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The '''redshift''' of a given object is a measure of the amount that the wavelength of its emitted or reflected electromagnetic radiation has increased. This increase in wavelength is due to the relative motion of a source with respect to an [[Scientific observation|observer]]; a [[light]] emitting source moving away from an observer will have its spectrum shifted toward longer (in optical light, redder) wavelengths. In practice this is analogous to the [[Doppler shift]]ing of sound waves emitted from a moving source. Light emitted from a source moving towards an observer will experience a blueshift. In the case of redshift, however, most of the redshift is believed to be due not to the object moving through space, but to the expansion of space itself.
The '''redshift''' of a given object is a measure of the amount that the wavelength of its emitted or reflected electromagnetic radiation has increased. This increase in wavelength is prevailingly interpreted as due to the relative motion of a source with respect to an [[Scientific observation|observer]]; a [[light]] emitting source moving away from an observer will have its spectrum shifted toward longer (in optical light, redder) wavelengths. In practice this is analogous to the [[Doppler shift]]ing of sound waves emitted from a moving source. Light emitted from a source moving towards an observer will experience a blueshift. In the case of redshift, however, most of the redshift is believed to be due not to the object moving through space, but to the expansion of space itself.
== Support for the Big Bang theory ==
== Support for the Big Bang theory ==
is Hubble constant, <math>c</math> is speed of light in [[vacuum]], and <math>R_E</math> is "Einstein radius", or radius of [[curvature of space]], about 13 billion light years).
is Hubble constant, <math>c</math> is speed of light in [[vacuum]], and <math>R_E</math> is "Einstein radius", or radius of [[curvature of space]], about 13 billion light years).
==Alternative Interpretations of the Redshift==
The redshift phenomenon pertains to observation of spectra of [[light]] emitted from luminous bodies such as [[nebulae]] (stellar systems). The true nature of light is however still uncertain. With current body of knowledge, the light can be portrayed as out-spreading electromagnetic wave or as travelling in bullet-like parcels of energy called quanta. Waves have various wavelengths; quanta carry different amounts of energy. Since the same phenomenon can be described by both concepts, it is regarded as evidence that there is some underlying connection between them. This connection is expressed in the very fundamental relation between the energy-content of a quantum and the equivalent wavelength:
:''energy x wavelength = constant''
:<math>E{\lambda} = constant</math>
Because of this relation, two possible effects can be identified:
*a.) Increase of wavelength <math>{\lambda}</math> implies => a decrease in Energy E; If the primary change is in wavelength, then the red-shifts are probably velocity-shifts, what is nowadays prevailing interpretation.
*b.) Reduction of Energy E implies => an increase of wavelength <math>{\lambda}</math>; The primary change might be also a loss of energy, which would be observed as redshift.
As in either case it is only increased wavelength what is observed, there is no direct way of determining which of the two above effects is fundamental.
In order to be able to distinguish between two alternatives, a critical empirical test is needed that would establish whether or not a luminous body is receding.<ref name="Observational Approach">{{cite web
|title=The Observational Approach to Cosmology
|author=Edwin Hubble
|publisher=Oxford University Press
|year = 1937
|url= http://ned.ipac.caltech.edu/level5/Sept04/Hubble/Hubble_contents.html
|access date=27.09.2012}}</ref>
==See Also==
==See Also==
*[[Expanding universe]]
*[[Expanding universe]]