First off, my grasp of this topic is somewhat limited, so apologies if I'm   
   misunderstanding something.   
      
   Now, as I understand it, one of the effects of relativity is that an object   
   gains mass as its velocity approaches the speed of light, because of all the   
   kinetic energy that velocity represents.   
      
   However, if all motion is relative, wouldn't velocity be relative as well? An   
   object moving at 99% c relative to a stationary observer would have a lot of   
   velocity (and therefore additional mass) relative to that observer, but from   
   the object's frame of    
   reference wouldn't it be the observer that is moving? (And has the increased   
   mass?)   
      
   I guess my main question is: Are the effects of increased mass from   
   relativistic speeds observable from the reference frame of an object moving at   
   those speeds, or does it only come into play when interacting with other   
   frames of reference? And if they    
   are observable from the object's frame of reference, how do you determine your   
   actual velocity/kinetic energy in order to calculate these effects?   
      
   For example:   
      
   > If a spaceship accelerated to a sufficient fraction of C, would the crew   
   detect an increased gravitational pull due to the ship's increased mass? Or   
   would this only be noticeable to stationary objects the ship passed by?   
      
   > Could an object theoretically (assuming sufficiently ridiculous means of   
   acceleration) reach a speed where its increased mass causes it to collapse   
   into a black hole? Or just neutronium? Could you achieve fusion this way?   
      
   > If so, would this be universal or could the object exist in both a black   
   hole/neutronium/fusing state and a non-black hole/neutronium/fusing state,   
   depending on your frame of reference? ie: a stationary observer would see and   
   interact with the object    
   as though it were a black hole, but an observer in the object's frame would   
   not.   
      
   > Would the lorentz contraction have any effect on this, or is it merely a   
   'visual' artifact due to differing orientations in spacetime?    
      
   To me, the biggest potential consequence of all this is that if the effects   
   *are* relative, a spacecraft wouldn't have to worry about the increased mass   
   making it harder for their engines to accelerate the ship. You'd still need an   
   infinite supply of    
   energy to reach the speed of light, but you could get closer since your engine   
   efficiency wouldn't start dropping off on you. That could make a big   
   difference when designing interstellar spacecraft.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)