Time Dilation
Recovery is a dull affair, all things considered. The poison wreaked absolute havoc over his systems, as expected. It is a wonder he has managed to survive at all according to the medics’ repeated reminders.
Tobirama nods along and smartly keeps his mouth shut about the sheer degree of calculation he put into measuring out his doses for the snakeroot extract. He’d aimed for maximum believability, yes, and that meant teetering dangerously close to the line of fatality, but he isn’t actually suicidal despite what Hashirama seems to fear. Tobirama had known that he’d come out of this alive if a little worse for wear, and that had been an acceptable level of risk to him.
Still, he is glad that he is expected to make a full recovery eventually, though it will take time and plenty of rest even after the several healing sessions he is put through to soothe the fraying in his coils. He is still unable to funnel any meaningful amount of chakra unfortunately, which means that sensing is beyond the realm of his ability at the moment. With just how much Tobirama relies on his sensory range to keep track of his surroundings, even if it is only passively, it feels a little bit like someone has tied one of his arms behind his back.
To distract himself in the meantime, he puts his extensive downtime to use by turning his attention to his non-physical pursuits. Tobirama has been meaning to continue writing his paper on the effects of temporal dilation but has simply found himself too occupied with other, more pressing matters. Now that he is pretty much bedbound, he may as well get to it.
Hashirama isn’t too pleased to see him working in any capacity, but he says nothing beyond pursing his lips and hovering in that way he thinks is subtle but truly isn’t. He knows that Tobirama doesn’t handle coddling or stagnation well—it’s a wonder that he hasn’t already attempted to escape the medics’ hall yet when he famously finds it to be stifling, preferring to recover in the privacy of their shared home whenever possible. Instead, Hashirama all but moves himself into his brother’s temporary room and brings his own work with him so he can keep Tobirama company. It’s a flimsy excuse to really keep an eye on him, but Tobirama accepts with grace since he still feels guilty about the hard time he gave his older brother with his political stunt.
Besides, he doesn’t really mind so much. Tobirama hates being out of commission because it sends his instincts into overdrive to know that he wouldn’t be able to protect those he considers pack should they need him. Usually, he can soothe the worry by simply tracking Hashirama’s chakra, but since that isn’t an option currently, it helps to have his brother in his physical vicinity.
He wonders if Hashirama knows it too; if he does this for Tobirama just as much as he does for himself.
A part of Tobirama realises that he can’t tell anymore. He knows how different he himself is in this lifetime, equipped with knowledge and memories of a past he did and didn’t live through, but he still finds himself surprised by the changes he sees in Hashirama because of this. His anija in the other life hadn’t necessarily been quieter or less sure about his love, but they’d both had a much harder time letting down their defences around each other, always too wound up and struggling under the weight of the war they were expected to wage until they either died or won. It was only with the safety of peacetime and being forced to relearn each other as they tried to build a village from a ground up that the brothers truly began to understand one another like they did when they were children.
This Hashirama isn’t quite what he remembers anymore though. He’s…softer somehow, taking time to think over his words, and watchful as though he is afraid of what will happen if he looks away from Tobirama for too long. He is louder about his hope, and more open now that he knows he has support for his efforts towards brokering peace. He fears for Tobirama far more than he remembers his brother ever doing in their previous life. In response to open support in this life, this Hashirama has doubled down on the idea of peace for his clan—for Tobirama—as opposed to peace for the sake of his personal ideology.
And Tobirama isn’t quite sure what to do with this realisation.
The brother he remembers had loved him, undeniably so, but Hashirama is also all things Senju. Love for him is something softer and more open-eyed than the unquestioning devotion that Tobirama himself finds love to be. It is not blind, since he is inherently too perceptive for that, but it is encompassing enough that seeing does not matter. In his other life, he had loved Konoha long before it meant something to him simply because it had been Hashirama’s. And he had known that once peace had been established, Hashirama would make no exceptions or allowances for anyone who dared to threaten his dream.
