The expanding universe implies a hot, dense early state and a testable cosmic origin.

Slipher and Hubble linked galaxy redshifts to distance, revealing cosmic expansion.

The cosmic microwave background is the near-uniform relic glow from the early hot universe.

Big Bang nucleosynthesis explains primordial hydrogen, helium, and lithium in line with observations.

Simulations and surveys show large-scale structure shaped by gravity and dark matter.