Creating Time Machines for Advanced Civilizations: A Plot Device for Writers

[Artribution]

Hello, lazy writer here. Got a question for you all; apologies if it's been asked before or needs to be moved.

Assuming an advanced civilization controlled the Milky May for a period of ~16 giga years (from the galaxy's formation until the merger with Andromeda) and had all that time to work on it, and was willing to go to any length (up to and including engineering supermassive black holes, converting all the available mass in the galaxy using von Neumann machines, etc.), what mega-engineering scenarios could said entities plausibly use to construct a time machine capable of sending a nano-scale piece of common matter back giga years, one way, to before the galaxy existed?

The question doesn't assume any particular cosmological model. Exotic matter OK. And no need to think about causality paradoxes because let's say the displaced matter will have no effect on the past once it gets there. I'm just asking for some thoughts on how a civilization with extreme tunnel vision and practically infinite time might conceivably accomplish this kind of thing, in hopes of giving my plot device at least a veneer of plausibility to shield it from inevitable nitpicking.

I have actually tried to research this myself - honest. But this is where my grasp of physics runs out, and with all the suggestions out there, it's difficult to judge the barely plausible from the less so.

 

[Ryan_m_b]

Doesn't matter how advanced, how vast and how long living a civilisation is it isn't going to be able to break the laws of physics.

If you want time travel in your setting just make up some system by which it works. So long as it's internally consistent and the consequences are logical it will be a good story.

 

[newjerseyrunner]

What about a simulated reality? A species advanced enough to put the entire population in a Matrioshka brain, then perhaps some internal social revolutions that made everyone forget that their world wasn't real and from there they could find passages through virtual time and space.

 

[Artribution]

That's one way to do it. The problem in this case is that if the universe (or the galaxy, anyway) is a simulation, there's no need to involve backward time travel in the story. The basic problem would already be solved and time travel would only complicate matters. It's not actually a story that hinges on time travel - that's just one possible answer to a story problem.

Simulation is something I've been wondering about anyway, in trying to extrapolate the society of a future giga-annum. Especially since multiple simulations, on Matrioshka brains or otherwise, would mean multiple universes with potentially different properties and the possibility of interaction. And it's certainly well within their capabilities.

But as long as your existence is contained within a physical machine, that existence is ultimately finite. And this is a civilization trying to get past finite.

 

[Hornbein]

That's one way to do it. The problem in this case is that if the universe (or the galaxy, anyway) is a simulation, there's no need to involve backward time travel in the story. The basic problem would already be solved and time travel would only complicate matters. It's not actually a story that hinges on time travel - that's just one possible answer to a story problem.

Simulation is something I've been wondering about anyway, in trying to extrapolate the society of a future giga-annum. Especially since multiple simulations, on Matrioshka brains or otherwise, would mean multiple universes with potentially different properties and the possibility of interaction. And it's certainly well within their capabilities.

But as long as your existence is contained within a physical machine, that existence is ultimately finite. And this is a civilization trying to get past finite.

You could look at the Godel universe. If the Universe is rotating in a certain way, then time travel is possible. That rotation is similar to the rotation of a superfluid. You could have the dark matter of the MIlky Way be a rotating superfluid, then take advantage of that to travel in time.

 

[Artribution]

Is that remotely plausible, though? I thought the Godel metric had been pretty conclusively ruled out as a model of the universe we're living in.

 

[mfb]

You could look at the Godel universe. If the Universe is rotating in a certain way, then time travel is possible. That rotation is similar to the rotation of a superfluid. You could have the dark matter of the MIlky Way be a rotating superfluid, then take advantage of that to travel in time.

You cannot change the global spacetime structure with dark matter rotating around the Milky Way, in the same way you cannot change the Milky Way by rotating water in your bathtub.

Solutions to GR with wormholes are very speculative as they need negative energy, but for science fiction they should be fine. The ridiculous estimates for energy needed are nice here.
It is unclear if or how you can make the wormhole end back in the past, however.

 

[Ryan_m_b]

Perhaps it would help us help you if you explained why it's important to the story for this civilisation to send an object back into the past? There may be methods of achieving the same ends narrative wise without time travel.

 

[Artribution]

It is unclear if or how you can make the wormhole end back in the past, however.

Well, if the existence of many universes is assumed, with careful astroengineering and a mathematical basis for calibrating it, you could maybe collapse a rotating group of precisely engineered stars into a singularity-free Kerr wormhole, with its exit point emerging in the "past" of another universe—but one functionally identical to your own. Or use some other hypothetical ultimate mega-structure to do something similar.

Once in that universe, you could repeat the process, creating another wormhole with its exit point in the "future" of your universe of origin.

Once finished, you'd have created a stable path between what is for all intents and purposes your "past" and your "present", and you can do anything you want in the past without violating causality, because the so-called past (SCP) will be causally disconnected from the so-called future (SCF).

Your goal in doing all that would be to send a probe into what is effectively your own galaxy's past—not to change the past, just to study it.

If your probe could duplicate itself and travel to all the star systems in the emerging galaxy, and stay there, it could potentially record the brains of every sentient creature that ever lived, in your SCP. And then it could transmit that information back to the present SCF. At that point, you could then digitally reincarnate everyone who ever lived in the galaxy, creating an ultimate society comprising all of us now living, plus all sentient beings that ever lived or ever will live, and all the memories and ideas ever produced, in the Milky Way.

