I think there is a distinction to be made when talking about multiple timelines.
On the one hand you could say that there is a timeline for every possibility.
This, of course, includes timelines where the laws of physics are different from ours and where there might be at least one where we live on a planet that looks like a can of peanuts and all humans look like scissors.
But on the other hand you could say that when you travel back in time you will arrive at a point in the past that is exactly the same like the past you've come from until to the point where you arrived.
"If" it would work that way, then we would never arrive in a timeline that's already been different.
And then there's the notion that a timeline is just used for semantics, i.e. to make it more easy to talk about the subjective view of the TT.
In reality it "might" be that we actually do travel back on our own timeline, but that from the TT's POV he thinks he is in a new timeline.
From the POV of the people he left (when he travelled backwards) it very well might be that they are continuing their lives without ever seeing the TT again, because from their POV he is many years in the past.
Since their perceived here-and-now is constantly moving forwards in relation to the here-and-now of the TT in the past, his changes will never propagate to them.
Example:
At time X Peter travels back 1 year into the past and thus arrives at time A. For simplicities sake let's say this travel is instantaneous:
----A-----------X------------>
<font color="white">.....[/COLOR]|<----------|
After Peter arrived at A, let's say he watches his clock and counts 5 minutes.
At the same time the people he left at X began to count 5 minutes as soon as Peter was gone.
So, following the POV of Peter and the people he left behind from the moment they saw eatch other for the last time, this could very well mean that both simultaneously counted 5 minutes:
Peter: A + 5 minutes
Others: X + 5 minutes
----A-----------X------------>
<font color="white">.....[/COLOR]|>|<font color="white">...........[/COLOR]|>|
If we follow this thought through:
----A-----------X------------>
<font color="white">.....[/COLOR]|--->|<font color="white">........[/COLOR]|--->|
----A-----------X------------>
<font color="white">.....[/COLOR]|------>|<font color="white">....[/COLOR]|------>|
Now, the moment when Peter get's to time X again, he will not see the here-and-now people he saw from a year earlier.
It took him a year to reach point X again, but simultaneously for the others they lived on for a year as well, way past time X.
So when he arrives at time X again, he WILL see the others again, namely a version of the others of exactly that point in time X.
But from the POV of the others from the moment they last saw Peter, they still moved forward with their here-and-now.
And THEY are still a year infront of Peter, since THEIR subjective here-and-now moved forward as well as Peters from his subjective POV:
----A-----------X------------>
<font color="white">.....[/COLOR]|---------->|---------->|
My point is NOT to say it is this way!
It's just a thought experiment to provide an explanation as to how TT with "multiple timelines" could work.
Of course everything is possible, etc... it can't be falsified etc.. it's of no use, etc...
As I said, just a though experiment to fuel some brainsm and to see what you think about it.
To sum up my thought/idea:
Multiple timelines could just be considered a symantic helper to describe different POV's.
What might actually happen is that any changes made by the TT from his POV will never propagate to the here-and-now of the POV of the people he left behind, because when the TT travels a year forward, the here-and-now of the others he left behind has travelled forward a year as well, resulting in them always being a year infront of the TT.
To be clear:
I always look at the POV of both in realtion to each other, simultaneously, from the moment they departed at time X! Like watching two camera feeds at once.
But again, this does not mean he won't see a "version" (just to distinguish them from the other others who are a year infront of the TT) of the others when he arrives at X again.
He will see them of course, they just won't be the one's he originally said goodbye to a year earlier, because they are still a year infront of him. The ones he's meeting at X again are the ones who were always with him (from his POV in his here-and-now) when he arrived at A.
I hope I could get everything into the correct words to understand everything I meant.
There are still some points where I have the feeling I didn't quite get it through, but I guess my thoughts->words processor is just not that good in quality.^^
Addition:
I'm aware that you can say the poeple from point X who move forward could get a visit themselves from an "earlier timeline".
That's absolutely ok, but the exact Peter who left them at point X is never gonna show up again. He would have to be able to travel to point X without just slowing down his own time in relation to the outside world, because this would just propagate his here-and-now faster to point X ALONG with all the changes he made.
This means that the "version" of the others a year in front of him would equally fast travel forward, which means he could never reach his "original" friends, only other "versions" of them.
There will always be friends a year in front of him who wil never see HIM again. Maybe another "version" of him, but not HIM.
Of course you could say: But what makes the others at point X Peter will see different from the others at point X + 1 year?
Well, nothing really, they are the same people, only in different times.
But the X people Peter will meet, will not be the same as the ones he said goodbye to.
Because the latter are already at time X + 1 year.
*Phew*
I hope this addition didn't make it even harder to get my thoughts.^^