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Template:Totallydisputed Tired light is the hypothesis that light slowly loses energy as it travels through space. Since a decrease in energy corresponds to an increase in wavelength, this effect would produce a redshift in spectral lines that increases with the distance of the source. It was originally postulated in 1929 by Fritz Zwicky as an alternative to the standard interpretation that the redshift is caused by expansion of the universe. Most physicists and astronomers do not believe that such an effect can account for cosmological redshifts.

The simplest form of a tired light theory assumes an exponential decrease in photon energy with distance traveled:

${\displaystyle E(x)=E(0)e^{-x/R},}$

where ${\displaystyle E(x)}$ is the energy of the photon at distance x from the source of light, ${\displaystyle E(0)}$ is energy of the photon at the source of light, and R is a large constant characterizing the "resistance of the space". To correspond to Hubble's law, the constant R must be several gigaparsecs. Various mechanisms to produce such a drop in energy have been proposed. Scattering by known mechanisms from gas or dust does not reproduce the observations. For example, scattering by any mechanism would be expected to blur the images of distant objects, which is not observed.

In recent years, new tired light mechanisms have been put forward (Marmet 1988), in which photons lose energy by interacting with electrons and other particles in intergalactic space. According to standard theory, bremsstrahlung is radiated away at any collision with a charged particle such as an electron so that a very small energy loss occurs at each interaction, which arguably results in a redshift.

However, such tired light mechanisms alone cannot fully explain cosmological redshift: they can not replace the Doppler explanation. 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.

References and External Links

• Zwicky, F. 1929. On the Red Shift of Spectral Lines through Interstellar Space. PNAS 15:773-779. Archived article (ADS)

• Wilson, O. C. 1939. Possible applications of supernovae to the study of the nebular red shifts. Astrophysics Journal 90:634. Archived article (ADS)

• Goldhaber, G., et al. 2001. (Supernova Cosmology Project). Timescale Stretch Parameterization of Type Ia Supernova B-band Light Curves. Archived article (ArXiv)

• P.Marmet, A New Non-Doppler Redshift, Physics Essays, Vol. 1, No: 1, p. 24-32 (1988).

• http://www.astro.ucla.edu/~wright/tiredlit.htm Edward Wright of UCLA provides a detailed criticism of tired light.

• The general time dilation (relativistic redshift in stationary clouds of dust) W. Jim Jastrzebski provides an explanation of how Einstein's General Relativity (of 1915) predicts a simulated tired light effect in clouds of dust, and consequently how it predicts the appearance of an accelerating expansion of space.

• Theories
• Cosmology