Editing Tired light (section)

{{short description|Class of hypothetical redshift mechanisms}}
{{cosmology}}
'''Tired light''' is a class of hypothetical [[redshift]] mechanisms that was proposed as an alternative explanation for the [[Hubble's law|redshift-distance relationship]]. These models have been proposed as alternatives to the models that involve the [[expansion of the universe]]. The concept was first proposed in 1929 by [[Fritz Zwicky]], who suggested that if photons lost energy over time through collisions with other particles in a regular way, the more distant objects would appear redder than more nearby ones.

Zwicky acknowledged that any sort of [[scattering]] of light would blur the images of distant objects more than what is seen. Additionally, the [[Tolman surface brightness test|surface brightness of galaxies evolving with time]], [[time dilation]] of cosmological sources, and a thermal spectrum of the [[cosmic microwave background]] have been observed—these effects should not be present if the cosmological redshift was due to any tired light scattering mechanism.<ref name="nedwright">[[Ned Wright|Wright, E. L.]] ''[http://www.astro.ucla.edu/~wright/tiredlit.htm Errors in Tired Light Cosmology]''.</ref><ref name="treu" /><ref name="Peebles">
{{Cite book
 |last1=Peebles|first1 = P. J. E.
 |year=1998
 |chapter=The Standard Cosmological Model
 |editor-last=Greco |editor-first=M. 
 |title=Rencontres de Physique de la Vallee d'Aosta
 |arxiv = astro-ph/9806201
}}</ref> Despite periodic re-examination of the concept, tired light has not been supported by observational tests and remains a [[fringe physics|fringe topic]] in astrophysics.<ref name="overduin-2008">
{{cite book
 |first1=James Martin |last1=Overduin
 |first2=Paul S. |last2=Wesson
 |year=2008
 |title=The light/dark universe: light from galaxies, dark matter and dark energy
 |page=10
 |publisher=World Scientific Publishing
 |isbn=978-981-283-441-6
}}</ref>