Scientists have observed that light from almost all distant galaxies is red-shifted, and that galaxies further away show a greater red shift than galaxies that are closer. Describe what these two observations tell us about the universe.

Model answer (4 marks)

Examiner tips

• Use the exact terms ‘red shift’, ‘wavelength’, ‘moving away’, ‘expanding’, ‘greater red shift’, ‘faster’, ‘single point’, ‘Big Bang’.
• Show the logical sequence: red shift → moving away → expansion → distance–velocity relation → Big Bang.
• Keep each point brief and to the point to hit the 4 marks.

Common mistakes

• Confusing red shift with blue shift or mis‑stating the direction of motion.
• Lacking the link between distance and velocity (the Hubble law).
• Using vague phrases like ‘the universe is changing’ instead of ‘expanding’ or ‘moving away’.