adjective: dogmatic
Inclined to lay down principles as undeniably true.
Now you're being insulting. The fact is, your own assertions here are based on some major misunderstandings, confusions, and mistaken assumptions. I'm just trying to point out where your understanding of science is mistaken and your logic is self-contradictory. If you refuse to admit that you're capable of error and that any criticism is merely a difference of opinion, then you're the one being a dogmatist.
This is the bit I don't understand. You're breathing air that wasn't previously breathed by you. You're introducing new strains of bacteria that did not previously exist in that time or location.
That's a myth, that you weren't there "previously." There is no "previously," except from the subjective viewpoint of the time traveler. If you went back into the past, then you were there all along. If you created a second time track, then that second track was there all along. As Dr. T'Viss said in
Watching the Clock, you can't understand time travel until you step outside your own subjective perception of time -- look at the whole thing as a timeless continuum where every event has already happened. If an event looks new to a given observer, that's only because that observer wasn't previously aware of its existence.
After all, it's a fundamental contradiction to talk about two versions of a single moment in time coming "before" and "after" one another. By definition, they are simultaneous. It only looks to the time traveler that one comes after the other, but that's an illusion caused by the time travel. If you rewind a video of a ball game and watch it again, that doesn't mean there's a second game being played. It just means you've altered your own perspective to experience the same moment in time at a subjectively later moment.
It just seems to me that saying a branch only comes into existence if there is a major change is entirely arbitrary. What constitutes a major change and who in the world of physics has decided through maths, observation, and quantification, what that is?
Okay -- strictly speaking, in real physics, if you went back in time, you couldn't change anything. As a quantum observer, you're already entangled/correlated with the events of your own timeline, so if you go back into the past, you correlate that past with your own future, and thereby guarantee that the future you perceive will be the one you started from.
http://arxiv.org/pdf/quant-ph/0506027.pdf
So a self-consistent time loop is actually the default. For a more classical perspective:
http://en.wikipedia.org/wiki/Novikov_self-consistency_principle
The fictional premise of altering history by time travel is actually pretty much a fantasy, although it might be justifiable through nonlinear quantum mechanics, which I won't get into here. Stories can fudge things to allow for it to happen, but realistically speaking, the self-consistent type of loop that you're dismissing as impossible is actually the more plausible outcome of time travel by an enormous margin.
Nonetheless, out of interest, how does the many worlds theory of time travel deal with temporal bottlenecks? If travellers from alternate futures can travel back to the same point in a shared past, aren't they adding additional matter to the shared past and if so is this the tipping point of the Big Bang?
They aren't "adding" anything -- they were there all along. If you mean that any time travelers are contributing mass-energy to the universe that wasn't there before the moment of their arrival in the past or future (from an objective observer's perspective), I've come across time-travel theories that account for that -- say, the time warp releases an amount of negative energy to balance the amount of mass-energy the traveler adds.
Strictly speaking, Many Worlds isn't about time travel specifically. It's about the nature and definition of alternate histories of a universe. I'm using it as a shorthand for the type of alternate realities I'm talking about, those that are alternate histories of a single physical universe, in order to distinguish it from the separate and unrelated type of alternate universes involved in the infinite-multiverse model, which are simply distinct physical realms that exist unreachably far away in space or in other dimensions.
And I have no idea what you mean by "tipping point of the Big Bang."
