Measurements of attractive forces between flat plates
M. J. Sparnaay
Abstract and summary · read the original at the source · none found
In one page
In 1948 Hendrik Casimir predicted that two flat metal plates facing each other in empty space would be pushed together by the vacuum itself, because the gap between them can hold fewer light waves than the room outside. Ten years later M. J. Sparnaay, at the Philips research laboratories in Eindhoven, built the apparatus that went looking for it — and this short Physica paper is the first time anyone measured the force Casimir described. Sparnaay reports what he found carefully: the plates do attract, and the attraction does not contradict Casimir’s prediction. He is equally careful about what went wrong earlier. His own previous runs, with clean and with silvered glass and quartz plates in an ionised atmosphere, had been reading a different effect altogether — a voltage difference between the two facing surfaces, pulling them together electrically. Naming that artefact is the second gift of the paper, because every precision Casimir experiment since has had to cancel exactly that voltage before it can see the vacuum.
Why it matters hereChapter 2 says the vacuum is a real medium a laboratory can push on, and this is the first time a laboratory pushed on it. Chapter 1 gets the other half: a first measurement that establishes the sign and the order of magnitude, states its own limits honestly, and hands the next generation the systematic error to beat — which is what Lamoreaux settled in 1997 and Bressi and colleagues repeated in Casimir’s own parallel-plate geometry in 2002.
What it claims
01Results of experiments concerning attractive forces between flat metal plates, together with a description of the apparatus used, are reported — and the observed attractions do not contradict Casimir’s theoretical prediction. That sentence, written in 1958, is the first experimental statement about the Casimir force in the literature.Abstract, first two sentences; Physica 24, pages 751 to 764
Settled physics02The force Sparnaay measured, in the units Casimir’s formula uses, is one to four times ten to the minus eighteen dyne centimetres squared divided by the fourth power of the gap, for separations between two and ten micrometres. Casimir’s prediction in the same units is 1.30 times ten to the minus eighteen. Sparnaay’s band contains it.Figures as reported by Steven Weinberg, The cosmological constant problem, Reviews of Modern Physics 61, 1 (1989), Section III, footnote on the Casimir effect — on this site at /library/stm-5610822bc8
Settled physics03The size of the achievement and the size of its error bar belong in the same sentence. This measurement showed an attractive force not inconsistent with the prediction, but with effectively one hundred per cent uncertainty: it settles the sign and the order of magnitude of the effect, not the coefficient in front of it.As characterised in the introduction of Steve K. Lamoreaux, Demonstration of the Casimir Force in the 0.6 to 6 micrometre range, Physical Review Letters 78, 5 (1997) — on this site at /library/stm-e8c853485e
Settled physics04The second half of the paper is a correction of the author’s own earlier work. Attractions previously measured between clean plates, and between silvered glass and quartz plates, all brought into an ionised atmosphere, were due to differences in the surface potentials of the opposing plates — an electrostatic effect, not a vacuum effect.Abstract, third and fourth sentences
Settled physics05That artefact became a permanent part of the method. Contact-potential differences between two facing metal surfaces are the dominant systematic in every Casimir measurement that followed, and cancelling the residual voltage before the force is read is now a standard step of the experiment rather than an optional check.Compensation of the residual electrostatic potential as practised in Bressi, Carugno, Onofrio and Ruoso, Measurement of the Casimir Force between Parallel Metallic Surfaces, Physical Review Letters 88, 041804 (2002) — on this site at /library/stm-208d347532
Settled physics06The configuration Casimir actually calculated stayed the hard one for forty-four years. Before Bressi and colleagues repeated it in 2002, the parallel-plate geometry had been attempted exactly once — here — with large systematic errors and uncontrolled electrostatic forces, while the easier sphere-against-plate geometry had already reached one per cent.Bressi, Carugno, Onofrio and Ruoso, Physical Review Letters 88, 041804 (2002), introduction, survey of previous attempts — on this site at /library/stm-208d347532
Settled physics
Read it · abstract
Abstract
Results of experiments concerning attractive forces between flat metal plates, and a description of the apparatus used, are given. The observed attractions do not contradict Casimir’s theoretical prediction.
An explanation of results of earlier measurements made by the author on the attraction between clean, and also between silvered glass and quartz plates, all brought in an ionized atmosphere, is suggested. These results were due to differences in the surface potentials of the opposing plates.
M. J. Sparnaay, Philips Research Laboratories, N.V. Philips’ Gloeilampenfabrieken, Eindhoven. Physica 24, pages 751 to 764 (1958). Abstract as deposited by the publisher.
(Abstract only — see the rights note above for why the fourteen pages of apparatus description, data and analysis are not reproduced here. They are at the source.)
The Casimir line on this site runs through here: Casimir’s own 1948 note predicting the force is at /library/stm-11433059a4; Lamoreaux’s 1997 measurement, the one that settled it, is at /library/stm-e8c853485e; Mohideen and Roy’s 1998 atomic-force-microscope measurement, a different apparatus in a different laboratory, is at /library/stm-911b036fc2; and Bressi, Carugno, Onofrio and Ruoso’s 2002 return to Sparnaay’s own parallel-plate geometry is at /library/stm-208d347532. Lamoreaux’s later review of the whole experimental history is at /library/stm-4c6743a6b7, and Weinberg’s 1989 review — which cites Sparnaay’s numbers while stating the cosmological-constant problem — is at /library/stm-5610822bc8.
The way in
https://doi.org/10.1016/S0031-8914(58)80090-7WHAT THIS IS. The first experimental test of the Casimir force, published as Physica volume 24, issue 6 to 10, pages 751 to 764 (1958). The author’s affiliation as printed and as carried in the OpenAlex record is Philips Research Laboratories, N.V. Philips’ Gloeilampenfabrieken, Eindhoven, Netherlands. REGISTRY NOTE. This library record was rebuilt from a corrected DOI and reached the sheet with a null year; the year is 1958, confirmed on the Crossref, OpenAlex and OpenAIRE records and on the CoLab article page, which also give the volume, issue and page range used above. LICENCE. Crossref carries only Elsevier’s text-and-data-mining licence for this DOI, Unpaywall and OpenAlex both report the article closed with no repository copy, and no preprint of a 1958 Physica paper exists — so no text of the paper is reproduced here beyond the author’s own abstract. WHAT WAS READ. The abstract below is the one Elsevier deposited, retrieved on 2026-09-08 from the OpenAIRE publications API for this DOI and checked word for word against the CoLab article record at colab.ws for the same DOI. The paper’s own body was not reachable, so the three claims that carry figures cite named published sources instead, each identified in its locator: Steven Weinberg’s 1989 Reviews of Modern Physics review, already on this site, for the measured force per unit area; Steve Lamoreaux’s 1997 Physical Review Letters paper for the size of the uncertainty; and Bressi, Carugno, Onofrio and Ruoso’s 2002 Physical Review Letters paper for the state of the parallel-plate geometry before they repeated it. Anything not attributable to one of those four sources is not asserted here.
How to cite it
M. J. Sparnaay (1958) Measurements of attractive forces between flat plates. doi:10.1016/S0031-8914(58)80090-7
Where it sits in the curriculum