Of course you are right: there is no way to distinguish the original from the copy, given that the copying process works as intended. And if you believe that everything possible exists, then there will always be at least one version of you who will definitely experience whatever outcome you are leaving to chance. Probability is just a first person experience of a universe which is in fact completely deterministic, because we cannot access the parallel worlds where our copies live, and because even if we could, we can only experience being one person at a time.

--Stathis Papaioannou

Bruno Marchal writes:

You made your point. Let me give you an argument showing (incorrectly) that the notion of probability is not applicable in the duplication situations. I let you find where is the error. The argument is of course (*) a thought experiment and I present it through an imaginary story. In the "copy and the chair" you reverse the situation. Here I show it to be completely arbitrary.

It is the story of my friend Jack. Jack is a computationalist practitioner, and he is also fond of the planet Mars. Unfortunately he married Jeanne who was anti computationalist. Nevertheless he promised to never leave her. And Jack is as honest as possible. Today, classical teleportation and duplication were common, but Jeanne just believes that those who are reconstituted are sort of "impostors", and that each time an "original" is scanned and annihilated, well, he just dye. One day Jack, who is a little bit tired arguing with Jeanne, found a proposition for a nice Job on Mars. He decides to duplicate itself, by being scanned, and then send on Mars and be reconstituted on it. All this without annihilation of the original, so as to be able not feeling guilty in front of Jeanne, and hurt her feeling in case she would know. Jack, who bet on comp, thought that he has a chance of 1/2 to "be the one who will enjoy working on Mars" After having done the experience. Jack-original was a little bit sad. Jack-1, the copy, was delighted: it has worked! Soon after, his news paper was offering even more jobs on Mars, actually 64 jobs. He decided to reiterate the "copy and paste" (no cut) 64 times. He thought that the probability he remains the original was 1/2^64 (= about 1/1,84 10^19) so that he would be rather unlucky to be the one feeling remaining the original! But as tautologies are tautologies, the original remains the original, so he was, as a computationalist, quite astonished failing again. He did even begin to doubt comp. On Mars, Jack-2, Jack-3, ..., Jack-65 were delighted and were thinking that they knew that trick could hardly fail! And then new jobs on Mars were still offered, dirty dangerous one. Jack (who is Jack-0) was beginning to doubt comp, and was thinking that Jeanne was perhaps right about the reconstituted people being "other". Still, its relation with Jeanne were bad enough he really wants to leave her, and its frustration not being on Mars was growing and growing. And perhaps Jack was not so honest, and he makes up the following plan: "I will just LET THE ORIGINAL GO ON MARS". And Jack promises to himself that, would he acknowledge to be the copy, he would stay with Jeanne. He even decides to delay the reconstitution, following that anti-comp superstition that being scanned, and reconstituted with a delay makes you sure to remain the original. So he scanned himself, with a program activating the reconstitution with a delay of one hour (say), and then, he was going on MARS, by usual 2 years trip by rocket (he was doubting! Note the irony here: he feels to leave Jeanne at the time he feels to get her point! ). You can imagine the disappointment of the copy on earth. "What! it fails again! Come on Please! Will I ever successfully quit earth? Jeanne did not see Jack was a copy, and Jack did not despair finding a way to go on mars, letting a copy or "an original" of him with Jeanne. In new attempts, he decides to select the one among copy/oiginal with a coin, among the original and the copy. It failed! He decides to use the decimal of PI written in binary as selector. It failed! He decides to use ieratively a quantum OR gate making the decision "arbitrarily sure": it still failed! This explains why my friend Jack was rather depressed the last time I saw him. Obviously, anyone on Earth will find eself with a necessarily disappointed "Jack", given that from our point of view the tautology alluded above is now: "the one who has been chosen to stay on Earth will have with certainty the experience of staying on Earth". For any strategy of choice (original/copy) we could suggest to Jack, we know, that the "Jack" who will stay on earth and come back to the bar will say: "it failed".
That day in the bar, my friend Jack was feeling being incredibly unlucky.
Was he right?


(*) Those who believe that we cannot argue or prove proposition through thought experiment can read the mathematical part of my SANE paper where I show how to translate similar argument in arithmetic and/or computer science. In SANE I say that I substitute the FOLK or GRAND-MOTHER psychology (of the philosopher of mind) by a self-referentially correct (universal) machine (correct with respect to provability and inductive inference).


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