You don't know what you don't know.
Sketching tight, clean lines across the transparent marker board, Barry tries to understand what has changed about Caitlin and Cisco. Under the guise of studying his equations, he studies them, working unceasingly to keep his hands busy. It's easier to process emotions without having to actively participate; he can read the room better when he isn't focused on conversation. The Speed equation is important, but Barry's universe has changed.
With computer-like detachment, he allows his mind to reboot, hoping to pick up on the new nuances of their relationship without needing to overtly ask for clarification. They don't know what has changed; they can't tell him what he needs to know. Even meticulous study of hard records would leave him at a net loss: he would miss all of the conversations and moments in time where Other Barry stepped out of the path he created.
He doesn't know Other Barry. The thought should bother him, but it barely interrupts the unceasing arc of his hand across the board. Other Barry and he are not the same person; thinking about him inspires a sense of detachment that chills Barry.
Stabbing him didn't leave Barry feeling guilty. On the contrary, it felt necessary, methodical, precise. Interrupting the timeline was a surgical event: pain was unavoidable. Managing it was only a secondary concern for Barry; his principle concern was correcting the future problem.
After all, death was unforgiving: it could not be reversed. Suffering could. Causing a momentary disruption in a timeline that was not his did not bother Barry; his goal was too important.
Thinking about how he has hijacked Other Barry's timeline does make his hand falter, cutting a sharp line across the marker board's surface.
Sixteen years ago, Eobard Thawne traveled back in time. An older version of Barry pursued him. The end result of that encounter was Barry: he would not exist if that night had not taken place. His entire future was based on that night because older Barry came from a different universe, one where that night was an ordinary and forgettable moment in his life. Coming back to it, he abandoned his own timeline and created a new timeline.
Every time Barry traveled back, he set into motion a divergent universe. Every choice was an opportunity for divergence, but crossover – taking a person out of one timeline and inserting them into an alternative timeline – only occurred when Barry traveled back in time. Really, it was worse than crossover: it was hijacking, taking over the timeline, living a life that did not belong to him.
Almost two years had passed since Hartley Rathaway tried to kill him. Where was that Other Barry?
In a chilling way, Barry knows the answer: I'm right here.
He came from a timeline of uninterrupted events, where that interruption never took place. But he exists in a universe built around a divergence, where it did, and where every subsequent decision was affected by it. All of the choices they made in this timeline – every decision Caitlin and Cisco and Other Barry created – led to his new reality.
Like the tsunami (did that even happen here?), like the Vandal Savage attack, there was a casualty in both events.
The other timeline did not survive.
Caitlin and Cisco think Barry is Other Barry, without even fully understanding the magnitude of their ignorance. The fact that they knew he was coming back at all, that they were prepared to meet a time wraith, saved his life. So Barry knows that the timelines were parallel: a similar sequence of events had to have taken place to lead to that moment.
But Hartley was proof that parallel did not mean identical. In his timeline, Hartley was still at large. In Other Barry's timeline, Hartley was on their team.
When did we start liking him? Barry wonders, scrubbing off an incoherent sequence of numbers and starting anew.
He has none of Other Barry's memories, so he can only speculate on a probable path. Only a truly exhaustive review of their history over the past year would reveal the exact sequence – and, undoubtedly, far deeper divergences.
Barry isn't sure he even wants to know.
There is something undeniably heady about hijacking: it should feel unnatural, walking in another person's shoes, but instead it feels like he's been here before. He has hindsight. He can see the differences and look at two perspectives of the same person and decide which half belongs to him.
It should feel unnatural.
But Barry can't deny that playing God is a lot more interesting than he previously thought.
Capping the marker, he steps back from the board, staring at the incomprehensible stream of numerical consciousness. In a Flash, he has it tidied up to a series of clean equations, taken from the hard drive that Eobard gave to him.
Why are you helping me? he wants to ask.
It doesn't actually benefit Eobard in the long run to give him a real copy. A fake copy would require a second visit to correct, and Barry's escape from the time wraith was so close he wouldn't dream of revisiting the same location without life-or-death motivation. (Is that not what defeating Zoom is?) Surely Eobard knew how unlikely punishment for a lie would be.
