The Voyager 1 space probe was launched by NASA in 1977. It's now the most distant spacecraft from Earth, as it hurtles into space at over 60,000 km/h. It has run out of fuel, so it can't change its own motion.

One of your friends says, "If Voyager 1 doesn't collide with anything and is too far from anything to be affected by gravity, it will gradually slow down and stop."

I have to either agree or disagree with my friend, then i have to explain.