### cosmological time dilation

**(cosmic time dilation)**
(very distant events appear to take longer)

**Cosmological time dilation** (or **cosmic time dilation**)
is the phenomenon that events observed at cosmological
distances (i.e., with a significant redshift) appear
to take longer than they would if they were nearby.
Given the expanding distance between us and the event
(Hubble expansion),
light takes increasing amounts of time to reach us over the
course of the event.
The lengthening ratio is (z+1)/z, the same ratio as
redshifted wavelengths from the same distance,
and the two can be considered the same phenomenon.
Some such time dilation would occur from the increase in distance
irrespective of relativity (just as a musical performance
would sound for a longer time if you are moving away from it),
but relativity does affect cosmological time dilation,
significantly for very distant objects.

Observation of distant events such as supernova light curves
do last longer than corresponding nearer events, in proportion to
the redshift(s) determined from recognizable spectral lines.

(*physics,cosmology*)
**Further reading:**

http://burro.astr.cwru.edu/Academics/Astr328/Notes/Redshift/redshift.html

**Referenced by pages:**

observable universe

time dilation

tired light

Index