Final answer:
Photons traveling from beyond the observable universe lose energy via redshift, as their wavelengths lengthen due to the universe's expansion. This process disperses their energy across space, but does not necessarily mean it's 'lost', as it contributes to the Cosmic Microwave Background. Energy conservation in a cosmological context is not strict due to spacetime properties.
Step-by-step explanation:
Understanding Photons and Energy Conservation
In addressing the fate of photons originating from beyond the observable universe, one must understand the principle that energy can transform into matter and vice versa. Initially, post-Big Bang, the universe was like a cauldron of high-energy photons colliding and sometimes creating pairs of particles, matter and antimatter, which in turn could annihilate, returning to pure energy. In modern times, the energy of photons is generally much lower than what is required for matter creation.
However, as photons traverse the cosmos, they lose energy through a process called 'redshift', where their wavelengths lengthen as the universe expands. Thus, photons' energy is not conserved over cosmological timescales due to the universe's expansion and the properties of spacetime. This redshifting means that photons from outside the observable universe have wavelengths stretched to a point where they carry significantly less energy. Consequently, the energy from these distant photons is not necessarily 'lost' but dispersed through space as the photon’s wavelength increases. Some even become part of the Cosmic Microwave Background (CMB).
Furthermore, the early universe's opaque conditions allowed for radiation to continuously interact with matter, propelling it forward similar to police cars letting a motorcade pass traffic lights. However, once the universe became transparent, this interaction decreased, allowing ordinary matter to fall into gravitational 'traps' such as those formed by dark matter.