Hacker News Reader

Comment by Malic | Hacker News Reader

This is somewhat related to a thought experiment of mine.

Suppose you had a means of transmitting information back in time - a one-node network that effectively could email to itself with a timestamp (in the past) being the message's "recipient."

Suppose such a thing existed in the world today. Assume the individuals in possession of such a thing were very intelligent, very careful and very guarded about its use.

Could you still detect that such a thing existed by observing real-world events - stock market changes, tech innovations, amazing coincidences and the like? What evidence would you look for?

View on HN

If you possessed such a device then errors in your "predictions" would be indicative of another party using a similar device. As such, I assume multiple parties would soon discover each other, engage in an incomprehensibly complex time-battle, and there would suddenly (instantaneously in all patched timelines) be only one such party.

Furthermore, I imagine it would be very easy for such a party to accidently blunder into a situation where they lose control of the time-messaging device, erasing all evidence of its own existence and leaving the timeline perturbation-free until such "time" as reverse time travel is rediscovered.

As a fan of time travel movies, I'd watch this.

Sounds like Dark.

Or an episodic series where every episode has a new main character inventing time travel and then accidentally destroying the conditions that allowed then to invent time travel.

You may like the anime Steins;Gate then. The plot is based on the idea of sending a small amount of information back in time and changing the sender's present, and then finds that another organization has been using this and is trying to control the world with the power.

Everyone in this thread should try Primer! Great little movie about a similar concept (smaller in scale though). Tries really hard to stick to its own rules.

It's approximately the plot of Primer

Future Diary has some pretty cool time battles. While it's not as good as death note, it definitely has it's moments. https://m.imdb.com/title/tt2069441/?ref_=m_nv_sr_1

In the book Singularity Sky [0], mankind invented the first time-looped computer, and it cycled up to a godlike overlord. After making a lot of very disruptive changes (which of course seem to be immediate to everyone else) it seems to have become surprisingly disinterested or uninvolved.

Anyway, it has only one hard "commandment": Nobody can violate causality anywhere inside its own historic light-cone, since doing so could be a potential attack (or competition) to its own existence.

[0] https://en.wikipedia.org/wiki/Singularity_Sky

Book was so much better than accelerando

Spoiler territory for Evan Currie's Hayden War Cycle Series ahead - which would deserve some spotlight and an editor for catching all the spelling mistakes both...

Anyways.

This is touched upon by a favorite sci-fi story of mine, where humans come in possession of such technology and make huge leaps in capabilities in short timeframes. Those leaps are unexplainable to most alien species they are in contact with.

Especially later on in the books a huge part of the story is told from alien POVs. The author has some interesting ideas about how other species may find us impressive, and in what respects they may consider us primitive.

The books are mostly about on-planet fighting and some ship-to-ship battles though. In fact there's little politics and communication at all until the cold-war arc. So don't expect the books to dive deeply into it at all.

But I really recommend the books just for how many interesting ideas Evan Currie managed to compress into a fast-paced action story. They left me with a lot of stuff to mull over long after putting the books down.

Also recoomend Evan currie

It depends dramatically on two things:

1. the type of time travel in effect. I'll assume Marvel-flavor time travel, where going back is really jumping to a different universe that shares the same history till the arrival time. But if it's something more complicated then relaying info back might Marty McFade the prognosticator out of existence.

2. the level of information available to the prognosticator (future communicator). Is it near-total, so they could tell the recipient to "duck… now!" or is it just public info like stock prices, weather, and what's on the news?

Best case for the recipient is that for each change they make, they still have an ally relaying valuable info from the future that includes those changes. And also that said ally has near-total information to help protect the recipient.

Worst case for the recipient is that after they make one change, they are now in a timeline where their future ally no longer communicates with them. This is also the most detectable for others in the recipient's time because the recipient will likely make some big bets based on the one-shot info they receive, and won't have additional info to help avoid detection.

To continue the thought experiment: if you developed that technology in the year 2120, how would you use it, and would that be detectable in the year 2020?

Sounds like a different anime to me. El Psy Kongroo.

Steins Gate is probably the closest answer to this (in which the time travel mechanism can only send back information) and is my favorite time travel mechanics system. Timelines diverge into their infinite possibilities but in self consistent ways. That is, some timelines can only exist as a result of information received from other timeline’s future; meaning the past is dependent on the future of a different timeline which won’t play out, but has added a sort of immutable constant to the first timeline.

