Red-shift and the Big Bang

• How it all began' is a tricky question that we just can't answer. Our best guess at the minute is the Big Bang.
• The Universe Seems to Be Expanding
• All its galaxies seem to be moving away from each other.
• Evidence for the Universe expanding

  1. When we look at light from most distant galaxies, we find that the wavelength has increased

  2. The wavelengths are all longer than they should be- they're shifted towards the red end of the spectrum. This is called red-shift

  3. This suggests the source of the light is moving away from us

  4. Measurements of the red-shift indicate that these distant galaxies are moving away from us (receding) very quickly and it's the same result whichever direction you look in

  5. More distant galaxies have greater red-shifts than nearer ones. This means that more distant galaxies are moving away faster than nearer ones and so all galaxies are moving away from every other galaxy, not just ours
• Red-shift


  The wavelengths of light from distant galaxies are shifted towards the red end of the spectrum, indicating the source is moving away from us
• The inescapable conclusion appears to be that the whole universe (space itself) is expanding.
• Simple model of the expanding universe

  • Imagine a balloon covered with pompoms. As you blow into the balloon, it stretches and the pompoms move further away from each other. The balloon represents the universe and each pompom is a galaxy. As time goes on, space stretches and expands, moving the galaxies away from each other.
• This Evidence Suggests the Universe Started with a Bang
• Theory of the Big Bang

  1. Initially, all the matter in the universe occupied a very small space. This tiny space was very dense and so was very hot

  2. Then it 'exploded'-space started expanding, and the expansion is still going on
• Something important to remember is that the Big Bang theory is the best guess we have so far. Whenever scientists discover new evidence, they have to either make a new theory or change a current one to explain what they've observed.
• Observations of supernovae from 1998 to the present day appear to show that distant galaxies are moving away from us faster and faster (the speed at which they're receding is increasing).
• Currently scientists think the universe is mostly made up of dark matter and dark energy. Dark matter is the name given to an unknown substance which holds galaxies together, but does not emit any electromagnetic radiation. Dark energy is thought to be responsible for the accelerated expansion of the universe. But no-one really knows what these things are, so there are lots of different theories about it. These theories get tested over time and are either accepted or rejected.