Where is Speed Speaks?

Thought Experiment: Can speed faster that light be achieved? Or where is the faulty logic?

• Imagine a train in outer space that is billions of kilometres in length. on top of that train is another train stacked over it, and is able to travel on top the first train (the lowest one). Similar to how once can stack two bricks on top of each other and slide the top of on top of the other. these train will be travelling from point a to point b. the top train, has a special particle on its front, that when it reaches the point b, will turn on the light bulb which is located there. When lower train starts moving, it achieves the speed 99% of the speed of light, however as it sets in motion the top train starts travelling as well, also at the speed equal to 99% of the speed of light. Although no train will be moving at a speed faster than the speed of light from their point of view, the particle that is located on the top train, will travel from point a to point b at a speed faster than light (and hence information is conveyed faster than light), which is in direct violation of special relativity. Where is the faulty logic in here?

• Answer:

  This question, or one essentially identical to it, has already been asked and answered many, many times on this website. The error is that if frame B is moving .99c relative to frame A and frame C is moving .99c relative to frame B, you cannot simply assume that C is moving more than 1c relative to A. For details, see any of these: