Photon hubbling, tired light. The photon is doing work as it moves through spacetime. Modeled as E_t / E_0 = e^(-Ht), where H is Hubble's constant, and t is tim

Photon hubbling, tired light. The photon is doing work as it moves through spacetime. Modeled as E_t / E_0 = e^(-Ht), where H is Hubble's constant, and t is time of travel.