Nomad by JL Bryan

looked up and down the terminal again. It was possible this man was here to distract and confuse her until the real attackers arrived. If so, he was succeeding--she felt very confused.
    "A nomad," he continued. "Listen now, what follows is a familiar example. If you travel back in time and kill your own grandfather when he is only a child, what happens?"
    "I recognize that. Is it a riddle?" Raven considered it, thinking that the boy had an odd way of speaking. "If you do that, you're never born."
    "And so?"
    "So if you're never born, then you can't travel back in time. If you can't travel back in time, then you can't kill your grandfather. But that means you do get born, and so you do travel through time, but then you stop yourself from being born...it's an endless loop, right? It's not possible. It creates a..." She struggled to remember the precise word, but her brain wasn't working properly.
    "A paradox," he said. "Which, some have feared, would unravel space and time, destroying the universe. It's not simply limited to bizarre cases of grandparent-related homicide. If you travel back in time to change a certain event in history, and you succeed, then what happens next? You return home?"
    "Why wouldn't you?"
    "Because if you succeed, you can't go home again." He leaned forward, his dark gray eyes burning into her in a way that made her uncomfortable. "Because of this, now listen....If you go back for a specific purpose, and you achieve it, then you never had a reason to go back in time. Right?"
    "Slower," Raven said. "I'm tired."
    "Let's say your goal is to save somebody, or assassinate somebody, twenty years in the past. Now, in the new course of history you've spawned, that person was already saved, or assassinated, twenty years ago. Why would you get into a time machine for the purpose of doing it yourself? It's already been done. There's no reason for you to change history. No motive for your trip through time."
    She thought about it, though she wasn't sure whether she believed anything he said, especially the part where he claimed to be from Atlantis in the deep future. She admitted to herself that having this far-out conversation with this odd boy, who was actually a little bit attractive under the grimy exterior and the strange eyes, was just possibly better than sitting alone all night.
    "Okay, let's pretend this isn't completely crazy," Raven said. "So, since history has already gone the way you wanted, you don't go back in time to change it. You don't have a reason to travel through time."
    "But if you don't go back in time, then you don't accomplish your mission, so everything goes back to the original history," he said. "In which you do go back in time, and then...it's a paradox. It's like going back to kill your own grandfather, but it doesn't have to be that extreme. If you accomplish your purpose, any purpose, you create a new future in which you never go back in time at all, at least not on that particular mission."
    "So what happens then? The universe blows up?" Raven asked.
    "The universe is slightly smarter than that. Instead of allowing the paradox to spread, unraveling all of space and time in a supreme Armageddon sort of catastrophe, the universe treats you like an infection. It isolates you. You become an abscess on the flesh of space-time. That's what I am, and that's what you're going to become. A nomad. Rootless, wandering back and forth in time. It's a very Slaughterhouse-Five kind of existence, cut off from the natural flow of time."
    "How am I isolated?" she asked. "What does it mean when you're cut off?"
    "It goes this way: you travel back in time, you change history. You spawn a new timeline in which you never travel back on that mission, and maybe your entire life is different. The universe replaces you, the way your skin regrows and knits together under a scab. Meanwhile, you're the scab. You fall off."
    "It replaces you with what?" Raven asked.
    "Another you. A probable self, we call it,