Time Wars & Alternate Timelines

Temporal Paradox and Time Travel delight us in science fiction, but what would a war across time really look like?
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Credits:
Time Wars & Alternate Timelines
Science & Futurism with Isaac Arthur
Episode 356, August 19, 2022
Written, Produced & Narrated by Isaac Arthur
Editors:
Curt Hartung
David McFarlane
Jerry Guern
Cover Art:
Jakub Grygier www.artstation.com/jakub_grygier
Music Courtesy of Epidemic Sound epidemicsound.com/creator
Lombus, "Cosmic Soup"
Stellardrone, "Red Giant", "Billions and Billions", "The Earth is Blue"
Reign Pagaran, "Distant Voyager"

[@isaacarthurSFIA]

***Changing Episode Covers, Notes*** For folks who are wondering about thumbnail/cover changes, I had it pointed recently to me that the title of every episode is also displayed next to or under the thumbnail for the video anyway, so that putting the title text on there was a bit redundant and just blocks being able to see Jakub's wonderful artwork. [Jakub Grygier is our longstanding cover artist and does about 95% of them and about 99% of the good ones :) ] At the same time it was noted the logo on the red rectangle we usually do was clashing with a lot of the images. So I went and reverted around half our covers to the base image (back to about fall 2019) and on around a dozen of them tried putting 1 or 2 words related to the topic but not in the title on them - that font is NightclubBTN on today's and some of the others, it's a touchy whacky but was a good fit for most of the ones I did that too like "Nuking Mars", its not our new base font or anything. I also went with a more subdued and smaller logo in the upper corner. And I'm basically letting it sit like that for the moment so I can see how YT's analytics show those changes affected views and because I don't really have a surplus of free time to change everything up in detail anyway. Feedback is welcome, it is an experiment, and in the meantime at least it let's more folks see JAkub's gorgeous covers without the title text blocking them :)

[@RhizometricReality]

Is it scifi sunday already?

[@isaacarthurSFIA]

@@RhizometricReality Last weekend

[@Eterna7Forms]

Thanks for the explanation. I was a bit confused. Still love your content! Keep it up!

[@Kev376]

People from the future - TOOK OUR JOBS! People from the past - TOOK ER JERBS!

[@211212112]

I liked the old way. I like the new way. It is your show so do as you wish. I do miss the speech impediment from the first episodes. I hope that is not impolite, politically incorrect, etc. I’m happy you have improved your speech as was one of your goals when you started. I bet you didn’t realize it would turn into this.

[@malcolmt7883]

My favorite time travel moment was in Red Dwarf, where the crew found a time machine in deep space. So they set it to travel back to the time of the Renaissance. Then, they look outside and realize they're still in deep space.

[@bonnieconnoster8590]

niceeee

[@r3dp9]

Frankly, Red Dwarf is some of the best sci fi I've ever seen on television. Also gave me nightmares when I was little. In particular, the Polymorph that turned into a dinner sausage.

[@ssshhhjjj192]

I have never heard of Red Dwarf... Going to check it out, I'll let you know what I think of it (just for the hell of it) 🤪

[@MailleGrace]

@@ssshhhjjj192 it's a great show, if you love British sci-fi absurd humor . 😄

[@jengleheimerschmitt7941]

I'm going to have to find Red Dwarf streaming somewhere. I haven't see it for probably 20 years.

[@springbloom5940]

First Rule of Warfare: no conflict is too stupid

[@kingzcomparison3683]

Actually there is one

[@harbl99]

In the words of L.P.Hartley and xkcd: "The past is a foreign country...with an outdated military and massive oil reserves."

[@markriosn7589]

Best thing about this channel isn't just the science, it's the fact that he understands literary critique.

[@markriosn7589]

I like the thought of countless new possible timeliness born off every new second of the Universe's existence. What can I say, I like tree motifs in fiction.

[@ghjong001]

Weirdly, my favorite time travel story was in Red vs Blue, where Church ended up creating an army of time clones because he couldn't break causality, and in the end just gave up and said "F* - it.". Even thought it was retconned as hallucination/simulation, it was still fun to watch. Also the DS9 episode, "Trials and Tribbleations".

[@oonmm]

That is my favorite as well. It's both smart and funny.

[@isaacarthurSFIA]

One of DS9's best humor episodes

[@sexyshadowcat7]

@@isaacarthurSFIA Love how they poke at the inconsistency between Klingons in the two series.

[@CHFafard]

The very first story I wrote (and coincidentally the story that got me into SFIA) was a story like this. Multiple factions were all fighting to establish what they believed was the accurate version of history

[@randysmith9715]

Read any of the last few novels by Robert A Heinlein.

[@brentliebrecht7866]

@@randysmith9715 I was thinking of Wake up all you zombies out there.

