There is the Grandfather Paradox where a guy goes back in time and kills his Grandfather, before the conception of his mother or father..
If the guy did kill his Grandfather in that manner, then there is no way he could go forward in time to his previous life because one of his parents is dead and therefore the guy does not exist...
To get around that Grandfather paradox, there is a theory that says when the guy goes back in time to kill his Grandfather, he automatically goes into an "alternative universe" which is identical to this universe except that changes can be made in it which does not affect this universe of ours...
So, the guy can pop back in time to that alternative universe and kill his Grandfather before either his mum or dad have been conceived, and then return forward to this universe where his Grandad is still alive and so are his parents, and the guy still exists
The theory of the Alternative Universe means that when ever we go back in time, the "Time Law" will automatically send you to another (alternative) universe where changes in that universe are allowed, and then when you travel forward in time, you automatically get back to this universe where nothing has changed..
If you went forward in time the "Time Law" would still exist and you would still enter an alternative universe, just like in the Grandfather Paradox, But of course its just a theory
The same(past) applies to the future, example, once you started to do something in past/future, whether you like it or not, there will be a new timeline or alternate reality created and therefore, you would expect nothing changed once you go back.