"How does it work? Off the central timeline we just left. Events of importance often cause divergent “tributaries” to branch off the main timestream.
But what’s astounding is there’s far more to it than that. On occasion, these tributaries return—sometimes feeding back into the central timeline, other times overlapping it briefly before charting an entirely new course.
An old friend is suddenly recalled after years of being forgotten.
A scrap of history becomes misremembered, even reinvented in the common wisdom.
There are hazards to Hypertime, of course....
Artifacts carried into differing hypertimelines dangerously break down the barriers between kingdoms... but you’ll learn more about that in the months and years to come. "
— (Rip Hunter, The Kingdom #2, 1999)
One reassuring thing is that, despite the fears of some, the timestream seems capable of absorbing paradoxes.
“Some would have you believe that time is a house of cards, and that if you remove one card, the house collapses.
The physics of time, however, allow for another possibility: remove that same card, and the house rebuilds itself— but never to its original form”
— (Chronos #9, 1998).
BRUCE BANNER: [Disgusted]
First of all, that's horrible...
RHODEY:
It's Thanos.
BRUCE BANNER:
...And secondly, Time doesn't work that way.
Changing The Past doesn't change The Future.
SCOTT LANG:
Look, we go back, we get the stones before Thanos gets them...
Thanos doesn't have the stones. Problem solved.
CLINT BARTON:
Bingo.
NEBULA:
That's not How it Works.
CLINT BARTON:
Well, that's what I heard.
BRUCE BANNER:
What? By who?
Who told you that?
RHODEY:
[counting with his fingers]
Star Trek,
Does not apply to Capt. Benjamin Sisko/Gabriel Bell,
Emissary of The Prophets,
or The Prophets of Bajor themselves —
It is Not Linear.
Terminator
Terminator actually exploits a Deterministic Bootstrap Paradox.
TimeCop
Time After Time -
Nobody Travels into The Past in Time After Time —
Jack The Ripper travels into The Present, pursed by H.G. Wells
SCOTT LANG:
Quantum Leap -
This is, in fact, exactly how Time Travel in Quantum Leap works — it's the entire premise for the whole show :
It's The Observer Effect —
You Change The Result by Measuring It.
The only reason Dr. Sam Beckett is able to make The Journey of crossing his own timeline, be an actor in events of The Past and change established history is because he has no memory of history, as a consequence of making The Journey.
That's also the reason why his range of travel is restricted to The Past within his own lifetime - he is not actually travelling history to change it, he is re-visiting events in Living Memory, making new memories and Remembering it Differently.
He is only able to do this, because he has completely forgotten The Past — or, at least, is far-from certain he is remembering it correctly
Meanwhile, Al, "The Observer" either does remember the original history, or is able to access it's records via Ziggy The Computer's Database — he is able to project an image of himself into the Memories of The Collective Unconscious to communicate information (in the form of stochastic Quantum Probabilities) to Sam, whilst being unable to directly affect any change himself)
It is significant that when Sam is able to recall memories of History or his past life, he invariably misremembers them, until 'corrected' by Al, who remembers Sam 'accurately'.
Sam initially misremembers Ziggy as being the 'Little Guy, with The Bad Breath.' But no, that's Gouschi, as Al correctly informs him.
Sam then misremembers Ziggy as being the Male Personality of the Quantum AI Supercomputer controlling Project Quantum Leap, for the next 3 Years —
Al never corrects him.
Ziggy is Male — until he swaps places with Al, arrives back home at his Point of Origin and Ziggy has become a female supercomputer (programmed with Barbara Steisand's ego).
And Sam is now a married man.
Which he wasn't before.
He returns to find himself released into The Present,
Facing Mirror Images that are finally his own,
And driven by manifest necessity to rescue his friend from History.
His only bride in this endeavour is Donna (neé Elisi),
A Science-WorkWife from His Own Field,
Who appears in the form of a Woman everybody else can See and Hear —
And so, Dr. Becket found himself, married to his former long-lost sweetheart,
whose life he successfully turned around in one of his earliest leaps, somehow happily married to him despite having previously having jilted two former financés at The Altar, with Sam being the second and latter of the two-time loser schucks she went and made them look ridiculous....
RHODEY:
A Wrinkle in Time,
Somewhere in Time -
Where Christopher Reeve travels into The Past via Deep Trance Hypnosis.
SCOTT LANG:
Hot Tub Time Machine -
The Theory of Time Travel in Hot Tub Time Machine actually plays to The Bootstrap Predestination Paradox —
You can visit The Past to create The Present, but you cannot create any outcome that hasn't always been True.
