Hubble's Law And The Expanding Universe - SS1 Physics Lesson Note

Hubble's law is a fundamental concept in cosmology that describes the relationship between the distance of galaxies from us and their observed redshift, which is a measure of how much the light from a galaxy has been stretched to longer wavelengths. Hubble's law is named after the American astronomer Edwin Hubble, who first proposed it in the late 1920s based on his observations of distant galaxies.

Hubble's law states that the recessional velocity of a galaxy is directly proportional to its distance from us. In other words, galaxies that are farther away from us appear to be moving away from us at faster speeds. This relationship can be mathematically expressed as v = H₀d, where v is the recessional velocity of the galaxy, d is its distance from us, and H₀ is the Hubble constant, which represents the rate at which the universe is expanding.

The implications of Hubble's law led to a groundbreaking discovery known as the expanding universe. Hubble's observations showed that almost all galaxies are moving away from us, regardless of their location in the universe. This suggests that the universe is not static but rather undergoing a process of expansion.

The expanding universe concept is closely linked to the Big Bang theory, which proposes that the universe originated from an extremely hot and dense state about 13.8 billion years ago. According to this theory, the universe has been expanding ever since its inception.

Hubble's law and the expanding universe have revolutionised our understanding of the cosmos. They provide strong evidence for the Big Bang theory and have led to the development of the modern field of cosmology. By studying the redshifts and distances of galaxies, scientists can estimate the age of the universe, track its expansion rate over time, and gain insights into its evolution and large-scale structure.