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Science

Reimagining of Schrodinger's Cat Breaks Quantum Mechanics -- and Stumps Physicists (nature.com) 273

In a multi-'cat' experiment, the textbook interpretation of quantum theory seems to lead to contradictory pictures of reality, physicists claim. New submitter Lanodonal shares a report: In the world's most famous thought experiment, physicist Erwin Schrodinger described how a cat in a box could be in an uncertain predicament. The peculiar rules of quantum theory meant that it could be both dead and alive, until the box was opened and the cat's state measured. Now, two physicists have devised a modern version of the paradox by replacing the cat with a physicist doing experiments -- with shocking implications.

Quantum theory has a long history of thought experiments, and in most cases these are used to point to weaknesses in various interpretations of quantum mechanics. But the latest version, which involves multiple players, is unusual: it shows that if the standard interpretation of quantum mechanics is correct, then different experimenters can reach opposite conclusions about what the physicist in the box has measured. This means that quantum theory contradicts itself.

The conceptual experiment has been debated with gusto in physics circles for more than two years -- and has left most researchers stumped, even in a field accustomed to weird concepts. "I think this is a whole new level of weirdness," says Matthew Leifer, a theoretical physicist at Chapman University in Orange, California. The authors, Daniela Frauchiger and Renato Renner of the Swiss Federal Institute of Technology (ETH) in Zurich, posted their first version of the argument online in April 2016. The final paper [PDF] appears in Nature Communications on 18 September.

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Reimagining of Schrodinger's Cat Breaks Quantum Mechanics -- and Stumps Physicists

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  • by Dwedit ( 232252 ) on Wednesday September 19, 2018 @02:32PM (#57343816) Homepage

    two physicists have devised a modern version of the paradox by replacing the cat with a physicist doing experiments -- with shocking implications.

    Is this just another way of saying "Number 7 will shock you!"

  • by lamer01 ( 1097759 ) on Wednesday September 19, 2018 @02:36PM (#57343836)
    Aren't the physicists in the box collapsing the function already by observing the coin? Unless we are saying that the system would behave like nested functions where the internal function collapses when the internal observation is made and a secondary function that includes the 1st one as a variable also collapses when the external observer performs their observation.
    • Re: (Score:3, Interesting)

      Yeah, this isn’t so much a quantum mechanics problem as an illustration of how journalists, bloggers, and the like can fall into the trap of thinking understanding some extremely simplified model of something means they also understand the complex underlying system.*

      In the end it’s a nonsensical self-contradiction by definition; sort of like when you were an 8-year-old kid and became fascinated with the conundrum “Can an omnipotent God make a stone too big for him to lift?”

      * Like put

      • Luckily the 8 year old kid successfully uses that thought experiment to correctly conclude that God is just an imaginary concept, and a self-inconsistent one at that.
  • by Zorro ( 15797 ) on Wednesday September 19, 2018 @02:39PM (#57343850)

    We replaced the cat with Folgers Crystals. Let’s see if anyone notices.

  • by fahrbot-bot ( 874524 ) on Wednesday September 19, 2018 @02:39PM (#57343854)

    In the world's most famous thought experiment, physicist Erwin Schrodinger described how a cat in a box could be in an uncertain predicament.

    Compared to the second most famous, but ironically similar: "Does this dress make me look fat?"

    Where your relationship is also in an "uncertain predicament" -- being both dead and alive -- until the question is answered.

    • In the world's most famous thought experiment, physicist Erwin Schrodinger described how a cat in a box could be in an uncertain predicament.

      Compared to the second most famous, but ironically similar: "Does this dress make me look fat?"

      Where your relationship is also in an "uncertain predicament" -- being both dead and alive -- until the question is answered.

      Even though the right answer is diametrically opposite, this is equivalent to the question: "Would you take a bullet for me?"

      Interestingly, it's not enough to just answer the question correctly. The person answering the question also needs to do so within milliseconds of it being asked. So even the timing of the answer leads to it's own uncertainty.

