Well, no. It's possible that a tree could fall in the forest and make any number of different sounds the specifics of which are impossible to determine until observed, though.

Keep in mind, too, that "an observer" includes basically anything interacting with an otherwise closed system, not just a thinking creature.

>"an observer" includes basically anything interacting with an otherwise closed system, not just a thinking creature.

Isn't that a bit of a philosophical debate? It could be that things are only "observed" when their cone of causality reaches a thinking creature. I thought that was half the point of the tree question in the first place.

This is what I hate about the popular understanding of the Copenhagen interpretation.

Bohr's original idea was that until there's some interaction it's pointless to assign a specific state - you can only talk about certain probabilities.

Schrodinger's cat is not both alive and dead. We know nothing about its current state, only how probable certain outcomes are.

>Schrödinger described how one could, in principle, create a superposition in a large-scale system by making it dependent on a quantum particle that was in a superposition. He proposed a scenario with a cat in a locked steel chamber, wherein the cat's life or death depended on the state of a radioactive atom, whether it had decayed and emitted radiation or not. According to Schrödinger, the Copenhagen interpretation implies that the cat remains both alive and dead until the state is observed. Schrödinger did not wish to promote the idea of dead-and-alive cats as a serious possibility; on the contrary, he intended the example to illustrate the absurdity of the existing view of quantum mechanics. However, since Schrödinger's time, other interpretations of the mathematics of quantum mechanics have been advanced by physicists, some of which regard the "alive and dead" cat superposition as quite real.

I was taught that Schrödinger's Cat was conceived of as intentionally absurd, but that physicists loved it because it pointed out how absurd physics was being. As the other comment said, its not just that a photon might have gone through either slit, it provably went through both.

The thing about quantum theory is that it's not just about propabilities. The double-slit experiment, for example, cannot be explained by adding propabilities alone. Instead the wave function gets added, with the phase considered. This is why an unobserved quantum state is more than a classical state hidden in a box and why we get results that seem paradox.

>Schrodinger's cat is not both alive and dead. We know nothing about its current state, only how probable certain outcomes are

That's the case with any cat we throw in a box and ask somebody to kill it or not based on a dice, and then we visit the place where the box is and open it...

In other words, the cat is in a certain state, but we merely don't know which.

But this doesn't capture what the Schrodinger experiment is supposed to show. Such an case wouldn't need the experimental apparatus Schrodinger describes either.

The core idea of the experiment is that quantum uncertainty is not just of the "we just don't know yet" kind, but of the fundamental "reality is inherently mixed-up and uncertain / many things actually hold at the same time until observed" nature.

The purpose of the Schrodinger's thought experiment then is to show how this fundamental quantum uncertainty (i.e. not mere not knowing: actual "fuzzy" reality) "pollutes" the macro world (in this case, a cat).

The quantum-based mechanism that releases the poison, is his trick to transfer the uncertainty of the quantum state into the macro world (the box with the cat). (Funnily, Schrodinger's purpose was to discredit this).

Those that believe it's clear that "the cat is in one state or another, we just don't know which", haven't understood the problem.

You've slightly misinterpreted the point of the previous post, or have at least overlaid some assumptions.

You're arguing against what one might call an objective Bayesianism stance. That is to say that our probabilities reflect our inadequate information concerning an objective (classical) state of reality for the cat.

However the phrase

> Schrodinger's cat is not both alive and dead. We know nothing about its current state, only how probable certain outcomes are

suggests a perspective in which there is not an objective (classical) state of reality for the cat. Rather, probabilities might be seen as subjective assertions about the outcome of interactions with the system. It is meaningless to talk about the cat being dead or alive before looking. This is closer to what one might call a subjective Bayesian stance.

>It is meaningless to talk about the cat being dead or alive before looking. This is closer to what one might call a subjective Bayesian stance.

In actual classical reality, it's not at all meaningless to ask whether the cat is "dead or alive before looking". It might be uncertain, but it's not meaningless.

