3 ms·
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.
by 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 agoIt 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
- awb 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. Is that true? I’ve seen references to observed macro superpositions without such a box: https://en.m.wikipedia.org/wiki/Quantum_superposition https://en.m.wikipedia.org/wiki/Quantum_superposition > A double slit experiment has been performed with molecules as large as buckyballs and functionalized oligoporphyrins with up to 2000 atoms. > An experiment involving a superconducting quantum interference device ("SQUID") has been linked to the theme of the "cat state" thought experiment. > A piezoelectric "tuning fork" has been constructed, which can be placed into a superposition of vibrating and non-vibrating states. The resonator comprises about 10 trillion atoms.
- jerf 4y agoYou're right about the experiments, but you underestimate how many orders of magnitude you are away from a cat. Not only is there the orders of magnitude in terms of atomic size, you also have to consider the orders of magnitude of time as well, since the thought experiment implicitly takes place at human time scales, where we are presumably waiting at least a couple of seconds to open the box. Adding them both together probably puts us a good 15-20 orders of magnitude away from a cat. It is difficult to imagine what box could isolate something that large that thoroughly for that period of time; it gets multiplicatively harder as you add those constraints, if not exponentially (depending on the circumstances), not merely additively.
- blueprint 4y agomaybe you edited your post but thought experiments are not supposed to be impossible at all. they're supposed to be realistic. that's why we consider them "experiments". Einstein's photon in a moving box counting time gedanken experiment was used to illustrate very real physics
- jerf 4y agoImpossible -> gedankan experiment != gedanken experiment -> impossible.
- blueprint 4y agoyeah you're right but the cat thing isn't a gedanken experiment because gedanken experiments need to start with rigorous statements of physical systems. the cat example is not remotely rigorous. if it were stated as such then it would be seen to be trivial
- cma 4y ago> This is obviously impossible... hence, "thought experiment". It seems like a four way black hole merger could possibly leave a space in the middle.