scrape_r_rational/data/cache/2u764c.md

[D] Time travel? Could you convince yourself?

Post:

You've found a time machine. It can't go forward in time, only backward, but you can return to your departure date once you're done in the past. A constraint of the time machine is that, upon arrival, you have 24 hours to find your past self and convince them of the fact that you are THEM from the future. If you can't, then you fade from existence.

How would you convince yourself of the truth? Do you think you could? Also for the sake of the argument, the "judge" of this isn't a machine that can be gamed, it's an intelligence that can't be lied to. (So no convincing your past self to "play along" if they're disbelieving)

EDIT: Let's say you have to leave right now, as you are. So no researching a meticulous list of future events and rattling them off (unless you're lucky enough to have an eidetic memory, so have said list prepared already in your head)

Comments:

• u/TheStevenZubinator:

  I have a password system in place that only I know just in case something like this happens. I could be convinced in 10 seconds.
  

  • u/eaglejarl:

    As with the others, I've also had a password in place for years, in case I ever need to convince myself that no, really, this particular me is a time traveler / clone / alternate universe copy. 
    
    I find it hilarious that there are not one but *several* people on this board for whom this was the instant answer. "Well, yeah, of course I have a password for that...doesn't everyone?"
    

    • u/alexanderwales:

      I don't have a system like that in place, mostly because I feel that it leaves me too vulnerable to mind readers. And really, mind reading seems a lot more feasible than time travel.
      

      • u/eaglejarl:

        It's easy to distinguish between a mind reader and a time traveler: a time traveler can make correct and statistically unlikely predictions about the future, a mind reader can't. 
        
        Now, an all-up telepath who can write to your mind as well as read it...then you're just screwed. You can't trust reality at all, they know your every plan and trick...I don't think that's a winnable fight.
        

        • u/None:

          A time traveler might not be able to make those predictions though, consider that just his traveling back would begin a chain reaction of alternate circumstances which would make it more and more difficult for him to predict accurately as time goes on.
          

          • u/eaglejarl:

            Yes, but he should be able to make SOME predictions, for a little while, before the butterfly effect gets too big. Those might be small things -- "tomorrow, Sally is going to ask you to prom" or "Thursday, 12:08pm, Billy will fall off his bike and skin his left knee" -- but they can still be verified. 
            
            Once you've verified them and both of yourselves are working together, there are plenty of ways to take advantage.
            

            • u/alexanderwales:

              The best bet would probably be to look up old transcripts of CNN broadcasts and memorize them, then quote them back a few minutes ahead of it showing on television. That would still be *really* easy to fake compared to creating a physical duplicate of a person or reading their mind, but it seems like it would be your best bet if you want a demonstration of predictive power.
              
              If someone told me "they're going to crash a plane into the Twin Towers" and then I saw it happen the next morning, my first thought wouldn't be that they were a time traveler, it would be that they were somehow involved in the plot.
              
              So you need statistically unlikely predictions about the future that the supposed time traveler couldn't have foreknowledge of, and couldn't fake, which is a pretty tall order.
              

              • u/STL:

                Supernovae, earthquakes, etc.
                

                • u/derefr:

                  Does NIST use an isolated atomic-decay source (like those in atomic clocks) for the random numbers it publishes on the hour? I'm not sure whether just showing up from the future would cause enough of a "ripple" in gravity or anything else to throw off such a source if it was out on a satellite or something, but if it wouldn't, that's all you need to know.
                  

              • u/cae_jones:

                This is why I specifically memorize natural disasters instead of geopolitical events. I usually plan for mental timetravel, but they'd still come in handy if James Randy decides that being the best predicter of storms/earthquakes/tsunamis ever is worth a million dollars.
                

      • u/ancientcampus:

        Can I just say that this post pretty much sums up this forum in a nutshell.
        

    • u/None:

      But how to differentiate between a time traveler and a clone?
      