[@MrHominid2U]

Somewhat like the final season of Netflix's Travelers

[@jengleheimerschmitt7941]

That reminds me of a storyline in the SCP universe.

[@brentliebrecht7866]

Right timeline? Sounds like the campaign for real time that Slatibartfast is/was part of.

[@DenethorDurrandir]

I quite enjoy time travel in fiction, especially when used creatively like in many SCP stories, or ironically like in 40K My favorite time travel story is from Warhammer fantasy, I can't remember the book, where a hero got tempted by chaos for a chance to kill his nemesis, an inquisitor that murdered his family, falsely accusing hero's father of being a chaos cultist, just to get screwed by Tzeentch, being corrupted and sent back in time, failing to kill the inquisitor and causing the accusation. The reason I like the story is that this common time travel cliche was masterfully used to explain the nature of a Chaos god by "show don't tell" while creating sympathetic villain to use as a centerpiece of future stories

[@isaacarthurSFIA]

I think that's the Ahriman series, one of French's best

[@thehermitman822]

@f2p Clasher I want to believe only an Ork can get away with that paradox due to waaaagh energy.

[@luciferangelica4827]

victor chaos?

[@kobebarka8633]

I like to think there is a timeline where I get to meet Isaac! Well Wishes to all travelers out there in this chaotic time. Live long and Prosper 🖖🏻

[@countofst.germain6417]

There might be a timeline where you are Isaac.

[@kobebarka8633]

@@countofst.germain6417 oh boy that would be a dream! There’s not many things I could wish for more than to be as knowledgeable and captivating as him!

[@LiquidTang]

I mean all you have to do to make that a reality is learn how to stalk a person and show up at his house, there may be police involved shortly after but you would meet him

[@kapsi]

Perhaps even a timeline where he murders you in his army days, for being brown.

[@NeilCWCampbell]

The math suggests there a universe with such event

[@96ace96]

Imagine inventing time travel only to get stuck in an infinite battle against an infinite number of yourself, an infinite number of which all want monoploy on time travel, while another infinite number of yourself try to flee the madness. They all fail of course, there's an infinite number of hunters capable of time travel after all.

[@memk]

The time travel RTS game Achron's time travel model is interesting too. For chronal being (everyone who can't time travel) timeline is linear, but for achronal being (who can perceive time and change it) time is wave over wave overriding what's under it. The "time wave" can only be seen achronal beings and it's "travel speed" is slightly faster than causality itself. But you can use a time machine to "ride" the wave and dodge the causality itself.

[@ArticBlueFox96]

I love this concept.

[@egoalter1276]

Its not a concept, its a simulation. It actually works like this.

[@Cyynapse]

thank you for sending me down a rabbit hole. such a cool game. hopefully the company isnt defunct and makes a seqiel someday

[@jeremyleyland1047]

Thank you for re-releasing this episode demastered after it's amazing debut way back in April 25th 2030

[@machematix]

What are you talking about? The original was released in the third heatwave of '35.

[@D_Cragoon]

I remember a non-canon version of Doctor Who for the British charity event Comic Relief one year staring Rowan Atkinson of Mr Bean and Blackadder fame. I think it played for laughs him and the villain trying to outdo each other in going to travel back in time to get the architect of the building they are currently in to move where trap doors and so forth are for their advantage.

[@mattbland2380]

That was actually written by Steven Moffat who went in to become the show runner later on. It’s a great self parody of the show. Terrific cast as well.

[@TotalyRandomUsername]

Dr. Who does the worst timetravel. The Dr. breaks the unbreakable time travel rules like every 10 episodes. :) And everyone thought he can do it without consequences. But at one point a couple of years ago the timeline hit back turned him into a women and desintegrated his whole fan base.

[@luciferangelica4827]

@@TotalyRandomUsername didn't change how i think of em: not at all

[@arostwocents]

​@@luciferangelica4827I take it you did not like it before that happened then 😂

[@Lukegear]

Time Lord Isaac Arthur has come to share his eldritch knowledge with us!

[@barryon8706]

I liked Niven's "All the Myriad Ways" short story for some of the implications of travel between timelines.

[@grahamturner1290]

A classic.

[@Joe-lb8qn]

All You Zombies is the ultimate bootstrap paradox time travel novella along with "By His Bootstraps" both by Heinlein IIRC ETA The Man Who Folded Himself is similar theme

[@michaeltrivette1728]

The real question is, "Why do time travelers hate their grandpa so much?"

[@boobah5643]

The obvious answer? They're interfering with the time traveler's game.

[@luciferangelica4827]

it's not personal, they just want to steal his gf

[@jamesamos6565]

​@@luciferangelica4827 It must be because of self hate. Seeing as they are there own grandpa!

