If you were to invent a time machine, and go back in time with it, there are two possible theories of what could happen. Either you would go back to your current timeline ("timeline 1"), which opens the door to "killing your grandmother" paradoxes and such, or your act of going back in time would create a new timeline ("timeline 2"), in which killing your grandmother would only affect the future version of yourself in timeline 2.
However, if you don't kill your grandmother or do anything to adversly affect the future, the future you from timeline 2 would likely also invent a time machine and go back in time, creating another new timeline ("timeline 3"). Then the future you from timeline 3 would also go back in time, creating timeline 4, etc.
Thus a single person going back in time would potentially create an infinate number of new timelines, if we were to assume that altering the past creates new timelines at all.
However, if you don't kill your grandmother or do anything to adversly affect the future, the future you from timeline 2 would likely also invent a time machine and go back in time, creating another new timeline ("timeline 3"). Then the future you from timeline 3 would also go back in time, creating timeline 4, etc.
Thus a single person going back in time would potentially create an infinate number of new timelines, if we were to assume that altering the past creates new timelines at all.