      • u/eaglejarl:

        I'm willing to trust myself to the extent that, once I have given me the password I will believe me about what my weirdness-type is (clone, time traveler, etc)  -- at least until I see evidence otherwise.
        

        • u/ancientcampus:

          Ah, but if you lived in a literary-trope-filled universe (if you're meeting a time traveling version of yourself, don't rule it out! :P ) then a clone is far more likely to be evil or at least somehow subverted, than it is to be a true clone (rationalist fiction tropes notwithstanding)
          

  • u/scruiser:

    I have had a password system since high school (about 7 years ago).  I think it was a TvTropes page that inspired me.  I have multiple passwords and I have planned how many of them I will give to other people if I need to let myself know to trust them.  Thus I could also use them if other people are traveling back in time, or in the event of a memory gambit.  I also remembered the events that made me think of each password, so if I travel to an alternate reality I can guess at how likely it is for me to have the same password.
    
    > 24 hours to find your past self and convince them of the fact that you are THEM from the future.
    
    24 hours is like easy mode.
    

  • u/JackStargazer:

    Doesn't everyone?
    
    Seriously, it takes maybe 5 minutes.
    

  • u/itisike:

    How likely do you think this is that you spent time setting it up?
    

  • u/Kishoto:

    That's hilarious. I'm in a business meeting and you almost made me break character here.
    

  • u/Draconomial:

    I've had a password system to time travel/elder clone self introduction since I was seven years old. I had this paranoia that I was the only real human, and was really floating in a tube with my dreamed life being someone else's entertainment. There's a word for that.
    

    • u/Arandur:

      Solipsism.
      

    • u/notmy2ndopinion:

      I overcame solipsism when I realized I was too stupid to make up some of the world... and too smart to create some of the stupidity.
      
      I think a similar concept without invoking narcissistic qualities is post-positivism.  You can't KNOW the full truth, only disprove theories (and this whole exercise asks: how can you disprove that other people aren't just p-zombies or that the duplicate of me is a time traveler from the future?)
      

• u/IHaveNoTact:

  Doesn't everybody remember enough specific details about their childhood that nobody could remotely copy them?  Seriously I could list very detailed random shit and convince myself in under half an hour anytime after age 11 or 12.  Even if someone could have known a specific detail or three (depending on the date chosen), nobody could get them all.  Even my wife who has heard all of my stories.
  

• u/alexanderwales:

  You'd have to define "convince". I think it would be hard to convince myself, mostly because the situation sounds insane, and I would keep coming up with alternate hypotheses that also fit the evidence. There are a lot of advanced technologies that would explain someone who looks like me better than time travel. And my double saying that I have to be convinced would read as the setup for being taken advantage of, not to mention fairly nonsensical. Not to mention that he wouldn't be able to predict the future very accurately due to my poor (mostly outsourced) memory.
  

  • u/Kishoto:

    This is along the lines of what I was thinking. I feel like because of my hard belief in time travel being impossible, I wouldn't be able to convince myself in 24 hours. I think I'd posit too many alternate theories.
    
    E.g The government found a lookalike, plastic surgeried him into resembling me, and is attempting some sort of plan that involves my believing said lookalike is me from the future. In addition, barring eidetics, memory's more fluid than most people realize. There's no guarantee that I'll have the exact same memories as my past self. Not enough to break my disbelief in time travel anyway. Not in 24 hours.
    

• u/stalris:

  DNA test?
  
  It would kind of depend on the situation. Is my past self old enough to understand the concept of time travel? Would it it be easier to convince a child that I am him from the future and satisfy the condition?
  
  I'd go with a maybe.
  

  • u/itisike:

    You have so few secrets that you need a *DNA test* to convince yourself?
    

• u/clawclawbite:

  I don't have a password system, but I do have passwords. Anything in the past 20 years and iI should be able to login someplace to demonstrate
  

• u/thakil:

  If a person who looked extremely similar to me, but older, who had the same memories as me up to that point, and could probably give me a good description of how the next month will go, and can remember every secret I have turned up? I'd probably believe they were either a time traveller or a godlike deity who was messing with me, and probably go with the former for simplicity. So no, not particularly difficult.
  

