View source for Casimir Effect

The '''Casimir effect''' is an attractive force that appears between two closely spaced, uncharged, parallel conducting plates in a vacuum, and which is conventionally attributed to the fluctuations of the [[Quantum Theory|quantum]] electromagnetic field in the space between and around them.

The effect was predicted in 1948 by the Dutch physicist Hendrik Casimir, then at Philips Research Laboratories in Eindhoven, in the course of work with Dirk Polder on the forces between neutral atoms. Casimir's argument is that the presence of the plates restricts which electromagnetic field modes can exist in the gap: only wavelengths that fit between the plates survive, while the region outside supports the full continuum. The resulting imbalance in mode density produces a net inward pressure. For idealised perfectly conducting plates separated by a distance ''a'', the predicted force per unit area is proportional to 1/''a''<sup>4</sup>, so it is utterly negligible at everyday separations but becomes appreciable — of order atmospheric pressure — at separations of a few tens of nanometres.

The force was first measured with reasonable precision in 1997 by Steve Lamoreaux, using a torsion pendulum in a sphere-and-plate geometry, and confirmed in 1998 by Umar Mohideen and Anushree Roy with an atomic force microscope. Later measurements have tested the geometry, temperature and material dependence of the force. It is now a standard laboratory phenomenon and a practical nuisance in micro- and nano-electromechanical devices, where it can cause moving parts to stick together.

==A genuinely open question in the standard account==

The measurement of the force is not in dispute; its ''interpretation'' is. Casimir's own derivation is framed in terms of the zero-point energy of the vacuum, and the effect is very widely presented in textbooks and popular accounts as direct proof that empty space contains energy. That reading is not universally accepted within mainstream physics. Robert Jaffe of MIT argued in 2005 that the Casimir force can be derived entirely as a relativistic, retarded van der Waals force between the charges in the plates, without invoking zero-point energy at all, and that the force vanishes as the fine-structure constant goes to zero — which a true vacuum-energy effect arguably should not. On this account the Casimir effect demonstrates that quantum electrodynamics is correct, but says nothing decisive about whether the vacuum is "full of energy".

This matters because the vacuum-energy interpretation, taken at face value, produces the worst quantitative failure in physics: the energy density that quantum field theory naively assigns to empty space exceeds the value inferred from cosmology by many tens of orders of magnitude. See [[Cosmological Constant]].

==On this wiki==

Researchers catalogued here approach the effect from two directions: as evidence for a real physical medium, and as a possible energy source.

'''As evidence for a medium.''' The Casimir result is repeatedly cited in the [[Aether]] literature collected here as an experimental demonstration that "empty" space has structure. [[Michele Barone]]'s ''[[The Vacuum as Ether in the last Century]]'' traces exactly this line of argument, and the effect appears throughout the ''[[Ether Space-Time and Cosmology, Vol. 3: Physical Vacuum Relativity and Quantum Physics|Ether Space-Time and Cosmology]]'' volumes. [[Xing-Liu Jiang]], [[Li-Jun Han]] and [[Jin-Zhi Lei]] extend the idea to astrophysical scales in ''[[Casimir Effect with Vortex Filaments and Quasar Spiral Model]]'', treating vacuum structure as organised into filaments rather than as a featureless sea.

'''As a dissenting reading of the force itself.''' [[Scott Smith]] disputes the conventional interpretation directly in ''[[Casimir's Un-Attractive Theory & Transparent Quantum-Radiometers]]'', and pursues the propulsion consequences in ''[[A Quantum-Vacuum Thruster]]''. [[David T Lewis]] approached the effect from stochastic electrodynamics — the classical theory in which a real random background field replaces quantised vacuum fluctuations — in ''[[Stochastic Electrodynamics and the Casimir Effect]]''.

'''As a candidate energy source.''' This is the largest body of work here, indexed under [[:Category:New Energy]]. [[Thomas F Valone]]'s ''[[Understanding Zero Point Energy]]'' and ''[[Practical Conversion of Zero Point Energy: Feasibility Study of the Extraction of Zero Point Energy from the Quantum Vacuum for the Performance of Useful Work]]'' set out the extraction case; [[Moray B King]] and [[Claus W Turtur]] have worked on device-level proposals; and [[Thorsten Ludwig]] has surveyed the field. A useful corrective from inside the same community is [[Robert L Forward]]'s ''[[Casimir Forces]]'', which reports a US Air Force study concluding that the proposed experiments of its day were either inconclusive or technologically infeasible. A broader sceptical audit is ''[[A Critical Review of the Available Information Regarding Claims of Zero-Point Energy, Free-Energy, and Over-Unity Experiments and Devices]]''.

The general question of whether the vacuum holds extractable energy is treated at [[Zero Point Energy]].

==See also==

* [[Zero Point Energy]]
* [[Aether]]
* [[Cosmological Constant]]
* [[Energy]]
* [[Quantum Theory]]
* [[:Category:New Energy]]

[[Category:Quantum Theory]]
[[Category:Aether]]
[[Category:New Energy]]
[[Category:Electromagnetism]]