Age of the Universe

The universe is about 13.8 billion years old.^[1] We know this not from one measurement but from several independent lines of evidence that happen to agree. The simplest is the expansion itself: because space is undergoing metric expansion, distant galaxies recede — the pattern captured by Hubble's law — and running that expansion backward points to a beginning. If the rate had always been today's value $H_0$ , the age would just be its inverse:

t_H = \frac{1}{H_0} \approx 14 \ \text{billion years}.

14.0billion years

Hubble constant H₀ = 70 km/s/Mpc

The naive age is just 1 / H₀ — assume today's expansion rate held forever. Measured H₀ ≈ 67–73 lands near 13–14 billion years; the full answer needs the expansion history, not a constant rate.

That "naive" estimate is close by luck; the real expansion rate has changed over time, so the precise age comes from fitting the whole history. The tightest single clock is the cosmic microwave background, whose pattern encodes the conditions of the early universe, and it's cross-checked against the ages of the oldest stars and the cosmic redshift–distance relation. All three routes converge on the same answer — and they also fix where we sit on the whole cosmic timeline.

The precise age depends on what the universe is made of. Dial the amounts of matter and dark energy below to watch the expansion history change — and with it both the age and the ultimate fate:

13.5billion years old

Dark energy wins — expansion accelerates forever toward a cold Big Freeze.

Matter Ω_m = 0.30Dark energy Ω_Λ = 0.70

Curvature Ω_k = 0.00 (flat). Our universe sits near Ω_m ≈ 0.3, Ω_Λ ≈ 0.7 — flat, accelerating, and about 13.8 billion years old. Add matter or remove dark energy and the expansion slows; enough matter and it recollapses.