Casimir forces and non-Newtonian gravitation
Roberto Onofrio
Abstract and summary · read the original at the source
In one page
Roberto Onofrio, who works at Dartmouth College and the University of Padova, reviews a measurement problem that sits exactly where two frontiers meet. Several routes to unifying gravity with the other forces predict an extra, short-range force alongside Newton’s — parametrised by a range and a strength — and the micrometre scale is where the predicted window is still open. But at that scale the dominant force between two surfaces is the Casimir force, the attraction that quantum vacuum fluctuations produce between conductors. So any hunt for new gravity in the micrometre range is really a contest with Casimir metrology. Onofrio surveys the six successful Casimir measurements, the limits on new forces they set, and the systematic effects that can imitate a signal. He then proposes a way to compare experiments of different geometries: convert each measurement into a determination of the constant formed from the reduced Planck constant and the speed of light, then compare it with the value known to far higher precision from microscopic physics.
Why it matters hereChapter 2 rests on the Casimir force being measured, and this is the paper that says exactly how well it is measured and what still limits that accuracy — the finite-temperature correction above all. It also gives chapter 1 a clean piece of evidence discipline: turn every experiment, whatever its geometry, into one number that can be checked against an independently known value, so a claim of new physics has to survive a comparison it cannot arrange for itself.
What it claims
01The Casimir force — a macroscopic force originating from quantum vacuum fluctuations, predicted in 1948 alongside the measurement of the Lamb shift and the invention of renormalisation — has been solidly demonstrated by the last decade of experiments, in configurations spanning parallel plates, sphere-plane and dielectric surfaces.Section II, Casimir forces and quantum vacuum; Section III; Abstract
Settled physics02A short-range force added to Newtonian gravity is parametrised by a Yukawa range and a coupling strength relative to gravity, and such forces are expected in many attempts to unify gravity with the other interactions. Even a minimal unification argument predicts them: if spontaneous symmetry breaking is the universal path, it should produce intermediate gauge bosons with couplings between gravity and the other interactions, exactly as electroweak unification produced the neutral Z boson.Section I, Introduction, equation (1) and Figure 1
Published and peer-reviewed03In the micrometre range the Casimir force, or its variants for dielectric rather than conducting materials, is the major expected background to any search for a gravitational-strength short-range force. Constraints on extra-gravitational forces in the submillimetre range do not match the far more stringent limits at intermediate distances, which is why this window remains open.Abstract; Section I, Introduction
Published and peer-reviewed04Onofrio proposes a geometry-independent way to compare all the data: once every correction is accounted for, each Casimir force measurement amounts to a determination of the product of the reduced Planck constant and the speed of light, which can then be compared against the far more precise value known from microscopic measurements. A significant deviation between the two would be the signature of new physics — and the same protocol supports blind tests and open data sharing between groups.Abstract; Section IV, Precision and accuracy in Casimir force experiments; Section VI, Conclusions
Designed, not yet built05Three lines of hardware are named as the next generation. Cryogenic atomic force microscopy aiming at a sensitivity of the order of ten to the minus eighteen newtons per square root hertz; improved torsion balances, under development at Los Alamos for the sphere-plane geometry and at the Institut Laue-Langevin in Grenoble for parallel plates; and the cylinder-plane geometry at Dartmouth, whose first data acquisition on an upgraded apparatus aimed at the two to five micrometre range was underway as the review was written.Section V, Future experimental directions
On the bench now06No Casimir force measurement so far shows, within its claimed accuracy, any residual signalling non-Newtonian physics — and the urgent open item is the finite-temperature correction, without a solid understanding of which the limits on non-Newtonian forces remain weak. Onofrio expects a definitive result to come from complementary evidence across radically different classes of experiment operating at different length scales, naming neutron states in the Earth’s gravitational field, surface excitations in superfluid helium, and nanotube dynamics.Section VI, Conclusions
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Read it · abstract
Abstract
The search for non-relativistic deviations from Newtonian gravitation can lead to new phenomena signaling the unification of gravity with the other fundamental interactions. Various recent theoretical frameworks indicate a possible window for non-Newtonian forces with gravitational coupling strength in the micrometer range. The major expected background in the same range is attributable to the Casimir force or variants of it if dielectric materials, rather than conducting ones, are considered. Here we review the measurements of the Casimir force performed so far in the micrometer range and how they determine constraints on non-Newtonian gravitation, also discussing the dominant sources of false signals. We also propose a geometry-independent parametrization of all data in terms of the measurement of the constant formed by the reduced Planck constant times the speed of light. Any Casimir force measurement should lead, once all corrections are taken into account, to a determination of that constant which, in order to assess the accuracy of the measurement, can be compared with its more precise value known through microscopic measurements. Although the last decade of experiments has resulted in solid demonstrations of the Casimir force, the situation is not conclusive with respect to being able to discover new physics. Future experiments and novel phenomenological analysis will be necessary to discover non-Newtonian forces or to push the window for their possible existence into regions of the parameter space which theoretically appear unnatural.
The way in
https://doi.org/10.1088/1367-2630/8/10/237LICENCE — DOWNGRADED. The aggregator records label this DOI cc-by; that label could not be confirmed and is not used. The publisher’s page for the version of record, New Journal of Physics volume 8 (2006), article 237, published 20 October 2006, carries only ‘Published under licence by IOP Publishing Ltd’ and a footer copyright line for IOP Publishing. The phrase ‘Creative Commons’ appears nowhere on it — checked on 2026-09-08. New Journal of Physics is free to read, which is what the gold open-access status records, but free to read is not a licence to republish. The author’s copy on arXiv, hep-ph/0612234 version 1 of 19 December 2006, carries arXiv’s default non-exclusive distribution licence rather than a Creative Commons one, checked on the same date. IOP’s own site answers automated requests with an interstitial rather than the article, so no further publisher-side check was possible. With no Creative Commons version located, this sheet is abstract-only. TEXT. The body carries the abstract alone, as it appears on the arXiv copy of the manuscript, which matches the published abstract. The summary and the claims below were written from the full author’s copy, which was read in order to write them accurately and is not reproduced here; the complete text is at the source.
How to cite it
Roberto Onofrio (2006) Casimir forces and non-Newtonian gravitation. doi:10.1088/1367-2630/8/10/237
Where it sits in the curriculum
What the vacuum isInertia and gravity from the vacuumThe evidence ladder