Hubble volume

In cosmology, a Hubble volume (named for the astronomer Edwin Hubble) or Hubble sphere, Hubble bubble, subluminal sphere, causal sphere and sphere of causality is a spherical region of the observable universe surrounding an observer beyond which objects recede from that observer at a rate greater than the speed of light due to the expansion of the universe.^[1] The Hubble volume is approximately equal to 10³¹ cubic light years (or about 10⁷⁹ cubic meters).

The proper radius of a Hubble sphere (known as the Hubble radius or the Hubble length) is $c/H_{0}$ , where $c$ is the speed of light and $H_{0}$ is the Hubble constant. The surface of a Hubble sphere is called the microphysical horizon,^[2] the Hubble surface, or the Hubble limit.

More generally, the term Hubble volume can be applied to any region of space with a volume of order $(c/H_{0})^{3}$ . However, the term is also frequently (but mistakenly) used as a synonym for the observable universe; the latter is larger than the Hubble volume.^[3]^[4]

The center of the Hubble volume and observable universe is arbitrary in relation to the overall universe; instead it is centered around its origin (impersonal or personal "observer").

The Hubble length $c/H_{0}$ is 14.4 billion light years in the standard cosmological model, somewhat larger than $c$ times the age of the universe, 13.8 billion years.

^ Edward Robert Harrison (2003). Masks of the Universe. Cambridge University Press. p. 206. ISBN 978-0-521-77351-5.
^ N. Carlevaro & G. Montani (2009). "Study of the Quasi-isotropic Solution near the Cosmological Singularity in Presence of Bulk-Viscosity". International Journal of Modern Physics D. 17 (6): 881–896. arXiv:0711.1952. Bibcode:2008IJMPD..17..881C. doi:10.1142/S0218271808012553. S2CID 9943577.
^ For a discussion of why objects that are outside the Earth's Hubble sphere can be seen from Earth, see TM Davis & CH Linewater (2003). "Expanding Confusion: common misconceptions of cosmological horizons and the superluminal expansion of the universe". Publications of the Astronomical Society of Australia. 21 (1): 97–109. arXiv:astro-ph/0310808. Bibcode:2004PASA...21...97D. doi:10.1071/AS03040. S2CID 13068122.
^ For an example of mistaken usage, see Max Tegmark (2004). "Parallel Universes". In Barrow, J. D.; Davies, J. D.; Harper, C. L. (eds.). Science and Ultimate Reality: From Quantum to Cosmos. Cambridge University Press. pp. 459ff. ISBN 978-0-521-83113-0.

[Harrison-1] Edward Robert Harrison (2003). Masks of the Universe. Cambridge University Press. p. 206. ISBN 978-0-521-77351-5.

[Montani-2] N. Carlevaro & G. Montani (2009). "Study of the Quasi-isotropic Solution near the Cosmological Singularity in Presence of Bulk-Viscosity". International Journal of Modern Physics D. 17 (6): 881–896. arXiv:0711.1952. Bibcode:2008IJMPD..17..881C. doi:10.1142/S0218271808012553. S2CID 9943577.

[Davis-3] For a discussion of why objects that are outside the Earth's Hubble sphere can be seen from Earth, see TM Davis & CH Linewater (2003). "Expanding Confusion: common misconceptions of cosmological horizons and the superluminal expansion of the universe". Publications of the Astronomical Society of Australia. 21 (1): 97–109. arXiv:astro-ph/0310808. Bibcode:2004PASA...21...97D. doi:10.1071/AS03040. S2CID 13068122.

[4] For an example of mistaken usage, see Max Tegmark (2004). "Parallel Universes". In Barrow, J. D.; Davies, J. D.; Harper, C. L. (eds.). Science and Ultimate Reality: From Quantum to Cosmos. Cambridge University Press. pp. 459ff. ISBN 978-0-521-83113-0.

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