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If you fire a laser in space, does it just keep on going as there is nothing to draw energy from it so it would dissipate? As for a projectile, isn't this also the case as there is no gravity or air friction to stop it like on Earth?
The light from a laser in space would continue on forever unless it hit something. However, if you were far enough away, you wouldn't be able to detect the light. A projectile would also continue on forever unless it hit something.
Lasers produce light that can be tightly focused. That means over a long distance, the light doesn't spread out much. When you use a laser pointer, you only see a tiny spot across the room. If you were looking at the spot even further away, it would be slightly bigger. If you go far enough away, the light will eventually spread out far enough to be undetectable.
Newton's first law of motion states that an object in motion will continue in motion until acted upon by an outside force. Since there is no air in space, the projectile won't be stopped by drag. There is gravity in space, but the projectile will continue on until it gets close enough to a large object like a planet or star for that object's gravity to pull it in and stop it.