BRAINCAKEEvolution of the Universe
The universe has been expanding and cooling since the Big Bang. As it cooled, its particles could combine into more complex structures. A simplified timeline:
• t = 0: the Big Bang. The universe is extremely hot and dense, and space and time begin.
• t ≈ 10−35 s: a very rapid expansion (inflation). The universe is a hot 'soup' of fundamental particles: quarks, leptons and photons, with particles and antiparticles constantly created and annihilated.
• t ≈ 10−6 s: the universe has cooled enough for quarks to combine into hadrons, such as protons and neutrons. Slightly more matter than antimatter survives the annihilations.
• t ≈ 100 s to 20 minutes: protons and neutrons fuse to form helium nuclei (and a little deuterium and lithium). After this the universe is too cool and spread out for fusion, leaving about 75% hydrogen and 25% helium by mass.
Sign in free to see the rest of this lesson, the R.E.C.I.P.E. recall steps and the quiz
BrainCake is free. Make an account in seconds and pick up where this page stops.
Key terms in this lesson
- cosmic microwave background radiation
- Microwave radiation reaching the Earth almost uniformly from every direction, left over from the hot early universe and stretched by its expansion.
- quark
- A fundamental particle that combines with others, bound by the strong nuclear force, to form hadrons such as protons and neutrons.
More in Astrophysics and Cosmology
- The Cosmological Principle
- The Doppler Effect and Red Shift
- Hubble's Law
- The Big Bang Theory
- Cosmic Microwave Background Radiation
- The Age of the Universe
- Dark Matter
- Dark Energy
All 24 lessons in Astrophysics and Cosmology · All OCR A-level Physics topics