What ultimately happens to a photon? Can it exist indefinitely?

Photons are the smallest unit of light and are classified as elementary particles in quantum mechanics. As such, they do not have an infinite lifespan, but they do not decay either. A photon will continue to exist indefinitely unless it interacts with another particle.

When a photon interacts with matter, it can be absorbed or scattered. When it is absorbed, it can transfer its energy to the matter and cease to exist as a photon. In the case of scattering, the photon changes its direction and loses some of its energy. If a photon continues to travel through space without interacting with anything, it can exist indefinitely. However, photons can be affected by gravity and can be pulled into black holes or bent around massive objects.

There is ongoing research into the properties of photons and their interaction with matter. One area of interest is the possibility of creating a medium that can slow down or even stop the propagation of light. Another is the study of the interaction between photons and dark matter, which could shed light on the nature of dark matter.