Free space (electromagnetism): Difference between revisions
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Free space usually refers to a perfect vacuum, devoid of all particles. The term is most often used in classical electromagnetism where it refers to a reference state,<ref name=Weiglhofer> | |||
{{cite book|title=Introduction to complex mediums for optics and electromagnetics |author=Werner S. Weiglhofer and Akhlesh Lakhtakia |year=2003 |url=http://books.google.com/books?id=QtIP_Lr3gngC&pg=PA34&hl=en#v=onepage&q&f=false|publisher=SPIE Press |isbn=0819449474 |chapter=§4.1: The classical vacuum as reference medium }} | |||
</ref> and in quantum physics where it refers to the ground state of the electromagnetic field, which is subject to fluctuations about a dormant zero average-field condition.<ref name=Shankar> | |||
{{cite book|title=Principles of quantum mechanics |author=Ramamurti Shankar |url=http://books.google.com/books?id=2zypV5EbKuIC&pg=PA507#v=onepage&q=free%20space&f=false |pages=p. 507 |isbn=0306447908 |year=1994 |edition=2nd ed. |publisher=Springer}} | |||
</ref> The classical case of vanishing fields implies all fields are source-attributed, while in the quantum case field moments can arise without sources from virtual phonon creation and destruction.<ref name=Vogel> | |||
{{cite book |title=Quantum optics |author=Werner Vogel, Dirk-Gunnar Welsch |url=http://books.google.com/books?id=qRtnP1dPGmQC&pg=PA337&hl=en#v=onepage&q&f=false |pages=p. 337 |publisher=Wiley-VCH |year=2006 |edition=3rd ed. |isbn=3527405070}} | |||
</ref> The description of free space varies somewhat among authors, with some authors requiring only the absence of substances with electrical properties,<ref name=Pathria> | |||
{{cite book|title=The Theory of Relativity |author= RK Pathria |url=http://books.google.com/books?id=Ma4ZFefVKIYC&pg=PA119&hl=en#v=onepage&q&f=false |pages=p. 119 | |year=2003 |isbn=0486428192 |publisher=Courier Dover Publications |edition=Reprint of Hindustan 1974 2nd ed.}} | |||
</ref> or of charged matter (ions and electrons, for example).<ref name=Morris>{{cite book |title=Academic Press dictionary of science and technology |editor=Christopher G. Morris, editor |publisher=Academic |url=http://books.google.com/books?id=nauWlPTBcjIC&pg=PA880&hl=en#v=onepage&q&f=false|pages=p. 880 |year=1992 |isbn=0122004000}} | |||
</ref> | |||
==References== | |||
<references/> | |||
Revision as of 16:11, 24 November 2010
Free space usually refers to a perfect vacuum, devoid of all particles. The term is most often used in classical electromagnetism where it refers to a reference state,[1] and in quantum physics where it refers to the ground state of the electromagnetic field, which is subject to fluctuations about a dormant zero average-field condition.[2] The classical case of vanishing fields implies all fields are source-attributed, while in the quantum case field moments can arise without sources from virtual phonon creation and destruction.[3] The description of free space varies somewhat among authors, with some authors requiring only the absence of substances with electrical properties,[4] or of charged matter (ions and electrons, for example).[5]
References
- ↑ Werner S. Weiglhofer and Akhlesh Lakhtakia (2003). “§4.1: The classical vacuum as reference medium”, Introduction to complex mediums for optics and electromagnetics. SPIE Press. ISBN 0819449474.
- ↑ Ramamurti Shankar (1994). Principles of quantum mechanics, 2nd ed.. Springer, p. 507. ISBN 0306447908.
- ↑ Werner Vogel, Dirk-Gunnar Welsch (2006). Quantum optics, 3rd ed.. Wiley-VCH, p. 337. ISBN 3527405070.
- ↑ RK Pathria (2003). The Theory of Relativity, Reprint of Hindustan 1974 2nd ed.. Courier Dover Publications, p. 119. ISBN 0486428192.
- ↑ (1992) Christopher G. Morris, editor: Academic Press dictionary of science and technology. Academic, p. 880. ISBN 0122004000.