Schrödinger's cat is a perplexing animal that seemingly is both alive and dead before an observation is made of it.
This thought experiment was intended to show how the weirdness of quantum mechanics could be applied to everyday objects.
It's always bothered me that a human, or some other observer, was needed to make the twin potentiality of "dead" and "alive" become a single actuality. Why couldn't the cat observe itself?
In Amanda Gefter's book, "Trespassing on Einstein's Lawn," she has the best explanation of the Schrödinger's cat paradox I've ever come across. The implications of this are huge -- a subject I'll leave for another blog post.
These passages from near the end of the book carry on in that vein. Great writing, Ms. Gefter.
If an elephant could measure itself, collapsing its own wavefunction, then it needn't exist relative to anything outside itself -- in other words, it would simply, inherently exist. It wouldn't be observer-dependent. It would just be.
In an act of self-affirmation or quite possibly suicide, Schrödinger's cat would collapse its own wavefunction before anyone opened the box. But quantum mechanics -- through the uncertainty relations, complementarity, EPR -- has already proven that if we assume that elephants inherently exist in some objective, observer-independent way, we get the wrong answers.
By relativizing everything, [Carlo] Rovelli had rejected any kind of ontological distinction between observer and observed, leveling the playing field to a quantum monism where every perspective is a possible reference frame, none of them any better than the next.
That did away with the seeming paradox that an observer can't be a subject and object simultaneously, and yet somehow the observer is a subject and object simultaneously. I am the subject relative to me. I am an object relative to my father.
There's no God's-eye view from which both would appear true at the same time. But again, that hinged on the impossibility of self-measurement. If I could measure myself, I'd be both subject and object and quantum physics would fall apart. The prohibition on self-measurement upheld Wittgenstein's intuition that "the subject does not belong to the world: rather, it is a limit of the world."
Rovelli had shown that quantum mechanics seems bat-shit crazy as long as we assume the existence of a single reality shared by multiple observers. Give up that notion and all the quantum weirdness begins to make perfect, non-spooky sense. We can dissolve the problem of the second observer by embracing the cosmic solipsisms that physics demands.
It's not the brand of solipsism that Everett or Wigner momentarily considered, in which there is just one absolute observer. The solipsism that radical observer-dependence implies is itself observer-dependent -- as Rovelli emphasized, observer in one frame is observed in another.
...Boolean logic was just the ordinary logic we usually assume holds true, with its basic rules, like if p is true then not-p is false, or if p implies q and p is true then q is true. There was also the crucial law of the excluded middle: a proposition, p, is either true or false; there's no third option. Non-Boolean logic -- quantum logic -- openly defies the law of the excluded middle. A proposition p can be true and false, depending on who you ask.
But I now saw that logic becomes non-Boolean only when you compare the perspectives of two or more observers. According to any one observer, p is either true or false. We only violate the law of the excluded middle when we try to view p from more than one reference frame at the same time.
Classical logic tells us that the particle passed through one slit or the other. Non-Boolean logic offers a third option: it went through both. But the point is, there's no observer who can see it go through both. That would require an impossible God's-eye view, akin to seeing inside and outside a black hole's horizon.
No observer sees both elephants. Look at the slits and you'll see that it only goes through one. The phrase "both elephants" is totally misleading. Statements such as "The photon travels two paths simultaneously" are wrong. They assume there's some singular reality, a way things "actually are." There isn't. Nature has shown us otherwise.
...We never see simultaneously-alive-and-dead cats because superpositions represent a multiplicity of points of view, and, by definition, a given observer has only one.
...If, however, reality is radically observer-dependent -- if, that is, the universe is nothing, then we need interference to literally cancel out the diagreements between our perspectives. Interference -- the physical manifestation of non-Boolean logic -- exists because nothing is real. Or because reality is nothing. With this "many frames" interpretation of quantum mechanics, that bat-shit experiment was actually starting to make sense.
...But non-Boolean logic, I now knew, was a fictitious logic, the logic that crops up when you cut across horizons, when you try to describe reality from multiple points of view simultaneously. Quantum logic is non-Boolean because reality is radically observer-dependent. Because there's no way things "really are." There was my "really" and my father's "really," but never both.