I have long maintained that’s it stupid for us to believe that the human who opens the box qualifies as an observer but the cat itself doesn’t qualify. For that matter, I think the Geiger counter qualifies as an observer and the vial of poison is never in a superimposed state. I agree with wolfpup that the universe existed just fine for billions of years without any creatures of any kind observing it. Two protons colliding should qualify as one of them observing the other.
Are you thinking of the E-P-R “paradox”? Wherein two particles in a system can be entangled? Because the predictions of quantum mechanics are still borne out in such experiments.
I would say it is a very useful thought experiment and source of ideas for actual experiments to rule out hidden variables, etc.
Are they hidden variables or just ones we have not discovered yet?
I think the lottery example just showed me that I might never have understood what the cat example was about.
As I understand it, the metaphor of Schrödinger’s cat was at least partly satire. He was expressing his unease with QM and Uncertainty. I could be wrong about that.
We don’t need quantum computers to provide macro scale evidence of quantum manipulation. Tunnel Diodes exist, are part of the circuitry in billions of devices, have existed for over 60 years, and would not function at all if QM weirdness was not real or applicable to the macro world.
And Quantum mechanics and its randomness play a major role in providing a necessary tool for complexity - random behavior. It can be shown that if you had two perfectly smooth billiard balls (normal size) and could measure their center points down to the individual atom, you could drop one onto the other such that their center points would meet. In that scenario, you would think that the ball would bounce on the other one indefinitely, because there is no lateral force to cause it to go sideways. But in fact, quantum fluctuations will guarantee that the balls will diverge after 10-20 bounces (I can’t remember the exact details - been a long time since I read about it).
Complex systems (and the entire universe looks like it may be made up of nested and evolving complex systems) require randomness to function. And because they are nonlinear and sensitive to initial conditions, even quantum scale fluctuations eventually make their way into the macro world, and perhaps even with very dramatic effects.
This page summarizes a whole bunch of experiments that rule out Bell’s inequality, which is required by theories that assume there is such a thing as local hidden variables.
Note also that experiments show that a single particle can be in two places at once:
As for what an ‘Observer’ is, I think that’s a really bad word that has led to an awful lot of confusion.
I don’t think there is a single fully accepted definition of ‘observer’, because it probably differs slightly depending on your interpretation of QM. But I think the definition that leads to the most understanding is something along the lines of this:
“An ‘observer’ in quantum mechanics is any interactor with the quantum field that forces it to give up information about its state.”
Here’s an analogy which may be really suspect, as any analogies to quantum effects are. But maybe it will help us think about this: Imagine a superheated liquid in a perfectly smooth container. Such a liquid won’t boil, as there are no nucleation sites to start the process. The energy is in there, the gases are ready to erupt, but you can’t see them, can’t tell they are there, etc. But the second you try to measure the temperature or the gas content by interacting with the liquid, you create a nucleation site and suddenly the whole thing starts boiling. (by the way, this can actually happen to you if you microwave distilled water in a clean cup, and people get burned this way all the time).
I imagine the quantum world as a series of fields that are structured in a way that as soon as they interact with the non-quantum world the point of interaction collapses into a particle. The fields do not exist in normal spacetime, which is why quantum entanglement can happen instantaneously across a galaxy. So in this view, particles are almost like standing waves where two fields intersect. That point of intersection will result in a particle when it is ‘observed’ by something else, but there is a probability distribution that determines exactly where the particle will appear from that point.
This all could be totally wrong (almost certainly is), but it might be a helpful way to think about the situation if you can’t get your head around wave-particle duality and all that.
I much prefer the opposite conclusion. The Geiger counter doesn’t qualify as an observer, the cat doesn’t qualify as an observer, and the “observer” doesn’t qualify as an observer. The observer doesn’t perceive herself as being in a superimposed state, because she is only one branch of her own wavefunction.
I do not think there is a “non-quantum world”, as such. There is an aspect to reality that can only be studied indirectly and understood with acres of blackboard math, but it is not a separate realm to the physical reality we are familiar with. More like a mysterious substrate.
I tend to think of particles and other measurable things as being emergent properties of an underlying complex quantum world, just as humans are complex systems made up of atoms, but requiring an entirely different descriptive language to understand. And for all we know, the quantum world could be an emergent property of yet another system utterly unknowable to us.
