In quantum mechanics, often, no matter how much we know about sub-atomic particles, it is impossible to predict or control what they will do next. All scientists can do is tell you the probabilities. For example, there might be a 50-50 chance of a particle decaying in a piece of radioactive material in a given time. If no one observes whether or not a particle decayed, quantum theory DOES NOT SAY that it EITHER decayed OR it didn't. IT SAYS it NEITHER decayed NOR it didn't. Nothing is real unless it is observed. All that exists are two ghostly possibilities, that collapse into one reality when we make an observation.
In the world of sub-atomic particles whether or not, and how we are observing an experiment can make a profound and sometimes incomprehensible impact on how that experiment turns out. In some experiments with electrons scientists find that the electrons change their behavior according to how much attention the scientists pay to them. The electrons act like they are waves until scientists monitor them more closely, and then they change their behavior to act like they are particles.
The most famous thought experiment in quantum theory, "Schrodinger's Cat," looks at the implications of this uncertainty. It is named after its creator, Erwin Schrodinger (one of the founders of quantum mechanics). It is only an intellectual exercise. Here it is:
You place a piece of radioactive material that has a 50-50 chance of having one of its atoms decay in a box with an instrument set to detect whether or not that decay occurs. The instrument contains a vial of poisonous gas which it will release if an atom decays within the time allowed. Before you seal up the box, you put a cat inside. Then, when it is time to re-open the box, you try and convince yourself that its not that you don't know whether or not the cat has survived, but that the cat has entered the ghostly world of quantum probabilities and it is neither alive nor dead until we open the box and make our observation.
When I first heard this thought experiment explained I couldn't understand it. Apparently, I'm not alone. In the horror film, “The Prince of Darkness”, the main character, a graduate student in physics, complains that it makes no sense. Her professor in the film, like my own teachers, used the thought experiment to force quantum theory on the human world, and "prove" that nothing is real unless it is observed. What our teachers didn't tell us is that Schrodinger thought up the experiment to prove the inadequacy of quantum reality. He wanted to caution scientists from reinterpreting the human world to fit the rules of sub-atomic particles. He would have agreed with all the confused students that it made no sense to say that the cat was neither alive nor dead.
So it goes. The popular "explainers" of science usually run their theories rough-shod over everything as they try to reduce the whole to the sum of its parts.
The most interesting development in recent physics is the growing consensus that in some almost mystical sense, the whole is greater than the sum of its parts. In the sub-atomic world there are pairs of particles that always spin opposite each other. Scientists have been able to split these pairs up in such a way that it is impossible for them to communicate with each other. But still, when they mess with the spin of one particle of the pair, the other particle somehow knows that its partner has changed its spin, and immediately it alters its own spin accordingly. It is as if there is a principle of "wholeness" or unity in the universe that seems almost supernatural. This is why a lot of physics books have turned to mysticism, and come out with titles like, “The Tao of Physics” or “The Dancing of Wu Li Masters”.
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