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posted by Fnord666 on Tuesday August 18 2020, @12:53PM   Printer-friendly
from the one-way-to-find-out dept.

This Twist on Schrödinger’s Cat Paradox Has Major Implications for Quantum Theory:

What does it feel like to be both alive and dead?

That question irked and inspired Hungarian-American physicist Eugene Wigner in the 1960s. He was frustrated by the paradoxes arising from the vagaries of quantum mechanics—the theory governing the microscopic realm that suggests, among many other counterintuitive things, that until a quantum system is observed, it does not necessarily have definite properties. Take his fellow physicist Erwin Schrödinger's famous thought experiment in which a cat is trapped in a box with poison that will be released if a radioactive atom decays. Radioactivity is a quantum process, so before the box is opened, the story goes, the atom has both decayed and not decayed, leaving the unfortunate cat in limbo—a so-called superposition between life and death. But does the cat experience being in superposition?

Wigner sharpened the paradox by imagining a (human) friend of his shut in a lab, measuring a quantum system. He argued it was absurd to say his friend exists in a superposition of having seen and not seen a decay unless and until Wigner opens the lab door. "The 'Wigner's friend' thought experiment shows that things can become very weird if the observer is also observed," says Nora Tischler, a quantum physicist at Griffith University in Brisbane, Australia.

Now Tischler and her colleagues have carried out a version of the Wigner's friend test. By combining the classic thought experiment with another quantum head-scratcher called entanglement—a phenomenon that links particles across vast distances—they have also derived a new theorem, which they claim puts the strongest constraints yet on the fundamental nature of reality. Their study, which appeared in Nature Physics on August 17, has implications for the role that consciousness might play in quantum physics—and even whether quantum theory must be replaced.

Journal Reference:
Kok-Wei Bong, Aníbal Utreras-Alarcón, Farzad Ghafari, et al. A strong no-go theorem on the Wigner’s friend paradox, Nature Physics (DOI: 10.1038/s41567-020-0990-x)


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  • (Score: 5, Interesting) by meustrus on Tuesday August 18 2020, @01:46PM (12 children)

    by meustrus (4961) on Tuesday August 18 2020, @01:46PM (#1038340)

    I'm probably wrong here, but isn't Schrödinger's cat just a thought experiment? It's not supposed to be a thing that could literally happen, it's supposed to illustrate how superposition works with everyday objects.

    The thing that we pop culture scientists always miss is that observation is destructive. The same way your eyeball casts a shadow, any measurement of a quantum state interrupts it.

    We live in the same universe we're trying to observe. It's not like we're just opening up God's debug console and setting a breakpoint. Even if we were, sometimes the breakpoint itself changes the timing and you can't observe what you were trying to observe.

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  • (Score: 2) by rigrig on Tuesday August 18 2020, @02:04PM

    by rigrig (5129) Subscriber Badge <soylentnews@tubul.net> on Tuesday August 18 2020, @02:04PM (#1038344) Homepage

    As I understand it, Schrödinger wasn't happy with the idea of superposition and came up with this experiment to show how it could lead to "ridiculous" macroscopic results like a cat being both dead and alive at the same time.

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  • (Score: 0) by Anonymous Coward on Tuesday August 18 2020, @02:12PM

    by Anonymous Coward on Tuesday August 18 2020, @02:12PM (#1038348)

    I'm probably wrong here, but isn't Schrödinger's cat just a thought experiment? It's not supposed to be a thing that could literally happen, it's supposed to illustrate how superposition works with everyday objects.

    It's not just that: Schrödinger used this specifically as a reductio ad absurdum to demonstrate what he thought must be a problem with some parts of quantum theory at the time (and to some extent to this day). The idea that a cat could be simultaneously alive and dead was intended as an example that was so patently ridiculous that there is no way it could possibly be true.

    It's possible Schrödinger's argument was wrong, as some more modern interpretations do accept the possibility that cats can indeed be literally alive and dead simultaneously. However this paper might be evidence against such theories.

  • (Score: 2) by inertnet on Tuesday August 18 2020, @04:01PM

    by inertnet (4071) on Tuesday August 18 2020, @04:01PM (#1038393) Journal

    As I understand it, Schrödinger was right, but only for larger objects like cats and observers. It has long been demonstrated that those spooky things are true for subatomic particles.

  • (Score: 3, Interesting) by Anonymous Coward on Tuesday August 18 2020, @04:03PM (4 children)

    by Anonymous Coward on Tuesday August 18 2020, @04:03PM (#1038394)

    The more ridiculous the claim, the more likely it is to be true, when quantum mechanics is involved.

