About that train experiment. Everyone probably knows the story. For the person on the train, the flash of light hits both ends of the train at the same time. For the person watching on the embankment, the flash of light hits the back end of the train first. Now, I'm reading a book on SR which words the experiment slightly differently. It says that the flash of light triggers off the doors at either end opening. So, for the person on the train, the doors open simultaneously, whereas for the person at the other end, they do not open simultaneously. From this I'm guessing it must be possible for a flash of light somehow to complete an electrical circuit. I don't know the ins and outs of how this would happen - maybe it isn't even right. I seem to remember something about 'light sensitive diodes' from physics at school about 10 years ago. But still...I'll assume that it's possible. Let's replay the train experiment with a single, almost instantaneous flash of light. Both ends of the train are wired up to an electrical circuit, which when completed triggers an emergency braking system which stops the train. To the person on the train, the flash of light hits both ends of the train at the same time, thereby completing the circuit. But in the observer's frame of reference, the flash of light hits each end at different times and so the circuit is never completed. Is it then correct to state that, to the observer, the train is still going, whereas to the person in the train, it has stopped? I'm guessing everyone will say no to this, so where have I gone wrong?