Time Travel 

"When do you want it done by?" "Yesterday." "Suppose I cannot get it done by yesterday." "Then the day before yesterday will do nicely."

“Let me wish you an excellent 2020“ Well this aged like fine milk

...and the bartender said, "we don't serve faster than light particles here." A tachyon walked into a bar...

_"In relativity time is flat in the same way that planets are flat, in that they're not"_ I really love Isaac's videos

I heard it explained this way , " Time stops everything from happening at once "

I time traveled here from 2010. It took me 10 years but I made it.

You can make FTL even easier with time travel. You go back to a time when the universe was much smaller, and move faster to your destination, and fast forward to let the expansion carry you

Isaac: "I had a really good time travel joke to start the episode with but it turned out none of you liked it." Me: *Pauses the video and thinks for a minute.* "I see what you did there."

*My favorite grandfather paradox is fry being his own grandpa .*

“Wow is this a new episode?” *posted one year ago* “Oh, he’s good”

...turned out none of you liked it. We must be on a seperate time branch then.

I already heard that joke next week

My favorite type of time travel is the one described in the short story Palimpsest by Charles Stross. The main character is part of a time travelling organization that has an entrance test where you travel back in time and kill your grandfather. This does not in any way stop you from existing. If you travel back to where you came from after that, then no one will know who you are. The idea is to look at the whole timeline as a painting. Every trip through time alters the painting. This means that there are no branching realities.

I'm traveling into the future at the speed of regular time.

The past, the present, and the future walked into a bar. It was tense.

That explains everything! Isaac is from the future telling us about all the megastructures they built and traveling from today back to November to create this episode :P

An interesting book was Timelines. In it, the main character can, at will, change timelines. Allowing her to change reality, from small, but important, events to larger ones. For example, if she runs away from a pursuer and trips on a root she can choose to switch to a timeline where she didn't trip. She can't bring others with her, so she can never prove that she can do this, because

As a conlanger who's messed with it a tiny amount, it's really not all that complicated to figure out tenses for time travel if your language is made for it (at least it's nothing like what Hitchhiker's Guide to the Galaxy implies). In a one-timeline universe, all you need is separate tense systems for the timelines of particular people or objects and the universe (if it's meaningful to talk about the universe having objective time). For example, a society where time travel is frequent enough that more than one time-traveling person or object might benefit from having subjective timeline tense marked on nouns and universe-timeline tense marked nouns, e.g. That man-PST attack-FUT me-PST. = That man attacked me in the future. (i.e. both of our pasts but in the univers's future.) Special relativity already adds a slight wrinkle to tenses even in our universe. For an example, think about the New Horizon's probe encountering Pluto. Our convention is to pretend like there's some way for things to be spontaneous: We say that it came closest to Pluto at some point in time, and the information reached us a few hours later (about 3 I think?). Similarly, any information we sent to the probe actually got there the same amount of time later. Add these times up and you get the round trip time. If we view time as related to causality, then we could say that 3 hours ago at Pluto is "now" in terms of it affecting us, since anything before that has already affected us, and anything after that hasn't and is just as unpredfictable as our local future. On the other hand, in terms of us affecting it, 3 years in the future is "now" for Pluto, since everything before that is as unchangeable as the past, while everything after it is changeable by our actions (or at least affectable). Obviously, we have one way of dealing with this. A longtime interstellar civilization might improve on it slightly first by simply making a 5-way or 7-way distinction in time regions rather than our 3-way one: 1: Past that has affected us. 2: Visible "present", e.g., now and Beetelgeuse as we see it now, regardless of whether it's "still" there. 3a: Past whose light hasn't reached us yet. 3b: Simultraneous "present" as we understand it now. 3c: Future that hasn't been affected by our present yet. 4: "Present" being affected by us e.g., now as we send a Mars rover instructions and as it receives them 5: Future we can still affect (in our future). It is possible to differentiate between the three types of 3, but not really very useful. It is also possible to make even more distinctions, like dividing 1 and 5 by round-trip times. (Many real world languages differentiate between distant and recent past and/or soon and distant future. Some have other things, like a special "today" tense.) One remaing problem with the above system is that it's centered on one reference frame. For interstellar correspoindences (or, in fact, for many things we do now with writing and recording) to differentiate between the reference frame of when the message is composed and when it is read, i.e., 1st person and 2nd person time, which could, for example, be 2 separate tense affixes on verbs. (It is also possible to introduce 3rd person tense, but that is not as called for here and has already been aluded to in the top paragragh.) The biggest complication with this can be appreciated by considering books. When you write a book, your various different readers will likely be reading it at various different points in time, most of which are not even predictable to the writer. That is probably why our books tend to use writing time as their reference for tenses, except sometimes when addressing the reader in second person. My current time-travel story (as well as older ones I considered) works on the theory that every time you travel back in time, you create a new "time-branch". The reason I call it a branch rather than a line is that I basically ascribe to something like the multiple universes interpretation of quantum mechanics (even though my current main project is in a totally alien fantasy universe with no quantum physics or special relativity as we know it): Each timeline that can happen, does happen. This causes the universe to branch into an infinite number of future of other future universes every second. It is also possible th I'M GOING TO HAVE TO FINISH THIS LATER BECAUSE Y TABLET RANDOMLY DIED ON ME WHILE IT WAS CHARGING RIGHT AFTER I WAS ALMOST COMPLETELY FINISHED AND I'M JUST SLIGHTLY TOO PISSED OFF ABOUT IT. ALSO, IN ANY CASE, THE REASON IT DIED IS CLEARLY BECAUSE BEING ON DRAINS ITS BATTERY FASTER THAN ITS CHARGER CHARGES IT, EVEN WHEN THE BRIGHTNESS IS ALL THE WAY DOWN SO TYPING ANY LONGER ON IT WHILE ITS LOW CHARGE IS JUST INVITING IT TO DELETE ALL MY WORK AGAIN. Short version: My story universe's theory of time requires infinite dimensions and all sorts of confusing possibilities and invented terminology but mainly just requires some adapted epistemic modality (related to grammatical mood) and already common tenses to discuss, and I made a final note about languages that don't have tenses like European languages do (at least not mandatory ones).

