If you had a machine that created a window through which you could see the future, and in the future you wrote down the winning lottery numbers and relayed that information to your present self before that lottery number was drawn.
However, in your present selfs excitement, you turn off the machine before your future self wrote the winning lottery numbers into it for your past self.
What would happen?
This is fundamentally a variation on the question of a Temporal Paradox, also known as a Grandfather Paradox (“You go back in time and kill your grandfather. What happens?”). Although no killing happens in this variation, the basic idea is the same: Information is transmitted to the past from the future, but results in a situation where it cannot be transmitted in the first place.
Accordingly, there are several hypotheses to cover this. This isn’t even all of them:
I’m more of an Emergent Time/Timeline Curve theory guy. The others are cool for sci-fi and stuff but I just can’t conceive of that being how it works.
Closed Loop Theory seems like too cheeky of an explanation. It’s basically a bait and switch. Like: “What if you did thing? But then DIDN’T do thing!” with the answer being “actually you did but just later”. To be fair though isn’t the theory really just saying the universe will correct itself somehow?
Also since you seem knowledgeable on this, something I’ve always wondered about: is their any theory centered around our frame of reference having a past but not a future? As in we’re blazing the trail forward like an ice breaker ship for everyone else to follow? There’s probably a million fundamental laws of the universe that makes that impossible.
Sorry, I’m not very smart, but I do kinda love this stuff.
Disclaimer, I am not a physicist, just a guy with interest in sci-fi, science, and too much free time.
So, the answer is, yes, this is actually kind of a common theory on how time actually works. Maybe.
This has to do with physics, and the fact that no two observers have the same perfect frame of reference. For most of us humans, our frames of reference are close enough to be identical on a day-to-day basis. It’s even close enough for (most) science. But it’s not true on a perfect level. For instance, special relativity says that time passes differently for objects in motion; GPS satellites have to correct for the fact that their onboard clocks are experience “slower” time than us observers on Earth. Even astronauts “lose” about ~1/100th of a second for every year spent on the ISS.
What’s this got to do with the future not existing, though?
So we know no two observers have a perfectly identical frame of reference - there is no objective “truth” of when something occurred. Cool. Now what? Well, what we can talk about is historic light cones. Because the speed of light in a vacuum is a universal constant, we can determine how far from you a photon departing your actions would travel. Places that photon would reach at any given point in time following your action are said to be within your historic light cone, and in common parlance, the past. The boundary of how far that photon is reaching at any given moment is, from your frame of reference, “the present”. But since nothing can exceed the speed of light, it is impossible for an observer to view beyond the present, into the future.
The catch, of course, is reference frames. You used a plural - “our frame of reference”, “we’re blazing a trail forward” - but the reality is that each of us has a minutely different reference frame and is blazing a minutely different trail. Again, for almost any day-to-day purposes this is irrelevant… but there are certain scientific experiments which exploit or even rely on this absence of reference frame.
Cool, what about time travel again?
In my first comment above, I mentioned something called closed timelike curves. Those are an actual thing: By severely bending spacetime, you can theoretically cause a photon to “curve” around and end up at the same point in time it was produced, now in its subjective past, while mathematically not violating quantum physics.
This is where things get kind of freaky and headachy; if a photon can be sent into its subjective past, doesn’t that imply a future now existing, in which that photon will be generated? The answer is, not in the frame of reference of that particular photon. A historic light cone of that photon being generated, now in that photon’s future, still exists; but that photon is now generating a new, detached lightcone…
Like I said, headachy. I also have to emphasize that while the math holds up, there’s ample reason to believe CTCs don’t exist, chief among them that our mathematical understanding of quantum physics may still be imperfect.
tl;dr: Yes, absence of reference frames means that each distinct observer is blazing their own trail, which spreads into the “past” at the speed of light. The future, exceeding the speed of light, is unobservable. This framework does provide a mathematical concept of how you could send something into your subjective past, but such a means is still theoretical at best.
That was fascinating to read, thank you!
I think the idea of parallel universes solves time travel paradoxes in a pretty clean way.
Except for the fact it makes every decision, every moment of tension and every event that occurs irrelevant, because an infinite number of universe exist in which the events occurred and in which they didn’t occur.
I don’t see that as a problem. Every possibility co-exists, and every reality is equally real. Every moment and decision forks the universe in infinite ways, but you get to choose the one where you go.
You can save a drowning person, or let them die, but in the big picture, it won’t matter. That person will drown infinitely many ways anyway, but there are also infinitely many universes where they get saved. Don’t worry about the big picture. What matters, is how you act and how the world acts on you in this universe.
Apologies, I copied and pasted the answer below from another reply I made elsewhere in this thread
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I’m not talking about about the possibility of real infinite dimensions. I’m talking about sci fi, and stories, which is the context of the OPs question.
In a “real” scenario, the experience that matters is the one I’m having, not the one other versions of me might be having.
But in a story, there is no “true” timeline, or a more “real” timeline. They’re all being retold to us indirectly, and the choice of the version of the person retelling those experiences is arbitrary by the author. It doesn’t matter what perspective the author chooses, because every other outcome also happened, the author just didn’t tell us those stories.
I think the disconnect here is between objective and subjective meaning. In an infinite multiverse, ‘reality’ isn’t a singular objective truth—it’s a collection of subjective experiences. But that doesn’t erase meaning; it just means meaning is something we assign, not something inherent.
