Okay, I understand the experiement. There’s a cat in a box. Inside the box is a posion gas canister, triggered by the decay of a certain particle that has a 50% chance of decaying on any particular day. Until the box is open, there is no way of telling if the particle decayed thus Dead cat or didn’t thus live cat.
My question is, exactly what is this supposed to prove? That you won’t know the cat is alive or dead until the box is open? That you won’t know if the particle is decayed until the box is open?
For some reason the hesienberg uncertainty principle comes to mind, that there’s some information that cannot be known, but I suspect I’m on the wrong track there.
It wasn’t an ordinary cat, it was a quantum mechanical cat. As such it was not the case that, until we opened the box, we did not know if the cat was alive or dead, but that the cat was neither alive nor dead (or both alive and dead, whicever you prefer). The cat only settled on being alive or dead when the box was opened and the very act of observing it made the superposition of alive/dead states collapse into one or other, with a 50% probability for each.
The motivation was not to explain anything about the nature of cats. It was to illustrate the nature of quantum mechanics and show just how odd, compared to our everyday experiences, quantum mechanics is.
More specifically, it was meant to illustrate the big unanswered question in Quantum Mechanics: if atomic and subatomic particles exist in superposition, then why doesn’t the macroscopic world?
This question is the subject of an article in the latest Disocover magazine. Mathematician Roger Penrose proposes that the answer is that gravity imposes a time limit for how long an object can be superimposed. He postulates an experiment in which a macroscopically observable piece of matter ( a small piece of very light gold foil) could in his theory remain in superposition for about a second. By using this piece of foil in a beam-splitter experiment, you could demonstrate (if not directly observe) that it had in fact been superimposed.
His version of the thought experiment isn’t currently workable, but physicists are trying to modify it into something that could be performed in a lab.
You wanns know the worst/best part? That’s about as basic as physics gets after Newton. Schroedingers cat is arguably the least complicated idea in physics (of the commonly known problems, anyway).
The probability of the cat being alive when you open the box is 1/2. But the thought experiment is going further. It is speculating as to whether, if atomic and subatomic particles exist in superposition (that is, exist in two states at the same time till it is observed which state they are in), and if the macroscopic world is dependent on atomic and subatomic particles, the cat is both dead and alive until you observe which state it is in.
No, it’s Schrodinger trying to illustrate a problem with Quantum Mechanics. In the everyday world, a cat is either alive or dead, period. But in this experiment, it’s alive AND dead at the same time until you open the box. So Quantum Mechanics isn’t adequately describing reality.
Don’t worry about the uncertainty principle in this one. Basically, Schrödinger had figured out something that the equations said particles should do, but when you blow it up to the everyday world it was nutty. He picked this concrete example to link the two levels in an attempt to show that something must be wrong with the way everyone was going with quantum mechanics.
Basically, we have our little ideas about atomic particles, but we’ve got real experience with things like cats. Something weird at the atomic scale doesn’t trigger our “hey, that’s not right” reaction as much as something weird on the classical scale. So using the decay of an atom (an event at the quantum scale) to trigger the death of a cat (an event at the classical scale) turns the superposition of decays/doesn’t decay – which we might chalk up to “hey, particles are weird” – into a superposition of cat dead/cat alive – which is simply ludicrous. Obviously, then, quantum mechanics must have made a mistake somewhere. That’s Schrödinger’s point.
Except he was wrong. Quantum mechanics was dead-on, and particles do end up in superpositions. I don’t recall a link offhand, but I think someone’s even taken a picture of it (in some sense).
Sort of, but it’s also attempt that acknowledges its own failure. The assumption is that cats, at least as we know them, cannot be alive and dead at the same time. Thus the point is made that, quantum physics, at least as we understand it, cannot describe macroscopic objects such as cats. Thus, in order to find unifying theories, we must gain more understanding about either quantum physics or cats.
It has also been theorized that quantum physics actually describes the system accurately because cats can be superimposed into no less than 9 possible states.
Just in case the OP still doesn’t get it and because no one’s yet made it pervectly clear:
According to Quantum Mechanics, the particle does not have a 50% chance of decaying or not. The particle actually exists in a superimposed state of both having and not having decayed. Upon detecting the decay (by opening the box) the particle becomes fixed in one state or the other, ans so we have a 50% chance of finding a decayed or undecayed particle, but up to that point it was both. Schroedinger was showing how this could have problems at the macro scale.
What I don’t get is how you mathematcally define observation. Why doesn’t the gas canister “observe” the particle by either being triggered or not, thereby collapsing the waveform. What is it about human eyes (or a human brain) that affects uantum reality like nothing else does?
The way it was explained to me by ex Univ. of Calif. physics professor Howard Wilcox is that an interaction of a quantum entity with anything is an “observation.” Macro entities are always existing because their quantum particles are always interacting with each other and are therefore “observed” and so are in some defined state or other.
In the case of the gas canister, as I understand the experiment the quantum entity has not interacted with the canister until some kind of observation is made.
I think I understand it now. Thanks to everyone who contributed.
I think quatum/relativitic physics are facinating, but sometimes it’s a bit tough to fully understand.
I guess I’ll have to take another crack at reading The Elegant Universe, which I liked but had to quit because it simply became too difficult to comprehend after a certain point.
If nothing else, the cat has certainly made an observation. I don’t think quantum mechanics insists on human observation!
Schrodinger’s Cat is a good thought experiment. It’s not perfect, but it doesn’t have to be. Its point is to make you think about the implications of QM theory (and illustrate some of its potential problems), and it does that quite well.
