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As long as i understand this paradox says this : There is a cat in closed box with some radioactive stuff in it . Now as radioactivity is a purely quantum process the , the material both decays and doesent at same time , in other words , is in superposition. So should the cat be in some strange form of both dead and alive form in box , until we observe it. Now , what i think is : Shouldnt the cats information of weather the radioactive object decayed or not destroy the superposition .? Or because our timeline is different , there is different information in same box according to information one has and at what point in time one is in ? Doesent that mean that phenomenon cannot be observed by anyone or anything that has capability to store information?? I am really confused....I am just a year 10 student interested in these stuff , so dont laugh if i sound silly :)

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  • $\begingroup$ I believe the paradox is such that anyone outside of the box would need to observe it. Think of it like this: The observer will need to be able to tell someone else in either situation. You, me, anyone could tell someone if we saw a dead cat, but if the cat is dead, it cannot be the observer. $\endgroup$ – David Dec 13 '17 at 20:52
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What I'm going to say does not hold for all interpretations of quantum mechanics, but if we work in the so-called Copenhagen interpretation and assume that everything in the universe is fundamentally quantum mechanical, then the argument should work.

Whether or not the cat is in a superposition all depends on your point of view. From the point of view of the cat itself, it is simply either dead or alive, because it can directly feel ('measure') the radioactivity. From the point of view of an observer outside of the box, however, the cat is in a quantum mechanical superposition, as long as the box stays closed and the observer doesn't measure the state of the cat.

This illustrates among other things the difficulties one finds when dividing the world into a 'quantum system' and an 'observer', which is what the Copenhagen interpretation of Quantum Mechanics postulates. This division is in some sense arbitrary.

You can even go a step further and now consider another observer, let's call him Wigner's friend, while calling the first observer Wigner (since this is related to the famous 'Wigner's friend' thought experiment, which you might want to look up). Now suppose Wigner opens up the box, so he sees if cat is dead or alive and from his point of view 'the cat's wavefunction collapses'. However, as long as Wigner's friend, standing outside the laboratory, has not yet observed Wigner (or the cat), both Wigner and the cat are both still in a superposition from his point of view. So in this way of viewing things there is no absolute fact of the matter whether something is in a superposition or not. It all depends on your point of view.

If I'm not mistaken it can be proven mathematically that all these viewpoints are in the end equivalent, although I'm not completely sure about this.

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Schrödinger's cat clarifications

In quantum mechanics and in modern physics in general, the observer is often held as not really an entity which has nothing to do with the experiment, as it could happen in a classic environment more than a hundred years ago, but still as an entity which starts affecting the experiment only when, at the end of the experiment itself, he wears a white overall and starts carrying out measurements. On the contrary, the observer is part of the experiment since the beginning.
Schrödinger’s Cat-1935 (from Wikipedia):

“A cat is penned up in a steel chamber, along with the following device (which must be secured against direct interference by the cat): in a Geiger counter, there is a tiny bit of radioactive substance, so small, that perhaps in the course of the hour one of the atoms decays, but also, with equal probability, perhaps none; if it happens, the counter tube discharges and through a relay releases a hammer that shatters a small flask of hydrocyanic acid. If one has left this entire system to itself for an hour, one would say that the cat still lives if meanwhile no atom has decayed. The first atomic decay would have poisoned it. “

We are talking about Schrödinger’s supposition, according to which the cat is in an unknown state (alive or dead), as it is impossible, before opening the chamber, to know if the poison has been released or not. Let’s find some mistakes in the reasonings around that, hoping that they look like mistakes to the readers, too:

1) The steel chamber is not perfectly tight! Therefore, in the observer’s opinion, it is always open!!! Perfectly tight chambers do not exist (thermal or gravitational tightness).
The wave function would collapse on time anyway, as a perfect tightness of the chamber with cat, poison, counter and radioactive substance inside, is impossible. An external observer immediately interferes with the experiment, by the gravitational pull exerted by his own body on the cat, on the poison, on the counter and on the radioactive substance, or also by the heat of his own body, which is transmitted towards the chamber, which is not perfectly tight. Hence, the cat is surely dead or alive, but never a mixture of those two different states. The observer can’t even deny he knows the state of the cat before the opening of the chamber, as the death of the cat has an effect on the observer himself, as it transmits less heat towards the observer (cold body of a dead cat) and this would slightly change the physical state of the observer himself, who is a permanent and compelled observer. The same can be stated about an alive cat, which is warmer and which sends more heat to the observer, so sending a thermal information on its state and even though such information is not expressly requested by the observer.

2) Quantum physics would allow the observer to chose to observe or not. This is absurd!!! The observer is not free! He must always observe! Einstein’s God, that who is not playing dice, is not giving us such a freedom. The observer is not free to refrain from observing. If I don’t look at the Moon, does the Moon exist? My answer is yes, also adding that I cannot stop looking at the Moon, as also if I turn back, I still interact with the Moon, gravitationally etc (also this is a looking at). Since the beginning of the above experiment, as an observer I affect the events inside the chamber of Schrödinger by the gravitational pull exerted by my body, or also by the heat transmitted by my body. And even if I want to keep my eyes closed, at the end of the experiment the higher quantity of heat transmitted by an alive cat (or lower, in case of a dead one) throug a non perfectly tight chamber, inexorably informs my body on the state of the cat!

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  • $\begingroup$ I am confused what the question is supposed to be? Is it something along the lines of "since an experiment cannot be isolated from an experiment, its impossible to keep a superposition for its duration". $\endgroup$ – jacob1729 Jan 6 at 20:27

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