I don't really care about whether
Star Trek (2009) "erased" the original timeline or not. It doesn't erase any of my DVDs, so I can still watch whatever I want. I was, initially, annoyed that the Pine/Quinto movies don't take place in the original timeline. It took me a while, but I've mostly gotten past that. I still find it mildly annoying that the entire franchise isn't a single, cohesive-ish timeline. But once I realized that the time travel shenanigans were more of a marketing gimmick than a serious attempt at a time travel story, I stopped caring. CBS/Paramount can do whatever they want. This stopped being my main franchise sometime around 2002, back when
Nemesis bombed and I realized that nothing was ever going to top
DS9.
As Always, depends on what type of story you are telling. Because most time travel stories use the trope to tell a story, so say if your story involves changing history, and your protagonist is the only one that hasn't changed and wants to put history back right, then a changinging main line would work.
So its basically fit to your stories basic idea.
Marty should have been erased the second he interfered with Pops because he changed the when and where his mom and dad "Coupled" to make him, so that particular Egg and swimmer never met, so he was never born. So he should have disappeared like Bruce Willis in Looper once his present ended.
And in BttF 2, i doubt he met doc brown, so he should have disappeared once Biff changed history, same with Doc.
Honestly, the more time goes by, the more impressed I am by the elegance of the internal consistency of
Back to the Future's time travel. You can change time as much as you want and the time traveler is always protected by the changes UNLESS he does something that jeopardizes his own existence. Even then, if there's theoretically time to set things back on track, you won't fade away until you've completely exhausted those possibilities. The time travel has stakes but also the universe just kinda slowly snips away any spare pieces that don't make sense at the end. You can alter the timeline in such a way that your changes will remain even if you don't. (Although it does mean that Doc's concerns about world-ending paradoxes in
Part II are completely unfounded.)
As for George & Lorraine's children all looking the same, sure you have to ignore that side of the genetic lottery for the sake of dramatic clarity but it's a small price to pay. Also, keep in mind that, apart from George & Dave, ALL of the men in the McFly family look like Michael J. Fox, so his family may be somewhat locked onto that genetic template at a quantum level.
In the Heinlein books they would label the various timelines by the first person to land on the moon. We live in the "Armstrong" timeline.
Which book was that? I remember a bunch of alternate universes in
Job: A Comedy of Justice but I don't remember them naming them. (I don't think that the original universe that they came from even had space travel yet. They were in the universe where everyone was using zeppelins instead of airplanes.)
The grandfather paradox can never be tested until someone travels in time. You don't even have to kill your grandfather.
Yeah, but he's kind of a jerk, so it would be a nice perk.
Though one thing I do like in alternate timeline stories is the idea that fate might play a role in things happening much like they did in the original idea. Like maybe you go back in time and save JFK but Vietnam still happens and Nixon still get elected.
There's only one way that that can play out.....
I also like the idea of slight alterations. What if 9/11 happen on 9/12. What if the White House was in Philly instead of Washington. Maybe the internet is called the cyberweb. Things like that. One of things I loved about the show "Sliders."
One of the nice touches in the
Stargate SG-1 episode "Moebius"-- Our heroes leave a camcorder with a video message for their alternate selves in an ancient Egyptian burial site that they know will remain undisturbed for 10,000 years. When they unearth it in the alternate present, General Hammond mentions that it uses a power source not compatible with anything available on the commercial market in this altered timeline, so they had to jury-rig an adapter.
Basically, there are 3 kinds of time travel:
Grandfather paradox: There is one timeline and it can be changed. (e.g.
Back to the Future, Timecop, pre-2009
Star Trek)
Predestination paradox: You can't change the past. Anything that you do will only serve to create the past that you already came from. (Is
Bill & Ted's Excellent Adventure REALLY the best mainstream example that we have of this. That doesn't seem right.
12 Monkeys? I dunno. I haven't seen the whole thing.
)
Multiverse: Each instance of altering the past creates a new, divergent universe.
Grandfather & Predestination seem to be the most common types. Honestly, I think that the reason why the Multiverse isn't used so often is because it's the least dramatically satisfying. That's my biggest gripe with
Avengers: Endgame. They use Multiverse time travel, so they can go back and dick around with the past as much as they want with absolutely zero consequences to their own universe. (So they can do things like let Loki escape or potentially kill Star Lord given that he was PUNCHED IN THE FACE BY FRIGGIN' WAR MACHINE!) At least
Stargate uses Multiverse time travel properly by always having us follow the altered timeline, so there are proper dramatic stakes to making the changes.
A few pitfalls I would suggest avoiding:
Don't create a really tight Predestination story, then have the sequels mangle it beyond all recognition. *cough*
Terminator*cough*
Don't introduce a sexy Irish redhead, then strand her in a post-apocalyptic future, then change the timeline so that future never happens, then never mention her again!
*cough*
Heroes*cough*
