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Tired light mechanisms were 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. 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.

The term "tired light" was coined by Richard Tolman in the early 1930s .

Tired light models

Zwicky's models

Zwicky investigated a number of redshift explanations, ruling out some himself (Zwicky, 1929):

• The Compton Effect:

".. light coming from distant nebulae would undergo a shift to the red by Compton effect on those free electrons But then the light scattered in all directions would make the interstellar space intolerably opaque which disposes of the above explanation. it is evident that any explanation based on a scattering process like the Compton effect or the Raman effect, etc., will be in a hopeless position regarding the good definition of the images"

• Gravitational potential:

"One might expect a shift of spectral lines due to the difference of the static gravitational potential at different distances from the center of a galaxy. This effect, of course, has no relation to the distance of the observed galaxy from our own system and, therefore, cannot provide any explanation of the phenomenon discussed in this paper."

• The Gravitational "Drag" of Light:

".. gravitational analogue of the Compton effect It is easy to see that the above redshift should broaden these absorption lines asymmetrically toward the red. If these lines can be photographed with a high enough dispersion, the displacement of the center of gravity of the line will give the redshift independent of the velocity of the system from which the light is emitted.

Discussion

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.

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 people still propose novel redshift mechanisms which they describe as "tired light" (e.g, Marmet, 1988; Accardi, 1995) as part of alternative cosmology, but almost always receive little or no attention from the wider community.

In general, cosmologists consider tired light models to have too many problems to be worth serious consideration, e.g., Ref. . Tired light as a cosmological explanation 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.

References and external links

• Zwicky, F. 1929. On the Red Shift of Spectral Lines through Interstellar Space. PNAS 15:773-779. Abstract (ADS) Full article (PDF)
• 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. http://arxiv.org/abs/physics/0503070. Archived article (ArXiv)]

• Cosmology
• Theories
• Pseudophysics