Astrophysics Colloquium: Deciphering the Universe’s Light with gamma rays

Abstract: The light emitted by all galaxies across the history of the Universe is encoded in the intensity of the extragalactic background light (EBL), the diffuse cosmic radiation field spanning ultraviolet, optical, and infrared wavelengths. The EBL is a source of opacity for high-energy γ rays via the photon-photon interaction (γγ → e+e−), leaving a characteristic attenuation imprint in the spectra of distant γ-ray sources. In this talk, I will review the newest measurements of the EBL and discuss the potential for a precise determination of the Hubble constant using gamma rays.