Tired light

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Tired light is a hypothesis first proposed in 1929 by Fritz Zwicky as an alternative explanation for the redshift-distance relationship. While the Big Bang and the Steady State cosmologies both proposed that the Hubble Law was associated with a metric expansion of space, tired-light cosmology was a proposal that photons slowly lose energy as they travel vast distances through a static universe (for example by an interaction between the photons and some sort of homogeneous and isotropic medium). Since a decrease in energy corresponds to an increase in light's wavelength, this effect would produce a redshift in spectral lines that increase proportionately with the distance of the source. The idea is still promulgated by a few proponents, but the vast majority of physicists and astronomers accept the conclusions of various studies that such an effect does not account for cosmological redshifts.

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Tired light models

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

where <math>E(x)</math> is the energy of the photon at distance x from the source of light, <math>E(0)</math> 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.

To date, no mechanism to produce such a drop in energy has been proposed that reproduces all the observations associated with the redshift-distance relation. 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.

Occasionally new mechanisms are proposed (such as by Paul Marmet and later by Accardi), and compared to tired light in their mechanistic typology. Cosmologists consider such theories of proponents of nonstandard cosmologies to be fringe science.

Tired light as a theoretical description does not reproduce all the successes of the standard big bang cosmology. Tired light theories 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, number count, and surface brightness of high redshift galaxies and quasars. Furthermore, the fact that the age of the oldest stars is roughly equal to the inverse of the Hubble constant emerges naturally from a Big Bang cosmology, but is an unexplained coincidence with tired light models.

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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)
Marmet P.,A New Non-Doppler Redshift Physics Essays, Vol. 1, No: 1, p. 24-32 (1988).
Marmet P., Reber G. Cosmic matter and the Nonexpanding Universe, IEEE Trans. Plasma Science vol.17, no.2, p.264 (1989).
Accardi, L. et al, Physics Letters A 209, A third hypothesis on the origin of the redshift: application to the Pioneer 6 data, p.277-284 (1995)
Goldhaber, G., et al. 2001. (Supernova Cosmology Project). Timescale Stretch Parameterization of Type Ia Supernova B-band Light Curves. Archived article (ArXiv)
Geller J. et al,Test of the expanding universe postulate The astrophysical journal 174, p.1 (1972)
http://www.astro.ucla.edu/~wright/tiredlit.htm Edward Wright of UCLA provides a detailed criticism of tired light.
Moret-Bailly, J. 2005. Interaction between incoherent light beams propagating in excited atomic hydrogen; applications in astrophysics.