The need for a "conscious observer"

[entropy1]

Does unitarity of the evolution of wavefunction get rid of the need for a "conscious observer", and does collapse in contrast demand a "conscious observer"?

For with unitarity there are is no requirement for such an observer, and collapse can't be explained without such an observer.

The "conscious observer" seems to have been cast out of physics, it seems to me. I have no urgent desire for it scientifically, but the question does not appear entirely unscientific to me.

This inspired me to this question:
https://www.youtube.com/channel/UC1aPeLTxBgZmiuzkcUZBTIw (in particular Sean Carroll)

Perhaps best added to this thread: is decoherence a fact or a theory?
And this: should we speak of observed outcomes rather than of just outcomes?

 

[Halc]

With the exception of the Wigner interpretation (for which even Wigner himself eventually withdrew support), a conscious observer plays absolutely no role in any of quantum mechanics.
Collapse of the wave function (assuming an interpretation that posits it) is unrelated to consciousness, else the universe could never have evolved a conscious observer.

 

[StevieTNZ]

See my post in the main QM forum: https://www.physicsforums.com/threads/doesnt-schrodingers-cat-start-to-decay.996115/post-6418171

 

[PeterDonis]

is decoherence a fact or a theory?

It's been observed in experiments, so it's a fact. See, for example, this review article by Schlosshauer:

https://arxiv.org/abs/1911.06282

 

[weirdoguy]

is decoherence a fact or a theory

In science "theory" is not the opposite of a "fact"...

 

[Lord Jestocost]

... a conscious observer plays absolutely no role in any of quantum mechanics.

With all due respect, can you point to an operational way to underpin you "declaration"?

 

[Morbert]

Does unitarity of the evolution of wavefunction get rid of the need for a "conscious observer", and does collapse in contrast demand a "conscious observer"?

Instrumentalist interpretations do not imply a conscious observer is demanded by collapse. An "unconscious" decision-making computer could be programmed to gather information and make predictions using QM, based on gathered information. Wavefunction collapse would be one of its procedures.

 

[EPR]

An "unconscious" decision-making computer could be programmed to gather information and make predictions using QM, based on gathered information. Wavefunction collapse would be one of its procedures.

Actually, it's more subtle than that. Information exists only wrt minds. A computer is a collection of transistors which act as electrical gates. What you see on the monitor is photons emitted by diodes according to the momentary state of the gates in the microprocessor. You need a mind for this emitted light to become information. Otherwise, it's just light(photons). Like this sentence. It has meaning wrt to minds, but not wrt to photons with different wavelengths being emitted in a particular way.

 

[stevendaryl]

For all practical purposes, you can substitute a measuring device for a conscious observer. You can program a robot to write "The particle was measured to have spin-up" just like a human observer. The Rules of Quantum Mechanics would work just as well for the robot. Sure, you can take a skeptical stance and say that the robot doesn't actually know that the spin was up, you need a human to read what it wrote and interpret it. But you can apply the same skepticism to other humans---maybe only your observations collapse the wave function?

Anyway, the Rules of Quantum Mechanics say, roughly, that:

When a measurement is made, the result will be an eigenvalue of the operator corresponding to the observable being measured.

Some people interpret the measurement to be made when a conscious observer learns the result. But if you instead, you interpret it as: the measurement is made when there is a persistent, irreversible record of the result, you get a variant of quantum mechanics that is experimentally indistinguishable from the first interpretation.

 

[Lord Jestocost]

Does unitarity of the evolution of wavefunction get rid of the need for a "conscious observer", and does collapse in contrast demand a "conscious observer"?

Maybe, the role of consciousness within the framework of orthodox quantum theory (QT) might be misunderstood when not consequently thinking about the QT formalism. I recommend to read the paper "What are quantum theorists doing at a conference on consciousness?" by Euan J. Squires (https://arxiv.org/abs/quant-ph/9602006).