After all, that is what it means to be a leader—to place duty and responsibility above personal relationships and loyalties. Something Hashirama had managed even if it cost him his dearest friend, when Tobirama isn’t sure even now if he could make a choice like that if faced by someone that he has truly sworn himself to. To Hashirama, Konohagakure had so evidently come above all else, and that is what got him elected to the Hokage position in the first place.
“My peace is for you, you idiot, don’t you see that? What good is any of it to me if you’re not here to see it?”
Tobirama still doesn’t know just what to make of these words. He hadn’t known how to respond even as Hashirama had said them, too caught off guard by the desperation and frenzied grief clinging to the edges of his brother’s countenance as he had all but plead with Tobirama to refrain from any more borderline suicidal schemes.
He can rationalise it. Hashirama had been emotionally compromised and probably exhausted given the speed with which he handled the investigation and trial. Even if he’d meant his words, it is only on the basis of him not knowing any better—after all, this version of Hashirama hasn’t seen and held and nurtured peace with his own two hands, so it makes sense that he thinks Tobirama could be placed above a dream that does not yet exist in reality. Hashirama cherishes him above mostly everyone else, but some things are untouchable, and Tobirama knows this. He doesn’t mind it either; his brother’s nature cannot be helped.
But he thinks again of the abject terror and pain in Hashirama’s eyes, the anguished certainty of his claim, and Tobirama wonders if perhaps he has gotten too comfortable with the surety borne of his future knowledge. If he can acknowledge that he has changed enough that several events are now beyond his ability to predict, then surely he must extend the same logic to Hashirama.
“Is there something on my face?” Hashirama asks, tilting his head in bemusement as he pats at his face as if to make sure it is indeed clean. “You’ve been staring at me for a while now.”
Tobirama blinks and straightens. “Ah, no. My apologies, anija, I was lost in thought.”
Hashirama sets his pen down. “What were you thinking?”
Pausing, Tobirama chews on this for a moment. “You were afraid,” he says finally. “For me.”
“Yes,” his brother confirms, the edges of his mouth pulled down. “Of course I was. You were a hair’s breadth away from death, Tora.”
“And you believed I would. That I could.”
Hashirama’s brow furrows, hesitance bleeding into the careful way he regards Tobirama. “I know you are not infallible.”
That has been made exceedingly clear in the increased blatancy of Hashirama’s affection and protectiveness. Tobirama shakes his head. “That is not what I meant.”
Confusion lingers on his brother’s face for a heartbeat before understanding dawns in its place and his gaze flickers away, dark eyes turned to whatever document he is supposed to be reviewing. “I worried,” Hashirama admits quietly, “because I knew you would allow it if you believed it was a worthy enough cause. You would do it if—” his voice breaks “—it was for me.”
Tobirama doesn’t deny it; they both know it’s the truth anyways. “There will be no organised opposition to your policies for peace now,” he points out instead.
“We could have dealt with them some other way,” Hashirama insists, setting his jaw.
“Probably,” Tobirama agrees. It simply would have taken too much time and loss for that to happen, but he doesn’t think his brother would appreciate the sentiment, so he elects to keep his mouth shut.
For several long seconds, Hashirama simply looks at him, eyes knowing and shadowed with some unknown ache. “You did this because you love me,” he pronounces at last.
“Yes.” Tobirama observes, “That scares you too.”
Hashirama inhales deeply and offers a wry, brittle sort of smile. “I just—I struggle…with it.”
“You would do the same for me,” Tobirama points out, and this too they both know to be true. “But I understand. You do not wish to be left behind.” He knows the fear of that intimately, and even now, he can reach out and grip the phantom terror from the memory of his brother’s willingness to lay down his life because Madara had posed the choice for one or the other Senju having to die to repay Izuna’s death. Frowning, he lowers his gaze to where his hands are clasped together in his lap and repeats softly, “I understand.”
Before the stifling silence between them can truly settle, Hashirama lets out a strangled sounding laugh and scratches at the bridge of his nose. “Well, it’s alright now that you’re well on your way to recovery, I guess. So long as you remember what you promised me.”
