6 years ago, an event changed my life, in the bad sense. I exactly know what event it is, and how I could fix it. I decided that it would be a good idea to make a "Dear Selfpast" note, or a "Note to my past me". I know that changing the event will change my entire life, all the ideas, all I have learned, everything, but... If I could send the note to myself in the past, I would change, and then there is no need to, in the future, write a note, so I don't receive any note in the past, and it keeps looping. But I know that if I could keep the document in the past, there will not be any loophole, and I finally changed myself. How do I keep that note in the past, without entering a loophole?

EDIT: John Robinson's answer gets what I want more than AndreiROM's one, but it is still well worked. I got lost in Andrei's answer. Before accepting an answer, is there a way that I don't need to get involved in a loop, like not creating multiple parallel universes or not having to include the "send this to your past you" in a message. If there isn't, i think i will accept John's answer, it is clear and direct.

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    $\begingroup$ If this question were answered to your satisfaction, it would never have been asked. $\endgroup$ – Mikey Mar 1 '16 at 20:39
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    $\begingroup$ This is an example of the classic "grandfather paradox" problem with time travel. A future event causes a past event to not occur, but the past event was the cause of the future event, so the future event never happens. Time travel is tricky. $\endgroup$ – fiend Mar 1 '16 at 20:42
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    $\begingroup$ It may be worth your time to search the Worldbuilding Stack Exchange for "grandfather paradox." The question you have is a very famous question. In fact, it is probably the single most influential time traveling question ever conceived. As such, it has dozens of solutions, depending on the exact formulation of your time travel rules (for example, there are rules which make it impossible for such a loophole to occur, while others resolve it after it happens). A search should get you in touch with many of these solutions. $\endgroup$ – Cort Ammon Mar 1 '16 at 21:32
  • $\begingroup$ It seems pretty obvious to me. Just write a new note that says the exact same thing and send it back. That way, no time ending paradox will occur, and you don't eventually end up with a note so tattered and torn that it is no longer recognizable. $\endgroup$ – Xandar The Zenon Mar 2 '16 at 4:55

In the note, tell your past self's future self to send an identical note to their past self.

"Dear Past TheCrimulo,

This letter was written by you from the future. [Insert proof of who you are]. You need to avoid [place and time of the event]. Also, send this to your past self in order to prevent a universe-ending paradox.

Sincerely, Future TheCrimulo."


Avoiding the Paradox

Quite simply, the laws of the universe allow for theoretical travel to the future (by travelling faster than the speed of light time passes "slower" for you than for the outside world), but not to the past.

If you found a way to send something to the past, you would most likely actually be sending it to a similar, but parallel universe at a point in "time" equivalent to your universe's past. Even if a parallel universe had not previously existed, the very fact that you meddled with space time would cause that parallel universe to come into existence.

What that means is that the parallel you would be warned of a very likely negative event in the future, and would - we assume - take action to avoid it. I say a likely negative event because as similar as those parallel universes would be you cannot guarantee that your interference will not set other events off which will result in other, worse, or better outcomes.

Thus, his future would be different. But not yours.

This is why no loophole is created.

The Show Must Go On

However, if your present self isn't reaping the benefit of this effort why bother sending a message in the first place? What's his motivation?

This is where you, as the author, get to have some fun.

Let us assume that the second that message is send to the past a similar, but parallel universe is created - instantiated at that point in time at which the note was "aimed" at.

That universe had potentially existed all along, however your act of sending an item there has caused it to "come into focus", shall we say.

You now shift the story from Universe #1 to Universe #2. You make a note that the original character (Protagonist #1) sent a number of messages to the "past", not realizing that each time he was doing so he was "instantiating" a new parallel universe, and wreaking havoc in space time continuum. He never saw any results, and eventually gave up, assuming that his technology doesn't work, and not realizing its effects. He had basically spammed several parallel universes with various consequences.

However, you choose to focus on Protagonist #2. He gets the message, figures out its significance, and maybe even makes a note that he should send a message to himself in the past in order to avoid the incident altogether again - making the same flaw in his assumptions as Protagonist #1, and also ending up spamming the multiverse.

Your story can then continue in Universe #2.

  • $\begingroup$ I really appreciate the elaborated question, while this doesn't solve my problem, because I need it to affect and change the future of the person who wrote the note. Anyways in the other questions, there would still be a loop, only that instead of recieving/not the note, having to promise you will send it to the past and I have to copy it. I still have learnt something from the questions, I will find for the Grandfather Paradox. Thanks $\endgroup$ – TheCrimulo Mar 1 '16 at 21:46

Well, there's the obvious solution. Have the last line be "oh, and remember to send this note to yourself in the past, trust me". Presumably if you believe future you on the rest of it, then you'll believe you should send yourself the note.


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