I think we all know the story of the Schroedinger’s Cat experiment (here is Cecil’s take on it). IANAQuatum physicist. So my explanation and take on it might not be that good. But basically (as I understand it in my “limited” way) it says that reality only collapses into one form when we perceive it. Schroedinger’s experiment gives the example of a cat, and a device that kills it at random in a closed box (why the cat’s perception is not relevant also puzzles me–but I digress).
Anyways, forgive me, but I don’t believe this assertion at all. It goes totally against common sense, I think. For example, now I am at my computer in one room in my house. Just because I am not in another room, for example, doesn’t mean there is anything unusual happening in the other room/s. Anyways, I have an example which I believe demonstrates what I am talking about: clocks. The clocks in my house continue telling time, even when I am not directly perceiving them. Now, it is claimed the cat isn’t dead until perceived by a human. But if this was true of clocks, wouldn’t they show a different time or stop(-?) completely if I exited a room? Then when I come back to the room, I would notice this had happened–no?
Anyways, as I’ve said, IANAScientist. So please someone tell me what I am missing here (including as I said above, why the cat’s perception isn’t important BTW).
Actually, this is based on a misunderstanding of the Schroedinger’s Cat thought-experiment. His idea was actually to show why certain interpretations of quantum mechanics were ridiculous. He never believed that’s what actually happened. He agreed with you.
My understanding was that although Schroedinger himself proposed it as you say, it was nevertheless accepted by other quantum scientists then and now, with the reaction of “Yes, you’ve illustrated it quite well. And it does seem ridiculous. But it is nevertheless true and accurate. If only we could understand it!”
As soon as anyone says “It goes totally against common sense” about any aspect of QM, the battle is already lost.
Nothing about QM has any relation to common sense. In the first place, there’s not the slightest reason to think that the behavior of atoms at the most basic level of existence should have any relationship to what we see in the everyday world. Common sense tells us an amazing series of wrong things, like the obvious common sense fact that the world must be flat because people on the other side would fall off.
QM works as math. When people try to express it in words they need to use analogies, which are more or less bad but never can express things that otherwise have no correspondence to anything in the macro world. (Understanding exactly why there is a macro world is a great question, but not the one asked by people wanting common sense answers.)
But of course we continue to insist on “common sense” because that’s the human way. And we continue to insist on words because few of us want to study for the years needed to understand the math.
I just wish that people would stop blaming the analogies for not making sense. It’s very much like zen. You comprehend the answer by letting the truth emerge. It’s very much not like a textbook in which the answers are in back.
Still, the physics pedants on the Board are often fairly adequate at giving the subject some slight comprehensibility. Which in QM terms is high praise.
Of course, Schrodinger’s own opinion isn’t determinative. The illustration may be useful even if he was wrong.
There’s nothing special about clocks.
The walls in your house continue being the same color in the same sense (whatever that may, in fact, be) that the clocks continue telling time. You’d notice if the wall was suddenly a different color when you came back, too–but there’s no reason for such an inexplicable reality to collapse out of the quantum possibilities.
Think of it this way. If there is an observer effect, there must be some characteristic or quality which separates observers from mere objects in the universe. What is that characteristic? Does it imply or require consciousness? How much consciousness? Do all humans do it all the time, necessarily? (While asleep?) Conceiving of this characteristic as a functional boundary, actual cats might or might not be on the same side of it as we are. (If they are, substitute something else for the cat to keep using the illustration.)
There is a pretty accessible explanation of at least part of this issue in From Eternity to Here by Sean Carroll. (The book has received generally positive reviews though is not without its critics.) It is primarily about the nature of time, but does have a few things to say about QM. Most interestingly, Carroll explains one model used to describe this type of phenomenon, the “many worlds” interpretation.
He goes on to say that, in the many worlds model, after you observe an outcome, your consciousness splits off into two branches of the wave function; one, for example, who saw a dead cat and one who saw a live one. But that’s not how the experience seems to us, so it’s difficult to accept. Further, to clarify that “many worlds” is really a misnomer:
He also describes the Copenhagen interpretation that describes wave function collapse. He seems partial to “many worlds.”
