Cosmological Redshift
An effect where light emitted from a distant source appears redshifted because
of the expansion of spacetime itself. Compare Doppler
effect.
In physics (especially astrophysics), redshift happens when light seen coming from an object that is moving away is proportionally increased in wavelength, or shifted to
the red end
of the spectrum. More
generally, where an observer detects electromagnetic
radiationoutside
the visible
spectrum,
"redder" amounts to a technical shorthand for "increase in
electromagnetic wavelength" — which
also implies lower frequency and photon energy in accord with, respectively, the wave and quantum theories of
light.
Redshifts
are attributable to the Doppler effect, familiar in
the changes in the apparent pitches of sirens and frequency of the sound waves emitted by speeding vehicles; an observed
redshift due to the Doppler effect occurs whenever a light source moves away
from an observer.
Cosmological redshift is seen due to the expansion of the universe, and sufficiently distant light sources (generally more than a few million light years away) show redshift corresponding to the rate of increase of their distance from Earth. Finally,gravitational redshifts are a relativistic effect observed in electromagnetic radiation moving out of gravitational fields. Conversely, a decrease in wavelength is called blueshift and is generally seen when a light-emitting object moves toward an observer or when electromagnetic radiation moves into a gravitational field.
Cosmological redshift is seen due to the expansion of the universe, and sufficiently distant light sources (generally more than a few million light years away) show redshift corresponding to the rate of increase of their distance from Earth. Finally,gravitational redshifts are a relativistic effect observed in electromagnetic radiation moving out of gravitational fields. Conversely, a decrease in wavelength is called blueshift and is generally seen when a light-emitting object moves toward an observer or when electromagnetic radiation moves into a gravitational field.
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