Cosmology

Cosmology is the study of the origin, structure, and evolution of the universe as a whole. Over the past century, observations have transformed cosmology from philosophical speculation into a precise science with testable predictions. This lesson covers the key observational evidence and theoretical framework for our current understanding of the universe.

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Hubble's Law

In 1929, Edwin Hubble made one of the most important discoveries in the history of science: distant galaxies are moving away from us, and the further away they are, the faster they recede. This relationship is expressed mathematically as:

$v = H_0 d$v=H0​d

where:

• v is the recession velocity of the galaxy (m s⁻¹ or km s⁻¹)
• H₀ is the Hubble constant (the current best estimate is approximately 70 km s⁻¹ Mpc⁻¹)
• d is the distance to the galaxy (measured in megaparsecs, Mpc, where 1 Mpc = 3.09 × 10²² m)

Hubble's law tells us that the universe is expanding — the space between galaxy clusters is stretching. Crucially, this is not galaxies moving through space; it is space itself expanding, carrying the galaxies with it.