The Big Bang Theory and Cosmic Microwave Background Radiation — AQA GCSE Physics (Separate)
The Big Bang theory describes the origin of the universe, supported by red-shift and the cosmic microwave background radiation.
The Big Bang theory
The Big Bang theory states that the universe began from a tiny, very hot, dense region about 13.8 billion years ago, which expanded rapidly and has been expanding and cooling ever since.
Evidence: red-shift
Light from distant galaxies is red-shifted (shifted to longer wavelengths), showing the galaxies are moving away from us, and more distant galaxies move away faster. This shows the universe is expanding — consistent with the Big Bang.
Evidence: cosmic microwave background radiation (CMBR)
The cosmic microwave background radiation (CMBR) is low-energy microwave radiation that comes from all parts of the universe. It is "left over" from the early universe — as the universe expanded and cooled, the radiation it produced stretched to longer (microwave) wavelengths.
The CMBR can only be explained by the Big Bang theory, so it is strong supporting evidence. It was predicted by the theory and later discovered, which strengthened scientists' confidence in it.
Ongoing research
Observations suggest the expansion of the universe is accelerating, leading to ideas about dark matter and dark energy, which are not yet fully understood.
Exam tips
- The Big Bang: the universe began small, hot and dense, then expanded and cooled.
- Red-shift shows the universe is expanding.
- The CMBR is microwave radiation from the early universe — only explained by the Big Bang.
- Both red-shift and CMBR are key evidence for the Big Bang theory.