• u/lsparrish:

  In light of the edit, I'm not sure what I'm supposed to convince myself of. I don't remember a future me visiting, so this version of me is a slightly different person, one that got a visitor from the future. I could probably convince them that we have an identical past, using passwords and so forth, but does that make me actually them, in the sense needed for the experiment?
  

  • u/Kishoto:

    I suppose it depends on how time travel would actually work. I've always liked the divergence theory. The one that states that, when you travel back in time, you create an alternate timeline at that exact moment. So the future you wouldn't remember the meeting.
    

• u/nevinera:

  I assume it's reusable? Then I'd think of a serious password, wait 20 minutes, visit past-me just after he thought of the password, and then give it to him. Now he is (and I am) convinced of time travel, so I can use it arbitrarily in the future to visit my past at any point *after* that time, an extremely powerful tool.
  
  Sure, being able to visit arbitrary points before that would be *more* useful, but you were already time-limited by your birth, this just moves that limit forward a ways, while allowing you safety from the Great Fade.
  
  I am a little curious though - what is the definition of 'convinced'? A rational person ought to be convinced in some degree by various unlikely events, but the prior probability of time travel of that type existing and *not* having already thrown the world into significant disarray is significantly low. I can't imagine *any* evidence that would be sufficient to make me believe with *no doubts* that this other me is just future-me.
  

  • u/nevinera:

    If we need to stick to the spirit of the question and visit myself from well before receiving the machine, then I'm going to assume that 'convinced' means "assigns more than 50% probability to".
    
    In that case I wouldn't attempt to use the machine, because I can't realistically be more than about 95% confident that I could convince myself of something like that, and my life is already decent enough that a 5% chance of death isn't worth any improvement I can picture achieving via time travel.
    
    Even if I succeed in convincing past-me, I still have to interact with my past and produce a net-positive outcome for it to be worth *anything*, let alone a 5% chance of death.. and I am very *very* far from convinced that I can manipulate time with that kind of accuracy.
    

• u/Evilness42:

  I have a password system, but it isn't really developed yet, and I can't remember a couple of them, so if any of them are stolen I'm stuck. The only ones I remember are the ones for 'Yes, this is you,' and the one for 'Don't trust this guy.' 
  
  I'm feeling slightly paranoid about the fact that I can't remember 'Run Away!!!!', 'Play along for now, then run away,' and I really think I *should* remember those. It's important, you see. 
  
  Of course, a system like this isn't proof against Telepathy, but then, what is? Damn those Telepaths.
  

• u/E-o_o-3:

  Even if a doppleganger fould be found, I don't think most people would replicate birthmarks and scars for a joke. I'd believe *something* weird was happening, and time travel would be high enough on the list of options even before I did any "convincing". 
  
  >If you can't, then you fade from existence.
  
  You know, that's .... *scary*? But, at the same time, I do have a back up copy of me, and I've sufficiently dissolved the philosophical weirdness surrounding "souls" and "continuity of self" this to be *okay* with it even if not particularly happy about it. My level of unhappiness would *mostly* be a function of the number of memories lost - the little extra dollop of angst from the breaking of continuity, while significant, wouldn't be nearly as bad as *really* dying.
  
  (Or do they have to go through the same time machine?)
  

• u/notmy2ndopinion:

  Wouldn't your future self just remember your present self in this circumstance and just repeat exactly what it took to convince yourself?
  
  And since it didn't happen right now, doesn't that mean that future you just failed?
  

  • u/Kishoto:

    I posit forking timelines. So no :P
    

• u/Jace_MacLeod:

  If my future self could name the master passwords I use for password databases and various devices, I'd be pretty convinced. Current me would reason that either they are from the future, or have access to sufficiently advanced decryption and hacking technology as to be rather dangerous. Either way, current me would want such a person on his side.
  

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