Cosmological Redshift

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In Friedman-Robertson-Walker metrics, the wavelength of a photon expands in proportion to the scale factor of the Universe. This gives rise to the cosmological redshift; as the Universe epxands, wavelengths of light expand along with it, thereby shifting them to the red.

In this animation, a photon (or, really, one wavelength of light) is emitted by one galaxy in the direction of another. The photon moves through the Universe (across the surface of the sphere that represents the Universe, borrowed from The Expanding Universe animation). As it moves, the Universe expands, as does the wavelength of light (but not the galaxies). Eventually it arrives at the second galaxy ("us"), redder than it was when it started.

As with many of my movies, there is no narration or sound. It's designed to be used by a lecturer, who will pause it at opportune places to discuss it or ask questions of students.

This work is licensed under a Creative Commons License.

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