The difference between the cat and the clocks is the poison gas in the box. As soon as you lock the box, you have no idea if the gas has been triggered or not. So you have no rational way to know if the cat is alive or dead.
With a clock, there’s no reason to expect the possibility of them stopping when you leave the room. It is entirely reasonable to expect that they will continue keeping time while they are unobserved. Now, if your clock should happen to break while you were out of the room, you would not know about it until it was observed. Then you’d be into Schrodinger territory.
The problem I have with Schrodinger’s Cat is the mechanism by which the decay is detected and smashes the vial. I don’t think such an item can exist and if it did exist then how does that qualify as keeping the particle “unobserved.” So while the physicist can stay uninformed, that doesn’t mean the rest of the universe is uninformed.
Not only can it be ignored, but for any system in which multiple particles are in superposition (i.e. their states are not just complementary, as with entangled particles or a Bose condensate) the probabilities all mush out to a mean, such that the uncertainty is less than your ability to measure its variation, and for all intents and purposes, the object is in a single pseudo-quantum state. This isn’t just for everyday-sized objects; for the most part, even heavy composite particles and molecules have a quantum wavelength much smaller than the actual size of the particle, and thus, your ability to detect any spontaneous variations in position or momentum. In theory, it is infinitesimally possible that all of the fundamental particles that make up a cheerleader’s skirt could suddenly jump five feet to the right; in reality, the probability of any detectable amount of particles suddenly jumping in any direction by a measurable amount is so tiny that it literally just can’t be observed for any real timeframe; even if her skirt did suddenly disappear in a mass state change, it would return to the original decoherent state in a shorter interval than could be measured by any classical observer. For all intents and purposes, even if it happened, it never happened.
No, that’s a very salient point. The Schrödinger’s Cat gedankenexperiment is an attempt to conceive of a macroscale event that is directly influenced by a single quantum state change. The single radioactive particle and the detector make an isolated quantum system that triggers a macroscale event. However, in reality, the detector, the cat, the box, and the observer are all part of an interlinked quantum system in which there are a huge number of possible superimposed states; just as the cat may be both alive and dead, the observer may have both looked and not looked in the box, and so forth. Schrödinger obviously intended this as an absurdity; that the boundaries between quantum mechanics and everyday experience are not merely arbitrary states of relative perception, but actually form a fundamental break between isolated quantum systems and real world collections of objects.
The problem of Wigner’s friend extends this; he is outside the room and doesn’t know if the friend has looked in the box yet or not, so not only does the cat exist in superposition, but so does the friend, until the Wigner goes into the room and observes. This leads to two possible conclusions; either Wigner is a solipsist and no definite state exists until he personally observes it (absurd), or real collections of quantum systems are more complex than an assay of the individual systems themselves. Waveform collapse (or whatever other interpretation you invoke) is nothing more than a mathematical formality, a way of setting the initial condition for solving a defined set of interactions, with no physically real and discrete condition.
The scenario of the clock as posited by the o.p. is no different than the cat; the clock, while not resolved, is in a similar superposition of states, which in summed average equal the “real” time as measured by the clock when observed. Under any interpretation the clock never disappears or disintegrates into a quantum mist or stops working or anything like that; it just exists in an array of states that are mostly really, really close to telling the actual time. How you interpret “being in an array of states” is really up to you; you can take it as a mathematical formality, or dispense with local realism and assume that it doesn’t really exist unless you are looking at it, or whatever, but the incontrovertible fact remains that unless someone unplugs it or the power goes out, it’ll keep the same interval of time whether you are observing it or not within the tolerances of its mechanism.
That’s one of the best summaries of the responses to the cat that I’ve seen.
The only thing I’d add is that smart quantum greasemonkeys might point out that our common sense is often a limited version of what’s really going on. For instance it seems ridiculous that time goes slower when you’re moving quickly. But it does (as proven every day by your GPS); it’s just that we move so slowly that there’s not enough effect for our common sense to notice.
No, that’s what you find out by opening Schrödinger’s Bull. That was actually the true scientific basis of the ancient Greeks’ practice of reading animal entrails…
I thin it’s essential to understand that quantum mechanics is built out of observation, not understanding. (“Common sense” being a type of understanding).
At the quantum level, we observe all kinds of things happening that simply don’t make sense. They shouldn’t be happening. When someone says it is happening, we want to call him a total idiot, except that we can replicate what he said happened. We just know that it does happen.
Furthermore, it happens predictably and reliably so that we can fit it into a mathematical model and math can be used as a substitute for true understanding.
So, the bottom line for the cat is this: we can’t ever observe the state of the cat without observing it; and we know that observing it changes the state. We know what the cat was like at some previous point in time, and we know what it was like after the observation; for the entire time in between, we simply do not know. That’s not so far off from common sense, except that observations and match say that it really appears to exist in a dual state of maybe dead/maybe alive up until the point we make the observation.
This is a curious paragraph. It asserts that the clock never “disappears or disintegrates into a quantum mist,” then explains exactly how, in my understanding, it does just that. When I’ve read phrases like “quantum mist” before, I’ve understood that to be a direct reference to the array of states–“mist” indicating fuzziness, uncertainty, the “smeared” particle.
“Uncertainty” in quantum mechanics has a very specific meaning, to wit the limit of an inequality of a combination of two complementary properties of a single element (usually taken to be position and momentum). The composition of all possible states is not uncertain (for a finite system) and in fact is very precisely known. This leads to the principle of quantum indeterminacy: that this uncertainty isn’t just our inability to measure the state of the system, or some kind of filter between quantum states and the macroscale world, but an actual behavior of quantum particles, that they don’t exist in a precise location and momentum state. Quantum particles, despite coming in discrete packets, are actually spread out little blobs of conditional probability.
However, this doesn’t mean that quantum systems stop functioning on the macroscale in absence of an observer. The correspondence principle allows that while quantum mechanics describes bizarre and sometimes “spooky” behavior on the level of fundamental particles, when you get to a system of large quantum numbers (a system with a lot of particles or very high energies) the behavior of the system is fundamentally indistinguishable from classical mechanics. The system posed in the o.p.–the clock in a room–can be modeled as a superposition of all possible states of the particles that make up the system, but that doesn’t mean it literally disappears into a “quantum mist” (whatever that is) or stops functioning in an essentially classical fashion, or whatever. All of the possible states still sum to conditions for the overall system that are approximately classical, with a limit of the differences between states that is less than can possibly be observed.
Quantum mechanics applies to particles, or the rare coherent system in which probabilistic behavior is seen on a macroscale. For normal decohered systems, doing all the work to resolve the superposition of quantum states gives you something that converges to the same result you would obtain via an application of classical mechanics.