- last post: 01.01.0001 12:00 AM PDT
You can only accerlerate as much as you engine will allow: there will inevitably be a limit, and I will not even attempt the "What happens above the speed of light" argument that may come as a result.
The reasons for deceleration are: friction, gravity, air resistance, etc: thus, gravity from objects with large masses or gravitational pulls (such as planets, for instance) is the only thing that could really cause deceleration.