![]() The value of a redshift is often denoted by the letter z, corresponding to the fractional change in wavelength (positive for redshifts, negative for blueshifts), and by the wavelength ratio 1 + z (which is greater than 1 for redshifts and less than 1 for blueshifts).Įxamples of strong redshifting are a gamma ray perceived as an X-ray, or initially visible light perceived as radio waves. Gravitational waves, which also travel at the speed of light, are subject to the same redshift phenomena. All sufficiently distant light sources show cosmological redshift corresponding to recession speeds proportional to their distances from Earth, a fact known as Hubble's law that implies the universe is expanding.Īll redshifts can be understood under the umbrella of frame transformation laws. The main causes of electromagnetic redshift in astronomy and cosmology are the relative motions of radiation sources, which give rise to the relativistic Doppler effect, and gravitational potentials, which gravitationally redshift escaping radiation. The terms derive from the colours red and blue which form the extremes of the visible light spectrum. The opposite change, a decrease in wavelength and simultaneous increase in frequency and energy, is known as a blueshift, or negative redshift. In physics, a redshift is an increase in the wavelength, and corresponding decrease in the frequency and photon energy, of electromagnetic radiation (such as light).
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