I understand the concept, but every time I see one of these, the most compelling points are for me the ones that show how the setup makes no sense at all because, for starters, there's no way to make a real experiment that's truly equivalent.
Edit-> please, think about this: can the "result" of any thought experiment be surprising, not what you expected?
Isn't all of mathematics just thought experiments? No shortage of surprising results there.
Isn't Schrödinger's cat the classic example of this? Physicists at the time typically thought of quantum effects (like superposition) as being confined to the microscopic realm. Schrödinger pointed out that if you take the principles of quantum theory as serious and objectively ontological, then you end up with macroscopic superpositions.
Schrödinger conceived the experiment to "show" that the premises lead to an absurd result: that the cat is dead and alive at the same time.
But now people either consider it plausible (in multiple universes or depending on observer) or try to explain how superposition is lost before it reaches macroscopic objects.
The core of Mary's adventures is a false dicotomy: that matter is the only component of physical reality. But processes, structure and energy flow are as real as matter. Actually, at a very small scale, matter seems to be exactly that.
So as usual with all these dualism "enigmas", the only problem is starting from an old perspective that doesn't play well with current knowledge.
Consciousness seems to be a complex physical process seen from inside itself. There's no mistery or toughness in that, except that we can't compare it with anything else.
We can't use the inside and ouside outlooks at the same time. But Wittgenstein already stated that more than a century ago.
I always assumed everybody understood "observer" to be shorthand for "some entity that irrevocably changes state because of the quantum events", but I'm starting to realize that lots of people, even the famous physicists responsible for the theories and experiments, may understand "observer" as "Human being, with a conciousness".
I'm just a layman with a layman's understanding of quantum shenannigans, but.... am I too far off here?
Yes, "observer" is ambiguous at best.
One query with your proposed definition is: what do you mean by "irrevocable"? If you believe that the quantum state (wavefunction) is objective and independent - and does not collapse but evolves reversibly according to the Schrodinger equation - then nothing is irrevocable, it's just a technical challenge of "can we reverse the evolution of this patch of the universe". Yes, there is this decoherence process, but even that is reversible if you expand your "patch of the universe" sufficiently.
Not many famous physicists believe human consciousness is required for a physical quantum collapse process to occur. John Bell put it nicely:
> Was the wave function waiting to jump for thousands of millions of years until a single-celled living creature appeared? Or did it have to wait a little longer for some highly qualified measurer—with a PhD?
You might be interested to know that people have wondered about what happens if you replace the cat by something that is definitely an "observer": https://en.wikipedia.org/wiki/Wigner%27s_friend . Until the friend (F) tells Wigner (W) the outcome that he experienced when measuring a photon (P), then Wigner supposes that F is quantum entangled with P, i.e. they are in a joint superposition of states. However, the friend supposes that P is in a definite state.
Very good point, who knows! I guess whatever the universe can't pretend didn't happen, like a photon being absorbed and re-emited by an electron.
Which, what does that even mean? I don't know! Does anyone? I don't know!
It's hard to tell, with such difficult subjects, the difference between "I don't know" and "Nobody knows".
On top of that, people like to pretend they know. And some other people do really believe they know even if they don't, just because they know a dictionary definition, or something.
The thought experiment is not to produce a new artefact that you would traditionally call "a result", like a table of subjects responses, or a histogram of responses, etc.
It's to make the researcher consider stuff that cannot be tested, but might be feasible.
> how the setup makes no sense at all because, for starters, there's no way to make a real experiment that's truly equivalent.
That's the whole point. If you can make a real experiment, then it's not a real thought-experiment, is it? The article actually addresses this:
> But this issue need not concern us, because philosophical thought experiments depend on logical coherence rather than practical feasibility.
IOW, it depends on the argument being logically sound, not practically proven.
You can turn that around: the differences between the reality and the alternate reality in which the "experiment" is possible are the key to the question.
I understand, but ... you don't judge whether something is useful (or not) according to some arbitrary goal, you judge based on the specific goal intended.
In this case, the goal is "Does the process result in further lines of thought to exhaust, or further discussion?".
I mean, you wouldn't call a brain-storming session useless if it resulted in a conclusion of "no practical implementation is feasible at this time", would you?
The train is only a way to explain it, not a thought experiment. Actually, some equivalent experiments to that are not just possible, but has been executed.
Not necessarily for the framer of the experiment, but that's not the point - it's to get other people to think about a problem in a different way.