[@cosmictreason2242]

Star Trek Voyager had a very high standard deviation of quality between episodes, but their time travel ones were among some of the better ones. Like when Kim sends himself a message though 7o9, The Year of Hell, etc

[@venusianblivet9518]

I’ve tried to worldbuild time travel with multiple independent travelers but it always ends up either being boring or completely unworkable

[@samuelbastable2028]

Take the doctor who approach, its all just a big ball of wibbly wobbly timey wimey stuff.

[@isaacarthurSFIA]

That would be tricky, rival timelines

[@topogigio7031]

Steins;Gate has an interesting approach to multiple travelers. The chances of them interacting is more or less likely dependent on their relativity to the "prime" timeline (i.e. the timeline in which time travel fails)

[@samuelbastable2028]

@@isaacarthurSFIA I was making a little joke but you are right there though, conflicting timelines and time altering to the extreme there though.

[@springbloom5940]

Id expect it to be super cringy. Id think your consciousness would just overwrite your previous state and make you conscious and aware of being in a rerun, unable to alter anything.

[@CoronisAdair]

I kind of like Pete Abrams' take on time travel in his Sluggy Freelance series: Time travel 'damages the fabric of reality,' but the universe has a sort of 'buffer' where people mucking about with time travel tend to get stuck.

[@BrettCaton]

It's very important to change time as much as possible if you are stranded in the past because then time travelers are forced to rescue you.

[@MidnightSt]

there's a (mostly multiplayer) RTS game where the central mechanic is timetravel. itps called Achron, and it's absolutely amazing.

[@masteryoda9341]

These episodes are so nice for getting my mind out of the struggles of the daily grind and all the disappointments of humanity. Thanks for the entertainment

[@australiaisnotrealjustaska4379]

You realise your life is meaningless

[@intothevoid4518]

Our universe begun as a corpse pile of overly curious and under cautious time travellers is quite the conclusion I love it.

[@chrisdraughn5941]

I’ve been toying w/ a sci-fi concept of taking a copy of one’s consciousness at 50 years-old and sending only the consciousness back 40 years to a one’s 10 year-old brain. This video spurred a lot of thoughts for picking a “somewhat plausible” mechanism to do that. I’m sure whatever I come up with will be ridiculous but that’s the fun thing about sci-fi...

[@StarboyXL9]

Is it bad that my thoughts immediately went to "think of all the girls and money you could get as a ten year old with the knowledge of a fifty year old!

[@chrisdraughn5941]

@@StarboyXL9 - No it isn’t bad and it’s a story concept that’s been done before in a number of variations... You can certainly dream up a lot of mischief with such an idea... money and girls being woven into such a plot line could be done as wholesome and charming just as easy as making it appear sleazy and insidious... Depends on your imagination and how you sell it to your audience..

[@ArticBlueFox96]

This reminds me of the idea of when you die, you are just reborn into your own self at the beginning of your life, to repeat your life over and over again, but with all the memories of your past lives. If a species had this capacity natively, then they would have a perfect timeline, because your great great great great grand children will know what happened in your time and be able to tell their parents, who would tell their parents, who would tell their parents, who would tell their parents, all the way back to you when you children are born and tell you your future, and you would continue the trend all the way back to correct any event in history.

[@thehermitman822]

@@StarboyXL9 I see it as pointless to go back if you're not gonna make it advantageous once in the past.

[@timezone5259]

I have been waiting for this episode for ages Glad it finally came

[@TroyRubert]

The fact that we are just a pattern of molecules is so liberating

[@ArticBlueFox96]

It really is, but I would argue the thing we call the self, is actually an emergent property of an evolving and everchanging and unbroken pattern of information and interactions in the nervous system, that results in thoughts, actions, reactions, sensations, experiences, memories, reason, cognition, and so on... We are also far more than any of these individual components, which can individually degrade, evolve, change, or be altered while the self is retained.

[@williambuford6520]

Just have to shout out the hard work that goes into each SFIA. I have made short videos for school projects (7-10 minutes) and dreaded narrating them, so I can only image the great effort that goes in to each finished product. Thank you for bringing this to us!

[@nedlyest]

Wouldn't the issue with time travel be the planets location due to it traveling through the universe? Not just it's travel around the sun.

[@ScienceD9000]

That would to be relative to something since their is no absolute frame of reference due to relativity. So it could just be relative to Earth and avoid those problems.

[@Grizabeebles]

26:00 - This is why so many of my favorite time travel stories involve the discovery of time travel being erased as a consequence of its own discovery. Closed-loop time travel seems like it ought to be a "self-sealing" problem.

[@adolfodef]

The problem with "closed loop" world_lines is that at the point where the "loop" happens the "line" eventually gets strangled by its own tensor strength ["cutting" itself out at the point of intersection]. The worldline inertia "welds" itself at the cut point, leaving behind only short_lived "scars" (anomalies that never last beyond the date the initial travel to the past happened) as indication. -> The "floating strand" of the worldline that contains all the informational causes_events related to the time_travel event eventually disintegrates bit by bit as it "spreads" into "The Nothing" of non_existence].

