Jack the Poodle and Schroedinger’s Cat
In my house there lives a small poodle named Jack, who thinks he is very fierce. One day I asked him what he thought of the seeming paradox in the thought experiment posed by Erwin Schroedinger in 1935 to illustrate an aspect of quantum physics. Basically Schroedinger had said that one could imagine a cat shut up in a steel box, and that in that box were also a Geiger counter with a bit of radioactive material so small it would, on average, only emit one particle in an hour’s time as it decayed, and a mechanism linking the Geiger counter to a hammer that, if a radioactive particle were counted, would smash a vial of hydrocyanic acid, which would then kill the cat.
I explained to Jack the Poodle that, according to quantum mechanics, until the box was opened after an hour’s time and the cat’s status of being alive or dead was confirmed by observation, the cat could be supposed with equal validity to be both alive and dead at the same time. Because of this, reality was thought to be a function of the observer, and thus had no objective existence. The implications of this idea had far reaching effects, and indeed, whole philosophies used this cat as an example to illustrate their concepts.
Jack thought for a few moments in his doggie way, and then made the pronouncement that I was missing the point. When the box was closed, it didn’t matter whether the cat was alive or dead, because it was in the box. When the box was opened, he would sniff the cat, and if it was dead, he would know it. If it was alive, he would bite it.
“What you imagine about something you don’t know is irrelevant,” Jack continued. “It’s what you do about what you do know that matters. You could just as easily imagine the cat wasn’t in the box at all, because you couldn’t see it, and that opening the box and looking inside made the cat appear again.”
I thought for a while on what Jack had said, not having the advantage of his direct mind, and realized he might be on to something. I needed to know more. “What about the wave-particle conundrum,” I asked him, “where light can be demonstrated to behave as a wave when measured with wave detecting instruments and as a particle when measured with particle detecting instruments? Doesn’t that show that the observer determines the reality of what is observed?”
Jack appeared amused at the question, then said, “Do you see the rubber ball there, that you seem to think I want to run after endlessly until I’m exhausted?” “Yes,” I replied.
“Well ...,” said Jack, “is it round or is it red? Is it rubber or does it weigh 2.6 ounces? Any thing that you give a name to may have many qualities; the fact that you identify it with a name only means you are thinking of it symbolically for convenience’ sake. Giving it a name does not define it or its possible actions and relationships. Instead, the symbolic name you give it actually tends to limit your thinking about it.” He tilted his head, as he often does when he wants to see if I’m really paying attention. “You think that the idea of the ball, and the symbol of the name, and the mental construct you attach to the symbol, tell you some thing about that idea. But you don’t actually think about this ball, here and now. This ball is what it is, not what your idea of a ball is. In the same way, you think light, and believe you know what light is. Then you are surprised to find that light has as many properties as you have ways to measure them.”
I had to try once more to get Jack to see the marvelous possibilities of quantum mechanics as applied to philosophy. “All right, I said, what about Heisenberg’s Uncertainty Principle? If you interact with a particle to determine its location, you cannot at the same time determine its motion. No particle (if such things even exist) can be said to have a particular motion at a given location at any one time. Again, it is the observer that creates the reality of one or the other, and the particle’s state is undetermined until it is observed.”
“And when you observe it,” said Jack, “it is as you observe it. If you find my ball in the dark by kicking it, that is different from finding my ball by looking at it in the light. If you want to see where it is and how it is moving, you only have to turn on the light before you kick it. If you do both, you can see both, if you do only one or the other, you will only know one or the other.”
Jack sighed and again tilted his head. Then he patiently continued. “You imagine what you don’t know and are amazed to find that your imaginings don’t match what you later find to be true. You give something a name, as if naming it means you know everything about it, then you are amazed to find out something new that wasn’t contained in what you thought the name meant. You use one sense and are amazed when another sense tells you more. You think you see enlightenment in your confusion, but you are only confused because you refuse to see what is in front of you, and refuse to understand what is obvious. Simply open your mind a bit, and get over that business about opposable thumbs. The answers are there, when you are ready to see them.” Then Jack licked my hand, and trotted off to see what new things might have materialized in his dish.
The following is excerpted from “The Present Situation In Quantum Mechanics,” by Erwin Schroedinger, a translation from the 1935 original German by John D. Trimmer, and was found at: http://www.emr.hibu.no/lars/eng/cat/default.htm (site availability currently discontinued). Many other similar examples are also available elsewhere. The paragraphs preceding those that follow here discuss misunderstandings that result from equating mathematical descriptions (the psi-function) with reality. The emphasis is Schroedinger’s.
One can even set up quite ridiculous cases. A cat is penned up in a steel chamber, along with the following device (which must be secured against direct interference by the cat): in a Geiger counter there is a tiny bit of radioactive substance, so small, that perhaps in the course of the hour one of the atoms decays, but also, with equal probability, perhaps none; if it happens, the counter tube discharges and through a relay releases a hammer which shatters a small flask of hydrocyanic acid. If one has left this entire system to itself for an hour, one would say that the cat still lives if meanwhile no atom has decayed. The psi-function of the entire system would express this by having in it the living and dead cat (pardon the expression) mixed or smeared out in equal parts.
It is typical of these cases that an indeterminacy originally restricted to the atomic domain becomes transformed into macroscopic indeterminacy, which can then be resolved by direct observation. That prevents us from so naively accepting as valid a “blurred model” for representing reality. In itself it would not embody anything unclear or contradictory. There is a difference between a shaky or out-of-focus photograph and a snapshot of clouds and fog banks.