GCSE Physics - Red-Shift (GCSE AQA P1.5.4)

Nota:

• http://www.bbc.co.uk/schools/gcsebitesize/science/aqa/origins/

1. Doppler Effect
   1. DOPPLER EFFECT: If a wave source is moving relative to an observer there will be a change in the observed wavelength and frequency
   2. the wave source could be light, sound or microwaves
   3. when the source moves away from the observer, the observed wavelength increases and the frequency decreases
   4. when the source moves towards the observer, the observed wavelength decreases and the frequency increases.
   5. EXAMPLE - Ambulance passing you
      1. Coming towards
         1. siren is high-pitched due to a high frequency and short wavelength
      2. Going away
         1. siren is low-pitched due to a lower frequency and long wavelength
   6. the faster the wave source moves, the bigger the difference in pitch (frequency and wavelength)
2. Red-Shift
   1. RED-SHIFT: There is an observed increase in the wavelength of light from most distant galaxies. The further away the galaxies are, the faster they are moving, and the bigger the observed increase in wavelength.
   2. When an object moves away from an observer, its light is affected by the Doppler effect
   3. Red Orange Yellow Green Blue Indigo Violet
      1. away from you <----------^----------> towards you
      2. (Red SHIFT) stationary (Blue SHIFT)
         1. O Y G G --> R O Y Y
         2. O Y G G --> Y G G B
   4. Astronomers have found that the further from us a star is, the more its light is red-shifted. This tells us that distant galaxies are moving away from us, and that the further away a galaxy is, the faster it's moving away
      1. Since we cannot assume that we have a special place in the Universe, this is evidence for a generally expanding universe. It suggests that everything is moving away from everything else
   5. Spectra from distant galaxies
      1. Our Sun contains helium. We know this because there are black lines in the spectrum of the light from the Sun where helium has absorbed light. These lines form the absorption spectrum for helium
      2. When we look at the spectrum of a distant star, we still see an absorption spectrum. However, the pattern of lines has moved towards the red end of the spectrum
      3. The positions of the lines have changed because of the Doppler effect. Their wavelengths have increased (and their frequencies have decreased)
   6. HUBBLE DISCOVERED RED-SHIFT
3. The Big Bang Theory
   1. The observed red-shift provides evidence that the universe is expanding and supports the ‘Big Bang’ theory (that the universe began from a very small initial point).
   2. Current evidence suggests that the universe is expanding and that matter and space expanded violently and rapidly from a very small initial ‘point’. This has also led to the theory that the universe began with a ‘big bang’
   3. Big Bang happened about 13.7 billion years ago (that's 13,700,000,000 years using the scientific definition of 1 billion = 1,000 million)
   4. BIG BANG: The theory states that originally all the matter in the universe was concentrated into a single incredibly tiny point. This began to enlarge rapidly in a hot explosion (called the Big Bang), and it is still expanding today
   5. Astronomers have even detected a cosmic microwave background radiation, CMBR, that is thought to be the heat left over from the original explosion
   6. Reasons backing up Big Bang theory
      1. if the universe if expanding now, then in the past it must have been smaller
      2. trace the existence of our expaniding universe far back enough, there must have been a start
      3. the Big Bang created energy which created matter (E=MC squared)
      4. the light from other galaxies is red-shifted
         1. the other galaxies are moving away from us
      5. the further away a galaxy is, the more its light is red-shifted
         1. the most likely explanation is that the whole universe is expanding. This supports the theory that the start of the universe could have been from a single explosion
      6. the Cosmic Microwave Background Radiation, CMBR, exists
         1. the relatively uniform background radiation is the remains of energy created just after the Big Bang
   7. it is thought that the first thing created in the Big Bang was space and time
4. Cosmic Microwave Background Radiation
   1. COSMIC MICROWAVE BACKGROUND RADIATION (CMBR): A form of electromagnetic radiation filling the universe. It comes from radiation that was present shortly after the beginning of the universe.
   2. PENZIES & WILSON DETECTED ENERGY IN THE SPACE, WHICH THEY LATER REALISED WAS LEFT OVER MATTER AND CMBR PARTICLES FRO THE BIG BANG
   3. The ‘Big Bang’ theory is currently the only theory that can explain the existence of CMBR
   4. The Big Bang was a huge explosion (simply put) which means it must've been created by some sort of energy/heat. CMBR is thought to be the remnants of this energy/heat from the Big Bang throughout space