Tired light
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Tired Light (a.k.a. tired light effect) is the name given to the hypothesis that light increasingly becomes redshifted as it travels through space. It was originally postulated in 1929 by Fritz Zwicky as an alternative to Hubble's Law and as an explanation of the positive correlation between the redshift and observed brightess of galaxies. Often cited as further evidence is the small yet measurable differences in redshift of light from different parts of the sun; spectra taken from the limb are slightly more redshifted than spectra taken from the centre.
Photons are thought to lose energy as they travel from distant objects through the gas and dust of the intergalactic or interstellar medium, and thus become increasingly redshifted with distance. A cosmology that accounted for a tired light phenomenon would not require Hubble's law to account for galactic redshifts, and thus removes the need for an expanding universe.
Criticism
The underlying mechanism of a supposed tired light phenomenon is not known, but is presumed to be a result of photons interacting with matter, other photons or even the vacuum itself in some way. As a result of this uncertainty, tired light has been largely ignored in the mainstream of astrophysics and cosmology. Tired light models run into difficulty accounting for the observed time dilation of distant supernovae light curves (Wilson, 1939), the black body curve of the Cosmic microwave background and the Tolson surface brightness test of galaxies.
References and External Links
- Zwicky, F. 1929. On the Red Shift of Spectral Lines through Interstellar Space. PNAS 15:773-779. Archived article (ADS) (http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1929PNAS...15..773Z)
- Wilson, O. C. 1939. Possible applications of supernovae to the study of the nebular red shifts. Astrophysics Journal 90:634. Archived article (ADS) (http://adsabs.harvard.edu/cgi-bin/bib_query?1939ApJ....90..634W)
- Goldhaber, G., et al. 2001. (Supernova Cosmology Project). Timescale Stretch Parameterization of Type Ia Supernova B-band Light Curves. Archived article (ArXiv) (http://arxiv.org/abs/astro-ph/0104382)
- http://www.astro.ucla.edu/~wright/tiredlit.htm Edward Wright of UCLA provides a detailed criticism of tired light.