Mm, from the look I read from varies different thing, this is the VN have the best idea in terms of time travelling in my opinion, their time paradox seems to "make sense" to a certain extent. But as for time travelling, because it is as far as we're concern impossible, it is hard to describe it to be science in anyway :/ Even the theory itself is just...weird to a certain extent due to the whole time paradox. But I think that S;G did a great job in my opinion (from what I read is good already, I wouldn't think the VN itself is that bad)