Oh, finally we got here cool discussion. Here is how I explain that one "could" travel faster then the speed of light! HOWEVER, and this is VERY IMPORTANT, this depends on your definition of the speed. So imagine following experiment:There are two space ships which are built like these russian matroshkas. One smaller space ship is in the hangar of a bigger one. The bigger one starts from the earth and accelerates to the speed of light (or just until 0.999c). Now, the smaller ship starts and can again accelerate from the bigger ship point of view until 0.999c. So, if there is just a simple velocity measure instrument, which is measuring acceleration by F = m*a, and we know the relative space ship mass "m" as it was relative to the earth, then knowing how much force our engine produces we can compute the acceleration. And hence our velocity measurement device will add small "a" to the current velocity by every thrust of the engine.So given that type of measurement, our smaller space ship can accelerate to the speed of 2c relative to the earth. HOWEVER, due to the relativistic effects the people living on the earth would never ever realize that this ship was moving with 2c, since they are measuring speed by looking how far the ship went in the certain amount of time. And due to the time dilation they will never realize that this ship was actually much farther away then it looks like.So, regarding to this experiment, we can travel faster then the light. However, this is only due to the definition of the speed.A counter argument would be that the mass "m" is also changing. However, one could argue that the mass is represented by the amount of particles per volume unit and hence remain constant if volume remain constant. Ok, another guy could argue again that the size of the volume shrinks, but I could then argue that if size of the volume shrinks, then the density of the particles per volume unit from the earth point of view would increase and could end up in a singularity or just black hole, so big bang ?:confused:This kind of experiment fits well into my experience of the world, where I just cannot accept some of the constraints we get from the nature :) Yes, you cannot travel faster then the speed of light, BUT this is only because I stay at the earth and measure your speed by looking how fast you come back. But this pure guy who is traveling could measure the speed as I've proposed and would then realize that, in deed he was faster then the "earth's speed of light" :)

 Unfortunately, you are trying to impose a traditional world, where speeds are additive, onto relativity. It just doesn't work that way. A light beam fired from Earth would overtake the smaller ship, so in Earth's frame it is going slower than the speed of light.
 Yes, you are right, but you just didn't get the point what I was trying to say. In deed I was expected that I will be downvoted by this comment :)I never claimed that speeds are additive. I've just claimed that it fully depends on what you define as a speed. If you define the speed the classical way (space unit per time), then due to the relativistic effects, it will never work out for you.However, and this is the point, if you define the speed as just some counter running in front of you which add a value on every engine thrust, then it will work out for you that you are traveling faster, then the "earth's" speed of light!!!Imagine just another experiment. You are waking up at a space ship and there is nothing around you where you can fix your view to see if you are moving or not. So, the speed-counter on this ship shows you 0.9c (here c is "earth's c"). No, you press the accelerate button and accelerates to additional 0.2c. There is nothing which would stop you accelerating, because in your frame you can assume that you are at rest! So, adding now the new velocity amount to your previous you get 1.1c, HOWEVER, this the "earth's c" ,so the speed of light as it is measured on the earth!!! In your frame, since you have no clue if you was moving or not, you should assume that you have now only 0.2c or just 0c, since you cannot measure the speed in the classical way anymore (there is no other point to fix on).So, this is the way how to understand the relativistic effects. There is no "super-dooper" spaghetti-monster hand, which will for some reason stop you accelerating. No, this is just because everybody around you will never be able to measure your real speed, because they can only measure the speed relative to their frame.

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