One might say "I think it's alive" and another "dead" -- and they have a chance to be right even before opening the box -- we'll just need to open it and see which was right ALL ALONG.

In quantum physics, on the other hand, in most interpretations, none of them is right before opening the box. If one says "the cat must be dead", and we open the box and the cat is indeed found dead, that person, wasn't right all along. He only became right upon the opening.

That's the whole paradox that Schrodinger tried to point out as an absurd result of quantum mechanics -- but which nonetheless is accepted by physicists not as a counter-example against QM, but as something still paradoxical that actually illustrates a key point about QM.

You've described my position in a way I couldn't dream to reproduce, thank you.

It is not a philosophical debate in the arbitrary way that you suggest. "Observation" and "measurement" are not used by physicists in this context as common words, but as jargon with very precise meaning. Depending on what interpretation of quantum mechanics they're using, the meaning of said jargon could be subject to some debate, but that debate takes place in the context of other premises established in advance.

None of those premises involve the magical power of thinking to collapse wavefunctions, because that stems from a common conflation of the Uncertainty Principle, which is a physical phenomenon, and the Observer Effect, which is a product of poor experimental design and can be controlled for.

That would define reality as thought.

Which is not that different that "reality as information", which is quite probable.

Besides, the actual objective reality/universe could just be a set of hazy possibilities in constant flux.

And it's only what WE call "reality" (and consider it as "objective") that appears fixed -- because of how our perception/brain perceives it.

Or an ever-permuting mush of probabilities that only becomes "evaluated" when thought experiences it. There's no way to know, but I personally like that interpretation because it meshes well with the idea that our reality is a simulation. No need to waste computation when it's not necessary.

Contrary to popular misconception, the Observer Effect and the Uncertainty Principle are not actually the same thing. The Observer Effect is something that can happen in all sorts of experiments, classical or not, and is a result poor experimental design. The Uncertainty Principle is a quantum mechanical phenomenon that cannot be controlled for, because the uncertainty of a particle's position and momentum is an inherent property of the matter wave nature of quantum objects.

Part of this stems from early use of the words "observer" and "measurement" when describing the Uncertainty Principle. Most interpretations of quantum mechanics provide specific definitions of these words which differ from their use in common language. The Many Worlds Interpretation, for instance, has no Observer, and defines a measurement as any thermodynamicly non-reverseable process.

"The Many Worlds Interpretation, for instance, has no Observer, and defines a measurement as any thermodynamicly non-reverseable process." I'm interested in this, as I previously thought that the actual word "measurement" was still a bit of a mish-mosh for most interpretations. Do you have a reference for this?

I'm mainly operating on what I remember from when I studied this in grad school years ago. This FAQ about MWI seems pretty detailed, and includes references to other sources: http://www.anthropic-principle.com/preprints/manyworlds.html

More like the tree could both fall and remain upright.

A sound is by definition something heard by someone. An unobserved universe doesn’t make sense, trying to conceptualise one would be like arguing about what colour a ganabreeshlach is.

Does a dog-whistle not make an ultrasound? There are many examples and applications where sound has very legitimate but inaudible effects. Perhaps this definition has contenders? Seems to me there are audible and inaudible sounds. And since definitions tend to follow the masses regardless of logic or sensibility, "sound" probably should also mean "appear", as it's become an idiomatic (non literal) term you'll see peppered throughout Hackernews and elsewhere, e.g. "this sounds good; this sounds reasonable;" etc, used to describe one's interpretation of texts, which sans synesthesia, shouldn't be audible.

The original riddle about the tree in a forest is intended to illustrate the difference between philosophical idealism and materialism.

A dog whistle depends on the concepts of dogs and whistles, which don’t exist outwith the human semantic framework.

Historically, science has been heavily materialist but quantum physics has brought idealism back to the table.

Another thought experiment is 2 people at opposite ends of a room that contains a total vacuum. Ignoring breathing difficulties, if one spoke to the other, would he make a sound?