What happens in Sci-fi movies when a laser is shot into space, will it keep going and hit someone or something a few years down the line?

No it's not fiction. We have lasers aimed at the Moon from time to time to measure surface vibrations and such.

Lasers are not killing machines for the most part. We use them to measure rooms and to keep things level in construction for example. We even use lasers to point to things on the white board or projector screen. My point, most of the lasers used today are not...not..."powerful beam[s]" at all.

But some are. My last project before retiring from a missiles development company was to write the R&D software plan for developing the airborne laser, which was designed to knockout an ICBM over enemy territory as it rose from the silo. Now that was a "powerful beam of energy".

But to a point, photons are eternal. They last forever because time aboard a photon stands still. That's why we can see galaxies and such that existed over 13 billion years ago; their photons are still out there streaming at the speed of light through space.

Until they hit something that is. Even diffused, they are still out there; they're just harder to detect as they are very very...very very dim that way...diffused.

But no, lasers beamed today will not hit a ship at sea a few years from now. Those photons from today will have been long gone from Earth by then. They travel at close to 186,000 miles/second; so in just one second, the photons in that beam will have gone 186,000 miles. And that's roughly 7 times around the planet.

But laser beams can't bend around the planet. They can only go in a straight line. So that beam will end up almost to the Moon's orbit distance in that 1 second. It will be outside the Moon's orbit in two.

So if that "ship" is a space ship trekking the Solar System, if the laser hasn't hit it within few minutes, it won't. It'll be long gone out into deep space by then. And in a few years, that beam will be a few light years into deep space, on its way to Proxima Centauri our nearest star but for the Sun at 4.2 light years from Earth.