What evidence do we have for the change in size of the universe?
1 Answer
Early evidence for this was observed by Edwin Hubble. He noticed that special lines of far away galaxies were redshifted, meaning that they were moving away from us. Furthermore the redshift was greater for galaxies further away, meaning that the universe was expanding.
Explanation:
Early evidence for this was observed by Edwin Hubble. He noticed that special lines of far away galaxies were redshifted, meaning that they were moving away from us.
Redshift is a consequence of the Doppler effect. When an ambulance is speeding towards you the pitch of its siren seems higher as the sound waves are compressed. As it moves away the pitch lowers as the sound waves are stretched out. Similarly for a galaxy moving towards us, its lightwaves appear more blue as the wavelength is lowered by the galaxy's movement. The light from a galaxy moving away from us will appear redder, as its waves are stretched out (wavelength increased), which is called redshift.
Hubble knew what wavelengths he should have seen from these galaxies, but the light he actually saw was redder, due to redshift, meaning the galaxies were moving away from us.
Furthermore the redshift was greater for galaxies further away. This meant that the universe was expanding, because the galaxies further away from us were moving away faster. This has been compared to an expanding balloon. When you blow a balloon up, all points within it move away form its centre, but a point on the balloons surface will move away from the centre more quickly. Thus as the balloon is expanding, so the outer reaches of the universe are expanding!
