back to article They've finally solved it: Schrödinger's cat is both ALIVE AND DEAD

An international group of quantum physics researchers reckons it's come up with an experimental validation of the reality of the wave-function. It's one of quantum mechanics' most elusive concepts, ever since Erwin Schrödinger crafted the famous “Schrödinger's cat” thought experiment. In the current experiment, led by Martin …

  1. Allan George Dyer

    Quis custodiet ipsos felis?

    Is the cat an observer?

    1. Destroy All Monsters Silver badge

      Re: Quis custodiet ipsos felis?

      Yes, by nature of its massive size. Basically, the cat system observes the nuclear decay in the same way as the LHC detector observes the beam pipe: The superposition of states deep down will causally entail large changes in the macro objects (dead cats or energy changes in calorimeters). How this exactly selects the state of the micro system is not entirely clear but there are some sound mathematical approaches for dealing with this, maybe along these lines.

    2. Teiwaz

      Re: Quis custodiet ipsos felis?

      Not certain.

      Ophidia in herba

      I do certainly agree with Mr Pratchett, the cat would however most defenitly be 'bloody furious'.

      1. David Pollard

        Re: Ophidia in herba

        For a little while now I have been undecided as to whether to upvote or downvote this comment.

        1. h4rm0ny

          Re: Ophidia in herba

          Well now you can do both!

          1. Vector

            Re: Ophidia in herba

            "For a little while now I have been undecided as to whether to upvote or downvote this comment."

            "Well now you can do both!"

            Not if anybody's watching.

      2. MrDamage Silver badge

        Re: Bloody furious

        Only if aformentioned cat is Greebo.

        Although anyone attempting to put Greebo into a box should be clad in nothing less than a Sherman Tank.

        1. Dave 126

          Re: Bloody furious

          >Is the cat an observer?

          Wouldn't it be fairly straightforward to just place a physicist in the box, and be done with it? It would be easier than educating the cat to undergraduate-level physics.

        2. macjules

          Re: Bloody furious

          Ah, that was the THIRD state, alive, dead or bloody furious at being locked up in a box ... "he's just a big softy really".

    3. Andrew 99

      Re: Quis custodiet ipsos felis?

      so is an ameba an observer too?

      1. DropBear

        Re: Quis custodiet ipsos felis?

        "so is an ameba an observer too?"

        Disclaimer: I'm ludicrously out of my depth here and anything I write might be utter nonsense. However, as far as I understand it, "observer" is one of the most monumentally unfortunate terms for what was actually intended - exactly because many tend to think of it as "something self-aware, like a human being - woo woo human brain / soul / etc. OMG!" whereas it was merely intended to mean "anything that interacts with the original system and therefore 'measures' one of its properties by allowing it to influence one of the properties of the 'observing' system". In other words, even a single atom is an "observer" and unless the cat is floating in a vacuum, it's technically already being 'observed' billions of times each second. Arguably that sort of setup would make the cat pretty dead indeed though (unless it has a space-suit - oh, just forget it....)

        1. Flocke Kroes Silver badge

          @Dropbear: mostly right

          When someone wants to sell a book that proves their cult religion is sciency, they usually follow the sequence: quantum -> observer -> consciousness -> bullshit

          Inside the box: Either [the atom decayed and the cat is dead] or [the atom did not decay and the cat is alive]. The Geiger counter amplified the energy difference between a decayed/non-decayed atom until there was a clear macro-scale difference: a cat the is either angry about being shut in a box or dead. Inside the box, the Geiger counter is an observer.

          Outside the box: In the thought experiment, the box is so magical that no clue about the state of the cat can escape. Not the faintest vibration from her breath or heartbeat. No hint of RF from nerve impulses. No difference in which warm atoms vibrate differently because either the cat's immune system is digesting bacteria or the bacteria are digesting a dead cat. Because the box is magical, the wave function that describes the contents of the box is a superposition of states of a live cat and more states of a dead cat.

