Schroedinger's Cat

Most recent answer: 01/25/2013

Q:
Okay, so the Schrodinger's Cat experiment supposedly proves that things can lie in two states at the same time until reality "chooses" one or the other. I have a few problems with this. 1. Someone must observe our existence at all times, otherwise we either do or do not exist and it is all left to chance. How does this work? And how can an unpersonified "reality" have any sort of choice in the matter? 2. Now, if we observe our own existence, doesn't the cat observe it's own? In that case, the cat sees whether or not it is alive and the entire experiment collapses, doesn't it? 3. If the problem is that we don't know the state of the cat's existence, then that would mean that all existences are both personal and relative. The chances of everyone's separate realities (in this case) lining up is practically impossible, right? Last point. 4. Schrodinger's cat is also used to support multiverse and parallel universe theories. If the experiment fails, as I think it does, those theories have little to no foundation. However, what would it be that makes these parallel universes? Where do they come from? How many are there? There must be a finite number assuming that time is finite in which case where did time come from? Or if time is infinite, then by simple logic, the present would never arrive. So... How can anyone really support the experiment and applications of Schrodinger's cat? Sorry my question was so long... Thank you for taking the time to read and answer it.
- Leaena (age 15)
A:
That's an intense set of questions. Here's some answers in order of how definite I can be.

3. The beautiful thing about the basic quantum mechanical time-dependence equation (descended from Schroedinger's equation) is that although its solution contains many weird combinations (live cat and dead cat) it contains no inconsistent solutions. (Live cat+ you see dead cat) simply isn't part of the resulting quantum state. There's no part of the state where you see a live cat and your friend sees a dead cat. The simple formal math, with no tricks, already has everything "lined up" into a set of distinct, internally consistent, possibilities.

4. I don't know what you mean by "the experiment fails". Perhaps you mean that the basic equations of how quantum states change would fail. That's certainly a possibility that has been considered, but so far in every test the usual equations work, on increasingly large scales. If the basic equations, which are strictly linear (and unitary), do hold, then the different pieces (live cat, dead cat, etc. ) all are required to be there mathematically. I'm not sure I follow the rest of this question, so you may want to follow up.

2. Yes, those interpretations which hold that somehow consciousness plays a key role in "collapsing the wave function" always run into serious problems in deciding whose consciousness counts.

1. I'm not sure I follow this one either. It sounds like these are issues for consciousness-based interpretations but not for more physical ones. Again, you may want to follow-up.

Mike W.





(published on 01/25/2013)

Follow-Up #1: What did Schroedinger's cat mean to say?

Q:
Thank you for your time in reading this and explaining.In order of your responses... 3. So instead of some sort of subjective reality, the choices are consistent, right? How? I mean, if it's just up to chance, why isn't something different? 4. By failing, I was referring to the collapsing of the experiment spoken of in my previous questions. If the results prove nothing, really. The results of the experiment have been used to support multiverse and parallel universe theories (such as saying each possible outcome occurs in a parallel universe). The rest of my questions stemmed from that observation. 2. Is there any commonly accepted conclusion as to whose consciousness counts? If so, what is it and how is it supported? 1. According to the experiment, the cat is alive and dead at the same time until it is observed, correct? At that point, one state or the other is chosen and becomes reality. Using that logic, we would all exist and not exist simultaneously until we were observed. Therefore, someone must observe our existence at all times. How? And what exactly decides which state the being/object in question is in?
- Jessica (age 15)
A:
Jessica- before getting into the answers, I should clarify what we know from experiments that already have been done, and what we surmise, on the basis of theory or philosophy or something.

Many real experiments show that smallish things exist in quantum states that include parts which we feel shouldn't coexist. Molecules like buckyballs can wave their way through two spatially separate holes at the same time. Small vibrating rods can be a two distinct positions at the same time. Little quantum circuit loops can have mixed states of current going clockwise or current going counter clockwise. etc.

We know that there isn't some hidden answer to which hole the ball went through, etc. because any form of theory with those "hidden variables" obeys certain rules called the Bell Inequalities, which nature does not obey. You can search this site or the Web for more on that.

As for what goes on at the scale of cats and people, we know what experience is like at our scale. We never see some sort of combination of really different possibilities. A ball doesn't simultaneously go through hoops at opposite ends of the court.   If you solved the quantum equations, which work beautifully on a small scale, for large-scale objects, then the solutions have things in them like combinations of dead and live cat.  So the point of Schroedinger's story was to make us try to think about how to put together the quantum equations and our experience.

The two main families of answers are that
A. the equations always work and the resulting physical state must contain all the possibilities, including different versions of us.
B. Somehow there's something missing from the equations and at some point only one of the possibilities emerges as real, with pure chance deciding which one.

OK, with that background, let's go back to your question.

3. The solutions of the equations contain no terms like |dead cat> |you see live cat> So regardless of the interpretation, we don't have to worry about that. If we go with interpretations of type (A) ("many worlds") then there's no choice to worry about. It all happens, with each result being fully self-consistent, following the basic rules. If we go with interpretations of type (B) ("wave-function collapse"), then we actually do run into a problem in explaining how the collapse of different parts of the state at different places in space manages to happen in a consistent way. I don't know of any satisfactory solution to that problem.

4. No further question here, if I read you right.

2. No, there isn't.

1. These questions bedevil interpretations of type (B). Some people have tried to make explicit theories in which the quantum state actually collapses over time according to some sort of rules. Consciousness plays no role in those rules. At any rate, these efforts haven't succeeded. Given these problems, you can see why some types of physicists are leaning toward interpretations of type (A) these days.
In type (A) interpretations, when your mind interacts with the cat, say by looking at it, the state of your mind splits into two distinct branches, one seeing the live cat and the other seeing the dead cat. These interpretations also have a technical problem in accounting for the particular probability rule, since there's no extra collapse step where you can make up the rule needed to get the right probabilities. You can see why a lot of people do not find type (A) interpretations appealing either.


Mike W.

(published on 01/27/2013)