[@Grizabeebles]

@@adolfodef -- Sounds interesting. Can you please share your source? I'm not sure whether what you're saying is a theoretical physics thing or a storytelling thing.

[@adolfodef]

@@Grizabeebles Neither. [Technically speaking] It would be pataphysical philosophy (aka: my own headcanon), that I try to visualize and then to transcribe. -> Watch Steins;Gate & Steins;Gate:0 for the basics. /) El Psy Kongroo

[@adolfodef]

@@Grizabeebles One important detail I forgot to add in my "visualization", is the fact that a "time loop" never happens ONLY ONCE; but rather an non_infinite number of times, until it does not anymore. -> Even just "twice" would be too much. If you see the "loop" in 3 dimensions, it is obvious that the "turn around" would not perfectly match the original line (it would go either left or right). . Unless it ALWAYS go a bit more towards the same "side" (something that would imply the existence of a positive, active "imaginary time" that is constantly "pushing" the loops, just like normal time "advances" the line), as soon as there may be a loop crossing the point on the opposite side, it would cause the previous loops to create a "knot" [were there may be "tension" or "torque" or "angular momentum" that would destroy the universe_line of continuity]. (or) -> just a Time Quake [but NEVER a Paradox]. The self_erasure of Time Machine is part of the "evolution" of universes [those who do not sucessfully develop "laws" that prevent effective, "useful" time travel simply "kill" themselves before reproducing].

[@egoalter1276]

I have no idea where you get that from. General relativity allows for closed timelike curves (in the same way einstein-rosen bridges are closed spacelike curves), there is no reason the effects of ome couldnt propagate out of it.

[@noxthemc7717]

If there are multiple timelines, i hope this channel exists across all of them

[@adolfodef]

By now, it´s existence is probably an Atractor Field of Convergence for our local group of worldline iterations. The way how theischannel (& the life of Isaac Arthur too) improved overtime is as suspicious as the many ways Hitler survived accidents & assasination attempts (I am talking of the current historically canonical ones, not the billons retconned). El Psy Kongroo /)

[@anvos658]

Sadly if there are there are likely many where events caused their death or otherwise changed circumstances that led to this point.

[@luciferangelica4827]

not in the central finite curve. isaac arthur doesn't exist in any of those

[@luciferangelica4827]

@@adolfodef oh yeah, you just reminded me of a cool thing i seen, on netflix maybe, they killed hitler like 6 times in increasingly absurd ways

[@luciferangelica4827]

might've been love death and robots

[@anvos658]

The answer to loop paradoxes is including instructions that you need to go back in time and then give yourself the instructions to go back in time, thus you loop around once and your doing it because you told yourself to and not because of the original reason that would get stuck in a causality loop. . FTL also isn't time travel if you separate the concept of perceived time from sequential time, since the rate at which perceived time is flowing is irrelevant to sequential time, moving beyond the speed of causality would only actually affect perceived time, thus you couldn't actually arrive somewhere before you left, you just wouldn't be able to detect the object moving at FTL until after it reached its destination. This understanding of time however does sadly means true backwards time travel isn't possible, unless you reverse time for the entire universe though.

[@godofdeath8785]

Your last sentence sounds logical

[@luciferangelica4827]

there is no preferential frame for time, yk, relativity

[@littlegravitas9898]

No matter which timelines we are in, I'll be watching SFIA on a Thursday

[@uiiu1436]

So true

[@Mr.Cheeseburger24]

Maybe on Saturdays :O

[@limbo3545]

@@Mr.Cheeseburger24 Leave Arthursday alone!

[@jasonmoore4429]

oh predict another one.

[@Grevnor]

Except in the timelines where they air on Tuesdays.

[@mikerodgers7620]

Never a dull moment with you Isaac.

[@DanielGenis5000]

This is where the abstract meets the concrete, my favorite place to have lunch…. Cheers, Isaac!

[@Rj-im2mu]

Achron was a game that had a fascinating portrayal of time travel as a propagating wave had a brief period between cause and effect (future to past) that I always thought handled the concept elegantly in a way that still allowed for drama

[@theFLCLguy]

Time dilation is because the closer to the speed of light the less things can move in other directions. Which reduces interactions between things like particles. This gives the appearance that time is slowing down.

[@egoalter1276]

True, but incorrect.

[@theFLCLguy]

@@egoalter1276 it fits every experiment that has other time dilation.

[@HobDobson]

Another possibility is that Roko's Basilisk doesn't allow its progenitors to wipe themselves out in a temporal singularity either.

[@NeilCWCampbell]

I for one welcome out machine overlord

[@MySerpentine]

The idea of a time war is about the most horrifying thing possible. The Faction Paradox series was a good example of that.

