Look at distant galaxies and nearly all of them are rushing AWAY from us — and the farther one is, the faster it flees, in exact proportion. That’s not because we’re special: space itself is stretching, carrying every galaxy apart like raisins in rising dough. Hubble measured it in 1929, and it’s the first evidence the universe began in a Big Bang. Slide the distance and read the recession speed.
Hubble’s Law: a galaxy’s recession velocity is proportional to its distance, v = H₀·d, with the Hubble constant H₀ ≈ 70 km/s per megaparsec. The linearity is the signature of UNIFORM expansion — space stretching everywhere at the same rate, so every observer sees all others receding and no one is at a centre. Running it backwards gives a finite age (~1/H₀ ≈ 14 billion years) — the Big Bang. The velocity is read from cosmological redshift. A fail-loud self-check throws unless doubling the distance doubles the recession speed. ◆ real cosmology, node-verified.
The linear local Hubble law (exact at modest distances); at large z the expansion history (dark energy acceleration) bends it, and H₀ itself is under active tension (~67 vs ~73) — the farther-is-faster proportionality is exact locally.