So the cat is in the box with the particle that may or may not have decayed after ten minutes, setting off a charge that would kill the cat. The physicist says the cat is in a superposition, viz., is both alive and dead.
Why does the physicist get to invent a property (the superposition) that is, in principle, unobservable, and then assign it to the cat? Why doesn’t the physicist instead say, “I don’t know if the cat’s alive or dead”, or “I can’t know if the cat’s alive or dead”? Isn’t science about what’s observable, not making up stuff about what isn’t or cannot be observed?
It’s just a thought experiment which illustrates the issues Schrodinger had with quantum theory. He began the description with the phrase: “One can even set up quite ridiculous cases.” It’s a piece of rhetoric, not an actual experiment.
It illustrates the question [v much paraphrased; v much more complex than this] - when does quantum uncertainty become real? The point being that he was posing a question, not making a declaration. He was taking the Copenhagen interpretation of quantum mechanics to its conclusion which, in his view, was a paradox.
The long answer is very complex, but the short answer is that with quantum effects we can demonstrate that in fact a particle is NOT “in one or the other of two states, but we don’t know which”; it IS true that “the particle is somehow in both states simultaneously”.
The Schrodinger’s Cat paradox scales that observation up to macroscopic objects, and there is probably some effect that destroys the paradox during the scaling, but at the particle level there is no doubt of what is going on.
That was his whole point to begin with. He came up with the idea to demonstrate his problems with modern quantum theories. It is both a paradox and a parody. He wasn’t trying to “invent a property”. He was demonstrating the absurdity of the theories.
I read the column long ago, and FWIW it seems in fact to bolster my point of view (that physicists should just say, “I don’t know”, not “It’s in a superposition”) (emphases added):
“The cylinder’s sealed. The hour’s passed away. Is
Our pussy still purring — or pushing up daisies?
Now, you’d say the cat either lives or it don’t
But quantum mechanics is stubborn and won’t. Statistically speaking, the cat (goes the joke), Is half a cat breathing and half a cat croaked.
To some this may seem a ridiculous split,
But quantum mechanics must answer, "Tough shit.
We may not know much, but one thing’s fo’ sho’: There’s things in the cosmos that we cannot know.”
I can accept that statistically the cat is alivedead, because statistics is just a measure of ignorance. But other treatments of quantum physics I’ve seen want to go beyond that. They don’t seem to say, “it’s even odds the cat’s dead”. They seem to say, “There exists a state of being that in principle cannot be observed, and the cat [or decaying atom, or whatever], when unobserved, is in that state.”
And THAT. Goes beyond good science. Or so it seems to me.
I realize that the example was invented to demonstrate the absurdity of certain interpretations of quantum physics. But from what I’ve gathered, mainstream physics has since determined that the absurdity is merely alleged; they bite the bullet and allow that the cat is alivedead. The property they’ve invented (or discovered, depending on one’s predilictions) is that of being in a superposition.
That’s the whole point of what I’m getting at, that that’s a heck of a bullet to bite (viz., rejecting the law of the excluded middle).
Not that I’m trying to argue for or against the Copenhagen interpretation, but I think we should point out that it “seems absurd” is an even weaker scientific argument than any one might be trying to refute. One should read up on a the actual theories before proclaiming them absurd; but that’s a big, big job and beyond me.
Seemingly absurd things happen in physics all the time - especially particle physics. Try firing a stream of electrons one at a time at two slits and you’ll see something that seems absurd. But it happens.
I’m pretty sure that is not the physicist’s position. The cat is either a live or dead, the question is not is there a superposition of the quantum particle involevd - There IS. Period. The question is, at what point does that superposition resolve itself? What is the observer and at what point does it observe.
Well, I don’t know. If a scientist performs an experiment and the result shows that my car is simultaneously blue all over and red all over, I’d say the absurdity of that result should give one pause.
We don’t take absurd results in mathematics (or philosophy) in stride; a mathematician who showed that 1+1=3 would have a lot of 'splaining to do. Why does the physicist get a pass?
He doesn’t. What makes you think he does? He gets extensively peer reviewed and scritinized. His papers and his experiments and his observations and his calculations are examined in minute detail by hundreds of very clever scientists. Years of further testing and observation prove the hypothesis to be true. Maybe a couple of decades later, they get a Nobel Prize for it. And then some guy on a messageboard proclaims it absurd.
Look at the subliminal neutrino debate going on right now. Did scientists say “oh, right, well we believe you - neutrinos move faster than light now”? Nope. The scientific community descended upon it in droves and are scrutinizing it in far more detail than we can even imagine.
The idea that you think physicists just “get a pass” is, however, somewhat absurd. (Sorry, that came across as rude, but it seemed a mildly witty turn of phrase and I couldn’t resist using it).
(1) Hey look, electrons are doing weird things in weird situations (like double-slit experiments) that classical physics can not explain.
(2) Well Jeez, let’s invent quantum mechanics to deal with that, and look, quantum mechanics explains all of those features of electrons, and a fuck-ton of other particles, too.
(3) But what if we applied the rules of quantum mechanics to cats? Then you have cats doing weird things that they clearly don’t do while we’re watching!
(4) Well, actually, for certain values of “watching” the electrons don’t do silly things while we’re watching either, so I think this is all right, just weird.
