Schoedinger’s Cast

Just one possible experiment in a theatre among many

Performed by Alan Cox at the Soho Theatre, 17th May 2006

Written by Caspar Addyman 2006

We are all familiar with Schroedinger’s cat. A simple little thought experiment that illustrates the bizarre nature of quantum mechanics.

But very briefly, a cat is placed in a sealed box with a flask of poison. Poised over the poison is a hammer held in place with a radio-active trip-switch. If a particular nuclear particle decays it trips the switch, dropping the hammer, smashing the flask and…. killing the cat.

In the course of the experiment there is a 50% chance the particle will decay. So there’s a 50% chance the cat will live or will die. Open the box and you’ll find out what happened to your cat.

All very clear, all very elaborate and all very cruel. So why are we doing this? Because the Copenhagen interpretation of quantum mechanics states that events don’t really happen until they are observed.. it is the act of observation that collapses the wave function of the system… whatever a wave function happens to be.. actually it’s sort of like a possible history of your system.. which in this case is the whole sealed box with cat and caboodle inside.

So what Schroedinger pointed out was that until you open the box, observe the health of your pet, your cat is a weird superposition of states, it’s alive, it’s dead, it’s both and it’s neither. It’s a great mystery, that act of measurement has profound consequences, having an audience changes everything.

Now this is a deeply unsettling and unintuitive idea. There have been lots of objections.. One alternative suggestion (Everett, 1957) is the universe itself splits into separate worlds, one where the cat is alive, one where he is dead. But only when we open the box is it resolved into which one we have moved. This seems to replace one mystery with an even bigger one but as of right now this ‘many worlds’ interpretation is the only alternative to the Copenhagen er.. orthodoxy. But it was another 30 years before anyone considered things from the cat’s point of view. Isn’t he an observer too?Yes and no. Yes there is nothing intrinsically wonderful about physicists that make their observations more important than a cats’. The cat is just as good an observer as any physicist, as you or I. But he is in a sealed box. Unable to interact with people outside. They cannot hear his whines, cannot know what he experiences for that itself would be an act of measurement and the box is sealed to all measurement. That is the point of the experiment.. Until the box is opened everything inside exists in this weird limbo.

But that still isn’t considering things properly from the cats point of view…

We are in a sealed box. There is a flask of poison… and a hammer. We are the cats. We are all observers..

We have an opportunity to perform the experiment from inside the box. We can test these two alternative theoretical interpretations for ourselves.

I don’t have any radioactive particles but fortunately that doesn’t matter. I have a coin and when a coin is flipped really high and let to bounce to the ground, the precise trajectory is so complex that chaos theory says even a minute change to the initial flip can alter the outcome.. the influence of one atom vibrating differently can change it from heads to tails.

So, if I flip this coin we have our atomic source of uncertainty.. If the outcome is heads nothing… it is tails I’ll smash the flask. Heads we live, tails we die.

Are you ready? Well, wait a second.. remember what our experiment is, we are cats in the box. We are sealed in here with no way the outside world will hear our whines. The front of house staff are physicists. They are! At the end of the show they are going to open those sealed doors come in here and observe the outcome of this experiment.

But we will already be experiencing it. From when we flip that coin we have to decide between the Copenhagen and Many Worlds interpretations.. we have to decide if it feels more like we are in some weird limbo of dead and alive,

neither and both, or if we move into a universe where we are completely dead or alive. So you’ll have to observe very carefully. Are you ready?


So how does it feel? Anyone feeling at all strange? It seems to me like we are travelling into the universe where we survived.. But does anyone feel any different? No? Thank goodness, then i think we made it.

Look! There are many, many branches to the universe.. The coin is flipped and the universe branches in two , and we branch with it.. and in one branch we live, in one we die.. but if that’s the case then which universe do we experience? Always the one where we survive.

Convinced? It was a 50% chance.. that’s hardly a strong empirical basis for choosing one theory.

So, double or quits?


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