Astronomers analyzing the light emitted by distant stars in other galaxies observe that the spectral lines are shifted towards the longer wavelength (red) end of the spectrum compared to light from the same elements on Earth.
Explain how this observed shift in wavelength provides evidence 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.