A Romany fortune teller told me that I will live for another twenty-three years. (Given my present age, that is not bad.) However, despite her apparent certainty in this matter, I cannot be sure that I will live longer even than the next twenty-four hours. But of one thing I am certain. If I do survive for any length of time, then I will do so as a single spatiotemporally continuous self-conscious individual. In other words, there will be only one person tomorrow (or the day after) who will remember having been me today. Obvious, you might think.
But suppose that there were going to be two people, A and B, each equally possessing all of my memories and sense of identity. (Either I split in two or I am perfectly duplicated so that there is no detectable difference between the original and the duplicate.) Would it make sense for me now to ask, "Which will I be, A or B?" No. I would become both although neither would be the other. If A and B inhabit divergent parallel universes, then there is no problem whereas, if they coexist in the same universe, then some issues arise.
In Poul Anderson's Harvest Of Stars, the organic Kyra Davis living on Earth:
knows that her personality will be recorded and downloaded into an artificial neural network;
knows that, after the downloading, she will continue to live on Earth while at the same time a self-conscious artificial intelligence with her memories and sense of identity will begin an interstellar voyage;
illogically thinks that there is a fifty-fifty chance that she, the pre-download Kyra, will be the version of Kyra that remains on Earth, knowing that she has done something worthwhile by donating her download to an extra-solar colony.
There is not a fifty-fifty chance but a 100% certainty that the Kyra who is on Earth will be the version of Kyra that remains on Earth. However, the download in the spaceship remembers thinking that there was a fifty-fifty chance... She, the download, is not the one who did something worthwhile but the one who must fulfill the vow to remain in existence long enough to help found the extra-solar colony.
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There's a joke featured in a Roman-era book of humor, a dialogue between a sick man and his astrologer.
Man: what do the stars say?
Astrologer: Good news, best one! You will live another thirty years!
Man: Excellent, wise sage! I will pay you your fee tomorrow, and a bonus besides.
Astrologer: But best one... what if you die before morning?
Kaor, Mr. Stirling!
And that reminded me of how St. Augustine criticized the nonsense of astrology in his CONFESSIONS. I recall how he wrote about two landowners he knew who recorded everything on their estates, including even the birth of puppies, for casting horoscopes. And none of their laboriously calculated predictions came true!
Ad astra! Sean
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