In a terrestrial laboratory, the absorption line of singly-ionized calcium (Ca-II K) is measured at a wavelength of 3.934×10−7 m3.934 \times 10^{-7} \text{ m}3.934×10−7 m. When astronomers observe a distant galaxy cluster, they record the wavelength of this same line as 4.228×10−7 m4.228 \times 10^{-7} \text{ m}4.228×10−7 m.
Explain how this observation supports the theory that the Universe is expanding.
53 exam-style questions on Edexcel GCSE Physics 7.2 The Universe and red-shift, covering 7.2.1 Big Bang and Steady State theories, 7.2.2 Evidence for the Big Bang, 7.2.3 The Doppler effect and red-shift, 7.2.4 Red-shift as evidence for an expanding Universe, and 7.2.5 The CMB and the accepted model. Each one has a worked solution and a mark scheme showing where the marks go.