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Quantum Physics: Are Observers Necessary? - by John Prytz

In an essay I did on Schrodinger’s cat, where the cat’s fate (to live or die) is determined by an unobserved random event with a 50/50 probability, I noted how, according to some, it takes an observer to determine the fate of the animal, and until there is such an observation, the cat is both 50% alive and 50% dead at the same time. This thought experiment was an analogy for something in the quantum world that some outcome can have equal but mutually exclusive possibilities (i.e. – an outcome where you can have both being and not being simultaneously), at least until a measurement/observation is made and things fall into place as either being or not being.


There’s an interesting variation on that cat thought experiment. Say the cat-in-the-box is in a room and I’m also in the room, and after one hour I peek in the box and determine the aliveness or deadness of the animal. But, say you are outside the room when I do that. As far as you are concerned, the cat’s wave function hasn’t collapsed and the cat is still dead-alive. So you have got to look too! But then what about a third party in another room in the house, then the neighbour next door, and hence other residents of the town, then state, hence country and then the entire world. Of course the cat would be in a limbo dead-alive state to extraterrestrials on another planet until they looked, and so on. In fact, taken to a logical extreme, nothing has reality until the entire Universe observes, which is again (IMHO), absurd seeing as how it could take billions of years for that cat observation to reach the farthest regions of the cosmos!


In a similar way, there are those who argue that nothing is real unless that something is observed. For example, the Moon dissolves into quantum uncertainty, the Moon is and is not, if nobody is actually looking at the Moon! As soon as someone looks at the Moon, it solidifies back into physical reality. The absurdity (again IMHO) of that is that if the Moon faded away into quantum uncertainty that would play havoc with the tides and be noticed.  Perhaps observing the tides is sufficient to give the Moon reality without actually observing the Moon!


Extrapolating, there are those who believe and would argue that the entire Universe exists (has reality) only because there are observers to observe or measure it.  Clearly (unless you count God [if He/She/It exists at all] as an observer from Day One), the Universe was in a lifeless state and evolved in a lifeless state from Day One through several billions of years at least. That is, there were no observers at all. The Universe had to exist in a pre-observers stage in order to evolve the complexity required to produce observers. An early Universe consisting of only hydrogen, helium and radiation doesn’t hack it as far as being a suitable environment for observers. So, in terms of this chicken-or-the-egg question, the Universe-or-the-observer question, the answer must clearly come down on the side of the Universe. The Universe can exist either with or without observers; observers exist only because there is a Universe.


Lastly, no one has defined exactly what constitutes an observer. What about an inorganic things like a Geiger counter or thermometer? Can it be anything that’s alive like a plant or bacteria, or does it have to have a sophisticated nervous system (higher sensory capacity)? Maybe there has to be a complex brain within. Maybe an observer is only a bona-fide observer if it has intelligence, but what degree of intelligence? A one day old baby or someone who is brain damaged might look in the box and see Schrodinger’s cat but has no capacity to understand what they are seeing.  What about an artificial intelligence?


I conclude (or believe) that observers and measurements have bugger-all to do with reality, existence and how things work on either a macro or micro scale. The proof of that pudding, if any were necessary, is that radioactive substances decay with a measured half-life. The entire science of radioactive dating depends on this. And radioactive elements decay whether or not observers are present – they have; they do; they will.


Science librarian; retired.

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