You’re right that if every possible outcome exists, no single timeline is ‘objectively’ special. But in fiction (and arguably in reality), what matters is the perspective we focus on. A story isn’t weakened by the existence of other timelines—it’s strengthened by the fact that, out of infinite possibilities, this particular one is being told. The act of choosing a narrative is what gives it weight.
It’s the difference between nihilism (‘nothing matters, so why care?’) and absurdism (‘nothing matters* inherently, so we get to decide what does’). A multiverse doesn’t have to make things meaningless—it can highlight how rare and significant certain choices are, precisely because most versions of a person might not make them (e.g., Invincible).
I get the sense you’re resistant to this because it feels like it undermines objective meaning. But what if meaning was never objective to begin with?
Think of it this way.
“I went back in time to save my family” in an infinite timelines story means that going back in time spawns in infinite number of worlds that didn’t exist before, in which the family doesn’t make it, and an infinite number in which they do. And not a single one of those families is the “real” family of the person who went back in time.
The fact that the author choose to focus on one perspective in which it seems like the time travel has made a difference, doesn’t change the fact that it didn’t make a difference, and the family they were trying to save is gone. The infinite copies weren’t “saved” from anything, because there are infinite versions that weren’t.
The only way to tell a meaningful story in that situation is to create situation where the actions of jumping back in time alter the future of the person jumping back in time. And that means you either suck up the paradoxes, or you write a clever story in which the paradoxes are neatly accounted for before they ever occur (or you write a closed loop story)
Edit - Or you could tell a non infinite loop story, where a single universe is spawned by the act of jumping back in time. That still won’t save the “real” versions of the family you jumped back to save, they’re still gone, but at least it creates only a single version of them that the character can save.
Even knowing that everything happens every way in some other branch of the wave function (other universes) doesn’t really affect our own little section of it. There’s no communications or travel, so other universes if they exist have the same meaning to us as if they don’t. Except in time travel stories like this.
Besides, the same “irrelevance” of decisions and events comes free with even one single universe given that it’s deterministic - as physics seems to be. (Yeah there’s quantum randomness, but random doesn’t help either)
That said I still believe in free will and the importance of decisions. I just think it has to be defined so weakly that it still works in a deterministic universe. (So I have free will, but so do dice and pocket calculators.)
I’m not talking about about the possibility of real infinite dimensions. I’m talking about sci fi, and stories, which is the context of the OPs question.
In a “real” scenario, the experience that matters is the one I’m having, not the one other versions of me might be having.
But in a story, there is no “true” timeline, or a more “real” timeline. They’re all being retold to us indirectly, and the choice of the version of the person retelling those experiences is arbitrary by the author. It doesn’t matter what perspective the author chooses, because every other outcome also happened, the author just didn’t tell us those stories.
That would be the most boring story ever.
It becomes interesting at that point where one (or some) of the possibilities get a special meaning “above” all the others.
That’s exactly my point! In an infinite timelines story, there is nothing that has special meaning over the others, making it boring, because it’s all irrelevant!
I get what you mean, but I have to disagree a bit. The slice of the multiverse we’re looking at is special because we’re looking at it. It only makes it irrelevant if the slices are treated as fully replaceable.
Take for example Invincible. The comics & series focus on a young superhero who could have become incredibly evil, but didn’t. The multiverse is used to highlight this: it shows alternative versions of him that did become evil, and it even says that most alternative versions did so. This makes the version of him we focus on that much more special, and allows for interesting character progression through being confronted with his fears.
But it only works because of the restraint of the writers, never showing us another good version of Invincible, only focusing on evil alternatives.
Invincible can’t move between the infinite timelines though, and no storyline is hanging off of the important changes he makes those timelines by travelling through time/dimensions. He’s not “saving” anyone by jumping through to another universe
I’d say that the one that’s written is the ‘true’ timeline in the story the same way that the reality we experience is the only one that matters.
The reality I experience is the only one that matters to me. To an outside observer, all of them are as equally real and there is no true timeline.
In a story, there is no real, there is only outside observers…
Well, “no objective reality” is a lot more accurate to the truth of the world than any alternative. It might not be as narratively satisfying as a story where objective truths exist, but I suspect the human desire for objective truth is a cultural value that would be in our best interest to shed.
I don’t get it. Where’s the paradox here? He gets to see the future but turns off the machine before getting any information from it so nothing changes. What I’m missing?
His future self showed his past self the lottery numbers through the open window, but he closes the window, so his future self can’t show them to his past self.
I’ve read your message and the OPs like 5 times and I still have no idea what is being described… I might be stupid.
Got it. We’re good so far.
This is what I’m stuck on. So he didn’t actually? I get the irony of saying a paradox doesn’t make sense but I’m not even following the thought experiment. His future self opens a window and says “Hey, get some paper and a pen, I’ve got some winning lottery numbers for you!” and his past self goes “Oh boy!” and then immediately CLICK (closes the portal) before ever being shown the numbers.
Could it be restated to say he gets the numbers from his future self but then 30 years later just forgets to do the same thing for his past self?
Here’s your issue - it’s not the future self opening the window, it’s his past self. The future self can only speak through the window, but he can’t open it. So since the “current” self closes the window, the future self won’t be able to speak through it.
I would assume they sent them after the number was drawn, to before the number was drawn, which means the future self doesn’t need their own message to learn the numbers.