Key learning points

1. Light from nearly all galaxies is redshifted, showing they're moving away, with distant galaxies receding faster.
2. Evidence shows that galaxies were all in the same place about 14 billion years ago, showing their movement apart since.
3. The Big Bang Theory suggests that the universe began from a very small region that was extremely hot and dense.
4. A scientific theory is our best understanding based on all evidence and is subject to rigorous testing.
5. We do not fully understand dark matter or dark energy.

Common misconception

Keywords

• Redshift - the increase in the wavelength of light (and decrease in its frequency) caused by the movement of a star or galaxy away from us

• Big Bang Theory - the theory that the our whole universe started in a hot, dense state, then expanded and cooled over fourteen billion years

• CMBR - cosmic microwave background radiation is electromagnetic radiation produced in the hot early universe which has since been ‘stretched’ to the microwave part of the spectrum.