When debating the nature of quantum physics, you question what does it all really mean? One of the central points requiring pondering features a thought experiment by physicist Erwin Schrodinger. He, along with Albert Einstein, didn’t agree with the idea that probabilities rule the quantum universe, and that observations or measurements were central to turning a probability into a certainty. By linking a quantum uncertainty event, with a macro outcome, Schrodinger hoped to show the absurdity of the former.
Schrodinger’s Cat has got to be one of the strangest thought experiments ever conceived, but it was conceived with the idea of putting the boot into the Copenhagen Interpretation of all things quantum. The Copenhagen Interpretation basically means that everything is in a state of probability until, and only until, an actual observation or measurement is made; then, and only then, probability morphs into reality and certainty. Prior to that observation or measurement, the various possibilities are said to be in a state of superposition. Translated, if you throw a dice and it rolls under the sofa out of sight, the top value of the dice is in a state of six superpositions. The top of the dice is at the same time simultaneously one, two, three, four, five and six. That superposition of state, that combination of all possibilities is called the wave function of, in this case, the dice. Only when you remove the sofa and look will the six probability superpositions collapse (the collapse of the wave function) into one actual value. The point is, according to the Copenhagen Interpretation, prior to looking, the top face of the dice actually, in reality, has a value of one, two, three, four, five and six – simultaneously.
Okay, now back to the cat. The idea is that you have some unstable (radioactive) atom, and there’s a 50/50 chance that it will go ‘poof’ and give off a decay particle within one hour. That’s the quantum or micro bit. Now you have a box that contains a Geiger counter or some radioactive decay particle detector (that’s part of the macro part). You also have a hammer in the box poised over a glass vial of poison gas (also part of the macro part). If the Geiger counter detects a decay particle, it triggers a switch which releases the hammer which smashes the vial, releasing the poison gas. Oh, there’s also a cat in the box (the really essential macro part). After one hour, there’s a 50/50 chance that the cat is either alive or dead. That’s what rational people would say. Some, those of the Copenhagen Interpretation School, would argue that the cat exists in a dual state of both 50% aliveness and 50% deadness until such time as an observer looks into the box and measures the cat’s 100% aliveness or 100% deadness. Then, and only then, does nature make up her mind (in quantum theory, the wave function – a measurement of probability – collapses to an exact value) and you find either a dead cat or an alive cat, which tells you whether or not the radioactive substance did, or did not, emit a radioactive decay particle. In a way, the cat itself serves as a sort of Geiger counter!
This thought experiment was to illustrate the apparent absurdity maine coon cat for sale that in quantum theory some ultimate outcome can have before-the-fact equal but mutually exclusive possibilities (something can both be and not be at the same time – the upper dice face can be all six values at the same time) or that in quantum physics, there’s no definite state of existence until there is a measurement or observation (same difference).
The idea is that if in the micro or quantum world something can have equal but mutually exclusive possibilities (again, an outcome can both be, and not be at the same time – wave-particle duality comes to immediate mind), yet the macro or classical world is made up of micro or quantum bits, then that suggests that macro objects (like a cat) can simultaneously exist in two mutually exclusive states or possibilities (the cat can both be, and not be, alive at the same time). In this case, the cat is both alive and dead until such time as someone looks!
Perhaps a better analogy is in showing how probability remains probability until an observation is made is in a hand of cards. All possibilities are equally probable, all possibilities are realised in actuality, but you don’t know the specific outcome, your precise hand, until you look and the probability wave function, that superposition of all possible outcomes, collapses to one, and only one certainty. The observer is the be-all-and-end-all.
On that point, does it have to be a human that does the measuring or observing if all it takes is an observer to collapse the wave function in order for Mother Nature to decide either this or that? Could any observer do? I mean the cat itself is an observer! So if after only one minute a decay particle is given off, the cat will observe the results (hammer falling; vial breaking) just prior to dying, and there will be a dead cat in the box for the next 59 minutes. What if an insect crawled into the box and observed the cat. What about a bacterium in the box. Would nature, via the bacterium then decide that the cat is to be declared really dead and act accordingly? What if a computer, or some form of artificial intelligence or a robot did the observing? Of course it doesn’t have to be a visual observation. I mean if you hear the cat meow, the cat is alive. If you smell the rotting corpse (or the poison gas), then obviously the cat is dead. If you feel the cat and it’s moving, then it’s obviously alive, and so on.