And oddly, a good chunk of the internet message board community (albeit not this one, because this one is lousy with physicists) jumped all over the superluminal neutrinos with claims that all of physics is shattered and those mean scientist-priests are being dogmatic assholes by criticizing the results. Teh Intarwebs seem very split upon whether or not physicists should get a free pass or not.
I think I see what you’re saying. So if the mathematician shows that 1+1=3, and that result is confirmed over and over again, then we’re supposed to accept the absurd (or “absurd”) result and maybe give her a prize. I suppose I should’ve said, “Why does physics (meaning the original experimenter and all those who verified the result) get a pass?”
But.
For one thing, note that, if shown true, neutrions moving faster than light wouldn’t entail an absurdity. It would show that a fundamental proposition about physics was false, yes, but there’s nothing logically impossible about a neutrino, or a '67 Buick Skylark, going faster than light; there’s no absurdity there. Maybe something like that is going on in the two-slit experiment–the result is weird, but not absurd. (Also, there may be some confusion because I’m using “absurd” in the strict sense of “entailing a contradiction”.)
The assertion of the existence of a state wherein a cat is simultaneously alive and not-alive (viz., in a superposition) would by definition entail a contradiction and is therefore (it seems to me) an assertion we’re entitled to ignore. The laws of logic/math are more basic than the laws of physics, after all.
If a physicist tells me they’ve found a particle that weighs a pound at time t and also doesn’t weigh a pound at time t, and if that result is replicated over and over, then I think it’s safer to say there’s something systematically wrong with how everyone’s going about it, than it is to say a contradiction obtains. (Those who are inclined to quote Whitman here can save their keystrokes. :))
I don’t really understand where you’re going with this. I mean, you’re not supposed to believe anything; it’s not a crime not to. The experimenter believes it, and the hundreds of scientists who verify it believe it, and the tens of thousands of scientists who subsequently verify it over the decades believe it. I honestly don’t know where this “get a pass” thing is coming from. Get a pass from whom? You?
I guess you’re welcome to not believe established scientific principles. I don’t think the scientific community minds all that much. It’s not going to stop them using the principles they’ve discovered.
Relativity sounds absurd. But your GPS works, so it’s clearly not. Quantum computers work, so it can’t all be nonsense. But, like I said, anyone’s welcome to believe whatever they want to. The scientists aren’t asking you for a pass; they’re just getting on with their work and if you’re interested they’re happy to tell you about it.
But it’s been experimentally proven that individual particles can exist in a state of superposition. There have even been experimentsthat show superposition large collections of particles. You can call it a logical contradiction if you want, but its true.
I mean “entitled to ignore” in the same sense that we’re entitled to ignore someone who claims to have squared the circle. Rationality allows us to ignore propositions that are, well, irrational. If one assumes a contradiction, anything can be shown. So, we’re allowed to dismiss contradictions; we can ignore them.
It looks like, in positing a situation wherein something is simultaneously P and not-P, the physicist has made a statement that entails a contradiction, and therefore anything whatsoever follows from it. The physicist’s statement can, in principle, prove anything: that Caesar and my banker are the same person; that the moon is made of green cheese; that all equilateral triangles are equiangular triangles; that five is twenty more than 138; that a carrot is an alarm clock; that dogs bark. Anything. As such, AFAICT the physicist’s statement is worthless and subject to be ignored.
I think there are some misunderstandings in both of these sentences. It is tempting to view logic and mathematics as basic, with physical laws somehow building on these. But physics is fundamentally an empirical science, not a logical one; if empirical physical results contradict logical derivations then it’s the logic that’s broken, not the physics.
Of course what’s more likely than an inconsistency in logic is that there’s been an error in the attempt to translate from physical measurements to physical laws to logical statements; and this is what I think is wrong with your first statement. (This is especially easy to do if you’re reading popular accounts, which may not be terribly precise in their use of language.) You say that a cat must be either alive or not-alive (excluded middle), and implicitly count this as two distinct well-defined states exhausting all possibilities. At least one of these two properties is empirically shown to fail in quantum mechanics, however. The usual informal way in which physicists talk about this is to label two particular states of the cat system as “alive” and “dead” and then understand that quantum mechanics allows superpositions of these two states. Now you see that there’s not actually a logical contradiction. There are more than two possibilities, so excluded middle does not apply, and “not-alive” is not the same as “dead”.
So more formally what quantum mechanics predicts–and as already mentioned this has been experimentally verified, though not for actual cats–is that there is a continuum of possible states, each of which has some probabilities of having particular values when actual measurements such as “is the cat alive?” are made. The difference between this prediction and the statistical incomplete-knowledge prediction is that for a superposition there are some measurements that always give the same value.
These measurements are somewhat difficult to describe for cats, but they are pretty easy to describe for an electron, say. If we call |up> and |down> the states in which an electron’s z-component of spin (i.e., measured along a chosen z axis) is +1/2 and -1/2 respectively, then measuring the z-component of spin for the state |up>+|down> will give +1/2 half the time and -1/2 half the time. However, measurement of the component of spin along a particular axis orthogonal to the z axis will give +1/2 all the time. This is distinct from the statistical case in which you have no information about the electron’s spin; in this case measurement along any axis will statistically give +1/2 half the time and -1/2 half the time.