          As soon as the box is opened, the wave function collapses. That term needs some explanation: either the probabilities for different states of a dead cat collapse to zero, and the sum of probabilities for states with a live cat zoom up to one, or the other way around. The rate at which the probabilities change depend on the sum of the energy differences between the possible states. A nerve impulse from a live cat might cause a photon of RF energy to escape from the box just as the lid opens. That photon could cause a molecule outside the box to vibrate. That vibration could change the way other molecules vibrate. Because the difference between a dead and a live cat is macro-scale, billions and billions of differences between the states leap out of the box the moment the lid starts to open. Those differences create other differences outside the box that grow exponentially. That exponential growth or amplification is what collapses the wave function.

          The key feature of an observer is amplification. If one atom can change electronic state, and the only possible result of that change is another atom changes electronic state then the result is a wave function in a superposition of states. If that second atom consequently emits a photon into a photomultiplier, the photomultiplier amplifies the difference between possible states and collapses the wave function.

        2. Anonymous Coward
          Anonymous Coward

          Re: Quis custodiet ipsos felis?

          "a lethal quantum event like radioactive decay triggering a gas release"

          The radioactive decay product must enter some sort of detector to trigger the gas release; doesn't the interaction between the particle and the detector constitute an "observation" of the state of the particle?

          Can't machines observe and measure? Who said that only humans can do so?

          If a tree falls in a forest and nobody is there to hear it, does it make a sound? Is a sound the vibration of the air, or only the sensation experienced by a listener?

      2. Black Betty

        Re: Quis custodiet ipsos felis?

        I believe it (the amoebae) might be.

        The largest item successfully put through the quantum wringer (double slit experiment) is a 114 atom buckeyball.

    4. itzman

      Re: Quis custodiet ipsos felis?

      Is the cat an observer?

      No, an observation.

      Remember Descartes, If you dont think rationally you dont exist.

      Felix non cogitaris ergo felix non est

      1. Jes.e

        Re: Quis custodiet ipsos felis?

        "Re: Quis custodiet ipsos felis?

        Is the cat an observer?

        No, an observation.

        Remember Descartes, If you dont think rationally you dont exist.

        Felix non cogitaris ergo felix non est"

        Next question.

        Are humans rational?

        A: No. We rationalize.

        Therefore I don't exist.

      2. P. Lee

        Re: Quis custodiet ipsos felis?

        >Felix non cogitaris ergo felix non est

        Ah, the Matrix view of reality: only understand that there is no cat.

        1. Anonymous Coward
          Anonymous Coward

          Re: Quis custodiet ipsos felis?

          > Ah, the Matrix view of reality: only understand that there is no cat

          Didn't I just see that cat a moment ago?

    5. Forget It

      Re: Quis custodiet ipsos felis?

      A cat may look at a king ... if that helps any.

    6. JeffyPoooh

      The 'Russian Dolls' extension to Schrödinger's cat

      The observer with his boxed cat is also in a slightly larger box. After he peeks at the cat, he is now in a strange quatum world of two states. We leave him there for a while. He's safe from the cat poison of course, in case you're concerned.

      We weigh the box, to see if it really contains two observers. Nope.

      We tap on the side, to give him a minute notice. Rip the lid open and ask him what it felt like. He'll say, "Nope, just one of me. The cat was ..."

      Of course the committee itself is in an even-larger box. They'll be interviewed next. Ah, there's the tap. One minute to go and the whole world will be in two states.

    7. Crisp

      Re: Quis custodiet ipsos felis?

      From the cat's point of view, it's always alive.

  2. Ian Johnston Silver badge

    If a single scientist enters the room with the box in it, opens up, looks inside and then dies of a heart attack before telling anyone how the cat was, what happens? Does the cat's state uncollapse itself until someone else has a shufti?

    1. Destroy All Monsters Silver badge

      No, this works only for very small cats.

      This is a nice experimental trick though: 1) Measure small cat, capturing cat state is a qubit 2) Do not extract classical YES/NO from qubit just move it around a bit 3) Reinject qubit into small cat system 4) Small cat STAYS unmeasured!

