What does Hubble's law tell us?
Hubble's law is a fundamental principle in cosmology that describes the relationship between the distance to a galaxy and its recessional velocity, or how fast it is moving away from us. Specifically, Hubble's law states that the recessional velocity of a galaxy is proportional to its distance from us.
Mathematically, Hubble's law can be expressed as v = H0 * d, where v is the recessional velocity of a galaxy, H0 is the Hubble constant (which represents the rate of expansion of the universe), and d is the distance of the galaxy from us.
By observing the redshift (a shift of light towards longer wavelengths) of light emitted by galaxies, astronomers can measure their recessional velocities. By combining this information with measurements of their distances, we can apply Hubble's law to determine their velocities relative to us and infer the current rate of expansion of the universe.
Essentially, Hubble's law tells us that the more distant a galaxy is from us, the faster it appears to be moving away. This observation is one of the key pieces of evidence for the Big Bang theory and the expanding universe. It has provided important insights into the age, size, and evolution of the universe.