An Assessment of "What does photon energy tell us about cellphone safety" by Dr. William Bruno

Abstract

Dr. William Bruno asserts the well-known fact that cell phones radiate microwaves in the classical regime. This, he says, means that the photon energy is not relevant to assessing safety. Citing optical tweezers as an example of biologically relevant non-thermal effects of electromagnetic radiation, Bruno concludes that all other reports of non-thermal effects from microwaves are likely valid. He seeks safety thresholds based upon requiring that cell phone energy density be less than kBT. This proposal and related ideas produce thresholds many orders of magnitude below present values. While Dr. Bruno is correct that cell phone microwave radiation is generally in the classical regime, he uses peculiar estimates (number of photons per cubic wavelength) that overstate the circumstance by more than 20 factors of ten. He misunderstands the operation of optical tweezers and ignores their significant thermal effects. He credulously accepts poorly supported claims of non-thermal effects. He mistakenly believes that kBT is the average thermal energy (per cubic wavelength or per cell) in materials. It is not. It is twice the average energy per molecule per degree of freedom in the material. The thermal energy density is (1/2)kBT X (average number of degrees of freedom of the molecules) X (Avogadro's number). (Avogadro's number is 6 X 1026 molecules/mole.) Thus, Bruno's proposed safety thresholds are more than 1025 too low. Using the correct value for the average thermal energy would place the thresholds close to today's standards. Throughout his analysis he neglects the index of refraction of living tissue, n \cong 9, or the absorption length, {\alpha} \cong 1 cm-1, in the microwave region.