Was the Big Bang really an explosion?
Not in the usual sense. It wasn't a blast at one point in space but the expansion of space itself. In 1929 Hubble found that more distant galaxies show greater redshift—they're receding faster (similar in spirit to the Doppler effect). Run the movie backward and the universe was once tiny and incredibly hot.
What's the evidence?
In 1965 Penzias and Wilson stumbled on the cosmic microwave background, the cooled afterglow of the early universe. The roughly 3-to-1 ratio of hydrogen to helium matches Big Bang nucleosynthesis predictions. Planck satellite data put the universe's age at about 13.8 billion years. Dark matter, dark energy, and what came "before" remain open questions.
FAQ
- Who named it the Big Bang?
- Fred Hoyle, a critic of the theory, on a 1949 BBC radio broadcast.
- Is the universe still expanding?
- Yes—and the expansion is accelerating.
Sources reviewed: 2026-10-25
References
- Hubble, E. (1929). A relation between distance and radial velocity among extra-galactic nebulae. PNAS, 15(3), 168–173.
- Penzias, A. A., & Wilson, R. W. (1965). A measurement of excess antenna temperature at 4080 Mc/s. Astrophysical Journal, 142, 419–421.
- Planck Collaboration (2020). Planck 2018 results. VI. Cosmological parameters. Astronomy & Astrophysics, 641, A6.