1. 1
   A science communicator is preparing a public talk explaining the leading scientific theory for the origin and evolution of the universe, and the observational evidence that has led most astrophysicists to accept this theory.

   (a)

   A science communicator is explaining the leading theory of how the universe began to a public audience. What is the name of this widely accepted theory describing the origin and evolution of the universe?

   [1 mark]

   • AThe Big Bang theory
   • BThe steady state theory
   • CThe Doppler theory
   • DThe nebula theory

   (b)

   The communicator explains that the Big Bang theory describes the universe as having expanded from an extremely small, hot and dense state. According to this theory, what has been happening to the universe since this initial state?

   [1 mark]

   • AThe universe has stayed exactly the same size
   • BThe universe has been continuously expanding
   • CThe universe has been steadily shrinking
   • DThe universe expanded once and then instantly stopped

   (c)

   State two pieces of observational evidence that support the Big Bang theory, and briefly describe what each piece of evidence is.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   An observatory technician is analysing spectral lines in light received from several distant galaxies, comparing each galaxy's spectrum with a reference spectrum obtained from the same element in a laboratory on Earth, in order to determine how each galaxy is moving relative to Earth.

   (a)

   An observatory technician is analysing light received from a distant galaxy and comparing it with light from a laboratory source of the same element on Earth. She finds that a particular spectral line from the galaxy has a longer wavelength than the same line measured in the laboratory. What does this observation indicate about the galaxy's motion 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's motion cannot be determined from this observation

   (b)

   The technician then examines a second, more distant galaxy and finds that its red-shift is even greater than that of the first galaxy. What does this generally indicate about the second galaxy compared with the first?

   [1 mark]

   • AThe second galaxy is not moving at all relative to Earth
   • BThe second galaxy is moving towards Earth, unlike the first galaxy
   • CThe second galaxy is closer to Earth than the first galaxy
   • DThe second galaxy is moving away from Earth at a greater speed than the first galaxy

   (c)

   A spectral line with a reference wavelength of $6.0 \times 10^{-7}$ m is observed from a distant galaxy at a wavelength of $6.3 \times 10^{-7}$ m. Using the relationship $\dfrac{\lambda - \lambda_0}{\lambda_0} = \dfrac{v}{c}$, calculate the velocity of the galaxy relative to Earth, given that the speed of light $c = 3.0 \times 10^{8}$ m/s.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A group of cosmologists is compiling red-shift and distance data from many galaxies observed by different telescopes, in order to build a clearer picture of how the universe has evolved and continues to change over time.

   (a)

   A group of cosmologists is compiling data showing that galaxies at greater distances from Earth generally show larger red-shifts than galaxies closer to Earth. Explain why this relationship between distance and red-shift provides evidence that the universe is expanding.

   [3 marks]

   (b)

   The cosmologists also study the cosmic microwave background radiation detected uniformly from every direction in space. Explain what this radiation is believed to be, and why its existence provides further support for the Big Bang theory in addition to red-shift evidence.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A university physics department is producing an introductory lecture for first-year students explaining how observations of light from distant galaxies have shaped modern understanding of the origin and ongoing expansion of the universe.

   (a)

   A university is producing an introductory lecture explaining how red-shift evidence supports the theory that the universe is expanding. Explain the physical cause of red-shift when a wave source, such as a distant galaxy, is moving away from an observer, and describe how this general principle applies to light received from galaxies at many different distances from Earth.

   [6 marks]

   (b)

   The lecture also covers the cosmic microwave background radiation. Explain what this radiation is, why it exists at microwave wavelengths today rather than at much shorter wavelengths, and discuss how both this radiation and red-shift observations together build a coherent case for the Big Bang theory.

   [6 marks]

   Total for question 4: 12 marks

End of questions