I've been subbed since about 4-5k Crazy how big this channel s become and very pleasant to see as its very well deserved

This channel has me hooked! I can’t stop watching his videos, so intriguing and fascinating 🥲

Happy Arthursday!

I thought the joke was pretty funny, but this one's OK too.

That might be the best segway in to an advertisement I've seen yet. You and your team continue to outdo yourselves, thanks for all that you do and I hope this new year brings you guys nothing but continued success.

Off the top of my head, I can't think of any RU-vid series other than this one that has remained consistently good for 6 years.

With an infinite number of realities to travel back in time to, you'll find these paradoxes impossible, except in the universe where they're not.

I was about to make an astounding breakthrough in the field of nonlinear time, but then it dawned on me that the theory hadn't occurred to me yet!

Best way to start 2020: *watching an Isaac Arthur's video*

Wish I could time travel back to 2019 to tell myself to stock up thousands of surgical mask and hand sanitizer.

Isaac's videos get an automatic thumbs up from me.

Happy new year Issac! Us: January 2020 Issac: January 3030

Starts off the decade with a dad time joke... I like it.

I loved End of Eternity. I'll always remember the tag line on the copy I read. "Due to circumstances within our control, tomorrow has been cancelled.":

"I had a really good time travel joke, but, it turned out none of you liked it." And that's where you're wrong.

Make a gravity chamber, a suit that can withstand the extreme amounts of gravity, and crank it up. you will watch thousands of years go by in minutes..

The problem with your joke is that its both outdated and ahead of its time.

I'm not a smart man by any stretch of the imagination. One of the reasons I love watching this channel is you bring up ideas I've never had before. Like if you could travel to another dimension and bring something back to our dimension enough matter could be brought in that essentially our universe would become a black hole.

So thats why cafein gives you energy, im learning so much.

A most fantastic and informative episode on such a complex topic Isaac. A great start to the New Year and 2020.

last time i was this early i was still in the future.

I remember the DS9 and Voyager episodes of time travel. Issac explains time travel in such an understandable way.

Considering unlimited multiverse is existing, there is a small portion of universes where Lord of the Rings story precisely occured, even with the same faces as in movies.

> Tense Try Achron's approach: The time of the time-traveler: Meta-time. For example: 3 minutes in the future is player A's 2 minutes meta-past, and player B's meta-now.