      • >>> "Does this dress make me look fat?"
        There's only one valid answer to this question:
        "You look marvelous, darling. Would you like to go to dinner?"

        You get reassurance, followed by a quick change of subject before she realizes that you haven't answered the question. But it only works once...

    • "Does this dress make me look fat?"
      If you are fat: yes!

    • > "Does this dress make me look fat?"

      The *correct* answer is:

      I love you regardless of how you look.

      One of the many counter-examples that truth is NOT binary.

      The other classic is:

      Have you stopped beating your wife?

      Again the correct answer is:

      Mu. The question is invalid -- you are presupposing existing conditions that never existed. How do you stop something when you never started it in the first place???

      • "Does this dress make me look fat?"
        The *correct* answer is: I love you regardless of how you look.

        You realize that means "yes" - right? :-)

      • by djinn6 ( 1868030 )

        The other classic is:

        Have you stopped beating your wife?

        Actually the answer is no. "Stopped beating" described a transition from "beating" to "not beating". Since "beating" never occurred, the transition never occurred either.

      • by quenda ( 644621 )

        The *correct* answer is:

        I love you regardless of how you look.

        You are not married, are you?
        The correct answer is "no". This is the least bad answer. Do not elaborate. There is no good answer.
        A possible alternative is to pretend not to hear, mumble an excuse, and run away.

        • The least bad answer is to avoid the question altogether and answer something along the lines of "I like $her_favorite_dress better".

          Or, if you're horny, "I'd prefer you to not wear anything right now..."

        • by Cederic ( 9623 )

          The correct answer is, "Why the fuck would you ask me a question the answer to which is guaranteed to piss you off? Just fucking yell at me already."

    • No... in this case your relationship is alive until the question is answered, when it certainly dies no matter what you answer.

  • Comment removed (Score:5, Interesting)

    by account_deleted ( 4530225 ) on Wednesday September 19, 2018 @02:41PM (#57343860)
    Comment removed based on user account deletion
    • What we do know is that quantum mechanics works. It is one of the most successful theories of the physical universe that humanity has ever devised.

  • ...but only if you believe in it, like Tinkerbell.

    Finally the ultimate class separation, into those who can believe in magic and those who cannot.

  • I never understood how it should work when the cat is a conscious observer anyway.

    • by lgw ( 121541 ) on Wednesday September 19, 2018 @03:16PM (#57344046) Journal

      "Conscious observer" has nothing to do with it. The Geiger counter rigged to the poison is the observer that collapses the wave state.

    • Observation / interaction have NOTHING to do with being conscious. It could be a rock and a can of spray paint.

  • If scientists can't agree on this will it be a cat fight.

  • by dlleigh ( 313922 ) on Wednesday September 19, 2018 @03:02PM (#57343968)

    Most physicists don't give much credence to the Copenhagen Interpretation. There are better ways to think about quantum mechanics.

    https://en.wikipedia.org/wiki/... [wikipedia.org]

    • Still has credence (Score:4, Informative)

      by aepervius ( 535155 ) on Wednesday September 19, 2018 @05:30PM (#57344884)
      The mathematical equation are still used. What your itnerpret them as MW, copenhagen wave collapse , or angel on a pin is pretty much unfalsifiable. Among my colleague copenhagen is still the majorly used interpretation , just look at QM article they speak of measurement and collapse. Not other world or angel on a pin.
      • Exactly. Every interpretation is just a way for dumb monkeys to try to visualize something that inherently can't be conceptualized in terms of our experience. All of them are consistent with the maths, therefore all of them are as 'correct' as each other.

        Schrodinger's cat was just an illustration, using the Copenhagen interpretation, that quantum maths can't be extended to the macro world, and that somewhere in the transition from quantum to macro, there must be an increasing level of certainty embedded

    • by novakyu ( 636495 ) <novakyu@novakyu.net> on Wednesday September 19, 2018 @06:14PM (#57345064) Homepage

      Do you not know how to read? Read the actual link you linked to; there is basically one person who claims this orthodox interpretation is "now widely felt to be unacceptable." Given how wrong Einstein turned out to be about quantum mechanics, it wouldn't be surprising at all if this one Nobel laureate also turned out to be wrong.