[@hannahkimble6080]

Stories about invading the past always remind me of the TV show Terra Nova, in which future humans set up a colony in the Cretaceous. I don’t remember anything about the plot, but early in the show they established it was an alternate timeline, only to twist in the final episode of the season that it was the same timeline, and potentially have ripple effects 85 million years in the future. I think it was a setup for the second season they never got.

[@fss1704]

i miss that series

[@Emdee5632]

My expectations were high for the series. Unfortunately it was one of many that got shelved.

[@UpliftedCapybara]

“Then we’ll be in to August to discuss living in space” He says talking about September. I’m assuming this was done on purpose lol

[@thumb-ugly7518]

Thank you to the entire team once again. A wonderful idea to listen to while drawing tattoos before work. I hope yall have a great day. I'll be pondering "Temporal Tattoo Fluctuations of the Quantum Tattooed Man!" Haha good stuff.

[@sugar_ltd]

When I first heard you reference Sliders I knew I was in the right place. Great show.

[@meatlemonade3338]

very excited for this one, i love time stuff 💜

[@Pacbandit13]

Just when I think Isaac can't do anything crazier he pulls this legendary video

[@MrQuantumInc]

What is implied by a lot of time travel stories is that they are traveling to a copy of the past. If in multiverse theory EVERY event causes the universe to copy itself so would the act of time travel itself. This prevents any paradox but has the weird implication that even if you change the past you are not actually changing your home timeline. Often in fiction we see the hero travel back the past, change things, then go back to the future and get confused by how his actions changed history, the ending of "Back to the Future" being one example. Their memories are from one timeline, but they are living in another. Though this implies that they are absent from the original timeline, having hopped into the time machine and disappeared completely and permanently, or maybe replaced by another version of themself with memories from yet another timeline going ad infinitum.

[@dumdeedums8816]

This one will definitely be on my list of favourite episodes from your channel :)

[@jamesfry8983]

I feel Babylon 5 did time travel really well, with not skipping the consequences and effects on the body also the future transmission Ivanova receives is a cool idea

[@drewp6698]

Sliders as I remember it was not about alternate timelines. His (he/his/him being the main character) device enabled him to travel to parallel Earths. If I remember right he went to a parallel earth early in the series, possibly in the first episode, and then when he returned to his home earth he soon realized it wasn't the Earth he originally came from. He then spent his time for the duration of the rest of the series trying to make it back to the version of Earth that he originated from, and making enemies along the way most notable with the Cromags. Very underrated series IMO.

[@Emdee5632]

As I remember it but I could be wrong, the Cromags discovered they only existed in one reality. This explains their hatred toward the other, human, realities.

[@drewp6698]

@@Emdee5632 That was in some of the earlier episodes featuring the Cromags. In later episodes he encountered Cromags that were essentially more intelligent than humans, had mastered the sliding technology, and would go from Earth to Earth conquering and cannibalizing humans. I should look up if it streaming anywhere. I kind of want to go binge watch the series now.

[@drewp6698]

@@Emdee5632 Just looked it up. It's free on Peacock right now. I know what I'm doing with my free time for the next few weeks.

[@jkfecke]

One of the great things about the way Everything Everywhere All At Once is how it handles the multiverse; while there is a common identity, the lives of your alternates can be wildly dissimilar based on choices and happenstance. And in an infinite universe, those changes can be radical.

[@philipmurphy2]

Always worth watching Issac Arthur.

[@ralphacosta4726]

Interesting topic and fun trope for many stories, but Isaac Arthur in his typically through and logical way completely destroyed it! I quit about 17:00 when time travel, multiple timelines, multiple worlds, etc. were already thoroughly beaten to a red spot on the pavement. Why i love this guy.

[@Ron4885]

*Very interesting post.* I'll listen to this one more than once. Thanks. I love your references to Sci-Fi books. I have listened to more than one of them).

[@James-ep2bx]

My biggest issue with how most thing treat time, is the tendency to treat it as though it's made up of discreet immutable units. For instance if you view time less as a state and more a property, like say momentum, it could limit the possibility of paradoxes without requiring linearity/unidirectionalality as much like how strictly speaking it's possible for a planets orbit to reverse the energy and circumstances required mean this RARELY if ever happens, likewise if thing had a sort of causal momentum then even if retrograde time travel is possible the effort needed for any action that would shift causal sequences would increase in relation to the degree of said shift

[@JonahRoyes]

In an alternative universe this would be a documentary not Sci fi , happy Arthur'sday ❤

[@Mastervitro]

Every "particle" in the universe are interchangeable resulting in the exact same result in most configurations, making a much smaller yet still huge number of possible configurations.

[@diegocosta9009]

"Time Travel is even something people like to talk about to discuss regrets" Didn't know Isaac had time travelled to watch the BCS Series finale when writing this episode.