It depends. If these are spherical rationalists in a vacuum, they’ll know what you know about how to detect it’s use and set their usage to the highest undetectable level. Having a time machine might make this trivial to achieve, depending only on if it’s possible to change the past in this model of time travel.

Time machines can be used as computers to reduce PSPACE (which includes NP) problems to constant time.

Is polynomial space something to assume every time traveler has?

Even ones without a TARDIS?

PSPACE[0] is a computational complexity class, not about topology ("larger on the inside").

Any timemachine that produces self-consistent timelines (arrives at a fixed point after a finite amount of iterations) can be used to solve problems in PSPACE.[1]

[0] https://en.wikipedia.org/wiki/PSPACE [1] https://www.scottaaronson.com/papers/ctc.pdf

A particularly clever member of the Twitterati: https://twitter.com/Theophite/status/1062816091892674561

@Theophite: the existence of nonzero interest rates implies the nonexistence of time travel.

I see what they did there but I don't know if I agree. The market can stay irrational for longer than it takes to invent time travel...

The whole point of time travel is that it doesn't care about time; once time travel exists in the future, people in the future will be able to do all kinds of fun arbitrage with it.

Maybe, look for "Butterfly effects[1]" happening around you, i.e., small insignificant events that have huge, enormous after-effects.

Essentially, if there were a system that could send information from the future to the past, the future agent would want to be "as discreet as" possible, while still achieving "nearly perfect" outcome. Note that the future agent has the advantage of reiterating over and over his/her choices, because, well, the "future-future" he/she can still send a signal to his/her past about want went wrong the previous time.

This happens to be a common plot for a lot of various time-travel movies and TV shows like Dark, Umbrella Academy, etc.

[1]https://en.wikipedia.org/wiki/Butterfly_effect

There's an Asimov short story called The Red Queen's Race which deals with this question: what if the ancient Greeks had received a few hints about modern chemistry? I won't spoil how it relates more directly to your question.

Mark Twain's A Connecticut Yankee in King Arthur's Court

the original isekai?

This plot is the basis of another (very good) anime called Steins;Gate actually.

Assuming it's a reasonably high-bandwidth channel, very careful and guarded use seems much more boring than bootstrapping the singularity. So, hopefully you can find them and supplant them.

You very much would want to keep it guarded until you have secured your goal.

Bootstrapping the singularity is unlikely to be achieved with a single application of a time machine since you are only sending information to the past, not the technology itself.

And repeated application allows other actors to intervene during each iteration, which may result in the CTC settling into a different fixed point than the desired one.

You can't expect to own and use a time machine and be left alone while doing so.

You can write all of the advancements off as luck, inspiration, or drugs and blend in until some brain scanning technology is invented that could find out that you're being disingenuous with high confidence. By then, the idea of time travel might not be that exotic. Maybe you send back a way to fool that technology and then it's a cat/mouse game.

A fun read where the "could you still detect" portion turns out to be a very important plot point: Thrice Upon a Time by James P Hogan (https://www.goodreads.com/book/show/849488.Thrice_Upon_a_Tim...)

I would search for people living a "perfect" life: no mistakes ever made, not a single cent lost to investment, not a single car key forgotten or an umbrella staying at home, absolutely nothing negative in their life. The more there are, the less the chance that pure luck is driving it, it must be a communication from the future.

This seems too easy, if the thought experiment played out with anyone remotely intelligent I would bet they would purposefully make 'mistakes' so as to not gain too much attention from a perfect track record.

I wonder, can they A/B test alternatives with that time machine ? Would they settle for a comfortable 'small' one time lottery winnings? Or try and create a dynasty for a longer lived family/institution. Also the person in the future, would they 'join' their new history ?

If allowed to send a message back in time any mistakes made by such a person could be fixed presumably. It would seem to me that you would have to detect that someone is playing with time, find out who that is and then capture them before they learn that you know and send a message back to kill you.

Well, not if you make a mistake that leads to you being unable to send a message back. That's part of the plot of a sci-fi story I read: there's a machine that does this, and the messages stop at a specific point in the future. (It's 'the Arrows of time' by Greg Egan. The Orthogonal trilogy is good stuff.)

I’m not an accountant but I’ve heard that accountants often use number frequencies to look for fraud. IIRC, amounts of money starting with 9 are less likely. Looking at those kinds of distributions in the world can maybe show influence of non normal factors.

Assuming the owner is smart and does not want anyone to detect that such a thing exists, then no one can. As soon as the owner feels that someone else knows, they will send a message back as a warning and tell themselves to be more careful.

That is very nearly the plot of Primer

Reply on news.ycombinator.com