As Feynman said when asked if he was looking for the ultimate truth, “I don’t even know if there is one. Maybe our universe is like an onion, and we’ll keep peeling back layer after layer without end, until we get tired of peeling.”
In one sense it’s all just physics, but in another the emergent properties of complex systems are not understandable or describable using the language we use to describing the underlying system creating those properties.
For example, I firmly believe that ‘consciousness’ has a wholly physical cause in that it is created by the interactions of networks of neurons in our brain. But if I asked you to define consciousness, you could not do so by describing the mechanics of neuron firing.
This would also argue against the existence of a grand unified theory of physics. There may not be one, as the rules at each level may be emergent.
onions all the way down
This is in the right direction, but even then not problematic:
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quantum mechanics talks about measurements not observers. An observer seems like it may be a necessary component of a measurement, but you need to do some interpretation to relate an observer to QM.
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A measurement does not require interaction as such. An absence of interaction can count as a measurement.
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A quantum field is something specific in QP and they’re not used in basic quantum mechanical descriptions. I would choose the term ‘system’
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A measurement doesn’t give you direct information about the state before measurement and a system can in principle be prepared to that its precise state is known. A measurement will tell you the state of the system after measurement.
Keep in mind that a “new” scientific theory like quantum mechanics must still explain all previously experienced phenomena. A wall that is solid without considering quantum mechanics must still be solid when considering quantum mechanics. Thinking about the world in a different way doesn’t actually change the world.
I prefer to be in a superposition of interpretations. 
Just a note on the lottery ticket in a box example. (This much I do “understand.” :)) Unlike the schmeared cat (“smeared” is Schroedinger’s exact word), that ticket, by all the rules in the known Universe, barring the probability that the ink on it will chemically re-segregate into a different and specific set of patterns/words, is either a winner or a loser. Which is saying a whole lot more than you can regarding a “particular” quantum state.
In fact, the Clinton Principle, as I heard it used in a YouTube of a Stanford Physics lecture, applies: the fact that one can even state what is is (“is either a winner or loser”) is already answered in this lottery example, which makes it damn simpler.
Shrek: For your information, there’s a lot more to [del]ogres[/del] the universe than people think.
Donkey: Example?
Shrek: Example? Okay, er… ogres… are… like onions.
Donkey: [sniffs onion] They stink?
Shrek: Yes…NO!
Donkey: Or they make you cry.
Shrek: No!
Donkey: Oh, you leave them out in the sun and they turn brown and start sproutin’ little white hairs.
Shrek: NO! LAYERS! Onions have layers. OGRES have layers. Onions have layers… you get it. We both have layers.
Donkey: Oh, you both have layers. [pause] You know, not everybody likes onions
I just made up the lottery ticket example on the spot, so I don’t have a great investment in it to dfend, but it does seem as though it would still be affected by the information hidden in the box.
With the quantumn erasure expeirment, you can have either a difffraction pattern, or a set of completely random plots, and it is based on infortmation that you may not yet have. You can sit and stare at the screen full of dots all day, but until you get the information from the other half of the experiment, (which you could delay arbitrarily long), it’s just a random array of dots. Once you have that info, though, you can create the interference pattern.
It doesn’t work for pretty much the same reason why the cat in the box doesn’t work, in that you cannot actually hide the information and “prevent collapse” by putting it in there, as there is no such thing as a perfect macroscopic container. But, lets say you throw your lottery ball picker into a black hole right before it chooses the numbers. Now, maybe (BIG maybe, the jury is not just still out, it is still being picked for this) you can detect all the hawking radiation given off by the black hole from now till it evaporates, and then learn the state of the lottery machine, but until then, your ticket is not determinable to be a winner or loser with the information to which you have access.
Wouldn’t that be the case for a cat that is either alive or dead, as well?
[quote=“k9bfriender, post:57, topic:811823”]
“Either” is quite different than “neither.”
The wall is there, and you will bump into it, when you get close. And a cat cannot be dead and alive at the same time, irrespective of Schrodinger. That has been my experience in life anyway.
[quote=“Leo_Bloom, post:58, topic:811823”]
So, the cat is “neither” alive or dead?
The 6 year old who you took the cat from, are they happy their cat is alive, or crying that their cat is dead? Is there anyway to determine that without opening the box?