In physical cosmology, a cosmological horizon (also known as a particle horizon) is the maximum distance from which particles could have traveled to the observer in the age of the universe. It represents the boundary between the portion of the universe which could have conceivably been observed at a given time (the observable universe) and the unobservable regions of the universe.[1]
The existence, properties, and significance of a cosmological horizon depend on the particular cosmological model being discussed.
Background
In terms of comoving distance, the particle horizon is equal to the conformal time η0 that has passed since the Big Bang, times the speed of light c. The quantity η0 is given by,
where a(t) is the scale factor of the Friedmann-Robertson-Walker metric, and we have taken the Big Bang to be at t = 0. In other words, the particle horizon recedes constantly as time passes, and the observed fraction of the universe always increases.[1][2]
The particle horizon differs from the event horizon in that the particle horizon represents the largest comoving distance from which light could have reached the observer by a specific time, while the event horizon is the largest comoving distance from which light emitted now can ever reach the observer.
Source
- Lars Bergström and Ariel Goobar: "Cosmology and Particle Physics", WILEY (1999), page 65. ISBN 0471970417
See also
External links
References
- ^ a b http://books.google.com/books?id=kNxeHD2cbLYC&pg=PA447&dq=%22Particle+horizon%22&as_brr=3#v=onepage&q=%22Particle%20horizon%22&f=false Cosmology: the science of the universe By Edward Robert Harrison, p. 447
- ^ http://books.google.com/books?id=xma1QuTJphYC&pg=PA418&dq=%22Particle+horizon%22&as_brr=3#v=onepage&q=%22Particle%20horizon%22&f=false General relativity: an introduction for physicists By Michael Paul Hobson, George Efstathiou, Anthony N. Lasenby, p. 419
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