What the Propagation of Energetic Light can Tell us about the Evolution of Stars, Intergalactic Magnetic Fields and Fundamental Physics

Photons at energies beyond a billion times that of X-rays cannot reach us from the outer edges of the observable Universe. Only a fraction of these very-high-energy gamma rays reach our atmosphere to produce firework-like visual displays called air showers. While our eyes can’t see these rapid air showers, telescopes can observe gamma rays and tell us the story of their travels. CTA will measure these gamma rays with its improved sensitivity and will write down the chronicles of gamma-ray propagation on cosmological scales….