How does cosmology study the universe as a whole?

Cosmology is the branch of astronomy that studies the universe as a unified whole, focusing on its origin, evolution, and large-scale structure. Because astronomy is primarily an observational science, cosmologists rely on theoretical models, computer simulations, and data from space-based and ground-based instruments to understand the cosmos.123

Key methods and principles include:

• The Cosmological Principle: This fundamental assumption states that the distribution of matter in the universe is homogeneous and isotropic on a large scale, meaning the universe looks the same regardless of an observer's location or the direction in which they look.45
• The Big Bang Model: This widely held theory describes the universe's evolution from an extremely hot, dense primordial state approximately 13.8 billion years ago. Cosmologists use this model to calculate the history of the cosmos and predict the abundance of elements and radiation.4
• Observational Evidence: Scientists study the cosmic microwave background—the remnant radiation from the early universe—to detect density fluctuations that eventually led to the formation of galaxies and large-scale structures.63
• Dark Energy and Dark Matter: By measuring the expansion rate of the universe and the formation of structures, researchers study the influence of dark energy and dark matter, which dominate the universe's mass-energy budget.67