| Yeah, that explanation was dead wrong. Here is the real one. The phrase "at the same time" means different things in different inertial reference frames. So what is FTL to one observer, is traveling backwards in time to another. If you can warp from any reference frame, you can therefore travel backwards in time. As for why "at the same time" changes meanings, let's adapt Einstein's example. I'm in the middle of a moving train. You're on the train station. As we pass, lightning strikes right between us. Will the light from the lightning arrive at both ends of the train at the same time? According to me, obviously. In my reference frame the train is not moving. Light has a constant speed. It will reach both ends at the same time. According to you, obviously not. Light travels at constant speed, but the train is moving. Therefore the back of the train is moving towards the light, and the front is moving away. So the light gets to the back of the train before the front. So when the person on the train says that an event in front and behind happened at the same time, the person not on the train says that the event behind happened before the event in front. Now consider this. I'm on a spaceship with a warp drive. This is a great warp drive, travels instantly in whatever reference frame I'm in.. I warp forward a long distance - like a light year. I accelerate forward. I warp backwards and arrive back a bit behind where I started at. I decelerate, and I'm in my own past! That's the causality problem. |