The text is published under the title "Why Are Quantum Theorists Interested in Consciousness?" in the book "Toward a Science of Consciousness II: The Second Tucson Discussions and Debates" (edited by Stuart R. Hameroff, Alfred W. Kaszniak and Alwyn Scott).

 

[PeterDonis]

Information exists only wrt minds.

Not in physics. The physics definition of information has nothing to do with minds.

 

[Lord Jestocost]

For all practical purposes, you can substitute a measuring device for a conscious observer. You can program a robot to write "The particle was measured to have spin-up" just like a human observer. The Rules of Quantum Mechanics would work just as well for the robot. Sure, you can take a skeptical stance and say that the robot doesn't actually know that the spin was up, you need a human to read what it wrote and interpret it. But you can apply the same skepticism to other humans---maybe only your observations collapse the wave function?

Nevertheless, why should a physicist - even for all practical purposes - place an "Heisenberg cut" somewhere in a "von Neumann chain"? From a physical point of view, one gains nothing.

 

[stevendaryl]

Nevertheless, why should a physicist - even for all practical purposes - place an "Heisenberg cut" somewhere in a "von Neumann chain"? From a physical point of view, one gains nothing.

Gains compared to what?

 

[PeterDonis]

why should a physicist - even for all practical purposes - place an "Heisenberg cut" somewhere in a "von Neumann chain"?

Because you have to make correct predictions for further measurements made on a system that you've just made a measurement on and observed a result.

From a physical point of view, one gains nothing.

Only if you think being able to make correct predictions is "nothing", which doesn't seem like a defensible viewpoint.

 

[Lord Jestocost]

Gains compared to what?

In case quantum theory really applies to all physical systems^**, viz., if one bases oneself on the formalism of quantum theory and the Schrödinger dynamics in particular, the arbitrary introduction of a “Heisenberg cut” somewhere in the “von Neumann chain” merely burdens, to my mind, quantum theory with a classical view of reality.

^** As a result of the interaction between a physical "object" and a physical "measuring instrument", the "object" is - so to speak - entangled with the "instrument".

 

[stevendaryl]

Gains compared to what?

I didn't really understand the comment, but to elaborate on my answer without being sure in what direction it needs elaboration...

if one bases oneself on the formalism of quantum theory and the Schrödinger dynamics in particular, the arbitrary introduction of a “Heisenberg cut” somewhere in the “von Neumann chain” merely burdens, to my mind, quantum theory with a classical view of reality.

Well, that seems like an aesthetic response, which I have sympathy with. But as far as making an empirical connection between quantum theory and observation, the standard prescription involves measurements producing one outcome, with probabilities given by the Born rule. The more aesthetically appealing choice is to treat everything quantum mechanically, as Many Worlds does. But then the meaning of the probabilities in QM seem obscure. I know that there are attempts to understand probabilities in MW, but I don’t find them particularly compelling.

 

[entropy1]

Does this issue also have to do with realism? For instance, suppose the reflection in my window of my ceiling lamp throws an artefact on the wall, which I don't see for I am not looking. When I look, I see the speck on the wall. That does not mean that the speck is not there when I am not looking, right?

I think this was the dispute between Einstein and Bohr? So did Einstein win the argument?

If we consider MWI, in case of measuring a quantum property, there is an observer reading outcome 1 and yet a another observer reading outcome 2. However, the moon has settled for every observer. Or is Schroedinger able to put the moon in superpostion again? Does the moon make quantum measurements that entangle it with particles flying into it?

My writing reveals confusion. Yet I place this post because someone might have something useful to say about it. Sorry for the confusing nature of it (what else is new).

 

[Halc]

Does this issue also have to do with realism?

Yes it does, but seemingly not in the way you are thinking.

For instance, suppose the reflection in my window of my ceiling lamp throws an artefact on the wall, which I don't see for I am not looking. When I look, I see the speck on the wall. That does not mean that the speck is not there when I am not looking, right?

No, it merely might mean that you don't know about it because you're not looking. If it's always there when you look, then you probably know about it anyway. Regardless, you looking at it has nothing to do with whether it is really there or not. You are entangled with it regardless of your being conscious of it.

