An astronuat in a nuclear ship accelerates away from earth and gets very near the speed of light, .99999% in fact. The accelerometer on the ship indicates the ships acceleration has been decreasing during this feat as the mass of the ship has increased greatly and the nuclear engine can no longer continue to accelerate the craft to any great degree. The engines are cut, the astronaut is happy that he has achieved the fastest speed ever, and after 10 years of coasting at this speed he calculates that he has just traveled past all galaxies and into a deep part of space where no stars exist. He dies, but a stowaway baby boy was on board when the ship left earth and is now 10 years old. The boy looks at the accelerometer and it reads 0. There is no speedometer as speed is relative so they didn't put one on the sip. The boy figures the ship is at rest and fires up the engines, but to his surprise the ship does not move (accelerate) more then just a tiny tiny amount as the ship is already traveling so fast and further acceleration is almost impossible. The boy knows the thrust of the engine, knows the rest mass of the ship and can read the accelerometer and from this was able to determine how much mass the ship now has. From this he was able to determine the ship is traveling at .99999c or in other words the absolute velocity of the ship relative to nothing. Where is the flaw in my logic?