Tired light is a class of hypothetical redshift mechanisms that were proposed as an alternative explanation for the redshift-distance relationship. Tired light was first proposed in 1929 by Fritz Zwicky who suggested that photons might slowly lose energy as they travel vast distances through a static universe by interaction with matter or other photons, or by some novel physical mechanism. Since a decrease in energy corresponds to an increase in light's wavelength, this effect would produce a redshift in spectral lines that increase proportionally with the distance of the source. The term "tired light" was coined by Richard Tolman in the early 1930s Qan8pC-k15hfxl8ipWbog" target="_blank">http://books.google.com/books?vid=ISBN0792340442&id=2-0p1eOCYeIC&pg=PA29&lpg=PA29&dq=%22tired+light%22+coined+tolman&sig=wi74K_Qan8pC-k15hfxl8ipWbog.

Tired light mechanisms were among the proposed alternatives to the _Big Bang and the Steady State cosmologies, both of which proposed that Hubble's law was associated with a metric expansion of space. Through the middle of the twentieth century, most cosmologists supported one of these two paradigms, but there were a few scientists who worked with the tired light alternative. As the discipline of observational cosmology developed in the late twentieth century and the associated data became more numerous and accurate, the Big Bang emerged as the predominant cosmological theory and is accepted in the current parametrization of the state and evolution of the universe. The vast majority of physicists and astronomers accept the conclusions of various studies that such an effect either does not or cannot account for cosmological redshifts.