Quantum theory is bizarre.

In order to try and understand it we need to forget everything we know about cause and effect, reality, certainty, and much else besides. This is a different world, it has its own rules, rules of probability which make no sense in our everyday world. Richard Feynman, one of the greatest physicists of his generation, said of quantum theory

"It is impossible, absolutely impossible to explain it in any classical way"

here we look at the famous "cat-in-the-box experiment"

Schrodinger's 'Cat-in-the-Box Experiment'

According to the Copenhagen Interpretation, the probability wave of an electron requires the act of observation by a conscious observer to collapse it into a definite particle, and thus have a definite location. We can imagine a closed box containing just a single electron. Now until someone looks in the box, the probability wave associated with the electron will fill the box uniformly, thus giving an equal probability of finding the electron anywhere inside the box. If a partition is introduced into the middle of the box that divides it into two equal boxes, still without anyone looking inside, then common sense tells us that the electron must be in one side of the box or the other. But this is not the case according to the Copenhagen Interpretation; that says that the probability wave is still evenly distributed across both half-boxes. This means that there is still a 50:50 chance of finding the electron in either side of the box. When somebody looks into the box the wave will then collapse and the electron will be noticed in one half of the box or the other, but it will only at the moment of observation 'decide' which half it will be in. At the same time the probability wave in the other half of the box vanishes. If the box is then closed up again, and the electron no longer observed, its probability wave will again spread out to fill the half box, but cannot spread back into the other half of the box that was empty. The way that a quantum wave moves is described by Erwin Schrodinger's wave equation and describes the probability for finding a photon, or electron, at a particular place. Schrodinger did not however, go along with the 'collapse of the wave function' theory, he thought it was nonsense, and designed 'thought experiments' to prove his point. In an attempt to demonstrate the foolishness - as he saw it - of quantum theory, Schrodinger devised the cat-in-a-box thought experiment.

In Schrodinger’s original thought experiment he used radioactive decay because that also obeys the rules of probability. We however, shall use our box with the partition and electron again, as we are now familiar with it.

Imagine we have our box with the partition in place, and the electron's probability wave evenly spread between both halves of the box. We have now added a device that will, at a given time, automatically open up one half of the box to the room. There is a 50:50 chance that when opened the box will contain the electron that is now free to enter the room. The room is sealed and has no windows that would allow any outside observations to be made. Inside the sealed room there is a cat, a container of poisonous gas, and an electron detector. The experiment is so designed that if the electron detector detects an electron it will release the poisonous gas into the room, which would prove very unfortunate for the poor cat. If, on the other hand, that half of the box does not contain the electron, the poisonous gas will not be released into the room and our cat, henceforth known as Lucky, will continue to enjoy good health, providing it keeps away from busy roads.

Taking a common sense view of the situation, we would say that when the experiment has run its course, and an observer enters the room, they will find the cat either dead or alive. But we already know enough about quantum theory to realise that common sense doesn't apply here, and instead we have to turn to the Copenhagen Interpretation for an explanation.

According to the Copenhagen Interpretation, when the lid of one half of the box is opened, it is not an electron, or not as the case may be, that is released into the room, but the probability wave of the electron as it has not yet been observed. This raises the question of whether or not the cat can be regarded as a conscious observer. If it can be then where do we draw the line? Would a fly or an ant count? How about a bacterium? As this is again getting into rather deep and murky water, we will skip over this problem and continue with our experiment; otherwise we run the risk of becoming seriously side-tracked. So the probability wave spreads into the room, not an electron (or no electron). The electron detector is itself composed of microscopic entities of the quantum world (atoms, particles and so on) and the interaction of the electron with it would take place at this level, so the detector is also subject to the quantum rules of probability. Taking this view, the wave function of the whole system will not collapse until a conscious observer enters the room. At that moment the electron 'decides' whether it is inside the box or in the room, the detector 'decides' whether it has detected an electron or not, and the cat 'decides' whether it is dead or alive. Until that moment, according to the Copenhagen Interpretation, the cat is not either dead or alive; it describes the situation as a 'superposition of states'. Only the act of observation will cause it to become one or the other. Schrödinger described the situation as 'having in it the living and the dead cat mixed or smeared out in equal parts.' The Copenhagen Interpretation does not allow for the room to actually contain a cat that is both dead and alive at the same time, or a cat that is neither dead nor alive, suspended in limbo. But contains either a dead cat or a live cat, until someone looks, and it is then that the actual reality of the situation is determined. Cat lovers please note. This experiment has never been carried out, and never will be. This is not only because it would be a very cruel thing to do, but because it wouldn't prove anything. An observer upon entering the room would find either a dead cat or a living one, but could not observe what processes preceded this event. Any previous observation would of course defeat the object of the experiment.

The problems highlighted by the cat-in-a-box experiment raise some very deep questions. What for example are the requirements needed to qualify as a 'conscious observer'? Do the probability waves of particles spread out again when not observed and particles somehow become less 'real', as described by the Copenhagen Interpretation? Does the universe exist only because we are here to observe it? Could a cat really be in a 'superposition of states', either dead or alive until the moment of observation? This goes entirely against all our common sense experience of life, we would naturally conclude upon finding the cat alive that it had 'obviously' been alive all the time. Quantum theory is telling us that we could be very wrong in our thinking regarding what reality really is.

Quantum theory has yet another surprise in store for us, and this time it's not simply another bizarre phenomenon that challenges our common sense. This time it contradicts one of the central principles of Einstein's theory of relativity, that nothing can travel