Does light have an unending journey? When we shine a torch in a room its light travels to the back of the room.
What happens to the light of a star ? I dont suppose we can say it continues to travel to the back of the universe as the universe has no back. Does the light continues its journey forever ? Or does it somehow end into black holes which might work as light sinks ?
 A: Light is emitted as photons. The inverse square law implies that the
density of photons decreases as the distance from the source
increases, exactly as it would if billiard ball were emitted in random
direction, rather than photons. The photons do not necessarily have
all the same energy. It depends on their wavelength. The energy of a
photon is not attenuated with distance (only the number of photons
is). However it is attenuated (red shifted) by spatial expansion of
the universe, while it is travelling, but that is a considerably
slower attenuation.
Now, if we were in a stable (non-expanding) infinite universe with
uniform average density, the question of the photon ultimately
encountering an obstacle would be similar to Olbers'paradox (why does
the sky have dark patches rather than a shining star in all
directions?).  There would be an obstacle in all directions that the
photon would ultimately hit.  And since this question refers to the
future rather than the past as in Olbers' paradox, we cannot eliminate
the existence of this ubiquitous obstacle by relying on the young age
of the universe.
However, I think this inverse of Olbers' paradox can be dismissed with
an other argument relying on the expansion of the universe. Though the
universe may be infinite (I do not know), the reachable universe is
finite. The reachable universe has a radius such that the expansion at
the periphery has the speed of light with respect to the centre (it is
expansion, not motion), as made precise by the Hubble constant. The
reachable universe being finite, it may have direction where no
obstacle exist (depending on average matter density), and a photon
going (at light speed) in such a direction may go for ever.
This is only an approximation of an answer. Actual figures probably
matter, and there may be other phenomena.
A: Light beams are electromagnetic radiations, they stops when they meet some material that can stop them, in space generally they continue propagate until they have energy.