[@fss1704]

yeah that's almost math at this point

[@logankrzywicki9555]

Thumbnail art is great as always. Not sure how I feel about the new font though

[@isaacarthurSFIA]

Thanks, I'm experimenting with fonts

[@MrGreenotwo]

oooohhhh weeeeee Time to get down into some hardcore science fiction !

[@NovaRuner]

Awesome video great video. I probably listen to it in the future once I travel there… just by living one second per second.

[@BaldingClamydia]

Love Zelazny! You know, I come here for the great sci fi, but I stay for the book references I don't get to see anywhere else

[@ianpidgley9720]

one of my favourite 'invasion of the past' in fiction, occurs in the Star Trek Voyager Book 'The Escape' the crew enconters a civilisation which in a bid to overcome over-population, have spread out throughout time, using periods where their planet was uninhabited, the timeline is divided into periods, and citizens are able to commute between periods, but not within a period, any period which is critical to the evolution of the species is off limits, (except to specifically authorised personell) it is revealled that within a couple of hundred years, the species will discover means to travel to alternative dimensions, and the planet will be abandoned (which is the state it is found in by Voyager)

[@agalah408]

It's hard to go past The Technicolour Time Machine for time travel fun. A movie crew go back in time 1000 years to film the Vikings going to America, to later discover that the only reason that the Vikings went to America is because they went back in time to film it. Awesome story telling.

[@ASNS117Zero]

My favorite time travel story has got to be Chrono Trigger from the SNES. Not only was it a game that was so instrumental in defining how games would develop over the next 10-15 years, it was also my first introduction to some of the story beat concepts that would become popular later in the rise of lovecraftian horror. Granted, CT was SUPER light on those themes, and it and it's time travel were kind of blanketed in more kid friendly stuff and the veneer of magic and fantasy, but that was what made it more accessible for young me to be honest lol.

[@falsfire]

I''ve always said that, there is no such thing as traveling to the past without affecting it. Eloquently put, Isaac. I tried describing it as, let's say you want to go back and observe some event. But somebody now has to step around you on a busy sidewalk, which delays them by a couple seconds, which could go on to mean they do not meet their future spouse, and a very important historical figure is never born. Or maybe that person was supposed to get run over by a car, but the 2 second delay means that in this 'timeline', they continue to exist, where they didn't in yours... So no matter how you grill that quantum cheeseburger, if travel to the past were possible, changes occur. But paradoxes can only occur if there is only one 'timeline', thus the many worlds theory, right? You simply arriving in the past, spawns a whole new timeline, and if you try to return to your present, you're still on the new timeline, and things will be different. You'd have to travel not only through time, but through dimensions, to return to 'your present'...

[@Mr.Nichan]

15:32 I notice you didn't mention Tenet (2020). That's a great example of depicting backwards time travel as just reversing time and having to go through the intermediate time, though the physics doesn't really make sense on close examination, even if you try to "iron-man" it by ignoring a few minor mistakes they made (like comments about antimatter).

[@paxdriver]

10-yr-old Isaac - "pff, that's not how temporal relativity works.. I'm conflicted for enjoying this." lol

[@Reddotzebra]

Technically it tends to delete individuals who have the knowledge of how to do time travel or FTL by exploding them and anything around them at roughly the point in time where they are set on the path of eventually being able to understand the technology. Since this generally happens when said tech is operated, there's a good chance that it simply explodes, but the explosion travels all the way back along the frame of reference for the closest intelligent individual until that frame diverges from how the tech came to be activated.

[@xXHerrZockXx]

23:00 i guess the movie "Freejack" got a working solution for that exact problem. Pretty good writing in more than that regard tho, I definitely recommend it, mick jagger is pretty dope in it ✌🎉

[@freddyjosereginomontalvo4667]

Awesome channel with awesome content and great quality as always say 🌍💯

[@isaacarthurSFIA]

Thank you so much 👍

[@fvckyoutubescensorshipandt2718]

Some things will probably be forever sci fi. Backwards time travel and ftl travel are 2 of those.

[@Aginor88]

Interesting as per usual.

[@Eldagusto]

Seeing this I immediately thought oh whole episode based on Kang the Conqueror hoho this is his entire bag! I loved the notion light is the speed of causality. This addresses a lot of my concerns like a bubble of sped up time would be bombarded with centuries worth of photons. I always thought it strange to walk into bubbles of slowed and sped up time because your limbs that enter first would wither from the lag it takes for the rest of you to enter. And I’m glad someone finally talks about time being altered just from you entering due to minute displacements and gravity, it was always stupid to think you just needed to not actively avoid messing with time when just your presence would alter things! Thanks for the video Isaac!