      1. Anonymous Coward
        Paris Hilton


        I thought this only worked for spherical cats in a vacuum??

        Besides, the cat is dead, I mean exactly how long ago did Shrodinger PUT the cat in the box, and what is the maximum lifespan for a cat??

        Paris, my favourite box AND pussy - all rolled into one.

  3. Destroy All Monsters Silver badge

    Quantum mecahnics: Nature's trick to avoid having to be Newtonian-precise

    This sounds like a "null experiment": Testing that things we suspect are true are actually true.

    After all, the whole attempt at building quantum computers is based on the idea that the complex-valued probability density function is an element of a (non-classical) reality, which we are going to damn well exploit the fuck out of.

    The system's absence of a classical state before measurement (i.e. before extraction of a few classical bits) clearly follows in the footsteps of Anton Zeilinger's GHZ states, which I frankly can't remember the details of.

    “we can't easily simulate quantum systems on a classical computer.”

    Indeed so. You can do it, but with exponential slowdown. And not for continuous systems. The question of whether a continuous wave function even exists in nature is open and will probably remain so forever, after all you cannot measure it.

  4. Graham Dawson Silver badge

    Everyone always seems to forget that Schrödinger's Cat was a thought experiment he devised to demonstrate what he believed to be the absurdity of the conscious observer effect, which holds that a particle is in a superposition of states until "observed" by some mysterious "observer", which has led to the silly idea that the universe doesn't exist until someone looks at it.

    1. Destroy All Monsters Silver badge

      And of course the difference is not between "conscious" and "non-conscious" observers but between massive and small systems.

      It makes for some good story-telling though. Anyone read Greg Egan's "Quarantaine"?

    2. itzman

      What is silly about the idea...

      ..that the universe as she is perceived doesn't exist unless it is perceived by someone?

      The only silly part is the belief that the universe in itself is in fact anything like one's perception of it.

      "Of course I know how a computer works: You just push the on switch, and wiggle the mouse and stuff happens in an orderly way on the screen"

      "So what's inside all the chips?"

      "Smaller pictures and sound things of course".

      "So what do you make of all this theory about 'software'?"

      "Preposterous nonsense."

    3. David Pollard

      Esse est percipi (aut percipere)

      The notion that the universe is there only because it is observed was not entirely new in 1935 when Shrödinger came up with his eponymous paradigm. illustrating that the equations of quantum mechanics can be seen to imply this.

      From the English ecclesiastical tradition, back in the eighteenth century, George Berkeley had coined the seminal phrase quoted above. At the turn or the nineteenth century, Alfred North Whiteheads's process philosophy continued in the much same vein. In the German tradition, Ernst Mach used broadly similar reasoning when he argued that the existence of rotational inertia depends on some sort of interaction with the fixed (i.e. distant) stars; without being able to 'see' them in some way we wouldn't be able to know if and when we are spinning, and we can do this inside a closed and isolated box.

      The Muslim tradition holds, if I understand correctly, that one of our primary duties is to observe and understand. And Buddhism too puts great importance on this aspect of existence.

      The debate continues over whether such luminary insights have any validity.

    4. Preston Munchensonton

      "...which has led to the silly idea that the universe doesn't exist until someone looks at it."

      I'm pretty sure this was the chief premise behind Oolon Colluphid's "Where God Went Wrong"...

  5. Anonymous Coward
    Anonymous Coward

    OR, OR...

    Just tap on the box, every half hour or so, and go, "Puss, puss......are you alright puss?"

    1. Charles Manning

      Re: OR, OR...

      or put the box on the freeway and the wave function will become planar pretty smartly.

  6. Anonymous Coward
    Anonymous Coward

    Maybe things are just fuzzy

    Maybe there is no particle or wave, just fuzz (e.g. a matter field) and the appearances of particles or waves is just over simplification, inadequate understanding or too narrow sensing.

