1. 1
   An astronomer observes light from a distant galaxy, NGC 4321. Using a spectrometer, she compares the absorption lines in the galaxy's light with the same absorption lines produced by a hydrogen lamp in her laboratory. She finds that the absorption lines from the galaxy are shifted towards the red end of the spectrum compared with the laboratory lines.

   (a)

   (a) What term describes this shift of the absorption lines towards the red end of the spectrum?

   [1 mark]

   • ARed-shift
   • BBlue-shift
   • CDiffraction
   • DRefraction

   (b)

   (b) What does this red-shift indicate about the motion of the galaxy relative to Earth?

   [1 mark]

   • AThe galaxy is stationary relative to Earth
   • BThe galaxy is moving towards Earth
   • CThe galaxy is moving away from Earth
   • DThe galaxy is orbiting Earth

   (c)

   (c) Describe how the wavelength and frequency of the light from the galaxy compare with the wavelength and frequency of light from the same hydrogen source at rest relative to the observer.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A radio astronomer points a detector at a patch of sky containing no known stars or galaxies. She still measures faint microwave radiation reaching the detector, corresponding to a temperature of about 2.7 K. When she points the detector in a completely different direction, away from any galaxy, she measures almost exactly the same faint microwave radiation.

   (a)

   (a) What is the name given to this microwave radiation that arrives uniformly from every direction in space?

   [1 mark]

   • AReflected radio waves from satellites
   • BSolar radiation
   • CGamma radiation from pulsars
   • DCosmic microwave background radiation

   (b)

   (b) Which theory of the origin of the Universe is best supported by the existence of this radiation?

   [1 mark]

   • ASteady State theory
   • BBig Bang theory
   • CGeocentric theory
   • DHeliocentric theory

   (c)

   (c) Explain why the discovery of this radiation was strong evidence against the Steady State theory.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Two students, Amir and Priya, are debating the origin of the Universe. Amir argues that the Universe has always existed in roughly its current state, with new matter continuously created to keep its overall density constant as it expands. Priya argues instead that the Universe began from an extremely hot, dense point and has been expanding and cooling ever since.

   (a)

   (a) Describe the key difference between the theory Amir is describing (the Steady State theory) and the theory Priya is describing (the Big Bang theory).

   [3 marks]

   (b)

   (b) Both students agree that red-shift is observed in light from distant galaxies. Explain how each theory accounts for this observation, and state which theory is currently more widely accepted by scientists.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A science writer is preparing a public lecture on the history of ideas about the origin of the Universe. She wants to explain to a non-specialist audience why scientists now overwhelmingly favour the Big Bang theory over the Steady State theory, even though both theories were once taken seriously.

   (a)

   (a) Explain, using evidence from red-shift observations, why the expansion of the Universe supports the idea that the Universe began from a single point.

   [6 marks]

   (b)

   (b) Explain how the discovery of the cosmic microwave background (CMB) radiation strengthened the case for the Big Bang theory, and describe one way in which methods of observing the Universe have changed to help scientists gather this kind of evidence.

   [6 marks]

   Total for question 4: 12 marks

End of questions