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Redshift - GCSE Physics Definition

Reviewed by: Leander Oates

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What is redshift?

In GCSE Physics, redshift refers to the phenomenon where light from distant galaxies and other celestial objects is shifted towards the red end of the visible light spectrum. Redshift occurs because these objects are moving away from Earth, causing the wavelengths of the light they emit to stretch out and appear longer.

Dark lines on two visible light spectra. The dark lines on the spectrum of a distance galaxy are red-shifted when compared to the dark lines of the Sun, GCSE & IGCSE physics revision notes
Dark absorption lines are shifted to the red end of the light spectrum for distant objects, showing they are moving away from Earth

In GCSE Physics, redshift provides important evidence for the expanding universe theory, suggesting that the size of the universe has been increasing since the Big Bang. This idea is supported from observations that most galaxies appear redshifted, indicating they are all moving away from us and from each other.

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Leander Oates

Reviewer: Leander Oates

Expertise: Senior Physics Content Creator

Leander graduated with First-class honours in Science and Education from Sheffield Hallam University. She won the prestigious Lord Robert Winston Solomon Lipson Prize in recognition of her dedication to science and teaching excellence. After teaching and tutoring both science and maths students, Leander now brings this passion for helping young people reach their potential to her work at SME.

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