the expanding universe

• Red-shift


  The change in wavelength of light from a distant star moving away from Earth
• Theories about the development of the Universe, such as the Big Bang theory, are based on astronomical observations and ideas such as red-shift and dark energy
• Emission spectra


  • Light from a star does not contain all the wavelengths of the electromagnetic spectrum
  • Elements in the star absorb some of the emitted wavelengths, so dark lines are present when the spectrum is analysed
  • Different elements produce different patterns of dark lines
• Spectra from distant galaxies show an increase in wavelength, with the dark lines shifted towards the red end of the spectrum
• The more red-shifted the light from a galaxy is

  The faster the galaxy is moving away from Earth
• Astronomers see red-shift in virtually all galaxies, which is a result of the space between the Earth and the galaxies expanding
• Theories about the development of the Universe, such as the Big Bang theory, are based on astronomical observations and ideas such as red-shift and dark energy
• Big Bang theory


  The scientific theory that describes the early development of the Universe
• According to the Big Bang theory, about 13.8 billion years ago the whole Universe was a very small, extremely hot and dense region. From this tiny point, the whole Universe expanded outwards to what exists today
• Evidence from red-shift


  • Astronomers have discovered that, in general, the further away a galaxy is, the more red-shifted its light is
  • This means that the further away the galaxies are, the faster they are moving
  • This is similar to an explosion, where the bits moving fastest travel furthest from the explosion
  • Red-shift data provides evidence that the Universe, including space itself, is expanding
• Evidence from CMBR


  • Astronomers have also discovered a cosmic microwave background radiation (CMBR)
  • This comes from all directions in space and has a temperature of about -270 °C
  • The CMBR is the remains of the thermal energy from the Big Bang, spread thinly across the whole Universe
• Prediction from Big Bang theory: More distant galaxies should move away faster


  Evidence observed: More distant galaxies have greater red-shift
• Prediction from Big Bang theory: Initial Big Bang heat should now be thinly spread across the whole Universe


  Evidence observed: CMBR is everywhere at a temperature of about -270°C
• The discovery of red-shift in light from distant galaxies led to the development of the Big Bang theory
• The discovery of the CMBR, after it had been predicted by the theory, provided very strong support for the Big Bang theory
• Theories about the development of the Universe, such as the Big Bang theory, are based on astronomical observations and ideas such as red-shift and dark energy
• Scientists have tried to work out the density of the Universe to determine if it will expand forever or eventually contract in a 'Big Crunch'
• Astronomical observations of distant galaxies have suggested that the expansion of the Universe is accelerating
• Dark energy


  An unknown form of energy that is thought to cause the Universe to expand faster all the time
• Astronomers have calculated that dark energy must account for 68 per cent of the Universe
• Dark matter


  An unidentified form of matter that accounts for galaxies rotating faster than their visible mass should cause
• Astronomers have calculated that 27 per cent of the Universe must be made of dark matter
• Only 5 per cent of the Universe is made of the matter (stars, galaxies, people, planets and so on) that is currently understood