I think this was the dispute between Einstein and Bohr? So did Einstein win the argument?

The quote you refer to was a quip, but being that it is impossible to un-measure the moon, the moon is just as much there when nobody is looking at it as when they are looking at it.

If we consider MWI, in case of measuring a quantum property, there is an observer reading outcome 1 and yet a another observer reading outcome 2. However, the moon has settled for every observer.

The two observers see moons in different outcomes (not an identical moon), and under MWI, most of the worlds have no moon at all, but those worlds don't have humans observing its absence.

Or is Schroedinger able to put the moon in superpostion again? Does the moon make quantum measurements that entangle it with particles flying into it?

The moon is over a light second away, and thus is always in various states relative to the event of observation. It is probably improper to call this superpostion since the various states are well beyond the point of interfering with each other. They've put (barely) macroscopic objects into actual superposition, but had to resort to extreme measures (cold, dark) to keep it in that state for a couple nanoseconds or so.

 

[EPR]

But then the meaning of the probabilities in QM seem obscure. I know that there are attempts to understand probabilities in MW, but I don’t find them particularly compelling.

This is the Achilles heel of the MWI, isn't it?

Certain outcomes are not going to happen more often than others - they all will take place with equal frequency. Branching will lead to incorrect predictions... unless it's biased towards certain classical laws we know from the macro world. Like phone screen breaking more often than not, when dropped from the 4th floor. It will break 99% of the time, not 50%, as you'd expect from a quantum perspective(break/not break or a superposition of the 2). If the world splits in 2, every interaction should produce an equal chance that the phone's screen remains intact as it should get broken.
I am looking to understand how classical law 'bias' can be accounted for in MWI.

 

[Lord Jestocost]

I didn't really understand the comment, but to elaborate on my answer without being sure in what direction it needs elaboration...

I merely want to point out that – to my mind – questions like

Does unitarity of the evolution of wavefunction get rid of the need for a "conscious observer", and does collapse in contrast demand a "conscious observer"?

are in principle answered. If all chain links in a von Neumann measurement chain are treated as pure physical systems – up to the end, one ends up - when basing oneself on the physical formalism of quantum theory and the Schrödinger dynamics in particular - with nothing but an entangled state. If the object of interest which is measured is, for example, represented by a superposition state $a|+> + b|−>$, the last chain link of von Neumann’s measurement chain ends also in a superposition state

$a|+,A+,E+,Me+> + b|−,A−,E−,Me−>$

where $A+,E+,Me+$ and $A−,E−,Me−$ represent the state of the apparatus, the environment and the “observing” system at the end of the chain.

That's the "physics"! There is - when all chain links are considered as pure physical systems - nothing which reduces the superposition of two possibilities to one unique actuality.

As Euan J. Squires puts it (see reference in post #10):

“So, where is the problem, and what has all this got to do with consciousness?
The complete description of the “physics” in orthodox quantum theory is the state displayed above, which contains both terms, i.e. both “results”. The unique result of which I am aware does not exist in physics - but only in consciousness. The Born rule does not have anything to say about physics - it says something about consciousness.”

 

[stevendaryl]

“So, where is the problem, and what has all this got to do with consciousness?
The complete description of the “physics” in orthodox quantum theory is the state displayed above, which contains both terms, i.e. both “results”. The unique result of which I am aware does not exist in physics - but only in consciousness. The Born rule does not have anything to say about physics - it says something about consciousness.”

Well, the formalism of QM and the empirical evidence don’t actually say anything about consciousness. That’s a way to resolve the measurement problem, I suppose, but it’s not forced on us. And I don’t like it because it’s trading one mystery (the measurement problem) for another (consciousness). The other thing that is unsatisfying to me about invoking consciousness is that it doesn’t actually seem to be an independent degree of freedom. We might not understand consciousness, but our experience tells us that it isn’t independent of our brain state. Whatever goes on in our conscious mind is mirrored by phenomena in the brain: synapses firing, etc.

