The Expanding Universe

• Usually, when an object emits waves, the wavefronts spread out symmetrically

  • If the wave source moves, the waves can become squashed together or stretched out
• Diagram showing the wavefronts produced from a stationary object and a moving object

  A) stationary

  B) moving

  
• A moving object will cause the wavelength, λ, (and frequency) of the waves to change:

  • The wavelength of the waves in front of the source decreases and the frequency increases
  • The wavelength behind the source increases and the frequency decreases
  • This effect is known as the Doppler effect
• The Doppler effect also affects light

  • If an object moves away from an observer the wavelength of light increases
  • This is known as redshift as the light moves towards the red end of the spectrum
• Redshift is an increase in the observed wavelength of electromagnet radiation emitted from receding stars and galaxies
• Light from a star that is moving towards an observer will be blueshifted and light from a star moving away from an observer will be redshifted

  A) blueshift

  B) redshift

  
• Light from a star that is moving towards an observer will be blueshifted and light from a star moving away from an observer will be redshifted

  A) not moving

  B) lower

  C) higher

  D) red shift

  E) blue shift

  
• The Milky Way is just one of billions of galaxies that make up the Universe
• Light emitted from distant galaxies appears redshifted when compared with light emitted on Earth
• The diagram below shows the light coming to us from a close object, such as the Sun, and the light coming to us from a distant galaxy

  • shows that the light coming to us from distant galaxies is redshifted
  • This indicates that the galaxies are moving away from us
  • The lines on the spectrum are shifted towards the red end

  
• The diagram below shows the light coming to us from a close object, such as the Sun, and the light coming to us from a distant galaxy

  A) close

  B) distant

  
• If the galaxies are moving away from us it means that the universe is expanding

  • The observation of redshift from distant galaxies supports the Big Bang theory
• Another observation from looking at the light spectrums produced from distant galaxies is that the greater the distance to the galaxy, the greater the redshift

  • This means that the further away a galaxy, the faster it is moving away from us
• Graph showing the greater the distance to a galaxy, the greater the redshift

  A) redshift

  B) distance