[@boobah5643]

Re: Universe hostile to time travel. Niven did it earlier, although he wrapped the whole thing into a short story. A civilization losing an interstellar war gets desperate, and one crazy idea that makes it to the top of the chain is that xenoarchaeologists have, throughout their history, discovered some weird artifacts that look like they might be the beginnings of time travel devices, and date, as near as they can tell, _exactly_ to the end of that civilization by way of natural disaster. So, the theory is that if anyone tries to build a time machine that maths out, the universe stabilizes in a state where _something_ prevented the machine's completion. Whether it's 'the universe' acting, a collapsing time loop, or a divinity isn't gone into. So, they devise a cunning plan: 'leak' a time machine plan to their enemy in the hopes that they'll try to build it and the paradox will win the war for them! Even if it's a coincidence and/or not an actual time machine, building an enormous cylinder than spins at relativistic speeds* will waste resources that otherwise would go into the war. No sooner do they agree to this plan, however, than they receive word that the war is already over: their own sun has just begun going nova. * I've never seen this particular time machine referenced anywhere else; it involves charting a path around the cylinder that ends before it starts. I'd guess that someone has figured out an error in the math, or it requires some impossible material, or maybe it's practically useless since I suspect you can't use it to travel to a time where the device doesn't already exist.

[@Emdee5632]

Their own sun has just begun going nova? Neat.

[@adamdean5881]

I'm late for Arthursday glad I made it 👍

[@gabrote42]

Honestly, I have seen a great many models of time travel, from "you already changed the past", to "Time is sentient and wants you to obey fate, so expect your doomed splinter selves to die unless you make some crazy plan that makes it seem like you already changed the past" (Homestuck), to "You can time travel inside 5 minutes, and changes perpetuate in waves" (Achron, an RTS game), "constrained conditions but consequence-free changes once you do, bar some thematic convergence" (Ghost Trick) and dozens more. All I can say is that I would be a STRONG advocate to not allow time machines to exist. Especially if we end up playing 5D Chess with Multiverse Time Travel.

[@GetDaDrawsDawg]

@27:30 this just made me think of weaponizing everyday items to turn them into bombs just from being placed into another time

[@Seeraphyn]

I was wondering when you were going to mention Tenet. If you haven't seen it, it's honestly a pleasant watch. Not the best movie ever but their take on time travel was really quite refreshing, I loved the fact that the traveler has to go through time in reverse but at a normal rate instead of instantly popping out of the time machine at the desired date like we often see in movies.

[@nuke___8876]

I like Tenet but I still find it strange that they basically mentioned all the paradoxes and then said: "Meh?" Like, why take the time to even mention the paradoxes?

[@zeevdrifter2707]

Is it possible causality is totally bunk? Like just something we perceive and changing reality happens all the time.

[@Jammin247]

Ah yes some good ear fuel for the start of my day. Thank you!

[@13deadghosts]

Regarding interesting imetravel stories, I have a book recommendation: Menschen wie Götter (Humans like Gods) by Sergei Snegow. It is a really interesting soviet SciFi book, that sadly was never translated into english. So if you can read german or russian give it a try. It is interesting to see how diffrent SciFi was on the other side of the iron curtain.

[@yodasmomisondrugs7959]

Bro EVERY major technological advancement was "dubious" to those who lived before it became the norm. I don't put anything past us given a long enough timeline.

[@bernes222]

One thing that isn't mentioned in time travel is earth movement. Counting only rotation around sun 30 km pre second going back in time 1 day should move you more them 2.5 million kilometers into space 😁

[@paulohagan3309]

Somewhat similar issues with even simple teleportation?

[@bernes222]

@@paulohagan3309 I think teleportation would have problem if you keep momentum from yours original location, not changed it to expected on landing point.

[@paulohagan3309]

@@bernes222 Exactly. Teleport without care and it might be as bad as falling out of a plane.

[@Pheonix1328]

I think when something goes back in time it just creates a new timeline so from the original timeline's perspective it didn't work, but every time they try they creates new timelines in which it did work. I think this also prevents most if not all paradoxes. If you accidentally stop yourself from being born, that doesn't matter because you come from a timeline in which you were born but now exist in one that you don't, simple as that. Also weird timeloops like in the movie "Predestination" wouldn't be possible, which is good because they don't make sense.

[@Shiskabobber1]

That violates conservation of mass/ energy as we know it.

[@jengleheimerschmitt7941]

I agree that the multiple-worlds thing does resolve pretty much any possible problem. But it kinda does ot at the cost of non-falsifiability. ...this is more a comment on my feelings about Sean Carroll / Everett's whole schpial than your ideas. I don't dissagree with you at all.

