How the stretching of light reveals a growing universe
In short: By observing how light changes as it travels across space, astronomers can determine if distant galaxies are moving toward or away from us. This video explains the mechanics of red shift and why it serves as foundational evidence for an expanding universe.
Red shift occurs when the wavelength of light increases, shifting its appearance toward the red end of the spectrum. This phenomenon happens because distant galaxies are moving away from Earth. When these objects move, the light they emit is stretched out.
To identify this movement, scientists look at absorption spectra—patterns created by elements absorbing specific wavelengths of light. By comparing these patterns to known standards, researchers can see how much the lines have shifted for distant galaxies, providing a measurable way to track cosmic expansion.
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- Summary by Intellect · source: GCSE Physics - What is Red Shift? (2026/27 exams)
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