A ball thrown in a vacuum, where there is no gravity, will continue to move indefinitely due to Newton's first law of motion, which states that an object in motion stays in motion unless acted upon by an external force. In the absence of gravity and air resistance, there are no forces to slow the ball down. Therefore, it will not stop moving unless it encounters an obstacle or force. This principle highlights the importance of external forces in altering the state of motion. Thus, in a vacuum, the ball will indeed move forever.