“I do,” Tobirama assures, seeing that Hashirama clearly needs to hear it from him again. “I gave you my word and I will keep it.”
Something like relief settles across his brother’s face, his shoulders slumping ever so slightly like a weight has been lifted off them. “Good,” he breathes, offering a more certain smile. “That’s good.”
‘What a conundrum,’ Tobirama muses even as he smiles back faintly, thinking about the contradiction in preferring to having his guts spilled out than to be the one holding the knife when it comes to Hashirama, and how his brother probably feels the same way. Thinking about how even now neither knows how to love the other in a way that is easy for them to accept.
How odd that it is easier for them to love than to be loved.
Time dilation, as predicted by the theory of special relativity, elucidates the phenomenon of time appearing to pass differently for observers in motion relative to each other. The theory's postulates establish the invariance of physical laws for all inertial observers and the constancy of the speed of light across inertial frames. Derived from these principles are the Lorentz transformations, which detail how space and time coordinates alter between reference frames in relative motion. These transformations shed light on how time appears to dilate or contract for observers in motion relative to each other, contingent upon their relative velocities.
At the heart of time dilation lies the relativistic Doppler effect, delineating how observers in relative motion perceive variations in the frequency and wavelength of light. As an observer moves relative to a light source, alterations in the observed frequency and wavelength occur, resulting in apparent shifts in time intervals. This effect stems from the finite speed of light, underscoring the interconnected nature of space and time within the framework of spacetime.
One of the most intriguing consequences of time dilation is encapsulated in the twin paradox. In this hypothetical scenario, one identical twin remains on Earth while their counterpart embarks on a journey to a distant star at velocities nearing the speed of light. Upon their reunion, the traveling twin, experiencing time dilation as per special relativity, has aged considerably less than their Earthbound counterpart. The apparent "paradox" arises from the misconception that the situation is symmetrical.
However, this is not the case, as special relativity specifically pertains to motion at a constant speed along a straight line. As the twins are together at both the commencement and conclusion of the journey, the traveling twin must undergo phases of acceleration, deceleration, and direction reversal. These phases invoke elements of general relativity due to their resemblance to gravitational effects. When the mathematical computations are adjusted to accommodate this acceleration, it becomes apparent that the spacefaring twin does indeed age more slowly than their Earthbound counterpart, akin to a form of time travel.
It is one thing for Izuna to know in theory that Senju Tobirama is a scholar who evidently spends his free time gallivanting about in the most prestigious scientific institution on the fucking continent. It is an entirely separate thing for him to now actually have written proof of the fact in his hands, the journal article on advanced relativity theory staring back at him offensively with Tobirama clearly credited as the writer.
The journal is apparently a monthly publication run by the University of Science and Technology, not that Izuna had ever read a copy until today when it arrived via messenger from his mother’s clan. His cousin Banri had sent it over with a note that began quite succinctly with: Suffer with me. Izuna hadn’t understood then but he sure as hell gets it now.
According to Banri’s letter, the university’s rumour mill has it that something big went down with the Senju clan recently and that Tobirama may or may not have suffered through an assassination plot because several of the Senju soldiers serving in the capital had been called back home urgently and weren’t due to return to duty again. Either way, the Senju heir is clearly fine now if he’s off publishing his papers in big-shot journals or whatever. However, something about the ordeal still makes Izuna want to sink his teeth into something until he draws blood.
If that hardheaded freak had actually gone and gotten himself killed in some political ploy, Izuna would have had to figure out some way to resurrect him, appropriately mock him, and then kill Tobirama himself as the heavens rightfully intended.
But no. Tobirama lives and he makes waves in the scientific community with his research like it’s just another spring day for him. Izuna might not understand half the technical jargon referenced to in the paper, but he’s learned enough to glean that this a more thorough investigation of the principals Tobirama must have built his teleportation technique on. The idea that he’s jumping not just through space but also time is kind of throwing Izuna for a loop, but it makes an unfortunate amount of sense from a physical perspective.
