>>6
no it's not obvious that time flows "forward"(into the future),remember that little thing called "spacetime"? Well basically it means time and space are together, meaning that time and space are the dimensions of the universe, so instead of thinking about time and space separately you should just see them as x1,...,x4 and when you plot the universe you get some shape in that space. Now a point on that surface can move on it and that's how time "flows", but this is separate from time as a dimension. (see flows on a manifold)
tldr, the point is that flows can go forward or backward on manifolds(high dimensional surface)