13.8 billion years agoReputable source · 2 sourcesWell documented
The Big Bang
On the timeline · around 13.8 billion years ago · Cosmic
What happened
The universe began expanding from an extremely hot, dense state; space, time, matter, and energy originate here.
Why it matters
It is the origin of everything — the start of cosmic time and all subsequent structure.
How we know
The cosmic microwave background, the observed expansion of the universe, and Big Bang nucleosynthesis all converge on an age near 13.8 billion years.
Sources
- NASA Science. The Big Bang · Reputable source
- ESA. Planck reveals an almost perfect Universe (2013) · Reputable source