Tired light

Tired Light is the name given to the hypothesis that the energy of photons of light decreases slowly as it travels through space due to some interaction with matter along the way. As the energy of a photon decreases, so does its frequency whereas its wavelength increases: visible light is shifted towards the red. It was originally postulated in 1929 by Fritz Zwicky as an alternative to the interpretation that the redshift is caused by expansion of the universe, and as an explanation of the inverse correlation between the redshift and the observed brightness and size of galaxies. Most physicists and astronomers do not believe that such an effect can account for cosmological redshifts, and believe the standard explanation that redshift is due to the Hubble's law redshift of an expanding universe.

Related Topics:
Energy - Photon - Fritz Zwicky - Redshift - Expansion of the universe - Hubble's law

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In the tired light theory, photons are thought to lose energy as they travel from distant objects through the gas, dust, other photons, gravity, or vacuum of the intergalactic or interstellar medium, and thus become increasingly redshifted with distance. A simple model for this resistance is that the energy of a photon would decrease exponentially as it travels through space:

Related Topics:
Intergalactic - Interstellar medium - Redshift - Model

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:E(x) = E(0)e^{-x/R},

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where E(x) is energy of the photon at distance x from the source of light, E(0) is energy of the photon at the source of light, and R is a large constant characterizing the "resistance of the space". In order not to be detectable in the laboratory, the distance R must be very large. A cosmology that accounted for a tired light phenomenon would not require universal expansion to account for galactic redshifts. Gas and dust are unlikely causes of tired light, because they reflect photons rather than decreasing their frequency while preserving their trajectory. Photon interactions are also an unlikely cause of tired light, as they would most likely cause as many blue shifts as red shifts.

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Tired light models have not reproduced the successes, beyond Hubble's law, of the standard big bang cosmology. They do not account for the observed time dilation of distant supernovae light curves (Wilson, 1939 and Goldhaber, 2001), the black body spectrum or anisotropy of the cosmic microwave background, and the observed change in the morphology of high redshift galaxies, quasars and stars. No physical mechanism for tired light has ever been demonstrated, but is presumed by its advocates to be a result of photons interacting with matter, other photons, gravity, or even the vacuum itself in some way.

Related Topics:
Big bang - Supernova - Cosmic microwave background - Galaxies - Quasar - Star

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