Hubble’s Law is a fundamental observation in cosmology that shows galaxies are moving away from us, and that their recession speed increases with distance. In other words, the farther away a galaxy is, the faster it appears to be moving away. This relationship implies that the universe is expanding.
Discovered by Edwin Hubble in 1929, this law was based on two key observations:
- Redshifted light from distant galaxies, indicating they are receding.
- A linear relationship between the galaxy’s redshift and its distance from Earth.
This discovery transformed our understanding of the universe. Rather than being static and unchanging, the universe was shown to be dynamic and evolving. Hubble’s Law provided strong support for the Big Bang theory, which proposes that the universe began from an extremely hot, dense state and has been expanding ever since.
The rate of expansion is described by the Hubble constant (H₀). Measuring its exact value remains an active area of research, with different methods yielding slightly different results—highlighting an ongoing mystery in modern cosmology.