A Limit on the Redshift due to Interaction with Electromagnetic Radiation

Abstract

IN a recent letter¹ Pecker et al. discussed the possibility that a part of the “cosmological” redshift could result from the interaction of photons with an interstellar radiation field. Although this suggestion is old^2,3, it has recently regained prominence with the discovery of the 3 K blackbody radiation. Pecker et al. discussed a formula for the energy loss of the propagating photon, v₁, where Δ(v₂) is the coupling constant between the propagating photon and the radiation field of frequency v₂, n₂ is the number density (cm⁻³) of the photons at v₂, and δl is the length of the interaction path, in cm. Assuming that Δ(v₂) is independent of v₂, they suggested an experiment to determine an upper limit for its value. The proposed experiment, measuring by the Mössbauer effect the energy loss of gamma rays traversing a laser beam, is very difficult to perform. But another Mössbauer experiment was performed a number of years ago to test just this question. In that experiment⁴, gamma rays were propagated through a microwave cavity filled with photons of 9,234 MHz (λ≈3 cm) radiation; the fractional energy shift of the gamma rays due to the microwave field was found to be 0.4±6.0×10−¹⁶, corresponding to a value of Δ(v₂)<10⁻³³ cm⁻¹. This limit is far smaller than the value Δ(v₂)≈10⁻³⁰ cm⁻¹ proposed in ref. 1 from the analysis of solar redshift data.