Cosmology

Almost fourteen billion years ago the universe came into being and we’re still not one hundred percent sure exactly how this happened. The evidence we have available suggests that the universe expanded from a single dense point in a huge explosion, spewing out cosmic matter which became the stars and planets.

The Big Bang

Cosmic Microwave Background Radiation (CMBR)

CMBR is heat energy which is ‘left over’ from the big bang during the initial hot explosion. It has very low frequency and is emitted from all parts of the universe, in all directions. As the universe expands and cools down, the background also cools, causing the CMB radiation to have a lower frequency. This ‘leftover’ radiation is strong evidence in support of the Big Bang theory.

Red-shift

Waves emitted from moving objects which show a change in frequency (and wavelength) as they move. This is the phenomenon which explains why the pitch of an ambulance siren changes as it moves past you and is referred to as the Doppler effect.

The same thing happens with stars emitting light waves - as it moves further away, the light it emits will have a lower frequency. Lower frequencies of light correspond to the red end of the visible spectrum, which is why we call it red-shift. This means that the further away the star is, the lower the frequency of light it will emit.

Astronomers have discovered that the greater the distance a star is from Earth, the more it emits light in the red part of the spectrum. This suggests that the stars are moving away from us and provides evidence that the universe is expanding.

Red-shift calculations

You can calculate how much the light emitted from a galaxy has ‘red-shifted’ using the following equation:

Worked example: