Temporal Novice
Ok, I have been reading posts all morning about or relating to John Titor, and I have some questions that keep nagging me that I have not yet found answers for in my searches.
1. In one of his posts John gives a basic description of the worldlines relating to time travel. He says that he starts from his worldline (A) in 2036, and then jumps to another worldline (B) in 1975 with a 2% divergence. By being on worldline (B) in 1975 he creates worldline(C), and then decides to jump forward to 2000 on worldline(C) which by him being there creates worldline (D).

Are we to assume that worldline (B) already existed?
If worldline (B) already existed and John was from worldline (A) isn't his past/future different from ours?
If his 'fix' in 1975 occurred on worldline (C) how does that help his future on worldline (A)?
If worldline (D) didn't exist before he got here, did his arrival in 2000 cause everyone's worldlines to split (C&D)?
If every event spawned a new worldline, wouldn't some worldline start to intersect? What happens then?
He says that if he were to go forward on (D) to 2036 it would not be 'his' 2036, so how does he know about future events on our worldline (D)?

I am genuinely interested in all this, so please go easy on me, if these seem like dumb questions. Thanks
Probably the best way to think about it is that there is a "density" of universes.

You have to think like probability density functions, not individual countable

There is an infinity of jumpers jumping to an infinity of targets. The probability
of apppearing in any one target point is the probability density.

But anyway this is all real speculative mumbo jumbo.

Personally, I believe there is one universe, the quantum wave function
is physically real and universes do not split upon observations. That
is a fallacy by considering the observer as being classical when all
observers also have to obey the laws of quantum mechanics.

I believe the Heisenberg equation of motion very accurately describes
the evolution of the wave function for all time, and there is
no 'popping' that is outside that time evolution. The popping of the
wave function upon observation is a physical process described
by the Heisenberg equation, and the randomization comes from
lack of knowledge of the quantum phases in the atoms of the
macroscopic observational device. I.e. it is exactly akin
to a roulette wheel: the wheel (phases) spin very rapidly and
so where you have the ball fall in the hole (irreversible interaction) is
practically indeterminate even though the equations of motion
are described by Newton (Heisenberg).

This requires irreversibility and is probably due to interactions
with the thermal bath of the environment which cannot practically
be eliminated. It is still open to me whether there may be tiny
nonlinear terms.

Quantum computers are devices which attempt to minimize this interaction
for as long as possible to make interesting calculations feasible, i.e.
avoid popping the wave function.