Red-shift

Red-shift from Distant Galaxies

Redshift is the increase in the wavelength of light emitted from objects that are moving away from the observer. 

When distant galaxies are moving away from us, the light from the galaxies is stretched to longer wavelengths. Hence the light from these galaxies is red-shifted (appears more red) from the light we expect to see. 

Conversely, if a distant galaxy was moving towards us, the light would be squashed to shorter wavelengths and it would appear more blue than the light we would otherwise expect to see. We call this blue-shift.

When we observe distant galaxies, we find that they are all red-shifted. This means that all the galaxies are moving away from us. We also find that more distant galaxies are more red-shifted and so are moving away from us faster than nearer galaxies. This suggests that the universe is expanding which is evidence for the Big Bang theory. 

Scientists have also found that the expansion of the universe appears to be speeding up. This is difficult to explain with the current theory.

The Big Bang Theory

The Big Bang theory states that:

• At first, all of the matter in the universe was in one tiny point. This point was very hot and very dense. 
• This tiny point began expanding and this expansion is still occurring. 

It is this expansion that we observe using red-shift. 

 

A useful analogy for the expansion of the universe are spots on a balloon. When the balloon expands, the space between the spots expands. The universe is similar to this, except there are galaxies inside the volume as well. 

The Big Bang theory is the best explanation scientists have for the evidence that they have so far. In the future, new evidence may be discovered and the Big Bang theory may have to be altered or changed entirely.  We already know there is much we do not understand about the universe such as dark matter and dark energy. These are thought to be causing the expansion of the universe to speed up.