Re: Casimir force (was Faster than light?)

Damien Broderick (
Thu, 19 Dec 1996 10:59:26 +1000

At 12:55 PM 12/18/96 -0800, Robin Hanson wrote about:
>James Rogers writes:
>> ... The net result is that the
>>concentration of electrons in the space between the plates is significantly
>>higher than the concentration on the outside of the plates, due to
>>significant overlap of the electron density curves. This generates a
>>repulsive force
>Um, isn't the Casimir force between conducting plates *attractive*,
>not repuslive? The usual explanation has you consider the zero point
>energy of the photons in the space between the plates, and notes that
>this (negative) energy gets larger as the plates get closer

In February 1996, Robert Forward wrote an interesting report (PL-TR-96-3004)
on `Mass Modification Experiment Definition Study', a US Air Force Technical
Report on possible/proposed uses of the vacuum. He states there in an
introductory tutorial:

`Prior to the introduction of the plates, the region of vacuum between the
plates has an infinity of possible EM vibrations and an infinite amount of
quantum mechanical EM fluctuation energy. Since the plates are conducting,
they will short-circuit those EM vibrations that do not have zero electric
field at the position of the conducting plates. In effect, this cuts in
"half" the "infinity" of EM vibrations allowed... The vacuum now has less
energy than it did before the plates were introduced.'

He adds: `The Casimir force on closely spaced *conducting* plates has never
been measured accurately over a wide range of spacings or a wide range of
conductin materials'; it is therefore his prime option for a research project.

Damien Broderick

Dr Damien Broderick / Associate, Dept. English and Cultural Studies
University of Melbourne, Parkville 3052, AUSTRALIA