system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: If I shine a flashlight towards the night sky, how far does the light travel?
gpt
It just keeps on going until it hits something. 

That could be a bird, a plane, a cloud, the ISS, another planet, a distant galaxy...

The torch is a pretty weak light source, and the light intensity follows an inverse square law (IE if you're "X" times the distance away from the torch, the light is only 1/X^2 times as intense). 

This means that fairly quickly the light your torch produces is lost to the human eye. But the actualy photons/waves (however you want to think about light) will just keep going.