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34

This is is known as the Wigner's friend thought experiment. According to the many World's interpretation, the superpositions are not a problem. The whole universe ends up in a superposition where all experimental outcomes are realized, but such a superposition is entangled with the environment, from a macroscopic point of view it takes the form of a ...


29

In a bubble chamber experiment, film was the detecting medium, but film was taken automatically, by the thousands of frames. These bobbins of film went to the various laboratories involved in the experiment, and were scanned for interesting events which were measured and the cross sections for the interactions recorded. This is a clear example of an ...


21

This question strikes close to the heart of The measurement problem, which is the question of what (if anything) the process of measurement represents; and is all but synonymous with the question of how one ought to interpret quantum mechanics. As such, the answer to this question is (a) subject to debate; and (b) absent any substantial philosophical and/or ...


20

First, a historical subtlety: Schrödinger has actually stolen the idea of the cat from Einstein. Second, both men – Einstein and Schrödinger – used the thought experiment to "explain" a point that was wrong. They thought it was absurd for quantum mechanics to say that the state $a|{\rm alive}\rangle+b|{\rm dead}\rangle$ was possible in Nature (it was ...


11

What's wrong with my reasoning? Nothing! In fact you have more or less described decoherence. The idea is that any system inevitably interacts with its environment, and the more degrees of freedom the system has, i.e. the more complex it is, the faster it will interact with the rest of the universe and the superposed states will decohere.


9

"Since it is uncertain on whether or not the cat could be dead or alive, it is concluded that it depends on the observer to make it either dead or alive." That would certainly be atrociously bad "reasoning", but that was not Schrodinger's argument at all. He introduced the cat thought-experiment as an attack on the idea that when a particle's wavefunction ...


8

It depends of what interpretation of quantum mechanics you are using. By interpretation it is meant that the mathematical predictions of the quantum mechanics formalism are the same, but the philosophical meaning of each is what differs. In the copenhagen interpretation that you seem to describe, the wave function collapses when a conscious observer makes a ...


7

The thought experiment aimed at illustrating one concept, and questioning the validity of such concept: 1/ The concept: in quantum mechanics, before an observation is made (note the cat is in a closed box, and nobody can see what is going on in the box), a system is not in a defined state, but only has a certain probability to be in any state - here the ...


6

You don't explicitly say so, but you're assuming the Copenhagen interpretation (CI) rather than the many-worlds interpretation (MWI). Your analysis is a perfectly good example of why the CI doesn't fundamentally make much sense. The CI treats measurement as a process that's different from other processes, even though measurement is a physical interaction ...


6

$\renewcommand{\ket}[1]{\left \lvert #1 \right \rangle}$ $\renewcommand{\bra}[1]{\left \langle #1 \right \rvert}$ We can see how decoherence really works, why it messes up superposition states, and why it's particularly prone to messing up states of large objects all through a very simple example $^{[a]}$. Single two-level system Suppose we have a quantum ...


6

The visualization method you choose is directly and completely determined by the information you need to see regarding your state. For the states of a single bosonic mode, there are multiple different visualization methods, and they all have their pros and cons. In particular, there is a direct trade-off between the amount of information you can display on a ...


5

It is because of quantum statistical irreversibility, which is closely related to entropy, as the OP suspected. Qualitatively it is quite easy to understand this. From the laws of quantum mechanics on the microscopic level emerges a classical behaviour for macroscopic (i.e. many particle objects). Of course this is not sufficient though and does not give a ...


5

This is an excellent question and stresses one of the weird features of quantum mechanics. Indeed, the scientist would in turn be in a superposition. And we could even measure this if we'd be able to maintain coherence of such large systems. Ultimately, your question is asking for the solution of the Measurement problem: Why don't we see any ...


4

The expression in the picture contains kets only. Kets represent states of a system. In this case, the "alive" state is the first one and the "dead" state the second. The numerical factors are there for normalisation. It is assumed both states are equally likely, so they have the same numerical factor. If we call the expression in the picture $|\Psi\rangle$,...


4

Large classical objects such as cats or humans are next to impossible to place in a superposition of states. They basically decohere immediately. As far as i know the largest object placed in a superposition is a micromechanical resonator and there is currently work being done on placing a bacterium in a QM superposition ( quantum superposition of a ...


