J Thomas wrote:But this is not what is observed. What is observed is that the statistical distribution of buckyball detections fits a pattern of interference even when it appears that on average one buckyball passes through the slits at a time. The actual passage of buckyballs through the slit is not observed, and cannot be observed without destroying that statistical distribution. The path of each buckyball is undetermined. It is not known that each buckyball goes through both slits, unless you know there is no other way they could produce that interference pattern.

As doogly already mentioned, the problem with this assertion is that you still see an interference pattern on the sensor even if you shoot only one particle down the line.

However, I'm not certain that the double-slit experiment is really the right example to clarify what the Schrodinger's Cat thought experiment was meant to demonstrate. The double-slit experiment just shows that particle behave in some wavelike ways; that particles really are just waves, perturbations of fields of energy. Waves that can only exists in multiples of discrete units, which makes them in some ways unless ordinary macroscopic waves we are familiar with, and more like ordinary macroscopic particles which also come in discrete units.

But the behavior of waves can still be plotted deterministically just as easily as the behavior of particles can. Schrodinger's Cat is all about indeterminism. The point of it is that there is absolutely no way to tell with certainly whether a radioactive particle will decay or not at any given moment, so if you do not make any observations of the particle for some time then there is absolutely no way to tell with certainty whether or not it has decayed. You cannot predict it, in principle: the information is completely inaccessible until you actually observe the particle and see whether or not it has decayed. Information which is in principle completely inaccessible is effectively nonexistent.

For illustration, most people will intuitively agree that there is no concrete fact of the matter

right now about whether the particle will decay five minutes from now; there is only a particular probability, as the future is undecided. But if we make no observations of the particle for five minutes - it's now five minutes later - then it is equally true that there is no fact of the matter

right now about whether the particle

has decayed by now or not; there is only a particular probability. There is a fact about the present which is not merely unknown, but completely absent. The universe contains precisely the information that a perfect model of it contains (that's what it is for the model to be perfect), and if quantum theory is correct then it is impossible for any perfect model to contain concrete facts about whether or not an unobserved particle will decay or has decayed, and therefore the universe itself does not contain such a fact; merely some set of different possibilities.

More particularly, the Schrodinger's Cat thought experiment is meant to discredit one particular interpretation (the Copenhagen interpretation) of how these sets-of-possibilities types of fuzzy impact us people in the world we're accustomed to. Everyone agrees that if the state of the particle is indeterminate, then the state of everything the particle is interacting with must also be indeterminate, such as a Geiger counter set up to go off if it measures radioactive decay. And then everything interacting with that must also be indeterminate, such as the can of poison gas set to be opened if the Geiger counter goes off. And everything interacting with that must also be indeterminate, such as the cat that would breath that gas and die if the can were opened.

The "box" that all of this is imagined to be in is some kind of impossibly insulating container basically set up in the hypothetical situation to prevent us from interacting with what's going on inside it until we decide to do so; think of it like a breakpoint in a debugger. The code has stepped through each line from the particle through everything else it's interacted with, and because the particle returned an array of possibilities rather than a single value, each other variable set at each step also has an array of possibilities rather than a single value, and then it hits the edge of the box and the execution breaks. We look in our debugger (our model of what's going on inside the box) and see all these arrays of possibilities as values for every variable -- including the life of the cat. It's not just a "0", or "1", but it's not a "0.5" either; it's something more like [0,0,0,0,1,0,0,1,1,1,0,1,1,1,1,1]. Then we step over the breakpoint (open the box) and...

...the Copenhagen interpretation has it that our act of observation essentially picks a value at random from the array of possibilities about the life of the cat and fixes the cat_life variable to that, which then requires that each other variable related to that one become fixed to values consistent with the cat being how we observed it. So all of these variables which had arrays of possibilities for their values now have fixed values. Information which did not exist before suddenly now exists: there is now a concrete

fact about whether the cat is alive of dead, where there was none before, solely

because we looked at it. Observing it

made the cat alive (or dead), when it wasn't really either until then. Observing the cat didn't just discover a fact, it created the fact. According to Copenhagen, at least.

According to Everett, whose many-worlds interpretation is Copenhagen's main competitor, what happens instead of that when we interact with the cat in its undetermined state (by observing it), the fact about what we observed also takes on an array of possibilities rather than a concrete value, and all the other facts about what we think and act in response to that observation take on arrays of possibilities rather than concrete values, and every fact about anything affected by what we do in response to that also takes on an array of possibilities rather than concrete values, and that since everything exhibits this indeterministic behavior a the base level anyway, every fact really has an array of possibilities rather than any concrete value, including facts about the state of the entire universe. It's not just that the values of these facts are imprecisely known to us, they really don't have concrete values; the cat really is both alive and dead, and we really do observe it as alive and as dead, and we remember seeing it alive and we remember seeing it dead, and we write in our reports both "the cat was alive" and "the cat was dead", and so on and so on... and the whole universe is working like this, with every way the universe could go, actually going that way, all together at the same time.

If there are indeterministic processes in the universe, those are basically our options. Either there is something special that happens at some level of interaction and facts can be created from nothing just by being observed to be so, or the whole universe exists in a superposition of possible states just as much as each particle does. Pick your flavor of weirdness. Personally, I prefer the option that has the universe consistent at all scales and doesn't ascribe magic powers to human observation.