      The farthest you can go (and not be laughably wrong) is that there is broad consensus that there is something to be fixed in Copenhagen interpretation—but there is no other interpretation that is more broadly accepted than Copenhagen interpretation.

  • It is a cat.

    When the cat wants to be in the box, it is in the box.

    When it wants to be out of the box, it is out of the box.

    Death of cats is expressly prohibited under the Rules of War.

    Now, parrots or songbirds, those are ok.

  • Missing the point. (Score:4, Interesting)

    by J. T. MacLeod ( 111094 ) on Wednesday September 19, 2018 @03:14PM (#57344030)

    Schrödinger's point about the cat thought experiment is that that cat is NOT in two separate states at the same time. That was his expressing his aggravation about the contradiction of the results of his work and reality.

    The question remains, "How does potential get resolved?"

  • This just seems like a reiteration of the Many world interpretation?

    https://en.wikipedia.org/wiki/... [wikipedia.org]

  • So is this more scientists arguing about the 2&3 polarizing filter Bell's theorem example?
    You know the one where 2 linear filters at 90 block a photon 100% of the time but if you add a third filter in between the two at 45 they all block the photon ~47% of the time?
    Like is this a Local Realism thing?
    Or is this more of a "what constitutes an observer" question?
  • ... different experimenters can reach opposite conclusions about what the physicist in the box has measured.

    Einstein introduced us to the fact that the universe can appear very different from different points of view. For example, if explosions of supernova "A" and supernova "B" occur, it may be observed that "A" occurred before "B", or that "B" occurred before "A", depending on where the observation was made. Either observation is equally valid, even though the conclusions are logically opposite.

    Once one accepts the notion that physical observations are "relative", why is it so shocking that quantum mechanical

  • I thought the purpose of Schrodinger's cat thought experiment was to illustrate the absurdity of the Copenhagen interpretation. So, now the new thought experiment is again reinforcing original thought experiment... that you can have two different conclusions?
  • It seems to me that much of the 'weirdness' of quantum physics comes from the complexity of mathematics that are meant to allow for a possible range of unknown values (aka probability fields).

    So, what I've never been able to understand is this. Just because we are unable to know both the position and speed of a particle, why is there an assumption made that the particle doesn't have both a position and speed?

    I guess the point is it seems like most of the 'weirdness' stems from the assumption that the model

  • Ahh, the old determinism debate - does God roll dice and if a tree falls in a forest does it make a sound?

    Quantum mechanics (and thermodynamics for that matter) are useful mathematical models rooted in statistics. They are extremely useful tools but ultimately not exactly how our universe works. A true model that infallibly predicts all actions would need to take into consideration the state of all matter and energy in the entire universe. Obviously this is utterly impractical for we mortal beings, so sta
  • Original paper (Score:5, Informative)

    by burtosis ( 1124179 ) on Wednesday September 19, 2018 @09:08PM (#57345704)
    FFS the linked article didn't mention the original paper, thank goodness they even mentioned the authors. After tracking down the authors publications, I have located the original paper on arxiv [arxiv.org]. It's interesting to read, and seems to lend more thought experiment evidence to the many world interpretation.
  • As a lay person with an engineering background, I find QM to be exceedingly weird. All our intuition stems from interaction with the classical (macroscopic) stuff around us. Trying to extend it to the quantum world is rather frustrating.

    I recently took up an opportunity to attend a few lectures on introductory quantum mechanics, just to see if I can develop some intuitive understanding of quantum mechanics. My key takeaway (please correct me if I am wrong) was that in the quantum world, measuring a quantum

  • Interesting. Reminds me of Gödel's incompleteness theorems: any consistent system of axioms contains statements that are unprovable within the system. Equally mindblowing in a way: the Gödel metric [wikipedia.org]

  • Is this unique to the Copenhagen interpretation? Does the same problem exist in Bohmian mechanics?

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