It’s important to remember that both interpretations of QM are mathematically equivalent, even though the way the math is interpreted seems contradictory.
The point of the Schroedinger’s Cat thought experiment is that the situation is set up in such a way that a macroscopic event (the killing or otherwise, of the cat) is dependent on the occurrence of events (radioactive decay of atoms) that occur at the quantum level. This is a very special and unusual circumstance. Very few macroscopic events are subject to quantum indeterminacy of this sort. Although everything is technically subject to some quantum indeterminacy, for most ordinary sized things, things observable at the human scale, it is vanishingly small, and can be ignored for all practical (and most impractical) purposes. Unless your clocks are somehow set up to be under the control of radioactive decays or some similar quantum level process, there is no reason to expect them to behave in an indeterministic manner, and whether you observe them or not will have no impact on how they do behave (just as common sense tells us).
Cheshire Human (who should know, if anyone does), is, of course, right to point out that the cat thought experiment was intended to show that something is wrong, or incomplete, about quantum mechanics (as interpreted by Bohr and Heisenberg). The story is meant to be absurd, but most physicists seem to have preferred to embrace the absurdity rather than reject the theory (because it works so well in so many other respects). However, be that as it may, quantum mechanics does not, in any meaningful way, predict anything absurd about your unobserved clocks.
I don’t know what Scroedinger intended, but it’s not absurd to have a mathematical model that defines multiple possibilities when there is an a unknown factor. njtt points out that the absurdity comes from the way the situation is posed. The system inside the box can’t have the cat alternate between life and death as random events occur, the first random event kills the cat. The model can’t determine whether the event occur or not at any specific time, and neither can you unless you open the box.
I don’t understand what happens in quantum mechanics, but if it exhibits the behavior of a mathematical model like that, there’s nothing absurd about it.
Exapno, people can’t fall off the other side of the world because no one could be there in the first place. If you make it past the monsters, mountains, and waterfalls that encircle the world, you’d just fall off and land on the back of a turtle.
By which he means that the possibilities–the “paths,” if you will, of the split consciousness in that interpretation–continue to coexist, right? No “worlds” have been added or removed; they’re all “there” all along, threads unwinding out of the same skein of possibility. But any one observer’s perception will seem, internally, to just follow one thread. (Correct me if I have misstated Carroll.)
This interpretation lends itself to many kinds of further speculation, like this.
And finally, if you like what reading this stuff does to your brain, be sure to check out the writings of Greg Egan, particularly the novel Quarantine (Copenhagen wavefunction collapse) and the story “The Infinite Assassin” (Everett-DeWitt many-worlds).
On the contrary, the whole point is that this could indeed happen. The probability is absurdly small, but that’s not the same as impossible.
All of the subatomic particles in that wall are very busy doing whatever it is that subatomic particles do, and one of the great things about being a subatomic particle is that you don’t have to do anything in particular. Of course, you’ll probably do this, and probably not do that, and the probabilities are such that on a macro level, the local humans will never notice the occasional particles that did the unexpected. But the fact is that the laws of probabilities do allow the unexpected to occur, provided that it doesn’t happen too often.
But once in a very great while – and for our purposes, this could take a googolplex years or more – all the subatomic particles in that wall could transmute their atoms into pure gold.
I will concede that for practical purposes this will never actually happen, but for theoretical purposes it certainly can.
You’re right. At least to the limits of my understanding.
I think the illustration still correctly suggests why the evidence of clocks seeming to keep time in accord with a pre-quantum understanding of reality is no more meaningful than the evidence of other parts of our physical surroundings seeming to keep existing as they are.
Schroedinger made up the story of the cat to say, “If what you’re saying about quantum mechanics is true, then the cat is both dead and alive. That’s obviously ridiculous, so what you’re saying about quantum mechanics must not be true.”
And the quantum greasemonkeys (what do you call comeone who works with quantum mechanics, anyway?) replied. “You’re right. In the large-scale, everyday world it would be ridiculous. But it’s a fact of life in the sub-atomic quantum world. Which is why quantum mechanics is such a bear to understand.”
