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Quantum cats and time travel

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  • Quantum cats and time travel

    I was laying in bed last night trying to get to sleep and for some reason I was thinking about how time works (probably because of the determinism discussion with seer recently)

    And I started thinking about Schrodinger's cat.

    Basically you have a cat in a box along with some device that can randomly kill the cat or not. This makes the cat in superposition until someone opens the box to check, at which time the cat will be either alive or dead. But until someone checks, it is both alive and dead.

    Let's say there is a poison that could be released or not released at T=1. And the box is opened at T=10. Basically when you open the box the cat will be either alive or dead, but until you open it, it is both. This is a thought experiment about particles. So just imagine it works that way in the real world and you won't smell whether the cat is alive or dead.

    What I realized last night was that once you do look in the box and find out whether the cat is alive or dead, you not only fix that state when you look, but you also change the past and that was the state all along. Let's say you look and the cat is dead. Then, that means instead of the cat being both alive and dead from T=1 through T=10 it means that at T=1 the poison was released and the cat died at T=1, meaning it was actually dead the whole time. There was no superposition, because when you looked, you collapsed it all the way back to T=1. Knowing something in the future can change the past.

    So, thinking that can't be right, I did a search on google to see if anything like that really happens. I searched for "Schrodinger's cat change the past" and I found this:

    Can the past be changed by the FUTURE? Bizarre quantum experiment suggests time can run backwards
    https://www.dailymail.co.uk/sciencet...backwards.html

    I think what is happening is that at T=1 two new possible universes are created, one where the cat lives and one where the cat dies. You don't know which universe you are in until you open the box. If the cat is dead then you are in the universe where the poison was released at T=1, but if you open the box and the cat is alive, then you are in the universe where the poison was not released at T=1.







  • #2
    How in the world did you expect to sleep with all that going on in your head?

    I went to sleep mulling over the few facts that Kasha told me about last night, like, shrimp have their hearts in their heads, and, if you shave a guinea pig it looks like a hippopotamus!

    Mind boggling!


    Securely anchored to the Rock amid every storm of trial, testing or tribulation.

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    • #3
      There's a long intellectual history to what you might call quantum retrocausality, where how we measure something in the present appears to determine how the system behaved in the past. It was first proposed as a thought experiment back in the 1970s, and lots of labs have now performed variants on it.

      This is probably where to start if you want to find out more about it:
      https://en.wikipedia.org/wiki/Wheele...ice_experiment
      "Any sufficiently advanced stupidity is indistinguishable from trolling."

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      • #4
        Originally posted by TheLurch View Post
        There's a long intellectual history to what you might call quantum retrocausality, where how we measure something in the present appears to determine how the system behaved in the past. It was first proposed as a thought experiment back in the 1970s, and lots of labs have now performed variants on it.

        This is probably where to start if you want to find out more about it:
        https://en.wikipedia.org/wiki/Wheele...ice_experiment
        FWIU, something like this has also figured into some religious/philosophical discussions over the nature of the Fall and it's consequences reverberating backward through time to explain all of the death on an old earth.

        I'm not a fan of it but then physics is not my thing.

        I'm always still in trouble again

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        • #5
          Originally posted by mossrose View Post
          How in the world did you expect to sleep with all that going on in your head?

          I went to sleep mulling over the few facts that Kasha told me about last night, like, shrimp have their hearts in their heads, and, if you shave a guinea pig it looks like a hippopotamus!

          Mind boggling!
          This is probably why I don't sleep well at night. I usually wake up at 3 or 4 in the morning and can't get back to sleep because my mind starts churning.

          After the cat thing I started thinking about the double slit experiment. Where a single photon or electron is shot at a screen with two slits on to a second screen. If the scientists don't measure which slit the photon goes through, it creates an interference pattern on the 2nd screen, meaning it went through both slits. But if they watch the photon then it only goes through one slot or the other. It is similar to the cat experiment.

          My question is, why doesn't the 2nd screen that registers where the electron or photon hits act as a detector and collapse the interference pattern? If putting a detector on the slits will change the outcome to one slit or another, why doesn't the screen that the light is shining on do the same? After all, it should just light up behind whichever slit the electron went through and therefore detect which slot it went through. But instead it shows an interference pattern until you detect the photon/electron at the slit itself.



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          • #6
            Originally posted by Sparko View Post

            This is probably why I don't sleep well at night. I usually wake up at 3 or 4 in the morning and can't get back to sleep because my mind starts churning.

            After the cat thing I started thinking about the double slit experiment. Where a single photon or electron is shot at a screen with two slits on to a second screen. If the scientists don't measure which slit the photon goes through, it creates an interference pattern on the 2nd screen, meaning it went through both slits. But if they watch the photon then it only goes through one slot or the other. It is similar to the cat experiment.

            My question is, why doesn't the 2nd screen that registers where the electron or photon hits act as a detector and collapse the interference pattern? If putting a detector on the slits will change the outcome to one slit or another, why doesn't the screen that the light is shining on do the same? After all, it should just light up behind whichever slit the electron went through and therefore detect which slot it went through. But instead it shows an interference pattern until you detect the photon/electron at the slit itself.
            Let me give this a try. Someone i've worked with was fond of saying that quantum objects move like waves, and impact like particles. So, while an item is in motion, it can create an interference pattern, including with itself. But to detect it, we need it to hit something (the detector), so it will behave like a particle.

            If we're checking at the slits to see which way the item goes, then it's hitting a detector at the slits—it behaves like a particle there, and so the formation of the interference pattern, which takes place beyond the slits, would happen after it's already a particle. If we're only sensing it further on, it has time to continue traveling as a wave, and form the interference pattern. It still hits the screen as a single particle, but the location of where it hits has already been influenced by its time traveling as a wave by that point.

            (It helps to remember that each individual item still only hits in one place, and the interference pattern is only apparent when we track the arrival of lots of individual particles.)
            "Any sufficiently advanced stupidity is indistinguishable from trolling."

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