4

In Schrodinger's cat experiment, the scientist is assumed to be an "classical observer" of the state of the cat, and thus all observations made by the scientist are assumed to be classical observations adhering to physics as we knew it before quantum mechanics came along. The thought experiment focuses on what sorts of statements about reality that ...


3

This is a thought-provoking question, but... the concept of observer is only important if one takes the Copenhagen interpretation. So let us stick to that for the purpose of answering the OP. The cat cannot be an observer of itself. In the logic of the Copenhagen set-up, there is a quantum mechanical object being observed, a classical measurement ...


3

In Schrodinger’s cat experiment there is a mixture of a macroscopic object, the cat, and a quantum mechanical object, the radioactive atom, which if decayed it would activate a hammer to break the flask, with the poisonous gas in it, and therefore killing the cat. This description is very straight forward and not very hard to understand: the cat in the box ...


3

You're right that this experiment isn't really a realistic one. In fact, it's difficult to imagine how we could even tell whether a given box were such a perfectly isolating box. However, if we put aside the (somewhat important) question of empirically determining whether we actually obtained a cat in a superposition of life and death, we can try to imagine ...


3

You really ought to watch the talk by Charles Bennett at http://pirsa.org/11050052/. At first, he analyzed the Mach-Zehnder interferometer and concluded the which-way information of the photon did not exist. Then, he went on to quantum Darwinism where redundant copies of the information are stored in the environment. This multipartite entanglement with the ...


2

Your question effectively reduces to that of where you place the Heisenberg cut in an idealized model of the experiment. That's not different from the issues that are already probed by the original thought experiment and the Wigner's friend variant. It's implicit in the quantum formalism that (unless one introduces POVMs) one models experiments using ...


2

There was a lot of disclaimer that was implied. For one, a "box" in physics is much better at containing things than the cardboard boxes you see containing cats on the internet. The box here is understood to not allow any information to pass through its walls except where and when we specify. That is, there is no environmental contamination to decohere ...


2

The experiment is intended to highlight the problem of quantum superposition applied to macroscopic objects. It's not inconceivable that a radioactive nucleus can be in a superposition of states. When you interact the nucleus with the detector, hammer and glass of poison, the wavefunction that describes these items become entangled with the wavefunction of ...


2

I have always disliked this thought experiment because, even though it was proposed as an amplifier of quantum mechanical effects, it is really nothing more than a game on probability, and one can get random probabilities by many classical means. Toss a coin, heads cat alive tails cat dead. The concept of both alive and dead is ridiculous in the ...


2

The equation (5.36) in the (newest version) of the paper is: $$ρ_S (x, x′ , t) = ρ_S (x, x′ , 0) e^{ −γt\left(\frac{x−x'}{\lambda_T}\right)^2} \tag{1}$$ where $\rho_S$ should be the off-diagonal term in the density operator, $\gamma$ the relaxation coefficient and $\lambda_T=\frac{\hbar}{\sqrt{2Mk_BT}}$ is the thermal de Broglie wavelength of the system. ...


2

Ket(s) and Bra(s) represent state of a system. The simplest interpretation is to see kets and states as (complex) vectors. In your case, the state could be described by the vector : $$\vec S = \frac{1}{\sqrt{2}} \vec{alive} + \frac{1}{\sqrt{2}} \vec{dead}$$ Here, $\vec{alive}$ and $\vec{dead}$ are a basis for the states, so they are orthogonal vectors : $\...


2

I think you misunderstand the purpose of Schroedinger's Cat as a thought experiment. The idea was to show the ridiculousness and weakness of the Copenhagen interpretation of quantum mechanics, not to present a realistic scenario.


2

That the clock functions implies that the wavefunction of a perfectly isolated clock would evolve almost deterministically. That's why Schrodinger chose a different setup involving a radioactive decay that can happen with a probability of 1/2.


2

If you really want to understand how QM formalism relates to the Schroedinger's cat and the double slit experiment, you should study a QM textbook. To answer your question in a simple way: The double slit experiment is indeed consistent with the Copenhagen interpretation, in the sense that wave mechanics predicts the outcome of the experiment correctly. ...


2

No they cannot. Any living system is an incredibly complicated, interacting quantum system. The countionous interaction (noise, heat bath, etc.) between particles makes it impossible for a coherent state to exist. However this is only true for the whole organism, on the level of single proteins, or other biomolecules quantum coherence may play an important ...



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