Here's why:

* Newton's First Law of Motion (Inertia): An object at rest stays at rest, and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.

* No Friction: In frictionless space, there's no air resistance or any other force to slow the ball down.

Therefore, the ball will continue moving in a straight line at a constant speed indefinitely without any additional force being applied.