (or empirically adequate).
Confirmed predictions made by Einstein's theory of relativity and Big Bang cosmology:
• Relativity-related time-changes on satellite clocks
• Curvature of light around stars due to matter
• Observations that galaxies are receding from one another from some point of explosion.