RHODEY:
Hot Tub Time Machine.
Bill and Ted's Excellent Adventure.
Again, Bill and Ted can cross their own timeline to create their present circumstance, but they can also generate future events and consequences simply by an Act of Will, through sincere intent —
'Once I and My Friend Have Succeeded and Triumphed,
I Will Go Back in Time After Now to Steal My Dad's Keys,
Therefore I Know Where They Are
and So Once I Collect Them, I Shall Have Them'
Small wonder it is then, that the people of the society of Rufus' era come to regard William S. (Hey, I only just noticed that one! —) and Theodore Logan as Nietzschan Superman —
Thus Spake Zarathustra : —
'No Way...!'
Basically, any movie that deals with time travel.
SCOTT LANG:
Die Hard? No, it's not one...
Now, There's a line to be pondered-over for decades to come, if ever I saw one....
If I was to speculate at this point, I would maybe suggest that Scott suggests this because he is remembering the line
'How Can The Same Shit Happen to The Same Guy Twice?'
Now, that's just a guess — and I am a good guesser, generally.
But I am certainly not prepared to commit myself emotionally to any answer on this, and definitely not at this stage, at a point so early into The Game —
Time May Tell — it usually does.
RHODEY:
This is known.
BRUCE BANNER:
I don't know why everyone believes that, but that isn't True.
Think about it: If you travel to The Past,
that past becomes Your Future.
And your former Present becomes The Past.
Which can't now be changed by Your New Future...
NEBULA:
Exactly.
SCOTT LANG:
So... Back To The Future's a bunch of bullshit..?
Well, Back to The Future Part II certainly isn't — and nor mostly is Back to The Future Part III, which is also fine, because it involves journeying into History beyond Living Memory (which is precisely what Dr. Sam Beckett is unable to do —
except for that one time when he was flung back into The Civil War, into his Family History, by swapping places with his own ancestor.)
So, how is it that Marty and Doc Brown are able to interact and commune across time in safety so relatively freely in 1955, and interact with Marty's closest blood relatives and immediate antecedents, whilst avoiding many of the most serious hazards (unless you happen to be a Pine Tree, of course), and have those interactions affect stable and lasting change in The Present?
Rather alarmingly, it appears to have much to do with suffering concussive head trauma —
Marty Mc.Fly gets knocked unconscious a lot....
Almost all of the major characters do, at some point or another, whether by means of Chloroform, gut-rot whiskey, the Doc's Delta-Wave sleep inducer, a bolt of lightning, getting chased by a bear over a cliff.....
But if you pay careful attention, almost any change in temporal location for Marty is usually either accompanied by, or swiftly followed by a severe blow to the head, which renders him completely unconscious for several hours — almost every character comments upon this, but Doc Brown's initial encounter with Marty in 1955 and all of his subsequent interactions occur beginning on the day he slipped, standing on the wet edge of his toilet and cracked his head against the sink, whereafter he first conceived of the Flux Capacitor as a vision in his unconscious stupor.
This is initially speculated to be the cause for his apparent failure to remember the subsequent events of November 5-12th 1955 whilst Marty stayed with him, and failure to prepare for What is to Come, in spite of giving him privileged access to and future knowledge of the finished and completed time vehicle he hasn't built yet.
Of course, as we all know, it eventually transpires that he does remember them (although whether or not he did before, and all along is somewhat open to debate, given the evidence of Lone/Twin Pines Mall), and the Doc's freedom and capacity to choose a New Future for himself ultimately hinges solely on his decision to trust his friend, and have faith in Marty's love and affection for him, irrespective of the fact that he is a friend who has not yet actually met yet, in a strictly linear sense of the causalities involved.
Just for good measure, at the start of Back to The Future III, now that things have become really complicated causally with respect to Doc Brown's memories, he throws in the additional piece of speculation, whilst Journaling about the previous evening's successful time experiment, that the consequence of having electromagnetic flux (fluxing), when having been stood directly next to a bolt of lightning striking a copper cable (with quite a considerable jolt of that old 1.21-JgW. likely having passed through his body) had erased part of his memory and induced a degree of retrograde amnesia of the past week's event — which is all very sound scientifically.....
Magnetic Pulses of relatively minute flux density, directed towards the frontal cortex and cerebellum are proven to produce (or rather, induce) profound subjective sensory and perceptual synesthesia, and can most certainly block formation of new memories, and even erase, re-contextualise or re-write existing memories, both recent and long-term.