    This result is meaningful, but not quite as Earth shaking as some say. The worst part is that peddlers of woo-woo will seize on it as more "proof" that their bunkum is true.

      The media reports all seem to be excited about this notion of subjectivity, but what's overlooked is that superdeterminism, nonlocality, and retrocausality also solve the problem, and most QM interpretations already incorporate, or allow for the possibility of, one of those.

    Personally, I am fine with retrocausality, which isn't as upsetting as it seems when you first hear about it.

    • (Score: 3, Funny) by meustrus on Tuesday August 18 2020, @05:45PM (3 children)

      by meustrus (4961) on Tuesday August 18 2020, @05:45PM (#1038437)

      Impressive, you took me from "you're absolutely wrong, ridiculousness is not a bellwether for truth" to "Your ideas are intriguing to me, and I wish to subscribe to your newsletter" in a mere 5 sentences.

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      If there isn't at least one reference or primary source, it's not +1 Informative. Maybe the underused +1 Interesting?
      • (Score: 0) by Anonymous Coward on Tuesday August 18 2020, @07:05PM (2 children)

        by Anonymous Coward on Tuesday August 18 2020, @07:05PM (#1038462)

        The first sentence was only semi-serious, but so much of quantum mechanics (including the original Schrodinger's Cat thought experiment) was intended to disprove it, because the predictions were so ridiculous. But then they turned out to be true.

        I don't have a newsletter, but Sabine Hossenfelder [blogspot.com] does. She prefers superdeterminism [frontiersin.org] (and I think Einstein would as well, were he still alive).

        • (Score: 0) by Anonymous Coward on Tuesday August 18 2020, @09:21PM (1 child)

          by Anonymous Coward on Tuesday August 18 2020, @09:21PM (#1038515)

          Ah. Her YouTube channel pops up in my recommendations. I haven't clicked on it because (besides having lots of other stuff I want to watch), it wasn't clear which side of the kook line she fell. As you mentioned, there is no shortage of bunkum peddlers peddling in QM topics. It feels like the 70's all over again!

          • (Score: 0) by Anonymous Coward on Tuesday August 18 2020, @10:37PM

            by Anonymous Coward on Tuesday August 18 2020, @10:37PM (#1038565)

            She's a contrarian, but definitely not a kook.

  • (Score: 2) by sjames on Tuesday August 18 2020, @06:21PM (1 child)

    by sjames (2882) on Tuesday August 18 2020, @06:21PM (#1038454) Journal

    My God, it's full of Heisenbugs!

    • (Score: 2) by Gaaark on Tuesday August 18 2020, @07:16PM

      by Gaaark (41) on Tuesday August 18 2020, @07:16PM (#1038469) Journal

      and it's breaking bad!

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  • (Score: 1) by khallow on Wednesday August 19 2020, @02:56AM

    by khallow (3766) Subscriber Badge on Wednesday August 19 2020, @02:56AM (#1038678) Journal

    I'm probably wrong here, but isn't Schrödinger's cat just a thought experiment?

    Thought experiments aren't just thought experiments. They may be extremely difficult to do even with technology far more advanced than our own, but they are possible.

    Here, we already have a number of proven technologies for blowing up quantum level effects to macroscopic effects. Shutting a person into near perfect quantum sequestration (for an adequate period of time) is impossible with our present technology, but feasible. Eventually someone will do it.

    The thing that we pop culture scientists always miss is that observation is destructive. The same way your eyeball casts a shadow, any measurement of a quantum state interrupts it.

    Only for the observer! In the Wigner's Friend example, the observer isolated in the lab makes the observation, but to the outside world, that observation is entangled with the state that the Friend is attempting to observe. The collapse doesn't happen until the outside world observes either the Friend's state or the state of the particle that the Friend was observing (and entangled with).

  • (Score: 2) by FatPhil on Wednesday August 19 2020, @03:43PM

    by FatPhil (863) <pc-soylentNO@SPAMasdf.fi> on Wednesday August 19 2020, @03:43PM (#1038845) Homepage
    Measurement is only destructive if you chose the postulate that makes it destructive. There's no experiment planned or performed that tells you whether accepting that postulate or rejecting it gives a better model for the universe. There are at least half a dozen different "interpretations" of quantum mechanics with some traction amongst academics, and this is probably the biggest question that divides them. Even accepting the measurement postulate, you're still left with the problem of defining what is "measurement", which is the nub of what Wigner was worrying about here.
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