Kagi Summary:

The passage discusses whether photons, the quantum particles of light, have a finite or infinite lifetime. It explains that while photons can be created and destroyed through various interactions, they cannot truly be "killed off" entirely. Even as the universe expands and photons redshift to lower and lower energies, new photons will continue to be produced, ensuring that photons will always exist in some form. The passage also dismisses the "tired light" hypothesis as a way for photons to lose energy, as it is not supported by observational evidence. Overall, the passage concludes that based on our current understanding of physics, photons appear to have an infinite lifetime and will continue to exist in the universe indefinitely.