Time Travel

Is time travel possible, and if it is, what sort of civilizations would result? We'll explore the science that might permit it as well as the classic science fiction examples to see if they make sense.

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Credits:
Time Travel
Episode 219, Season 6 E01

Written by:
Isaac Arthur

Editors
Darius Said
Jerry Guern
Keith Blockus
Victoria Kelly

Cover Art:

Graphics:

Produced & Narrated by:
Isaac Arthur

Music:

[DavidFMayerPhD]

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

[cassesvultus]

...and the bartender said, "we don't serve faster than light particles here."

A tachyon walked into a bar...

[raven]

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

[dyanreoliveira]

“Let me wish you an excellent 2020“

Well this aged like fine milk

[robertgriffin]

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

[whatsupinspace]

_"In relativity time is flat in the same way that planets are flat, in that they're not"_

I really love Isaac's videos

[lenin]

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

[TalkingAboutYooh]

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."

[Draecko]

...turned out none of you liked it.


We must be on a seperate time branch then.

[Mustachioed_Mollusk]

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

[svartsmurf]

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.

[Wolfphototech]

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

[MarcLombart]

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

[happyhammer]

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

[TheNoodlyAppendage]

There are two problems with time traveller meetups. The same guy keeps coming back to eat all the chips, sp I have to go back in time to get some chips. The other is that they are usually spontaneous with a very narrow window between a fixed decision to have the meeting and the actual meeting itself. One must travel to the window between the final decision on the place and time and the time when it actually happens. If you travel to before the decision is made, the butterfly effect can change the time and location. and After the meeting its obviously not going to get you to the meeting. So if you have a machine that has some error rate, of say +/- a week, you can easily miss any meeting with less than a 2 week window.

[Mr.Nichan]

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).

[nottheguru]

...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.

[diablominero]

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

[TSelNiNO]

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

[ckingpro]

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