Editing Zero-point energy (section)

=== Casimir effect ===
{{Main|Casimir effect}}
[[File:Casimir plates.svg|thumb|Casimir forces on parallel plates]]

A phenomenon that is commonly presented as evidence for the existence of zero-point energy in vacuum is the Casimir effect, proposed in 1948 by [[Netherlands|Dutch]] [[physicist]] [[Hendrik Casimir]], who considered the quantized electromagnetic field between a pair of grounded, neutral metal plates. The vacuum energy contains contributions from all wavelengths, except those excluded by the spacing between plates. As the plates draw together, more wavelengths are excluded and the vacuum energy decreases. The decrease in energy means there must be a force doing work on the plates as they move.

Early experimental tests from the 1950s onwards gave positive results showing the force was real, but other external factors could not be ruled out as the primary cause, with the range of experimental error sometimes being nearly 100%.<ref>{{cite journal|last1=Derjaguin|first1=B. V.|last2=Abrikosova|first2=I. I.|last3=Lifshitz|first3=E. M.|title=Direct measurement of molecular attraction between solids separated by a narrow gap|journal=Quarterly Reviews, Chemical Society|date=1956|volume=10|issue=3|pages=295–329|doi=10.1039/QR9561000295}}</ref><ref>{{cite journal|last1=Sparnaay|first1=M. J.|title=Measurements of attractive forces between flat plates|journal=Physica|date=1958|volume=24|issue=6–10|pages=751–764|doi=10.1016/S0031-8914(58)80090-7|bibcode=1958Phy....24..751S}}</ref><ref>{{cite journal|last1=Tabor|first1=D.|last2=Winterton|first2=R. H. S.|title=Surface Forces: Direct Measurement of Normal and Retarded Van der Waals Forces|journal=Nature|date=1968|volume=219|issue=5159|pages=1120–1121|doi=10.1038/2191120a0|pmid=5675624|bibcode=1968Natur.219.1120T|s2cid=4258508}}</ref><ref>{{cite journal|last1=Hunklinger|first1=S.|last2=Geisselmann|first2=H.|last3=Arnold|first3=W.|title=A Dynamic Method for Measuring the Van der Waals Forces between Macroscopic Bodies|journal=Rev. Sci. Instrum.|date=1972|volume=43|issue=4|pages=584–587|doi=10.1063/1.1685696|bibcode=1972RScI...43..584H}}</ref><ref>{{cite journal|last1=Van Blokland|first1=Peter H. G. M.|last2=Overbeek|first2=J. Theodoor G.|title=Van der Waals forces between objects covered with a chromium layer|journal=J. Chem. Soc., Faraday Trans. 1|date=1978|volume=74|pages=2637–2651|doi=10.1039/F19787402637}}</ref> That changed in 1997 with Lamoreaux<ref>{{cite journal|last1=Lamoreaux|first1=S. K.|title=Demonstration of the Casimir Force in the 0.6 to 6&nbsp;μm Range|date=1997|journal=Physical Review Letters|volume=78|issue=1|pages=5–8|doi=10.1103/PhysRevLett.78.5|url=http://web.mit.edu/~kardar/www/research/seminars/Casimir/PRL-Lamoreaux.pdf|bibcode=1997PhRvL..78....5L}}</ref> conclusively showing that the Casimir force was real. Results have been repeatedly replicated since then.<ref>{{cite journal|last1=Mohideen|first1=Umar|last2=Roy|first2=Anushree|title=Precision Measurement of the Casimir Force from 0.1 to 0.9&nbsp;μm|journal=Physical Review Letters|year=1998|volume=81|issue=21|pages=4549–4552|doi=10.1103/PhysRevLett.81.4549|arxiv=physics/9805038|bibcode=1998PhRvL..81.4549M|s2cid=56132451}}</ref>{{sfnp|Chan et al.|2001}}{{sfnp|Bressi et al.|2002}}{{sfnp|Decca et al.|2003}}

In 2009, Munday et al.<ref>{{cite journal|last1=Munday|first1=J. N.|last2=Capasso|first2=Federico|last3=Parsegian|first3=V. Adrian|title=Measured long-range repulsive Casimir–Lifshitz forces|date=2009|volume=457|issue=7226|pages=170–173|doi=10.1038/nature07610|url=http://nanoqed.synthasite.com/resources/nature07610.pdf|pmid=19129843|pmc=4169270|journal=Nature|bibcode=2009Natur.457..170M}}</ref> published experimental proof that (as predicted in 1961<ref>{{cite journal|last1=Dzyaloshinskii|first1=I. E.|last2=Lifshitz|first2=E. M.|last3=Pitaevskii|first3=Lev P.|title=General Theory of Van der Waals' Forces|journal=Soviet Physics Uspekhi|date=1961|volume=4|issue=2|page=154|doi=10.1070/PU1961v004n02ABEH003330|bibcode=1961SvPhU...4..153D}}</ref>) the Casimir force could also be repulsive as well as being attractive. Repulsive Casimir forces could allow quantum levitation of objects in a fluid and lead to a new class of switchable nanoscale devices with ultra-low static friction.{{sfnp|Capasso et al.|2007}}

An interesting hypothetical side effect of the Casimir effect is the [[Scharnhorst effect]], a hypothetical phenomenon in which light signals travel slightly [[Faster-than-light|faster than {{mvar|c}}]] between two closely spaced conducting plates.<ref name="Scharnhorst 1993">See {{harvp|Barton|Scharnhorst|1993}} and {{harvp|Chown|1990}}.</ref>