Quis custodiet ipsos felis?
Is the cat an observer?
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 …
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Sunday 8th February 2015 12:01 GMT Destroy All Monsters
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.
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Sunday 8th February 2015 13:02 GMT 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....)
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Sunday 8th February 2015 15:03 GMT Flocke Kroes
@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.
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Sunday 8th February 2015 20:56 GMT 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?
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Sunday 8th February 2015 16:11 GMT 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.
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Sunday 8th February 2015 19:35 GMT 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.
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Sunday 8th February 2015 11:55 GMT Destroy All Monsters
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.
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Sunday 8th February 2015 12:26 GMT Graham Dawson
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.
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Sunday 8th February 2015 14:16 GMT 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."
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Sunday 8th February 2015 14:25 GMT 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.
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Sunday 8th February 2015 14:11 GMT 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
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Sunday 8th February 2015 15:30 GMT 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.
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Sunday 8th February 2015 16:33 GMT 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).
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Sunday 8th February 2015 16:58 GMT Mike Bell
Re: If you really want to know ...
Agreed.
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.
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Monday 9th February 2015 14:13 GMT 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!
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Sunday 8th February 2015 21:48 GMT 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!
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Sunday 8th February 2015 22:51 GMT 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?
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Monday 9th February 2015 11:38 GMT 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.
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Tuesday 10th February 2015 11:30 GMT 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
Biting the hand that feeds IT
