  When we measure the spatial dimensions of an object, we are comparing it to an agreed upon standard. Ultimately all standards must have their root in physiological comparison. In this way Mach tries to bring physics back into psychology. Physics is based upon measurements, but measurements are ultimately physiological comparisons. According to Mach, physics can never escape its biological origins. Planck and Einstein accepted Mach’s critique of the old physics, that it was under the spell of concepts which were derivative of unreflective development, but rejected Mach’s claim that physics was stuck, so to speak, in psychology.