Astronomers observe a distant galaxy and measure the wavelength of a specific hydrogen spectral line to be 660 nm. The same hydrogen line, when observed in a laboratory on Earth, has a wavelength of 656 nm.
Explain how these observations provide evidence for the expansion of the universe and estimate the age of the universe.
Aim for 120–220 wordsWrite a clear linked explanation using precise physics vocabulary.
Standard OCR A extended-response question.
Your answer
Write a clear, structured response. Include definitions, equations with units, and a concluding statement.
