A specific spectral line of helium has a wavelength of 5.88 × 10-7 m when measured in a laboratory on Earth. When analyzing the light from a distant galaxy, astronomers measure the wavelength of this same line to be 6.15 × 10-7 m.
Explain how this observation provides evidence that the Universe is expanding.
53 exam-style questions on Edexcel GCSE Physics 7.2 The Universe and red-shift. Each one has a worked solution and a mark scheme showing where the marks go.