<p>The relativity stuff is over my head, but I can address a couple of minor points about your post, Maverick: </p><p>As for gaining mass, mass doesn't have any meaning in space. You could use one of the verticle thrusters used on our spacecrafts for leveling out the ship, to push a rock the size of texas through space. Mass has no meaning.</p><p>This is not actually true -- mass has a great deal of meaning in space. Just because you are weightless in space does not mean that you are massless as well. In fact, this can be a serious problem for spacewalking astronauts -- they can push a 200-kg object around, but that's mostly because they don't have to fight against gravity or friction. It still has 200 kg of mass, and if they're not careful, that can crush somebody.</p><p>Also, it's not effortless to push 200 kg around in space. It's doable, but not effortless. The more massive something is, the more energy you need to change its velocity vector. This is why it takes more propellant to get an Apollo spacecraft to the Moon than it does to get a small robotic orbiter to the Moon. </p><p>The ship wouldn't be nearly infinitely massive.. my concept is a recyclable energy source... thus is why fuel wouldn't matter. The fuel would continually be recycled and re-used, and since my idea doesn't involve combustion of any sort, the fuel source isn't damaged, or changed in a manner that would cause it to degrade, the ship would thus not change mass, yet still have an unlimited fuel source. Thus a space ship equiped with this particular system would remain the same weight in mass, while still being able to continually accelerate.</p><p>Rockets don't work the same way as cars. Cars combust fuel with oxygen from the air to produce energy to turn a crankshaft which in turn is used to turn the wheels of the car. The fact that the combustion byproducts escape out the tailpipe is an unfortunate happenstance, but has little effect on the car's operation. Rockets are different. Rocket engines are a type of motor called a reaction motor, which means they operate on the principle of every force having an equal and opposite reaction. In all cases, propellant is made to accelerate to high speed and blast out the back of the engine, producing thrust and shoving the vehicle forwards. Most engines are chemical bipropellant engines -- they combust a fuel and an oxidizer to produce a vigorous exothermic reaction that propels the products of combustion out the back, and the rocket forwards. There are other types which do not rely on combustion, such as ion drives. Ion drives electrically excite a propellant such as xenon gas, causing it to fly out the back of the engine, pushing the vehicle forwards. The thrust is very, very low -- barely enough to flutter a piece of paper. But it is very very efficient. This may be the ideal engine for your hypothetical ship, because although it takes a long time to accelerate, you can do it for remarkably little expenditure of propellant. But you do expend propellant. Reaction mass is lost as you accelerate forwards. On the plus side, as your vehicle gets lighter, it accelerates more rapidly. ;-)</p><p>However, neither of these affect the fundamentals of your thought experiment, I think. They're just the few things I could find that I could actually speak to!</p> <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em> -- The Tenth Doctor, "Blink"</font></p> </div>