system
Given the following post, respond as if you're commenting on Reddit:
human
Eli5. How its possible for the light to travel constantly with out stop slowing down from the most old galaxies?
gpt
Light is special because it has no mass and always travels at, well, the speed of light. This is one of its fundamental properties due to the laws of physics. You can’t really compare light to say, a spaceship, because it’s just not the same thing. 

But almost anything can move long distances in space without slowing down. By default, things continue moving at the same speed they’re already moving unless something acts to slow them. On Earth, everything needs to fight air resistance or water resistance or friction with the ground to keep moving. But in space there’s nothing to bump into (at least it’s very rare to hit something) so if you do nothing, you keep moving.