The weight of light

Abstract

The study explored whether the knowledge of Archimedes’ law of the lever can be used to measure subjective intensities. Participants were presented with two achromatic rectangles on a horizontal line-drawn lever, one on the left and one on the right of the fulcrum. The left rectangle had a fixed low luminance. For different combinations of luminance and distance from the fulcrum of the right rectangle, participants were asked to position the left rectangle at a distance from the fulcrum such that the weight of the light emitted by the left rectangle kept the lever horizontal given the weight of the light emitted by the right rectangle. Most of the participants solved the task in accordance with their knowledge of Archimedes’ law. This finding is interpreted to imply that the perceived distance of the left rectangle from the fulcrum was proportional to the perceived brightness of the right rectangle. It suggests that people’s explicit or implicit knowledge of ratios and proportions in Archimedes’ law of the lever, and perhaps in other physical laws, could potentially be used to measure any subjective intensity on a ratio scale.