Hey! So basically I studied General Relativity for a while and was moving on to Special Relativity and there's one thing in it that I can't seem to understand, simultaneity. So I've seen videos explaining it with a train, an observer in the moving train and an observer outside the train as the train gets struck by two lightning bolts. I understand how they see the events differently and are both right as time is dilated as light must always travel at the same speed. I get that, but when you take light out of the equation, and make it a larger distance, I really get confused, here's an example: So, if you watch the video, there is a man and an alien, many millions of lightyears apart. When they are stationary, time moves the same relative to eachother, yet when the alien cycles away, his 'now' is now our 200 years ago. How does this make sense? How can alien or any being far away deciding to take a cycle make their now so different to ours? Also if his now is our 200 years ago, has he just time travelled technically? Sorry if this sounds like madness but it really confuses me. I hope someone here would be able to help me!