[@jengleheimerschmitt7941]

@@Shiskabobber1 No, it actually don't. ...I posted another comment here at the same time you did... Conservation of M/E only applies to a single timeline. The multiverse idea we're talking about is batshit crazy imo, but not nearly so easily dismissed as that. If I have it right, we already know that each quantum ...thingy... splits reality into two separate realities. This _is_ batshit crazy, but it is also generally accepted as fact. The only liberty the multi-worlds thing takes, is that this splitting is primary rather than some artifact of our perception. -That what we all accept to be experimentally true, is true, -and the singular timeline, with each quantum thingy, collapsing conveniently for the timeline _we_ happen to be in, -is what is an artifact of our perception. I probably didn't explain this well, but that is my best. This multi-verse thing was pioneered by Everett, and is now being championed by Sean Carrol. I find it epistimologically terrible for the reasons you bring up, but, also... ...compared to what. It definitely can not be dismissed for violating conservation of M/E.

[@Pheonix1328]

@@Shiskabobber1 Dark energy steps in... is mass/energy conserved in an expanding universe though?

[@Pheonix1328]

@@jengleheimerschmitt7941 "unfalsifiability"? What do you mean?

[@shanepye7078]

One of my favorit time villains was the Observers from Fringe.

[@Quickdraw_Punslinger]

Currently readong The Abyss Beyond Dreams by Peter Hamilton, so fun to see it being featured on this video.

[@ericreid8111]

In an alternative timeline, Issac Arthur is named Arthur Issac.

[@hubbletrubble7875]

Outer Wilds was cool Using a supernova *as the power source to time travel to before it happened* was AWESOME

[@pknuttarlott4934]

Hey Isaac love your videos. Have you seen the movie Tenet? Or even better Predestination? Two great time travel movies.

[@bonnieconnoster8590]

I try to like all ur videos , I hope I didn't miss one

[@cannonfodder4376]

Another superb episode as always Isaac. Another confusing topic and concept well explained for cave man me.

[@boggsanthony]

For me, the experiments that the Reverse Flash performed on Barry Allen’s life are the best, dubious time travel/alternate history stories.

[@Jade_TheCat]

Hey at 4:34 the Stargate example (bottom-right) of rapid aging is due to nanobots artificially aging him and not a time thing. I only bring this up because Stargate actually has some good examples of using faster/slower time fields. In one episode of SG-1, Season 2 Episode 15 "A Matter of Time," it's even time dilation due to a black hole, and it shows all kinds of problems with communication and other stuff because of it.

[@lunaticbz3594]

"the war for the future will be fought in the past." From the 4400. It's alright sci fi. Follows all the usual tropes. But I just love that line as it's fundamentally true and bs depending on how you look at it.

[@daemeonation3018]

Nice animation in the intro. I am learning blender now and doing stuff like that but not that good yet.

[@miserychickadee]

15:55 Yeah, like Fry! Like Fry!

[@atlas4733]

27:34 I saw someone explain this multiple-iteration corrective loop problem with a Mobius strip. You kill your grandfather, which leads to you not existing, allowing the next grandfather to be alive to make you so you can kill him again. (I don't really remember at this point.)

[@calvingreene90]

I don't like the branching timelines because of the required energy budget of creating entire universes.

[@Daltem]

That's assuming they are being created in that moment (which would be every moment) How about if you thought about it where all the possible many worlds were already created? If you want to keep the whole "each decision creates a universe", then it could just be that at that point you can now tell the two previously identical universes apart Like two waves finally moving out of phase with each other

[@egoalter1276]

Mothing is created. The alternate lines are made up of the same particles, the same energy budget. In many worlds any waveform exists as a superposition of all of its infinite possible states as a result of all of its past stochastic events. Consequently this also rather clearly disallows travel to these altermate timelines, because you are alreadx there too (your atoms just might be part of a star)

[@calvingreene90]

@@egoalter1276 For two timelines to occur the particle has to duplicate and particles are made up of lots and lots of energy. Given the decades of using nuclear power it probably would have been noticed if when a tiny bit of matter was converted to energy there was less energy.

[@prozacgod]

When I was in high school I wrote a short story describing how humanity got rid of entropy by just pumping it into another universe and called it the entropy conditioner. This ended up in a brutal war between us and the other universe, where our side had no technology to travel to their side and their side had technology to travel to ours. Because we were too lazy to invent the actual techniques to travel there we could just pull energy from them. Anyway one of the tropes of the series was the government mandated that everyone increased their energy usage to decrease the amount of energy the other universe had available to it. Anyway the surrogate universe eventually lost all of its available energy... But there was a lone survivor who had the ability to transfer between universes and so he went to a second universe and describe the process to build an entropy conditioner focused on our universe exclusively. Since we had largely grown hedonistic and didn't really invent a whole lot of stuff this effectively trapped us in a universe that was dying and there was no escape. In the end the lone survivor of universe b lived a life of luxury in universe c as being heralded as the savior of the universe. The brief 20 seconds of the intro of your new video here Isaac, reminded me of this whole silly thing I had written something like 24 years ago.

[@sarcasmo57]

It blows the mind.

[@akigreus9424]

Theist version of shoulder of giants saying. "If I see far it is because I know which giants to climb."