 

[PeterDonis]

If all chain links in a von Neumann measurement chain are treated as pure physical systems – up to the end, one ends up - when basing oneself on the physical formalism of quantum theory and the Schrödinger dynamics in particular - with nothing but an entangled state.

"The physical formalism of quantum theory" includes the Born Rule and the projection postulate, in addition to Schrodinger dynamics.

What you are describing is the MWI, which is just one interpretation of QM.

 

[Lord Jestocost]

We might not understand consciousness, but our experience tells us that it isn’t independent of our brain state.

Of course, there is a linking between brain and consciousness. The question: When regarding the brain^** as a physical system, the brain - at the end of von Neumann's chain - can arrive at a superposition state according to the physical formalism of quantum theory. In case there is a one way dependence (brain -> consciousness), that wouldn't result in an unique event experienced by our conscious mind. There must be something which selects an experienced world from the possibilities provided by “physics”.

^** From a physical point of view, I regard the brain and its connected "sensors" as a physical measurement apparatus

 

[EPR]

There must be something which selects an experienced world from the possibilities provided by “physics”.

And it must very closely match a persisting classical-looking world obeying classical laws.

Good luck with that.

 

[bobob]

Conscious observers obey the same quantum theory as the rest of the universe. Conscious observers are irrelevant. Not to put too fine a point on it, but conscious observers are the ones who define "conscious," and aside from the inherent bias in that, there is no consensus to what that even means. Why would "conscious observers" be special aside from the desire of some conscious observers to think they are special and not subject to the same laws of physics that applies to the rest of the universe?

 

[Dale]

Several posts discussing another thread have been removed and the thread is reopened

 

[physika]

.

...and what was the observer at the beginning of the universe?.

 

[StevieTNZ]

.

...and what was the observer at the beginning of the universe?.

I would say consciousness is outside the realm of physical matter and exists independently of it (which can give rise to something observing the beginning of the universe). This is basically the essense of the mind-body problem in philosophy.

 

[PeterDonis]

I would say consciousness is outside the realm of physical matter and exists independently of it

Then how does consciousness affect physical matter? I consciously decided to type this post, and that conscious decision of mine affected physical matter. How does that happen if your statement quoted above is true?

 

[physika]

I would say consciousness is outside the realm of physical matter and exists independently of it (which can give rise to something observing the beginning of the universe). This is basically the essense of the mind-body problem in philosophy.

consciousness in the nothingness ?

 

[StevieTNZ]

Then how does consciousness affect physical matter? I consciously decided to type this post, and that conscious decision of mine affected physical matter. How does that happen if your statement quoted above is true?

One could presume everything is consciousness. See for example Richard Conn Henry's article "The mental universe" - https://www.nature.com/articles/436029a

I submit nothing in my initial post stops consciousness from affecting matter*.

*if materialism should play a role.

 

[PeterDonis]

I submit nothing in my initial post stops consciousness from affecting matter*.

*if materialism should play a role.

You can't just "submit" a claim like this. You need to explain how consciousness can affect matter if it's "outside the realm of physical matter and exists independently of it". You can't just wave your hands and say "I submit nothing stops it".

 

[PeterDonis]

One could presume everything is consciousness. See for example Richard Conn Henry's article "The mental universe" - https://www.nature.com/articles/436029a

"Everything is consciousness" (or more precisely "everything is mind"--"the Universe is mental" is how the article puts it) is not the same as "consciousness is outside the realm of physical matter and exists independently of it". Which viewpoint are you trying to defend?

 

[StevieTNZ]

"Everything is consciousness" (or more precisely "everything is mind"--"the Universe is mental" is how the article puts it) is not the same as "consciousness is outside the realm of physical matter and exists independently of it". Which viewpoint are you trying to defend?

That claim is separate from my previous, in the same post.

 

[StevieTNZ]

You can't just "submit" a claim like this.

One could claim the brain and mind are correlated, though consciousness is not caused by physical activity of the brain, as it is in a superposition state if we apply QM to micro- and macro- systems.