    The cat in a box thought experiment maybe just gross reductionism and that's why it seems so ambiguous. Fnord

  7. CCCP

    It hurts my brain so stop it

    Superimposed cats screaming at atoms, or photons, waving about. Honestly.

    Seriously though, there's some interesting stuff going to check at what size superposition collapses, the suspicion being that gravity is wot done it.

    My money is on Hawking in the library with a gravity.

  8. Chris Miller

    If you really want to know ...

    Read The Emergent Multiverse by (newly minted) Prof David Wallace. (Do not attempt this unless you already have a good understanding of (the maths of) quantum theory and a grounding in philosophy.)

    He makes a very strong case that we must accept what the equations are telling us, which is that the Everett (multiverse) interpretation of QM is the only one that is viable. Admittedly, he works in the Oxford school of the philosophy of physics, where (with leading lights such as David Deutsch) the multiverse has a very strong fan club. But with doctorates in theoretical physics and philosophy, he knows whereof he speaks and explains these concepts in as simple a way as possible (which is to say, not very simple at all).

    1. Mike Bell

      Re: If you really want to know ...


      From the article:

      the wave function described in quantum mechanics suggests the cat exists in a superposition of dead/alive states simultaneously

      A quick reminder: the wave function is a well defined deterministic function that describes the probabilities of things happening. The 'wave function' of the insurance industry describes very well how many cars will crash on Britain's roads in a given year. What it doesn't do is describe whether or not my car in particular will crash.

      And so to the cat and its wave function. In many-worlds there are vast numbers of 'universes' containing virtually identical boxes and cats, some of which are dead, and others that are alive. The observers in a live-cat universe will see a living cat; the observers in a dead cat universe will see a dead cat. This doesn't mean that the cat is both dead and alive at the same time, just that the universe has obliged by giving us - somewhere - all possible outcomes. This strikes me as being a parsimonious and elegant description. No need to come up with the notion of an observer, and the eternal conundrum of why a particular particle decays 'spontaneously' becomes irrelevant.

      1. Allan George Dyer

        Re: If you really want to know ...

        @Mike Bell: I would hesitate to describe an explanation that invokes "vast numbers of 'universes'" as in any way parsimonious.

      2. waifnstray

        Re: If you really want to know ...

        The way I try to think about multiverse theory (without having put in enough reading to see if this reflects what's intended) is this:

        Imagine for simplicity's sake there is only one quantum event - decay or not of a single particle inside the box - and we start from a single universe.

        It's not the case that a whole enormous new universe comes into existence instantaneously; it's more that the universe branches at the point of the quantum event, and the two branches spread out at the speed of actual cause-and-effect (which will be less than or equal to the speed of light).

        In the case of this magically shielded box (as @Flocke Kroes puts it), cause-and-effect slows down to zero at the boundary of the box, so the universe only branches into two box-sized sub-universes.

        When the box is opened, the effects leak out at the speed of light and the branching continues: the researcher is branched at that moment, consciousness and all. One of them sees the dead cat, one of them sees the live cat.

        This becomes harder to think about when you have multiple quantum events going on and interacting with each other. Either I'm way off track, or the analogy is limited to the simple case, or someone else can explain how it multiplies up!

    2. Anonymous Coward

      Re: If you really want to know ...

      Well it's conceivable that dark matter and dark energy are due to overlap influences from our neighbors (and their neighbors, ...). Since macroscopic objects are most likely to be in roughly the same spot, that explains why dark matter is congruent with those observed objects.

      Now as to the creation of whole new universes with every probable event that wanders of into continuous creation so I imagine Sir Fred Hoyle will be laughing to himself for rather a long time. Still, I wonder if there were some jitter that collapses universes into each other. That would definitely explain why some macroscopic object "you know for a fact" placed in one location only to find it in another.

      I need a beer!

  9. Zog_but_not_the_first

    Zog's Modifier

    Wouldn't you have to open the box nine times?

