6 ms·

it's absurd because pretty much every particle of the cat is measured and thus decohered by other particles in the cat

SuoDuanDao 4y ago
I really like the interpretation that if the cat is dead, it can't measure anything and is therefore reliably alive (quantum immortality). Of course, that doesn't change that someone else can observe the cat being dead after opening the box.
- nathan_compton 4y ago
  At this stage I don't think very many philosophers consider measurement as it takes meaning in quantum mechanics to have anything in particular to do with living creatures or brains or consciousness or anything.
nathan_compton 4y ago
gee wilikers, you solved it!
- blueprint 4y ago
  you act like I wasn't just talking with someone here on HN who was convinced we "live in a classical world" when in reality everything is governed by the same quantum physics on every scale.
  - denton-scratch 4y ago
    > you act like I wasn't just talking with someone here on HN who was convinced we "live in a classical world" I didn't understand your original reply to my comment; now I understand why, I think. Perhaps I failed to express myself clearly? I didn't say anything about quantum vs. classical worlds; I made a remark about the purpose for which Herr Schroedinger devised his cat story. His purpose was the opposite of the purpose implied by the article. He thought that the absurdity of a cat being both alive and dead demonstrated the absurdity of a particle being in two states at the same time. That is, I was talking about Herr Schroedinger's opinions, not my own. IANAPP, but FWIW I'm convinced that quantum theory in the sense of evolution of the wave function is correct. I don't know of any convincing explanation of wave-function collapse as a result of "observation". I don't buy many-worlds, and "just shut up and solve the equations" doesn't cut it for me. So in fact I'm convinced that we don't live in a classical world.
    - blueprint 4y ago
      no, no! it was an entirely different person here almost 2 wks ago who was arguing with me about whether quantum mechanics can be understood without the math, all while making claims that showed how little he knew of the topic. he might have been trolling anyway. In my reply to you I was merely agreeing, herr denton-scratch. many worlds doesnt (afaict) posit why/how branch selection even occurs so it's sort of incomplete IMO. wavefunction collapse doesn't seem to exist either, but rather is a result of entanglement with the observer. my personal guess is something like superdeterminism in principle but I keep an open mind. I suspect that there are some basic consequences/meanings of the existence of state/information and entanglement themselves which have been too subtle to have been seen as assumptions in the past, and I am slowly working on formalizing them.
jerf 4y ago
In the cat thought experiment, the "box" needs to be conceived of as something that totally isolates you from the cat. No "quantum influences" travel across it. Otherwise it has no point. This is obviously impossible... hence, "thought experiment". If you want to make the argument this makes it ultimately harder to understand rather than easier, well, I'd say the evidence overall would favor that. It seems to confuse more than it casts light on anything. But if we did have such a box, then the cat could be alive and dead simultaneously. The dead portion of the cat superposition would consistently see the cat as dead, the living portion would consistently see the cat as alive. From within the box nothing could collapse the superposition any further. Once opened you would see only one of them. People are bothered by the macroscopic implications of this violation of our intuition of how the universe works. It is not entirely clear to me that such a violation could ever manifest in reality, though; that is one heck of a box, in a universe with gravity, neutrinos, dark matter, etc.
- blueprint 4y ago
  It was not a gedanken experiment, though; it was a joke. The box is totally irrelevant, because a cat in a box is not in a box, because the cat is not isolated, because the cat is actually a compound system already. If you had a single particle in a box, okay, yes, that's valid. The cat would not be alive and dead simultaneously regardless of the box because it's totally entangled with and decohered / observed by the other elements in the box. A single particle, or a coherent system, can be thought of as being isolated though. Do you see what I mean
  - gpderetta 4y ago
    we have been able to isolate and keep coherent increasingly large systems. Isolating a cat is not beyond the realm of the theoretically possible.
    - blueprint 4y ago
      it would not be a cat then.
- 4y ago

I really like the interpretation that if the cat is dead, it can't measure anything and is therefore reliably alive (quantum immortality). Of course, that doesn't change that someone else can observe the cat being dead after opening the box.

nathan_compton 4y ago
At this stage I don't think very many philosophers consider measurement as it takes meaning in quantum mechanics to have anything in particular to do with living creatures or brains or consciousness or anything.

nathan_compton 4y ago

gee wilikers, you solved it!

blueprint 4y ago
you act like I wasn't just talking with someone here on HN who was convinced we "live in a classical world" when in reality everything is governed by the same quantum physics on every scale.
- denton-scratch 4y ago
  > you act like I wasn't just talking with someone here on HN who was convinced we "live in a classical world" I didn't understand your original reply to my comment; now I understand why, I think. Perhaps I failed to express myself clearly? I didn't say anything about quantum vs. classical worlds; I made a remark about the purpose for which Herr Schroedinger devised his cat story. His purpose was the opposite of the purpose implied by the article. He thought that the absurdity of a cat being both alive and dead demonstrated the absurdity of a particle being in two states at the same time. That is, I was talking about Herr Schroedinger's opinions, not my own. IANAPP, but FWIW I'm convinced that quantum theory in the sense of evolution of the wave function is correct. I don't know of any convincing explanation of wave-function collapse as a result of "observation". I don't buy many-worlds, and "just shut up and solve the equations" doesn't cut it for me. So in fact I'm convinced that we don't live in a classical world.
  - blueprint 4y ago
    no, no! it was an entirely different person here almost 2 wks ago who was arguing with me about whether quantum mechanics can be understood without the math, all while making claims that showed how little he knew of the topic. he might have been trolling anyway. In my reply to you I was merely agreeing, herr denton-scratch. many worlds doesnt (afaict) posit why/how branch selection even occurs so it's sort of incomplete IMO. wavefunction collapse doesn't seem to exist either, but rather is a result of entanglement with the observer. my personal guess is something like superdeterminism in principle but I keep an open mind. I suspect that there are some basic consequences/meanings of the existence of state/information and entanglement themselves which have been too subtle to have been seen as assumptions in the past, and I am slowly working on formalizing them.

jerf 4y ago

In the cat thought experiment, the "box" needs to be conceived of as something that totally isolates you from the cat. No "quantum influences" travel across it. Otherwise it has no point. This is obviously impossible... hence, "thought experiment". If you want to make the argument this makes it ultimately harder to understand rather than easier, well, I'd say the evidence overall would favor that. It seems to confuse more than it casts light on anything. But if we did have such a box, then the cat could be alive and dead simultaneously. The dead portion of the cat superposition would consistently see the cat as dead, the living portion would consistently see the cat as alive. From within the box nothing could collapse the superposition any further. Once opened you would see only one of them. People are bothered by the macroscopic implications of this violation of our intuition of how the universe works. It is not entirely clear to me that such a violation could ever manifest in reality, though; that is one heck of a box, in a universe with gravity, neutrinos, dark matter, etc.

blueprint 4y ago
It was not a gedanken experiment, though; it was a joke. The box is totally irrelevant, because a cat in a box is not in a box, because the cat is not isolated, because the cat is actually a compound system already. If you had a single particle in a box, okay, yes, that's valid. The cat would not be alive and dead simultaneously regardless of the box because it's totally entangled with and decohered / observed by the other elements in the box. A single particle, or a coherent system, can be thought of as being isolated though. Do you see what I mean
- gpderetta 4y ago
  we have been able to isolate and keep coherent increasingly large systems. Isolating a cat is not beyond the realm of the theoretically possible.
  - blueprint 4y ago
    it would not be a cat then.
4y ago