Distance measures (cosmology)

From Wikipedia, the free encyclopedia

Physical cosmology

Age of the universe Big Bang Comoving distance Cosmic microwave background Dark energy Dark matter FLRW metric Friedmann equations Galaxy formation Hubble's law Inflation Large-scale structure Lambda-CDM model Metric expansion of space Nucleosynthesis Observable universe Redshift Shape of the universe Structure formation Timeline of the Big Bang Graphical timeline Timeline of cosmology Ultimate fate of the universe Universe

Related topics

Astrophysics General relativity Particle physics Quantum gravity

This box: view • talk • edit

Distance measures are used in physical cosmology to give a natural notion of the distance between two objects or events in the universe. They are often used to tie some observable quantity (such as the luminosity of a distant quasar, the redshift of a distant galaxy, or the angular size of the acoustic peaks in the CMB power spectrum) to another quantity that is not directly observable, but is more convenient for calculations (such as the comoving coordinates of the quasar, galaxy, etc). The distance measures discussed here all reduce to the naïve notion of Euclidean distance at low redshift.

In accord with our present understanding of cosmology, these measures are calculated within the context of general relativity, where the Friedmann-Robertson-Walker solution is used to describe the universe.

Contents 1 Types of Distance Measures 2 Comparison of Distance Measures 3 See also 4 References

[edit] Types of Distance Measures

• Angular diameter distance or Proper motion distance
• Luminosity distance
• Comoving distance
• Lookback time (this is how long ago light left an object of given redshift)
• Naive Hubble's law, taking z = H₀d/c, with H₀ today's Hubble constant, z the redshift of the object, c the speed of light, and d the "distance."

[edit] Comparison of Distance Measures

[edit] See also

• Big Bang
• Comoving distance
• Friedmann equations
• Physical Cosmology

[edit] References

• P. J. E. Peebles, Principles of Physical Cosmology. Princeton University Press (1993)
• Scott Dodelson, Modern Cosmology. Academic Press (2003).