According to string theory, there are infinite number of universes, so called multiverse, anything that could possibly happen will or did happen, hence the parallel universe that could be identical to ours with subtle differences.
As a result anytime you make a decision (go left or right, buy or sell, love or hate, keep or destroy, accept or deny...) it results in a branched version of "new" universe, with that subtle difference.

"New" is actually not right, that's where I do not agree with Fang(human action will ridiculously create a new physical universe? ). That version (any version, for that matter) of universe is already there, or will be there, it is there as result of the events like big bang(or ancestor of it), not because of mind change or "wave of hand" or anything, it is predetermined, not influenced by anyone like you and me or anything of the resulted/created world at all.

In another words, whatever is going on in our universe is predetermined by the big bang. Your decision seems to be a "new", but it has been predetermined already, it is destined, the "fate" is already settled. Should we have a computer powerful enough to calculate any movement of any particle or energy transformation/transaction, we would be able to "predict" the future.

The above being said, regardless of the mentioned "paradox" related to time travel, a "new" version of future could be "created", just that it already meant to be there, as one of those possibilities, remember anything could happen will / did happen, if the grand-grand------father is killed by the son, in that "new" universe, that son does not exist in that "future" in that universe, there is no law of physics broken.