I really like multiversal timetravel. Immagine a timetraveler on an instantaneous/eternal Odyssey in search of his original timeline. Or one close enough.

I always liked the idea of CTC's seeing as an incursion from a civilization with such capabilities could happen at literally any moment. Imagine a group of scientists performing particle experiments & then they inadvertently create the starting point of some CTC that spans far into the future. All of a sudden, humanity would be open to an unimaginably large ensemble of opportunities & dangers spanning until potentially the very end of time. It is very fun to think about.

The earth is always moving in space so if you could time travel, you would also need to travel the same relative distance in space as the earth has or you would arrive in empty space, no?

Grandfather Paradox, the spiritual liege of Faction Paradox, was the 8th Doctor's future self in the novels during the series hiatus. His creation was no accident, Isaac!

I'm envious of my great grandchildren (to the 17th power) because they have the career path of "time pruner".

With infinite power comes infinite responsibility.

We need Timetravel sometime this year, so we can have Hindsight "2020"

23:23 The part when all the time travelers in the comment section have a good laugh

I had to travel about 5 seconds into the future to get Isaac’s opening joke, then I laughed:)

Time travel creates a very unique FTL. Its one where the onlooker would see you wink out of one place and appear in another but the traveller would have to travel the full distance and time.

so, thats why coffee is so powerful, lol. Great vid, and happy new year y'all. B)

That whole pretty much instant singularity of time travel being everywhere is a good point.

When you travel back in time so that you can watch the very first episode of Isaac Arthur at its launching

...Can we please get a time travel comedy where someone tries to kill some notorious mass murderer in the past without realizing that he/she is actually a direct descendant of said person, thus producing hilarious failure after hilarious failure? Please. I didn't know I needed this in my life.

7:30 - 2+2 does equal 5, in Common Core math!

@20:55 when you said "good news everyone!" all I could think of was prof Farnsworth from Futurama, ty for the nostalgic laugh

That was a good start. And Dark matter: The gravitational effect of all of these pesky unregistered time travelers...

Isaac, Any plans on a video strictly on Space Force and the roles it may or may not play in the colonization of our Solar System? I love your channel!

6:18 The formula doesn't show time going in a negative direction, but an *imaginary* direction. Clearly the square root of something negative.

If Time Travel was possible, who the hell would ever want to revisit this time period? Isaac Arthur videos are the only good thing about it.

-Sir- *God Emperor* Isaac Arthur!

😀"If my Civ discovers how to travel faster than light, we'll destroy your Earth" 😐"IF"

I really enjoyed the Moon: Industrial Complex episode, interesting to see which parts of it actually came to pass.

I enjoyed this episode when I first saw it 40 years ago. But it just seems kind of quaint today.

"Confusing stuff that's giving me a headache." When Isaac Arthur syas that about Time Travel, then we can readily assume that it is impssible.

Wasn't the "civilization at the end of time colonizing itself in the past" a plot in Dr. Who?

Pfft. Time travel exists. I went back and killed my grandparents, and there was no effect wh [ERROR USER NAME DOES NOT EXIST]

For the Moon Industrial Complex episode, I'd imagine that skiing, skateboarding, BMX and dirt bike courses would be attractive to tourists. And sports like basketball and football would be interesting to watch.

My grandfather tells me that I saved him from stepping under the bus in 1953.

The first rule of time travel warfare is to always show up before your enemy.

I keep referencing this book, but Ryan North's How to Invent Everything frames itself as a repair guide for a time machine that has no user serviceable parts, so it just tells you how to reinvent civilization yourself because that's just easier. Strangely, it's the fictional intro to that book that seems most relevant here. The intro even has a (fictional) section that deals with the ethics of creating universes for entertainment via time machine, and the answer to that question is "Our ethicists at Chronotix Solutions have looked at this and told us that this is totally fine. Besides, these universes aren't just used for entertainment. They're also used for resource extraction."

Welcome to the 2020's, Issac!

