Comment on Scifi question about time travel:
Zonetrooper@lemmy.world 4 days ago
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 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?
Disclaimer, I am not a physicist, just a guy with interest in sci-fi, science, and too much free time.
is their any theory centered around our frame of reference having a past but not a future?
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 reference how far from you a photon departing your actions would travel. Places that photon would reach 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 past 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 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.
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?
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.
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.
TranquilTurbulence@lemmy.zip 4 days ago
I think the idea of parallel universes solves time travel paradoxes in a pretty clean way.
ada@piefed.blahaj.zone 4 days ago
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.
TranquilTurbulence@lemmy.zip 3 days ago
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.
ada@piefed.blahaj.zone 3 days ago
Apologies, I copied and pasted the answer below from another reply I made elsewhere in this thread
==
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.
davidgro@lemmy.world 4 days ago
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.)
ada@piefed.blahaj.zone 3 days ago
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.