Part VI — Chapter 18
Cosmology & the Big Bang
Understanding the origin, structure, and fate of the universe
18.1 The Expanding Universe
In 1929, Edwin Hubble showed that galaxies are receding from us, with velocity proportional to distance — the universe is expanding. This implied a beginning: the Big Bang.
18.2 The Cosmic Microwave Background
In 1965, Arno Penzias and Robert Wilson detected faint microwave radiation filling all of space — the afterglow of the Big Bang, predicted by Gamow, Alpher, and Herman. This clinched the Big Bang theory.
18.3 Dark Matter and Dark Energy
Observations of galaxy rotation curves and distant supernovae revealed that ordinary matter makes up only about 5% of the universe. The rest is dark matter (~27%) and dark energy (~68%), which is accelerating the expansion. Understanding these remains one of the greatest challenges in physics.