A bit of random sci-fi about time travel stories I like... :) In John Varley's "Millennium" time travel works by opening and closing a kind of time-windows, one can go back to a specific moment in time only once and only in very specific moment later. Visitors from the future (from our perspective) work to [SPOILER WARNING] assemble healthy humans from the past (usually snatching them shortly before disasters) because they can't rebuild civilization themselves as they're all dying) and under guidance of capsules with massages that are coded to be opened only by a specific person at a specific time. On the other hand there's Geoffrey Landis's "Ripples in the Dirac Sea" where a man tries to escape death by using a time machine but the device after sending him where he wanted keeps resetting to point of origin, as he and the reality is anchored in one universe and places he visits are other universes and changing anything in them have so consequences in his own reality when he gets back - and as the fire keeps getting closer, he just buys himself time going back to various times and repeatedly lives there.

The joke feels real when have liked the video before hearing it.

I've thought about ways to avoid the grandfather paradox. One is call the Library of Alexandria principal. Say you wanted to ensure that the works in the Great Library wasn't unintended collateral damage. You could stop it from burning down but it maybe too hard and would end up creating the grandfather paradox. You could secret away the books destroyed in fire into a cave, however people may notice them missing and then butterfly effect. A much better way is to copy the works and hide the copies in cave like the Dead Sea scrolls. Have them be discovered a few days in the present after you left My favorite solution is to have a small hidden camera and just record the books. A side bonus is you can record ancient Greek, Latin and Egyptian being spoken.

19:09 Isaac Arthur is a confirmed time traveler!!! That explanation of a quirk of your video making was most amusing and a fantastic example of time travel and temporal discussions in itself. 😂😂🤣🤣

Happy New Year Isaac. Great going and keep going. I look forward to another year of your videos and narration. Simply the best and the most vast educational work on the internet.

"...wish you a great 2020..." That didn't age well...

All the best for 2020 Arthur & team. Amazing start this video .

I practice historically sword fighting because I know that one day I’ll be tapped to go back in time and I was sick of injuries in mma

Boy, October 2019 seems like such a wonderful time.

If time (from your perspective) stops when you reach the speed of light, then you can say the speed of light and the speed of time are the same thing. If I'm on a double-lane road and passing a car, if I match its speed exactly as I pull up to it, it will appear stationary to me. It's the same thing with light and time... while traveling at the cosmic speed limit, the difference between the velocity of light and the velocity of time is 0.

These are worth rewatching again and again.

I just assume that the universe self-censors time travel. Even if time travel becomes "theoretically" possible some day, any wannabe time travel inventor is going to become intimately familiar with Murphy's Law.

1:41 "and honestly we still don't really know" We know very very little and even some of those the important ones are being questioned often with facts that are disproving them .. Science is freaking awesome!

I invented time travel with a piece of string and two coconuts.

Nobody ever explained relativity to me the way you did at the beginning. Thanks, I'm gonna go learn more now. Awesome episode.

Finally, somebody advising me to add speed to my coffee, I knew it was the right thing to do.

Isaac, watch Netflix's _Dark_

Please do a spaceship checklist. This being the definition of spaceship followed by everything a spaceship should have like, engines, life support, fabrication, healthcare, communications, artificial gravity, shielding, hydroponics, etc... And also things you might want on a spaceship, like automation, holodecks, crew quarters, weapons etc...

Thank you my brilliant friend! Happy new year!

One of my favorite reads is the Harry Harrison Technicolor Time Machine, where a Hollywood film crew go back to the 10th century to make a historical movie about Vikings colonising North America - using real Vikings. Yet, it comes to pass that the ONLY reasons the Vikings went to Nth America was because a film crew showed up and paid them to do it. (A bottle of Jack Daniels per day)

I time travelled here from 2019. It was strange, it only took 24 hours to go from one year to the next... Crazy! 😵

I get what you're saying about wormholes, but I think the general idea of "instead of trying to move at speeds beyond 297000km/s, let's try to figure out other ways of getting from point A to point B before light would've done so" might prove to be far more useful.

Anybody else watching this in 2019?

I don’t know if it’s just me but I feel like your speech impediment is getting much better. If you look at older videos you are pronouncing your words much better! I’m glad for you! Also love your vids by the way, favorite RU-vidr by far

I remember that joke, it will have been good later

A fascinating notion that actual Mass "experience" time. I've never consider that surprisingly logical consequence of Einsteins relativity formula. This gives me a complete new perspective on reality, thank you for that.