Schrodinger's Cat Experiment Explained

Introduction

Let's take a look at one of the Quantum Mechanics' most talked about and undisputed mother of all thought experiments, Schrodinger's Cat. Erwin Schrodinger (1887-1961), an Austrian physicist and theoretical biologist, is considered one of the founding fathers of Quantum Theory and the creator of the Schrodinger Equation, for which he won the Nobel Prize in physics in 1933. He came up with a thought experiment to demonstrate the bizarre character of Quantum nature.

Schrodinger's Cat Experiment

Here is its crude version. Imagine there are two steel boxes, one empty and in the other, we have a live cat. Along with the cat, there is also a mechanism to detect the presence of an electron, inside the box. If the mechanism detects the electron, it will open the cork of a bottle filled with poison and release it, resulting in the death of the cat. If the detector fails to detect the electron, the cat is safe.

Now, let's assume that a single electron is sent to both boxes at the same time (this is possible according to the QM principle and we also saw it in the double-slit experiment earlier). The whole contraption with a cat, the electron detector, and poisonous gas, Inside the box, is isolated from the outside world and there is no way of finding out if the electron went to the empty box or to the box that had the live cat. Now the question is: How do you know, if the cat is dead or alive without breaking open the box or peeking inside the box?

Well, there are broadly two interpretations of the poor cat's ultimate fate. The first is called the Copenhagen Interpretation, strongly advocated by Neil Bohr, and says that the cat is both dead and alive at the same time! The argument goes like this. The electron is in superposition state and exists in both boxes at the same time until someone collapses it by observation. But since the set-up is isolated, there is no way to observe and collapse the wave function of the electron. Recall, that in the case of the double-slit experiment, it was easy to actually see the electron going all the way from the electron gun to the screen and passing through the slit onto the plate. We don't have that advantage here. We are not sure if the electron that exists as a wave function has really collapsed within one of the two boxes. The detector in the box where the cat is kept, may or may not have detected the electron. We don't know for sure if the detector can collapse the electron resulting in the release of the poisonous gas that will kill the cat. What about the cat? Could the poor cat have collapsed the electron by observing it and thus inviting its own death? Since we are not sure about what's happening inside the box, the argument is that the cat is both dead and alive at the same time. That is to say, the cat is in a superposition state.

An opposing argument by Schrödinger himself and supported by Einstein, is that the cat is either dead or alive. According to them, the result is deterministic. The cat is either dead or alive! and there is no ambiguity about its state. So, the cat is not in a superposition or limbo state as stated by Bohr, but actually in only one of the two states. But which state it is in, is anybody's guess. The debate between the two schools of thought, one in deterministic (the cat is both dead and alive at the same time). and the other deterministic (the cat is definitely dead or alive), has been going on for several decades with no agreement on the final fate of the cat.

Conclusion

It is now obvious from the thought experiment and the lab based actual experiments, that the world, at its smallest level, does not obey the simple laws of nature that we are used to. The quantum craziness of nature continues to baffle one and all. There continues to be differing views on the nature of the wave function, how it actually collapses, who is the real collapser and so on, but at best these are only interpretations.

Einstein, who contributed immensely to the progress of Quantum Mechanics, was uncomfortable with the idea of uncertainty playing a role in nature. The mathematical treatment and QM experiments provide a good deal of the weirdness involved in the quantum nature of our world, but they don't deliver all the answers. One of the interpretations of QM is that only a conscious observer can collapse an object from its waviness to its real state. But this proposal is too sensitive even to discuss as a scientific argument. It is as though science has encroached into the domain of consciousness, whether it wants to or not! We will shortly take up the touchy subject of QM's venture into the field of consciousness, but not before taking one final look at another spooky aspect of the Quantum Mechanics called Entanglement.