Resources for developing a time travel system [closed]

Question

I hope this is the correct forum for this question. I'm in the early stages of worldbuilding for a time travel story I want to tell. To be clear, I am not asking for time travel mechanisms. Instead, I'm looking for existing media on time travel (stories, articles, even scientific literature if there's something relevant) related to what I'm trying to do to help with my research.

I am looking for ideas about the finer details of time travel while I develop my system. Here are some questions I'm considering to give you an idea of my thoughts.

• Like in this previous question, the story is set in a war between two civilizations with easy access to weaponized time travel. How exactly could a civilization weaponize time travel, and how would they defend themselves from enemy time travelers? What are some wartime strategies uniquely targeted at time travel? What would such a war look like from a civilian's perspective? What are some reasonable abilities and limitations of the time travel technology available to each civilization? These questions need to be answered in such a way that the civilizations could have an extended war (no killing the first time traveler of the other civilization and ending the war just like that).

• There is no multiverse and the past is mutable. Both of these are necessary for time travel on a civilizational scale to make sense. By what mechanism are paradoxes resolved? What happens if you do kill your grandpa before he met your grandma?. It would be cool if this paradox resolution mechanism could be weaponized.

• A significant element of the story is lost timelines—information, people, inventions, history, etc., that never existed because time travelers overwrote the time in which they lived. There can be no mechanism for anyone (except the omniscient narrator) to peek into lost timelines. How would this work? How would these civilizations know there is an ongoing war, and how would they develop their time-traveling technologies without access to previous timelines?

• How do changes in the past affect the future? For narrative reasons, I don't like the idea of the butterfly effect because I want to maintain some stability in the war despite countless modifications to the timeline by various time travelers. However, time travelers also need to be able to create significant change; otherwise, these civilizations would have no reason to invest in time travel. The only counterexample I'm aware of (given a mutable past) is the idea of fixed points in time in Doctor Who, but this idea feels very arbitrary to me.

So, in summary, I am looking for any media or literature with well-thought-out time travel ideas involving:

• wars between time-traveling civilizations;
• paradox resolution in worlds with non-multiverse time travel and a mutable past;
• ideas for how history adjusts to changes in the past;
• experiences of non-time travelers;
• anything else relevant to the questions above.

Right now, I'm mostly looking for clever ideas to incorporate into my system, so I would be happy with a large variety of resources on time travel.

Thanks for your time, and I look forward to reading your recommendations!

Answer 1

Stories featuring time travel

Lists

• List of time travel works of fiction on Wikipedia.

• Best time travel fiction on Goodreads.

Books

• The two classics, Mark Twain's A Connecticut Yankee in King Arthur's Court and H. G. Wells's The Time Machine.

• Two perennial favorites, S. M. Stirling Island in the Sea of Time and Eric Flint's 1632. Both series emphasize that the future from where the time travellers came is no longer the future in the new timeline.

• Kage Baker's The Company series, beginning with In the Garden of Iden. Corporate entity somehow exists outside the flow of time, an old trope used very well.

• Directly addressing the question of how to weaponize time travel, David Drake and Eric Flint's Belisarius series. One faction sends a cybernetic superagent back in the Early Middle Ages with the mission to help the rise of a malevolent empire, the other faction finds out and sends a supercybernetic supersuperagent with the mission to help the Very Late Roman Empire of Justinian and Theodora crush the malevolent empire.

• Isaac Asimov's well thought End of Eternity. Addresses the question of what the effects of intentional timeline meddling would have on the world.

• Simon Hawke's TimeWars series.

• The much beloved Terminator series of films, featuring Arnold Schwarzenegger as the Terminator and Kristanna Locken as the Terminatrix.

Films

• Timecop with J. C. Van Damme in the role of an agent of the Time Enforcement Commission.

• Jeannot Szwarc's fascinating and heart-breaking Somewhere in Time with Christopher Reeve and Jane Seymour.

Answer 2

How to Make it a War: Temporal Protection & Observation

Each side's respective temporal agencies need to have some way of seeing changes in the timeline without being instantly over-written by them, otherwise time travel is a whoever strikes first wins scenario. For there to be a war, you need there to be some way to ensure a MAD (Mutually Assured Destruction) policy that prevents either side from abusing the timeline too greatly. This way, battles can be won and lost which you can't do if blowing up your enemy's ancient ancestors immediately eliminates your enemy from existence.

