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Why does the SPCA Hate Schröedinger? By: ScottN on 10/21/2001; 5:15 PM There are several interpretations of "what is the reality" behind Quantum Mechanics. The oldest, and most common interpretation is the Copenhagen Interpretation (CI). The CI was put forth by Niels Bohr in the 20's. According to the CI, no quantum entity has ANY properties until those properties are measured (properties include things like momentum, spin, polarization, etc...). So, getting back to the subject of this little post, why DOES the SPCA hate Schröedinger? Erwin Schröedinger was one of the pioneers of Quantum Mechanics. In fact, he derived the basic equation for Wave Mechanics. However, he also came up with a thought experiment that shows just how crazy the CI is. This experiment is called the "Cat-in-the-box" experiment. Take a cat, and lock it in a box (actually a steel chamber) with food and water (we're not totally cruel) and a diabolical mechanism. The mechanism consists of a single radioactive atom (with a suitably short half-life), a detector, a vial of poison gas, and a hammer. If the detector senses the atom going through radioactive decay, the hammer smashes the vial, and the poison gas is released, killing our cat (this is the part the the SPCA really doesn't like). Now, after we have sealed the cat and sundries into the box, we wait for a period equal to the half-life of the radioactive isotope. Without looking into the box, we ask "What is the state of the cat?" It turns out, that according to the CI, the cat is neither alive nor dead! Rather it is in a "superposition of states", which -- to my mind, at least -- is a fancy way of saying we don't know. Because there is no way to predict when a particular atom will decay (we only know that after a half-life, it has a 50-50 change of having decayed), there are two equally probable wave functions within the box. (A wave function is a quantum mechanical description of a system). One corresponding to a live cat, wondering what the heck is going on, and one corresponding to a dead cat. This is where the CI conflicts with everyday common sense. Either the particle decayed and the cat got killed, or it didn't and the cat is fine. But the CI states that neither is the case, it is both at once, and until we open the box, both possibilities are equally real. At the moment we open the box, the wave function for the system "collapses" and we find either a live cat or a dead cat. BUT the choice of a live or dead cat did not exist until we opened the box!!!! This experiment begs the question aforementioned principle of the CI that nothing exists outside of measurement. What is necessary to collapse the wave function? Is a human required? What about the cat? Surely it is able to notice that it just stopped breathing? If the cat's observations are insufficient to collapse the wave function, where do we draw the line? Is a geiger counter alone sufficient to observe a quantum event and collapse the wave function? Personally, I don't have the answers to these questions. I have my own opinions, but I'm not here to impose them on you. After all, I Could Be WrongTM. What I'm trying to do is intrigue you with the wonders and oddities that this branch of science has, so that you will go out and look for the answers on your own. A few titles to look at (in no particular order):
Happy Discovering!
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