If a photon were to travel forever without any interaction or absorption, there are a few implications to consider.
Firstly, it is important to note that photons travel at the speed of light in a vacuum, and according to our current understanding of physics, they do not experience time in the same way that objects with mass do. This concept is derived from Einstein's theory of special relativity, which states that as an object with mass approaches the speed of light, time dilation occurs, and from the object's perspective, time appears to slow down. Since a photon travels at the speed of light, time dilation would cause its journey to appear instantaneous from its frame of reference.
From an external observer's perspective, however, the photon would still take time to travel across large distances. For example, if a photon were emitted from a distant galaxy and traveled to Earth, it would take billions of years to reach us, even though the photon itself would not experience this passage of time.
Furthermore, if a photon were to travel indefinitely without any interactions, it would maintain its energy and momentum. This means that its frequency and wavelength would remain constant as it travels, in accordance with the principles of wave-particle duality. However, it is important to note that the universe is not a perfect vacuum, and photons can interact with particles and fields present in space. These interactions can lead to phenomena such as scattering, absorption, or redshifting of the photon's energy and frequency.
In summary, if a photon were to travel forever without interactions, it would appear to experience no passage of time from its own frame of reference. However, from an external observer's perspective, the photon's journey would still take time, and it would maintain its energy and properties unless it interacts with other particles or fields along the way.