 

[Artribution]

Wow, looks like my idea was just too much for you guys. =]

Not to worry, I can develop it alone. I'm curious if anyone is aware of any examples of this scenario having been done in sci-fi before, though.

 

[Ryan_m_b]

It's not that it was too much so much as it's not possible. Your just going to have to make something up. Unless you want ideas on how your plot could be advanced in a similar fashion without time travel. What is it this plot device is meant to achieve? Having an accurate record of everyone who ever lived?

 

[Artribution]

I think I'm satisfied with what I've made up. Right now, I'm just curious if there have been any other examples in sci-fi of the kind of scenario I'm describing. The Riverworld novels are the closest comparison I can think of, and they're not really that close. But it's such an obvious set-up, it seems like I must be missing a few.

Unless you want ideas on how your plot could be advanced in a similar fashion without time travel. What is it this plot device is meant to achieve? Having an accurate record of everyone who ever lived?

A deep scan of them, anyway, for future digital restoration. It's actually easy to imagine how it could be done without time travel. For all we know, there could be alien probes in our cells right now, scanning us. They could have been there since eukaryotic life evolved. Clarke's monoliths could be something like that, if they weren't actively tampering with our evolution. The problem is that in that case, it's some other, more ancient species responsible for our continuation, and not our far-future descendants. That could still work, but I think it might lose some story value.

And I don't think it's technically impossible, what I'm describing. I'm not tying it to the many-worlds interpretation of quantum mechanics or any other current science. Even if that's all completely false, the existence of other universes would still at least be possible.

 

[Ryan_m_b]

I think I'm satisfied with what I've made up. Right now, I'm just curious if there have been any other examples in sci-fi of the kind of scenario I'm describing. The Riverworld novels are the closest comparison I can think of, but they're not really very close at all.

There's a few examples that spring to mind, the most similar to this idea is The Light of Other Days. In the novel it's possible to project a wormhole anywhere in history but you can't travel through it (or detect it I think). People use it to view the past. In a non-fiction capacity the idea of resurrecting everyone who has ever lived through science is at least a century and a half old. Nikolai Fyodorov popularised the idea within the ideology of Russian Cosmism. Then there's Frank Tipler who argues that at the end of the universe will result in a situation of potentially infinite computation, not only allowing some ultra-far future species to resurrect everyone who ever lived through simulation but also everyone who could have possibly lived. I've read a few stories that feature this but their names elude me atm.

And I don't think it's technically impossible, what I'm describing. I'm not tying it to the many-worlds interpretation of quantum mechanics or any other current science. Even if that's all completely false, the existence of other universes would still at least be possible.

Time travel introduces so many paradoxes that it's very likely impossible. Creating a wormhole to join to another universe that just so happens to be an exact replica of our past...no idea how that's considered by modern physics though IIRC current understanding is that if alternative universes did exist there would be no way to ever reach them.

But yeah, it's a SF story so you can just make it up. Posit that this race manage to inflate and stabilise wormholes from the quantum foam (no idea if that makes sense but I've seen it in several SF novels) and somehow manage to influence this process so that the wormhole they stabilize goes to such a universe.

 

[Artribution]

There's a few examples that spring to mind, the most similar to this idea is The Light of Other Days. In the novel it's possible to project a wormhole anywhere in history but you can't travel through it (or detect it I think). People use it to view the past. In a non-fiction capacity the idea of resurrecting everyone who has ever lived through science is at least a century and a half old. Nikolai Fyodorov popularised the idea within the ideology of Russian Cosmism. Then there's Frank Tipler who argues that at the end of the universe will result in a situation of potentially infinite computation, not only allowing some ultra-far future species to resurrect everyone who ever lived through simulation but also everyone who could have possibly lived. I've read a few stories that feature this but their names elude me atm.

See, I knew I was missing something. Thanks a bunch.

Time travel introduces so many paradoxes that it's very likely impossible. Creating a wormhole to join to another universe that just so happens to be an exact replica of our past...no idea how that's considered by modern physics though IIRC current understanding is that if alternative universes did exist there would be no way to ever reach them.

Well, if a collapsing quantum wavefunction branches off and connects causally with events in two separate universes, then it does seem there's a way to affect other universes.

But considering modern physics' indecision on the subject, I wouldn't want to rule something impossible just because no one's yet come up with a method using the current model.

 

[mfb]

If you don't need the exact past, the civilization can simply run simulations of planets (or larger systems) with their species on them. And then wonder if they are in such a simulation as well.

 

[Artribution]

If you don't need the exact past, the civilization can simply run simulations of planets (or larger systems) with their species on them. And then wonder if they are in such a simulation as well.

They don't need the exact past, but they do need the exact people, exact memories, etc. Trying to derive us all via simulation seems problematic. Most species in the galaxy's history have died out before even making contact with anyone else. Countless other civilizations with long interstellar histories have vanished in the recurring AI wars that went back and forth for millions of years at a time. Considering the facts, it seems like constructing an accurate enough simulation to account for everyone might actually be difficult enough that "bridging two universes" or "traveling back in time" would look trivial by comparison.