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The Wolf Effect (sometimes Wolf shift) is a frequency shift in the electromagnetic spectrum. The phenomenon occurs in several closely related phenomena in radiation physics, with analogous effects occurring in the scattering of light. It was first predicted by Emil Wolf in 1987 and subsequently confirmed in the laboratory by Dean Faklis and George Morris in 1988 . "Under certain conditions", Wolf and James write, "the changes in the spectrum of light scattered on random media may imitate the Doppler effect, even though the source, the medium and the observer are all at rest with respect to one another.

Wolf and James have suggested that the Wolf effect might be a possible non-cosmological redshift in reference to the controversies surrounding the nature of quasars that occurred in the 1970s where certain astronomers believed that quasars were local and others believed that quasars were at cosmological distances. Quasars have subsequently been found to be the distant cores of Active Galactic Nuclei (AGN) and thus the Wolf Effect is not seen as a major component in the redshift of quasars by the mainstream community of astrophysicists.

Theoretical description

In optics, two non-Lambertian sources that emit beamed energy can interact in a way that causes a shift in the spectral lines. It is analogous to a pair of tuning forks with similar frequencies (pitches), connected together mechanically with a sounding board; there is a strong coupling that results in the resonant frequencies getting "dragged down" in pitch.

The Wolf Effect requires that the waves from the sources are partially coherent - the wavefronts being partially in phase. Laser light is coherent while candle light is incoherent, each photon having random phase.

The Wolf Effect can produce either redshifts or blueshifts, depending on the observer's point of view, but is redshifted when the observer is head-on. A subsequent 1999 article by Sisir Roy et al. have suggested that the Wolf Effect may explain discordant redshift in certain quasars .

For two sources interacting while separated by a vacuum, the Wolf effect cannot produce shifts greater than the linewidth of the source spectral line, since it is a position-dependent change in the distribution of the source spectrum, not a method by which new frequencies may be generated. However, when interacting with a medium, in combination with effects such as Brillouin scattering it may produce shifts greater than the linewidth of the source, which Wolf and James describe as frequency independent and "indistinguishable from those due to the Doppler effect".

Wolf effect and Quasars

An example of such a medium which could produce Doppler-like shifts was found in 1990 by Daniel James, Malcolm Savedoff, Malcolm and Emil Wolf, and involved a highly statistically anisotropic scattering medium, that is compatible with current models of quasars. A "no blueshift" condition has also been found by Datta, S. et al., .

Wolf and James note that:

"Although we make no claim that correlation-induced spectral shifts account for all, or even for a majority, of the observed shifts of lines in the spectra of extra-galactic objects, we note the possibility that correlation-induced spectral shifts may contribute to the shifts observed in the spectra of some astronomical objects such as quasars."

Notes

1. After James et al, 1990. Their original caption reads: Fig 2.—Two O_III lines (λ = 4959 Å and λ = 5007 Å) as seen at rest (solid line ), Doppler-shifted (dotted line ), and shifted by the process described in this paper (dashed line ), both by a relative amount z = 0.0714. The FWHM of both lines was taken as 84 km s. The constant C in eq. (23) was chosen so that the height of the stronger shifted line is the same as for the Doppler-shifted line. For shifts induced by the correlation mechanism and shown in the figure, σ = 50 μm, θ = 30°, and θ'= 21°89.
2. Emil Wolf, "Selected Works of Emil Wolf: With Commentary" (2001) p.638, ISBN 981-02-4204-2. See also: Marco Marnane Capria, Physics Before and After Einstein (2005) edited by M. Mamone Capria, p.303 ISBN 1-58603-462-6. See also: S. Roy, S. Data, in Gravitation and Cosmology: From the Hubble Radius to the Planck Scale (2002) by Colin Ray Wilks, Richard L Amoroso, Geoffrey Hunter, Menas Kafatos; page 104, ISBN 1-4020-0885-6
3. ^ James, Daniel, "The Wolf effect and the redshift of quasars" (1998) Pure Appl. Opt. 7: 959-970. (Full text, PDF)
4. ^ Wolf, Emil "Noncosmological redshifts of spectral lines" (1987) Nature 326: 363—365.
5. Wolf, Emil, "Redshifts and blueshifts of spectral lines caused by source correlations" (1987) Optics Communications 62: 12—16.
6. Bocko, Mark F., Douglass, David H., and Knox, Robert S., "Observation of frequency shifts of spectral lines due to source correlations" (1987) Physical Review Letters 58: 2649—2651.
7. Faklis, Dean, and Morris, George Michael, "Observation of frequency shifts of spectral lines due to source correlations" (1988) Optics Letters 13 (1): 4—6.
8. ^ Wolf, Emil, and James, Daniel F. V., "Correlation-induced spectral changes" (1996) Reports on Progress in Physics 59: 771—818. (Full text, PDF)
9. Roy, Sisir, Kafatos, Menas, and Datta, Suman, "Shift of spectral lines due to dynamic multiple scattering and screening effect: implications for discordant redshifts" (2000) Astronomy and Astrophysics, v.353, p.1134-1138 353: 1134—1138.
10. James, Daniel F. V.; Wolf, Emil, "Doppler-like frequency shifts generated by dynamic scattering" (1990) Physics Letters A, Volume 146, Issue 4, p. 167-171.
11. James, Daniel F. V.; Wolf, Emil, "A class of scattering media which generate Doppler-like frequency shifts of spectral lines" (1994) Physics Letters A, Volume 188, Issue 3, p. 239-244.
12. James, Daniel F. V., Savedoff, Malcolm P., and Wolf, Emil, "Shifts of spectral lines caused by scattering from fluctuating random media" (1990) Astrophysical Journal 359: 67—71. (Full text, PDF)
13. Datta, S., Roy, S., Roy, M., and Moles, M., "Effect of multiple scattering on broadening and the frequency shift of spectral lines" (1998) Physical Review A 58 (1): 720—723.
14. Roy, S., Kafatos, M., and Datta, S., "Shift of Spectral Lines due to Dynamic Multiple Scattering and Screening Effect: Implications for Discordant Redshifts" (1999) astro-ph/9904061

See also

• Scattering

• Scattering
• Spectroscopy