Qualifications of an Observer

[Harisankar]

Qualifications of an "Observer"

I believe that Quantum Mechanics places an onus on an "Observer" to collapse the wave function of any particle(take an electron for example).
My question is what defines an "Observer"?What are the necessary attributes required to be an observer?
I have read that there has been no consensus as to the credibility of the cat being an observer with regard to Schroedinger's Cat in The Box Paradox.
Is it intelligence or mere consciousness of life?Or something else?

 

[San K]

I believe that Quantum Mechanics places an onus on an "Observer" to collapse the wave function of any particle(take an electron for example).
My question is what defines an "Observer"?What are the necessary attributes required to be an observer?
I have read that there has been no consensus as to the credibility of the cat being an observer with regard to Schroedinger's Cat in The Box Paradox.
Is it intelligence or mere consciousness of life?Or something else?

Hi Harishiv,

neither consciousness nor intelligence nor any life form is required to collapse the wave function.

the wave function can collapse without any life form, any conscious entity, watching/observing it.

the wave function collapses due to instruments (in-animate, non-life) setup in particular ways.

 

[Harisankar]

Hi Harishiv,

neither consciousness nor intelligence nor any life form is required to collapse the wave function.

the wave function can collapse without any life form, any conscious entity, watching/observing it.

the wave function collapses due to instruments (in-animate, non-life) setup in particular ways.

Hi San,

You've given a true answer.But,then again how do we know an instrument has collapsed the wave function without us analysing the instrument?Do we effect the wave function collapse then or not?

 

[StevieTNZ]

Hi San,

You've given a true answer.But,then again how do we know an instrument has collapsed the wave function without us analysing the instrument?Do we effect the wave function collapse then or not?

Absolutely true. I have come to believe it is indeed consciousness that collapses the wave function, after much thought processing and reading.

 

[Naty1]

Any disturbance of the wave function will in general cause it to collapse. So for example an photon bumping into an electron will collapse it's wave function...by imparting some energy...subsequently if the photon is returned to an instrument and "observed" by a scientist, it will be "observed". Whether or not an eyball "sees" the photon after the measurement event is irrelevant.

Any Schrodinger wave of a quantum system (say a particle) psi(x) is a superposition of plane waves exp (ikx)….To measure a particle location in an interval, the various plane waves forming psi(x) have constructive interference within that interval and destructive interference outside the interval.

But even if a quantum particle is not observed, a particle (or equivalently a quantized wave) in a bound state (like confined in a box or orbting a nucleus) has a vanishing probability of being found at infinity...it has collapsed to a quantized state. The quantization of the energy of bound states is one of the most striking facts of quantum theory. But a particle in an unbound state does not remain localized in a finite region...[the electron spreads everywhere like a classical electromagnetic wave.]

 

[Naty1]

...consciousness that collapses the wave function, after much thought processing and reading.

There is no scientific evidence for this as far as I know. ...But it may not be impossible.

If "consciousness" includes emitting some wave energy that interacts with a wave function of a quantum system, wave function collapse would ensue. Foe example if "thinking" creates a tiny and temporary positive charge a nearby passing electron or photon wave function might be impacted...and collapsed. But I don't see this would constitute a "measurement" either.

Some viewpoints are discussed in Wikipedia:
http://en.wikipedia.org/wiki/Quantum_observer

 

[San K]

Hi San,

You've given a true answer.But,then again how do we know an instrument has collapsed the wave function without us analysing the instrument?Do we effect the wave function collapse then or not?

Hari,

you could put a clock, and other instrumentation, that is unobserved for a while and instruments/electronic gadgets that records the whole thing...without any human intervention for a while...

this also, in my opinion/understanding, leads to the answer/resolution to the Schrodinger cat.

I.e. the entanglement breaks as soon as we cross beyond the quantum world...

the cat is never entangled in dead or alive states...

 

[StevieTNZ]

There is no scientific evidence for this as far as I know. ...But it may not be impossible.

If "consciousness" includes emitting some wave energy that interacts with a wave function of a quantum system, wave function collapse would ensue. Foe example if "thinking" creates a tiny and temporary positive charge a nearby passing electron or photon wave function might be impacted...and collapsed. But I don't see this would constitute a "measurement" either.

