Archive for January, 2013

Schrödinger’s Cat

January 11, 2013

schrodingers_catNow let’s look at another thought experiment, that of Schrödinger’s Cat. This thought experiment is supposed to confound the micro and macro worlds of quantum physics and ordinary, human-size physics. A cruel device is built consisting of a closed box which contains a sample of radioactive material, a mechanism to release poison into the box if an atom of the radioactive material decays, a living cat, and a door that must be opened to reveal the condition of the cat to an external observer.

The story of the experiment goes that if the observer waits to open the box until there is a 50% probability that an atom decays, the state of the cat (hidden in the unopened box) to the observer will be both alive and dead. The cat’s so-called wave-function will be a superposition of the wave-function of a live cat and that of a dead cat, which will collapse into one or the other only by the opening of the door and the observation of the actual condition of the cat. This is called the Copenhagen Interpretation.

Some say that the detector of the poison release mechanism will be the true observer in this experiment, and before the external observer opens the door the cat will be definitely alive or dead because of the action of the mechanism. This might be considered the objective collapse theory. Others say that the world splits in two between a world where the cat is alive and one where the cat is dead. This is called a many-worlds interpretation.

There seems to me a similarity between Maxwell’s Demon and Schrödinger’s Cat. The fourfold elements of the experiment are shown above, but now consider these elements in a system in terms of Aristotles’s Four Causes. The material causes are the discreet constituents of the experiment, everything from box to atoms to cat to observer. The efficient cause is the decay or non-decay of a radioactive atom. The final cause is action of the observer in opening the box. The formal cause is the poor cat in its ambiguous state, simultaneously both dead or alive.

It doesn’t make too much common sense to say that the opening of the box and the observing of the cat “causes” the atom to have really decayed or not, and so concretize the past and the cat into a certain way of being, but that is mostly what the Copenhagen Interpretation is saying. Indeed, Linear Logic, which has been described many times on this blog, has been used to describe aspects of quantum physics for decades.