Mostly it just kind of pisses Izuna off, brings to surface an itch under his skin that he can’t scratch and can only burn off. Tossing the journal onto the table in his room, he shoots to his feet and goes digging for a clean set of clothes he can train in. So what if he sets another training field on fire? He can just go pout at Madara until he stops being mad about it later.
Except that plan dies a swift death before he can even set foot on his usual training grounds because it is currently occupied by one Uchiha Kagami.
The boy spots Izuna as he approaches, perking up like a particularly excitable sort of bird and waving hard enough that he almost stumbles with the force of his own motion. Izuna waves back automatically before frowning as he remembers, “Didn’t your mother ask you to stay inside?”
Kagami wilts, waving hand coming down to scratch at the back of his head as his gaze skitters. “Uh, no,” he tries, drawing the word out and peeking out at Izuna from beneath his lashes to check if he’s being convincing enough.
Izuna arches a brow and stares in silence, letting the boy squirm under the weight of his judgement. Kagami is a terrible liar even for his age. Distantly, Izuna can hear Akio’s voice echoing in his head, saying, “It’s a weakness. He will get himself killed like this one day.” But Kagami is still young, Izuna reminds himself. He has only recently begun learning and there is almost half a decade before he can even be considered for solo missions as per Madara’s policies. There is time yet to prepare him. Izuna can let him be.
“Mama said I wasn’t allowed to play with my friends,” Kagami admits, caving under the silent pressure, “but I’m not playing, I promise! I’m training. All by myself too!”
Ah, yes. Training. Something Kagami has gotten notably diligent about ever since his encounter with the Senju heir. Izuna charitably breezes past this.
“Well, you’re supposed to be inside instead of running around the compound without telling your mother.”
Kagami crosses his arms and looks away, pouting. “Well, mama’s being mean.”
Izuna openly rolls his eyes and flicks the boy’s forehead. “She’s being perfectly reasonable. You know how many of your little friends are already stuck in the medics’ hall because they’re sick? You looking to join them?”
Sniffing, Kagami reluctantly acquiesces, “No. I don’t wanna get stuck there too.” He shudders and leans closer to whisper as if it is some secret of national importance, “I don’t like the medics’ hall very much.”
Izuna cocks his head and places his hands on his hips. “Because it’s scary?” he says knowingly.
Offended by the (true) statement, Kagami glares and splutters, “I’m not scared! I’m too big to be scared of the medics.”
Snorting at this, Izuna tells him flatly, “When you get even bigger, you’ll learn it’s good to have a healthy fear of them.” Kagami doesn’t look convinced, but that’s fine. He’ll find out one way or the other; it’s an inevitability and not really Izuna’s problem. “Do you know if any of your friends got better?”
Kagami hesitates and then shakes his head, chewing on his lip. “Mama won’t let me visit in case I catch it too.”
Izuna hums and exhales slowly. “Probably for the best,” he says, dropping a hand onto a despondent looking Kagami’s head and ruffling through the messy curls.
They’re not entirely sure just yet what has been spreading among the kids. They’d assumed it to be the common flu at first since it typically makes the rounds as the seasons change anyways, but now that close to a week has passed since the first reported case, it’s starting to seem more like pneumonia. It’s been several years since the Uchiha had to deal with their last disease outbreak and they try to be generally careful to keep any contagious illnesses as contained as possible, but it’s already begun to catch among the youngest of their population and, if nothing is done soon enough, they could be looking at something more serious.
Right now, they’re hoping that it’s a viral infection as opposed to bacterial because that is much harder to acquire medication for and is a lot more severe. The best they can do is try to treat the symptoms and discourage further spreading. As for the cause itself—they’re still trying to figure that out.
Kagami peers up at Izuna from under his hands. “They’re going to be okay, though, right?” he asks, trying to look brave even as his hands twist in the fabric of his shirt. He’s so small that it makes something deep in Izuna’s chest ache.
“I hope so, kid,” is the best Izuna can offer him unfortunately, biting the inside of his cheek. “I really do.”