Some viewpoints are discussed in Wikipedia:
http://en.wikipedia.org/wiki/Quantum_observer

A quantum system interacting with another quantum system cannot collapse anything.

http://henry.pha.jhu.edu/The.mental.universe.pdf
In the article, an experiment is mentioned where nothing interacts with a quantum system, yet the wave function collapses. See more: http://books.google.co.nz/books?id=...utiful Invisible&pg=PA200#v=onepage&q&f=false

 

[StevieTNZ]

Hari,

you could put a clock, and other instrumentation, that is unobserved for a while and instruments/electronic gadgets that records the whole thing...without any human intervention for a while...

this also, in my opinion/understanding, leads to the answer/resolution to the Schrodinger cat.

I.e. the entanglement breaks as soon as we cross beyond the quantum world...

the cat is never entangled in dead or alive states...

Perhaps those clocks, etc collapse upon human observation. Nothing in your answer conclusively implies that because they're not watched they will be collapsed.

 

[Delta Kilo]

I have come to believe it is indeed consciousness that collapses the wave function, after much thought processing and reading.

This model is surprisingly close to many worlds. It would mean the universe was in many-worlds superposition for many billions of years until the first spark of consciousness appeared in it. And if it worked so well so far, I don't see any reason to stop now :)

Also the model requires further clarifications. Is Schroedinger Cat conscious? What about oysters? viruses? apes? What about fetuses and newborn babies, at what age does one start collapsing?

Now, I personally believe that consciousness can be (and hopefully eventually will be) modeled by Turing machine with appropriate software. I don't have any solid arguments to support my belief, just a general feeling that it must be so. I find it very hard to reconcile with the "consciousness causes collapse" idea.

Regards,
DK

 

[StevieTNZ]

All I can do really is say I'm conscious.

Of course I'm not preaching that others may not be conscious, but it is a philosophical problem.

And if there seems to be multiple people with consciousness, whose consciousness counts? All consciousnesses are part of one universal consciousness, to avoid logical problems - such as that one may choose to do one thing, another to do another. That seems like a plausible answer if one travels down the consciousness collapses the wave function route.

 

[Fra]

I think one must note that "the wavefunction" is relative to the observer as well. Thus there is NO such thing as THE wavefunction of an electron - there is in fact as many wavefunctions of the electron as there are others systems (=Observers) interacting with it.

What one might do in some situations, is to consider the equivalence class of wavefunctions.

But,then again how do we know an instrument has collapsed the wave function without us analysing the instrument?Do we effect the wave function collapse then or not?

I answering such questions one must again recap that there is no unique observer. There are rather many observers, and each observers owns it's own version of the description.

In your example, if you consider the instrument the "first observer", and a second observer that then observers the instrument then technically the instruments wavefunction with respect to the second observer can also collapse. But during certain approximations and scalings, the instrument <-> human interaction are effectively classical, but in this sense the information is already spread into the environment of the system.

The wavefunction should have two indices, the system, and the obsever. Alot of confusion in similar disucssions is because people mix up and try to compare wavefunctions between DIFFERENT observers without respecting that a physical comparasion involves physical interactions/communications between the observers.

Note: the equivalence class of ALL observers, properly encoding the state vector is still an open question. The only thing we have so far are the case for observers generated by SR (and part oif GR) transformations. But these transformations hardly exhaust/span all possible observers.

Instead of "consciousness" one could I think better think in therms of a systems awareness of it's own information, in the sense that the observing systems(an observers) action towards another system reflects the information the observers has about the system. There is no need to involve divine or biological notions of awareness here.

Therefore, there is no "objectivity" in the collapse. A collapse from the perspective of one observer, does not imply a simultaneous collapse from the point of view of a second observer.

/Fredrik

 

[StevieTNZ]

Instead of "consciousness" one could I think better think in therms of a systems awareness of it's own information, in the sense that the observing systems(an observers) action towards another system reflects the information the observers has about the system. There is no need to involve divine or biological notions of awareness here.

Don't quite follow what you're saying here. Perhaps you could re-word it.

 

[Naty1]

A quantum system interacting with another quantum system cannot collapse anything.

of course it does..take measurement as an example...

(I did not read the links you posted...if they say that they are not mainstream.

