I have a couple of things to say here that might clear things up! > I thought that time is like a film, where nothing moves except the observer. We are not me

I have a couple of things to say here that might clear things up! > I thought that time is like a film, where nothing moves except the observer. We are not merely observers of the universe - we are part of it. When we change where (or when) we are in the universe, we change the universe itself. > Also, I never understood the grandfather paradox. Instead of the "go back in time and kill your grandfather" idea, lets keep the scale smaller. Let's go back in time 1 minute, and then smash our time machine. Now, there are two "me"s in this timeline. But energy and matter can't be created out of thin air! Maybe it took a lot of energy to send me back, but that was in the future, and that future is gone, now that our time machine is smashed. We could very well send gold bars back a minute, and double our money! The way you typically resolve this paradox is through keeping infinite timelines. In our example, there's a timeline where we disappeared off the face of the earth, and a timeline where there are two "me"s. They each continue independently. But if there is only a single timeline, we can do all sorts of paradoxical things. > If I travel in the past and change something, wouldn't the change propagate in time at the speed of light? The speed of light is measured in meters per second. Time is measured in seconds. I'm not sure I'm clear on what your suggested propagation looks like.