Home / Topics / Particle Physics & Cosmology
Hubble's law
Intermediate
Galaxies recede at speeds proportional to distance.
v = H₀dGalaxies recede at speed proportional to distance: v = H₀d, with H₀ ≈ 70 km/s/Mpc. It's evidence of cosmic expansion.
A galaxy at 100 Mpc recedes at 7000 km/s.
Values from different methods disagree (Hubble tension).
In more detail
Hubble's law states that galaxies recede from us at speeds proportional to their distances, v = H0 d. It was the first evidence that the universe is expanding.
Real-world uses
- Hubble's law is used to measure distances to galaxies.
- Cosmologists use the Hubble constant to determine the age of the universe.
- Cosmologists use Hubble's law to measure the expansion rate of the universe from the distances and speeds of galaxies.
Open the interactive lesson, with simulation and quiz →
Frequently asked questions
Who discovered it?
Edwin Hubble, in 1929, using redshifts of galaxies.
Is the Hubble constant known precisely?
Measurements currently disagree slightly, a topic called the Hubble tension.
Is the constant H₀ well measured?
Its value is known to a few percent, but different methods give slightly different values, which is an active area of research.
Related topics in Particle Physics & Cosmology
Black holes in astrophysics · Galaxies · Milky Way · Expansion of the universe · Big Bang theory · Cosmic microwave background