I thought of something interesting just today. Let's say I have a decision to make, left and right, that will lead to different future. The idea is, there is a universe where I choose left which have different future than if I choose right, in that sense I have no problem. However, in order for me to choose let's say 'right', there needs to be certain pulses and chemical in my brain that makes me decide 'right'. In order for me to think 'left', there has to be something different in the past that triggers it, could be something like a piece of dust a supernova, that causes me to think differently or have different timing that could leads to it. And even that difference cannot happen unless there is something else different, and that keeps going indefinitely. Even when I use a computer to 'randomize' the outcome, I will still press the button at some exact time and the way the electricity goes inside the computer, if it says 'right', no matter how many times you rewind that event, the outcome will always be 'right'. Unless I press it very slightly differently or if the voltage changes ever so slightly that will change the outcome, which again require something else to happen. There has to be something different in the past that leads to a different outcome, otherwise the outcome will be exactly the same, every single time. In this case, parallel universe simply cannot happen since the past is like a 'closed system', unless probably if time travel possible, but that's another story. Is there a problem with this thinking?