You talked about two types of time travel. There's the type where every change you make changes everything immediately. You step on a butterfly, you've just erased yourself from existence. This type is confusing and stupid. The second type was strict-timeline time travel, where everything is set in stone. You kill baby Hitler, and the maid switches him with a different baby who turns out to be the real Hitler. Nothing can change because everything has already happened. This type makes more sense, but it's boring. Both of these theories have something in common - they each have only one timeline. In the former, it's fluid and malleable; in the latter, it's rigid - you can't change it. Now take the idea of a single, main timeline, and wrap it around itself like a big ball of wool. Throw in a bunch of other timelines and wrap them around it as well. Then add some yarn for good measure. You now have a ball of [i]time.[/i] If you fish around in the ball of wool, you'll find the little strand that you're currently on. Look, there it is. Say hello. With your time machine (you have a time machine, by the way) you can travel backwards or forwards along the strand of wool. Normally, being a rookie, you'd go back in time to kill Hitler, but you've misplaced your English-to-German dictionary so you decide to put that off. Instead, you decide to travel to, say, the Jurassic, so you can ride a T-Rex (which, by the way, weren't actually around back then). If this were strict-timeline time travel, you'd accidentally land in the late-Cretaceous, becoming the meteor that wiped out the dinosaurs, wrapping up that string nicely. Instead, you land right on target in the Jurassic, as a time machine that wipes out all the dinosaurs early. Fortunately for you, your time machine is shielded on the inside, saving you from the planet-wide destruction that you just caused (you absolute [i]jerk[/i]). Deciding to cut your losses, you head back to the present (or the future, or whatever). Now, if this were fluid single-timeline time travel (I really need a better name for that), you would have erased yourself and every other human from existence with your premature dinosaur nuking (which, on that note, again you [i]jerk.[/i] What did the dinos ever do to you?). But this isn't singular fluid timeline time travel, this is time as a ball of yarn time travel, so you don't start to fade away or poof away or whatever. Instead, you return safely to the present. Of course, it's not [i]your[/i] present any more. Because you see, when you annihilated the dinosaurs (jerk!), you dropped off the thread you were on, and onto a different, stranger thread. Things have indeed changed. Instead of humans, the dominant lifeform is, uh... chipmunks. Giant, intelligent chipmunks. With wings. And, uh, monocles. Because, although as far as you're concerned (due to your personal timeline) the year 2013 was not inhabited by giant, flying, classy chipmunks, you've now changed timelines, [i]so it is.[/i] Also, they're flying swastikas from their chipmunk-y buildings. Because, as Godwin's Law of Time travel clearly states: [i]any and all changes made to the timeline will result in the Axis winning World War II.[/i] Way to go. You just nuked the dinosaurs [i]and[/i] put national socialist chipmunks in charge. You absolute jerk! ... I hope that cleared things up.