(I know my ideas are purely phylosophical and contain no mathematic equations to back them up, but just listen to my reasons.)
I believe that in the subject of time travel multiple timelines are impossible as when we create a parallel timeline would that not violate the first law of Thermodynamics, as matter cannot be created or destroyed. In my eyes this would be the creation of a complete universe of matter.
Decide for yourselves if I am right and please tell me any consistencies in my hypothesis.