It may end with a star, as if it is widely exaggerated to think that space spans infinity, which may be true, but in our case, think of space as a collection of celestial bodies and gaps in between. So at some point, there must be a star in the green laser pointer path.
If the star does not exist or the distance is too far, then you need to know that the laser is a focused light, like the intensity of the light decreases as its propagation path increases (due to the propagation of photons away from the path) and the final intensity increases. .
The same happens with lasers. Although its dispersion range is spread in nanometers, it does disperse, and at some point it may cease to exist. According to what I have read so far: light continues to spread or spread. But it will be affected by many factors,
The deflection or absorption of objects in the path. In this case, the light will be completely absorbed and disappear. Or it will continue to move in the area between the atmosphere and the earth’s surface until it is absorbed or finally able to leave. It will continue to travel, unless strong gravity like a black hole is permanently or captured again, and it will be absorbed or deflected by space objects existing in its path.
It won’t travel indefinitely until it hits or absorbs something. Of course, as the distance increases, it will propagate in a square law. But I want to add to my unscientific but imaginative hypothesis. Because the square law explains “what will be done” and “what will be the result”, but there are not enough answers to “why?” For example, I have not read why photons can only travel? (Some people say “why?” is a philosophical question, but…)
Photons are one-dimensional. It has only one dimension to move. So it can only move the line marker.
Photon is also a passive passenger in space, more like a surfer. It is carried by waves that have not yet been determined laser pointer, but will cause gravity, time, etc. (Some people call it the gravitational wave of the Big Bang, but I think there are more).