Cosmic microwave background
The cosmic microwave background (CMB) is thermal radiation left over from the early universe, filling all of space at a temperature of 2.725 K — the oldest light we can observe, emitted roughly 380,000 years after the Big Bang.
Dark energy and the accelerating universe
In 1998, two independent teams discovered that the expansion of the universe is accelerating rather than slowing down, a finding so unexpected it earned the 2011 Nobel Prize in Physics.
Dark matter
Dark matter is a form of matter that neither emits nor absorbs electromagnetic radiation. It accounts for approximately 27% of the universe's total energy content and about 85% of all matter, yet has never been directly observed in a laboratory.
Stellar evolution and nucleosynthesis
Stars are born when gravity compresses hydrogen gas clouds until nuclear fusion ignites; their subsequent lives are governed almost entirely by mass, which determines temperature, luminosity, lifespan, and ultimate fate.
The age and size of the observable universe
The universe is 13.8 billion years old, a figure independently confirmed by the cosmic microwave background, the ages of the oldest stars, and the decay of radioactive heavy elements forged in ancient stellar explosions.
The Big Bang
The Big Bang is the prevailing scientific model for the origin and evolution of the universe, supported by three independent pillars of evidence: the observed expansion of the universe, the cosmic microwave background radiation, and the predicted abundances of light elements produced in the first minutes.
What is Cosmology?
Cosmology is a branch of astronomy that studies the origin, evolution, and eventual fate of the universe.