There are in general two approaches to this, you could have it so that each side has a "place" or "places" that are outside of the timeline (like the Vanishing Point from Legends of Tomorrow). This way even if someone wipes out your entire species, you still have an army of time travelers who are able see the change in the timeline and attack them before they can do this, or perhaps you then wipe out their species at its origin forcing both sides to go back and stop their own attacks before they happen as a negotiated way of restoring both peoples to the timeline.

Alternatively, you could have some kind of temporal shielding (Like in Star Trek: Prodigy) that can temporarily protect certain people or places from being changed by alterations to the timeline. So, that even if I'm sitting around in my own timeline and my civilization gets erased, my shields might protect me from being unwritten giving my fleet the opportunity to take a next move.

The outcome to either approach is about the same; so, the method you use is just a question of what flavor feels better to you.

How to Address Paradoxes

The typical Paradox of Time Travel is than you can not alter the past if it prevents you from doing a thing in the future that allows you to alter the past. So, simply don't start on the premise that the time traveler's own past is affected by his actions in the past. His entire history is a straight line leading up to when he time traveled even if that is not everyone else's entire history. You still originate from and remember everything you did, and you can evolve from that experience, but everything else simply goes back to how it once was with no recollection of things have changed, and can then take a different path forward because the traveler is a new variable.

So using this concept as a guide, temporal shielding or whatever you want to call it allows you to escentally copy yourself to the new timeline should your own timeline end. So again, you still follow a causal relationship of events similar to the time traveler. You just aren't necessarily moving anywhere on the timeline when you jump timelines.

So, long story short, I can kill my own grandpa just fine because in my own personal history, my grandpa still existed. However, as I choose to live out my life in the new timeline, I will never meet a younger me, because that version of me will never again be born.

A cool way to Weaponize this mechanic

In the Flash, there is a mechanic called time remnants that only works when you have a setting that allows someone to travel through time as a duplicate of themselves. So, if you go back in time for just a moment, then there are 2 of you. Do it again, and you have 4. Do it a few more times, and you could become a literal army of one. In the Flash, they try to keep this mechanic from being abused by sicking time wraiths on speedsters who do this... but this is a rather lazy approach to balancing time remnants IMO.

Since time travel is basically a way of duplicating your present self in the past, then the argument becomes "What about the conservation of matter." So you can't just jump back in time adding your own matter to the past, that would create something from nothing, instead time travel relies on finding some mass in the past that resembles your own and reorganizing that thing into you. So, maybe you don't just fall out of the sky but instead when John and Sally are out on their date, John disintegrates and is replaced by you. Need a an extra you? Sorry Sally from 2 seconds ago, but I need your biomass. Now there are 2 of you but no more John and Sally. This need for similar mass limits how much you can time remnant in a single place. It may also further limit manipulating the distant past where there is nothing in one place that has all the base elements you need to recreate your time machine... which will limit your concerns about the butterfly effect if any distant past trip means you will be stuck in the past without any of your future technologies to aid in your mission.

In contrast, this ability would be very powerful on a future battlefield. Imagine you have a fleet of 10 time ship fighting another 10 time ships, as each one gets damaged and it's temporal shields go down, it could be cannibalized by one of the other ship and turned into a time remnant of one of the remaining future ships. As such a small battle could rage on for quite some time until one fleet simply runs out of fuel and is finally consumed by the other.

How this addresses the Butterfly Effect

In addition to limited appropriate mass in the past to create yourself from, there is also the issue that the Butterfly Effect fundamentally ignores the law of averages. If the aliens kill Einstein it is just a matter of time before someone like Grossmann, Besso, Hilbert, or Poincaré steps up to hit those same milestones. If they helped the Carthaginians beat the Romans, all the hallmarks of Western Civilization will still emerge under a pan Mediterranean Carthaginian empire instead of a Roman Empire, but that empire will still eventually be beset by all the same plagues, famines, and barbarian hordes that undid the Romans until it faces its own similar fate.

So, instead of the future becoming progressively different from a long past change in the timeline, it may in most cases become progressively similar. Sure killing my great great grandfather means I am never born, but then the aliens just have a different, but equally motivated human adversary take my place. This could further force the aliens to focus on recent history to maximize the outcome on the present as opposed to the distant past.