Yet here they are.
The Speed equations.
They aren't what he expects. In fact, they're disturbingly dissimilar to his mathematical predictions, written in the physics equivalent of a different language. Evidently, Speed does not behave the same way that energy does, a discrepancy that he knows will translate into practical challenges.
You've phased through walls. You've traveled through time.
At your speeds? Neither of those should be possible.
And yet.
Stepping back, Barry lets time slow to a crawl, Cisco and Caitlin's conversation going silent as the world itself stills.
Here, he has all the time he wants. Here, he can think. Here, he can be.
I am God.
Real time clicks back into place like a glass shattering, startling him into motion. It takes Barry a hundredth of a second to realize that the marker is on the floor and all three of them – Harrison, Cisco, and Caitlin – are watching him. "You okay?" Cisco asks.
Do you even know who I am?
That's the thing about time travel: only the traveler knows.
He didn't see that the first time, how he would be stranded in another timeline, in a divergent universe. He didn't understand it, couldn't fathom that something like temporal reversion existed. He thought he'd come home, but no one else knew what had happened.
No one knew what he knew. They didn't know they weren't the same people. They just knew that he pretended to be the same person. They believed the elaborate lie. I'm not from your universe didn't sit well. I am now did.
Same message; different meaning.
Cisco walks towards him and Barry can see that Other Barry standing off to one side, looking confused and hurt.
It was so clear in his eyes, his voice, his gestures: How could you not know who I am?
That's the thing about being a hijacker:
You take over the host.
"Barry?"
You inherit their world.
"You okay?"
You destroy everything for one goal.
Survive.
Cisco puts a hand on his arm and Barry thinks, You're not him. "Barry?" he repeats.
I'm not him. He's not here.
I don't know what happened to him.
It scares him to think that one day, he could be the one who doesn't get to go home. Eobard almost made it happen. Had Barry's claim not worked, no one would ever have known he even died: that Barry would have been here now, looking at Cisco.
It's too much. "I need some air," Barry says. It isn't an answer, but it is a solution.
Cisco lets him go.
And Barry runs because it's the only thing that has not changed. It's the only constant. In a very real way it's all he has left from his own universe, from every universe.
The agony of being the loneliest person in the world makes him run until the thought can't keep up anymore.
. o .
Sunrise finds Barry at the falls.
Sitting on the edge of the cliff, Barry doesn't move when he hears footsteps. He doesn't turn when Harrison sits down on the cliff beside him. He doesn't have to: neither of them speak.
For a long time, they simply coexist, Barry's periphery flooded with that familiarity, that this-is-my-Earth air around Harrison. It doesn't alleviate his hunger for home, but it makes it bearable. It has an I-will-suffer-with-you camaraderie that soothes him more than any empty promise of reverting to normal could.
There is no going back.
Eobard misunderstood that: as soon as he and older Barry traveled back in time, they created a divergent universe. Had he succeeded in killing his original quarry, Barry would not be here, but the future Barry – the one who traveled – would have been fine.
He's not from my universe.
It would be like killing his Earth-2 counterpart. No matter what point in time he did it, it would not affect Barry. The game was over before it ever began: Eobard could not have destroyed his adversary through time travel. The paradox overruled: older Barry's existence proved that in the enduring, uninterrupted arc that was his life, nothing had interrupted it. By extension, nothing could interrupt it.
A fixed point in time.
Harrison taught him that. Some things you couldn't change.
He thinks back to what Cisco and Caitlin told him, how he wouldn't remember his old universe, he would simply return to a new life.
But they were wrong.
He remembered everything.
The traveler always knows.
"I never met your Earth-1 counterpart," Barry admits. "As far as I knew him, he was always Eobard Thawne." Reaching up to press his palms against his eyes, he says, "You were right. I shouldn't have gone back."
Harrison says nothing.
Barry drops his hands, feeling oddly compelled to say it. "This isn't home."
"This is home."
Harrison's voice is surprisingly sharp, adamant. Barry stares at him.
