How good are measurements Do they really confirm theory

It is curious how people working in different disciplines seek and see validation in different kinds of experiments. Only the liquid helium up-the-walls measurement, described in the preceding subsection, seems to satisfy most people that the Lifshitz theory quantitatively accounts for measured forces (see note 37 in the preceding subsection). As with the historical comments, this review of measurements is not intended to be exhaustive.39 

That s the worst. Several kinds of measurements reassure us that the Lifshitz strategy of converting spectra into forces works reliably enough to capture the key features of van der Waals forces. 

A fussier preparation that uses atomic force microscopy (AFM) demonstrates that there can be a lateral force between surfaces sinusoidally coated with gold.49 Sophisticates of earlier sections know that a probe such as AFM will see into a surface to a depth comparable with separation between probe tip and surface. When substrate structure varies with depth from surface, interpretation of van der Waals interactions can be problematic. Nevertheless, good success has been reported.50,51 

The optical properties of quartz cranked into Lifshitz s formula, for plane-parallel surfaces but modified by the Derjaguin transform for a sphere and a flat, gave an attraction that fit neatly with experiments. 

PROBLEM PR.14 Show how a Hookean spring works against an inverse-power van der Waals interaction in a force balance of a sphere and a flat surface. 

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PR.3. How good are measurements Do they really confirm theory ... 

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