  Szilard's argument was developed further after Shannon identified that the measure p ln p had operational significance for information theory, suggestive of a deeper connection between entropy and information. To illustrate the idea further, both Gabor (1964) and Brillouin (1951) constructed specific models of dissipative measurement that involve shining a light into one side of the engine to see whether that side contains the molecule. The light is scattered if the molecule is on that side, but is not scattered if the molecule is not present. However, if the system, including the electromagnetic field itself, is in thermal equilibrium then there is background radiation at that temperature with a blackbody spectrum. To see the scattered light it must be distinguishable from the background radiation. This requires a photon with energy much higher than the mean energy of the blackbody spectrum,  so  ℏ ν ≫ k T. A photon must be used whose energy is greater than the energy gained from the operation of the engine, thereby precluding a net conversion of heat into work.