"This is home," Harrison repeats. "You of all people should know that, Allen. The multiverse is a system. All universes exist within it." Looking him in the eye, he repeats, very firmly, "This is home. But, you're right." An odd, almost rueful smile. "It's not the past. So it's never going to be the place you remember it as. That's life. Get over it."
Getting up, he stands silently over Barry, the wash of the falls in the distant backdrop a contrast to the rising sun, bright and pink and spectacular.
"We all make choices. Yours brought you here. Live with them."
Barry doesn't turn to watch him walk away, doesn't go after him and ask for more answers because Harrison might have them, Dr. Wells always knew the answer, but this isn't Dr. Wells, it isn't Eobard Thawne, it's Harrison Wells.
Not the same person.
Still important.
Earth-2 Iris wasn't his Iris, either, but she kissed like Iris, she exuded warmth like Iris, she looked at him like Iris.
To him, she was Iris.
She just wasn't his.
It has a surprisingly inconsequential impact on how he feels about her.
The multiverse is a system.
Their membership in it meant that she wasn't from his universe, but she was a part of his life.
A constant.
Sitting near the falls, Barry thinks of all the constants: how the sun rises, how the grass feels under the palms of his hands, how good it feels to be alive. He thinks about Star Labs, about Team Arrow, about his strange and wonderful life.
At his core, he's not thunder or lightning. He's Barry. Speed gets to keep him company, enabling him to know what no one else does, but he gets to live his life.
My experiences aren't less worthwhile because they're mine alone.
It casts a comforting shadow over him, relaxing his shoulders and easing some of the tension from his spine.
He is alone.
Everyone is.
But he doesn't have to be an island.
. o .
On Kara's world, Barry finds peace in the constants: in ice cream and donuts, in grass under his feet and wind in his lungs, in the strength of hugs and the pleasure of spending time with another superhero.
And he takes joy in the surprises: alien spaceships and girls who can fly, James and Winn and Cat, taking down metahumans (let's settle this like women) and finally returning to that big open plain to do what he does best.
Run.
He'll always be drawn back to Star Labs, to Caitlin and Cisco, Joe and Iris, Team Arrow, Central City. Home is Big Belly Burger and particle accelerators; home is running late and forgetting to rip the tags off thrift shop clothes; home is spilled coffee and half-eaten candy bars. He'll always want to go home.
But in the multiverse, wherever he goes, whatever worlds he lands on and people he meets, he is always home.
So when he hugs Kara goodbye, it feels less like I'm sorry this has to end and more I can't wait to see you again.
Back home, he Flashes back into sight, skids to a halt in the open field, and exhales triumphantly. Turning, he sees Caitlin and Cisco already running and he has to smile. "I'm okay," he shouts, cupping his hands over his mouth to be heard. "Just took the long way!"
Cisco literally tackles him, the force of his momentum driving Barry off his feet, and he laughs, repeating somewhat breathlessly, "I'm okay! It's okay. I met Supergirl!"
"You met who?" Caitlin demands, helping him up as Cisco apologizes and berates him for scaring them in equal turns.
Barry grins, brushing himself and Cisco off for good measure, already looking forward to explaining everything to them as Caitlin walks up and hugs him like a normal person, without pinning him to the dirt. "I met Supergirl," he says again, squeezing her, and thinking, I would never be home without you two.
They demand explanations that he is happy to give over pancakes, and this – sharing stories and catching up and getting back on the same page – this is home. Spending time apart gives them something worthwhile to talk about when they reunite.
This is their life.
Barry doesn't know exactly what that entails, but he does know that this is his universe. This is the place he returns to.
He is here. Whatever that means, he is here, and he can work to better the lives of people he will not meet again soon, if at all, because they're family, too. Earth-2 Barry didn't walk away from him when he should have. His older doppelganger gave him this life. And Other Barry saved it.
Maybe time isn't as discontinuous as he thinks, interconnected along the way, brought together by experience if not origin.
Resolving to take it for what it's worth, Barry grins and digs in to a veritable mountain of pancakes.
Some things truly are universal constants. As far as Barry is concerned, food bringing friends together is definitely one of them.