system
Given the following post, respond as if you're commenting on Reddit:
human
My friend is convinced that, assuming earth is the only thing is the universe, if you threw a ball in space it would eventually stop and come back. It would go on forever, right?

Title ^
gpt
Depends whether it's going faster than its escape velocity. If it is, it goes on forever. If it's slower, it falls back down. If it's at its escape velocity, it stops right at infinity.  
Set kinetic energy + gravitational potential at earth's surface to zero, solve for v to find the escape velocity.