Space Physics and Astrophysics - SS2 Physics Past Questions and Answers - page 4

v = H0/d (where v is the recession velocity, H0 is Hubble's constant, and d is the distance)

Hubble's Law states that the recession velocity of a galaxy is directly proportional to its distance from Earth. This means that the farther a galaxy is from us, the faster it is moving away. Hubble's Law provided strong evidence for the concept of an expanding universe. It implies that the universe is not static but rather undergoing continuous expansion. The law also led to the development of the Big Bang theory, which suggests that the universe originated from a singularity and has been expanding ever since. Hubble's Law allows astronomers to estimate the distances and velocities of galaxies, providing insights into the structure, age, and evolution of the universe.

There are several pieces of observational evidence that support Hubble's Law and the expanding universe. One crucial piece of evidence is the observation of the redshift of light from distant galaxies. Redshift occurs when light from an object is stretched, causing its wavelength to increase. This stretching of light is due to the expansion of space itself. The degree of redshift observed in galaxies is directly correlated with their distances from us, confirming the relationship described by Hubble's Law.

Another supporting evidence is the isotropy and homogeneity of the universe on a large scale. Observations show that, on average, galaxies are distributed uniformly in all directions, indicating a homogeneous distribution. This supports the idea that the universe is expanding uniformly in all directions, as predicted by the expanding universe model.

Additionally, the cosmic microwave background radiation (CMB) provides strong evidence for the Big Bang and the expanding universe. The CMB is a faint, uniform radiation that permeates the entire universe and is considered the afterglow of the early hot and dense stages of the universe. The observed pattern of the CMB supports the idea that the universe was once much denser and hotter and has been expanding since its inception.