    1. Mark 85

      Re: Zog's Modifier

      Toss the box out a window. If lands on the bottom the cat is/was alive. If lands upside down, dead cat. You might have to do this at least 9 times to be sure.

  10. Anonymous Coward
    Anonymous Coward


    The statement is confusing the possible outcomes, with the actual outcome. Although the cat may be alive or dead, it will be one or the other, and that can be tested every single time.

  11. John Deeb


    Reality remains fundamentally ambiguous -- especially while trying to study it with more and more observations. What we call object remains all movement trying to escape analysis and almost succeeding.

  12. Anonymous Coward
    Anonymous Coward

    They've finally solved it: Schrödinger's cat is both ALIVE AND DEAD

    That can only mean one thing........'ZOMBIE PUSSIES'!!!!......which could make an entertaining Bonus Level in COD:/

    1. RyokuMas

      Re: They've finally solved it: Schrödinger's cat is both ALIVE AND DEAD

      Sounds more like Duke Nukem to me...

  13. Anonymous Coward
    Anonymous Coward

    AIR HOLES!!!

    Yes, thats right you heard me, Air Holes!! There had better be some in that box or i'm calling the RSPCA!.......and my punctuation teacher!",.

  14. JeffyPoooh

    I've always felt that the Multiverse explanations...

    I've always felt that the Multiverse explanations were violating Conservation of Mass.

    If a zillion Universes can be created every picosecond, then how come petrol is so expensive?

  15. Paul

    Schrodinger's dog still reported as missing, after a bizzarre experiment into wormholes went wrong.

  16. All names Taken

    Maybe ...?

    ... there are important differences in reality and what is perceived to be reality?

    If so, then it is a relativistic term for example is perceived reality to a human different to the perceived reality of the earthworm?

    And what if the cat was not bothered and did not participate as an observer?

    Edit: some creation theories are merely models of reality to explain observed phenomena so exist as realities of their own usually quite separate to that of the observed phenomena (for example: simplifying assumptions in mathematical modelling)? Discuss?

  17. Snowy Silver badge

    or there is

    The whole of "creation" is a simulation and the problems with quantum physics is just where the simulation break down due to the computational limits of the system running the simulation.

  18. Frumious Bandersnatch

    Lao Tzu couldn't decide

    If he was imagining himself as a cat or whether he was a cat imagining himself as Lao Tzu.

  19. tempemeaty

    ( -__^)b

    The cat was never really in the box. That was another reality...oh wait....

  20. Mark 85

    The big question

    .. that has Fartbook all atwitter is: Will there be a video of the cat?

  21. Herby

    Modern equivalent...

    Is a simple lottery ticket. You buy it for one buck/quid and that's its value. The "opening of the box" is when they draw the number and you find out if it is "dead" (valueless), or "alive" (worth something) for various values of "alive".

    The best explanation was the episode of _The Big Bang Theory_ when Penny and Leonard have their first kiss.

    Note: This show is not a comedy, it is a documentary. I have this on VERY good authority from my brother in law who works at JPL.

  22. Berny Stapleton

    It's turtles, all the way down.

  23. Gannon (J.) Dick

    Mad dogs and Englishmen go out in the midday sun.

    and when mad dogs and Australians go on picnics the Englishmen are shoveling snow in the dark. It is like they are mad, or something. At least they could get the dogs to shovel.

    Oh, by the way, geophysics is not quantum superposition.

  24. All names Taken

    Models of reality are just mere models that is all.

    I mean take Marylin Munroe or Madonna for example?

  25. Come to the Dark Side

    The part that always gets missed in discussions of this experiment is that nobody has agreed on what constiutes "alive" and "dead".

    eg if the cat could be resuscitated, could it be considered to be dead? If the cat is not capable of rational thought, can it be considered to be alive (not my own viewpoint but one espoused regularly round the sherry snifters)? etc

  26. dtncats

    why...a cat for a human "experience" of life n death...

    Perhaps you should use a HUMAN as the "observed"...that is..if we are talking about life and death on a humane level...

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