Suggest, for example, you read here:

http://en.wikipedia.org/wiki/Quantum_measurement#Wavefunction_collapse

 

[-dove]

OP, you opened one hell of a can of worms!

There's a number of things being said in this thread, the mainstream, and in the physics community, many of which are false, debatable, or misleading regarding this issue. The short answer to your question is that no one knows. This has been one of if not the largest open problems with non-relativistic quantum mechanics since its inception: http://en.wikipedia.org/wiki/Measurement_problem

Now for a longer answer:

The person that has come closest to saying the right thing was StevieTNZ:

A quantum system interacting with another quantum system cannot collapse anything.

Now this is wrong to the extent to which everything is a quantum system in some sense (if we believe QM is 100% correct), and we indeed "observe" wavefunction collapse in the lab (in whatever sense), so all we have are interacting quantum systems and we know they collapse. However, this is right in some sense as strictly speaking quantum mechanics offers no method for wavefunction collapse without introducing the measurement postulate (which is extremely ad hoc).

Strictly speaking, non-relativistic quantum mechanics says that the state of a quantum system unitarily evolves according to Schrödinger's equation with the the proper hamiltonian for the system. This only applies to a closed quantum system, so in the case of measurement you would have to look at the state space formed by the tensor product of the measurement device's state space and that of the system being measured. In this context, the state will deterministically evolve in time by rotating around in the state space according to Schrödinger's equation.

According to this, measurement devices will just get entangled with the state of the system being measured, as will everything else that interacts with it. In short, you can treat the entire universe as a closed quantum system (if you assume that there is nothing outside of our universe that pokes in and interacts in a non-quantum way) in which case the state of the universe should continuously and deterministically evolve, and there should be no collapses.

The issue, of course, is that in practice we don't see this happen when we introduce large enough systems like measurement devices which are composed of tons of individual particles. Instead, we can "make measurements" that cause a collapse. Not only is it contradictory that this is a discontinous collapse, but moreover its random! So how can quantum mechanics, a deterministic theory at heart, cause random results!?

No one has come up with a universally satisfying answer, and every approach seems to have some flaws or oversights. Some answers are that the universe isn't closed, in which case there would have to be a non-quantum external interaction (otherwise you could expand your system to include the post-universe). Another answer is the many worlds interpretation which says that there is no collapse and that the universe remains in a superposition of every possible outcome (not quite the physical splitting into parallel universes that is popularized), although this still doesn't really explain how our observation chooses just one element of the superposition to see (amongst other issues with the interpretation).

There is also the concept of decoherence which does away with collapse and instead predicts a continuous process by which states apparently collapse and superpositions decay into mixtures. This is more or less inherent in QM already if you accept the fact that systems are getting entangled with the environment and that when we make observations we are looking at a marginal state (i.e. a subsystem that doesn't include every single particle that interacted with the system). But, this doesn't solve the actual problem of what happens when we observe a system and how we actually see randomness. In fact, decoherence doesn't even really try to explain measurement in the first place.The whole "consciousness causes wavefunction collapse" has a huge list of issues. First of all, if we are quantum systems then consciousness is explainable by QM and so it doesn't solve the problem. So unless consciousness is post-quantum (and perhaps contains ways of the universe interacting with something external ;) ) then it doesn't solve the problem. The idea of the consciousness being post-quantum isn't totally farfetched even if it is not external to our universe, because in reality QM is incomplete since it doesn't take relativity into account. Moreover, relativistic quantum field theory(ies) makes the wavefunction a much less clear concept, and so far can only solve a number of pretty specific problems. Furthermore, to date it doesn't explain gravity so it too is an incomplete theory. Even in light of that, it isn't a theory of general wavefunction dynamics in the same way that non-relativistic quantum mechanics is. Not to mention that it has a number of non-understood issues of its own.

The biggest issue of all with the arguments for and against consciousness-caused collapse is that we can't even define consciousness! We can't explain it biologically let alone physically. We would need a definition/explanation in terms of physical interactions and processes before we could even attempt to involve it in any theory of physics. So it can't even be discussed meaningfully (yet).

The most likely scenario, I believe, is that we will need a new theory of physics to answer this question, because it doesn't appear to be answerable in quantum mechanics.

 

[Delta Kilo]

Let's consider the following gedanken experiment, call it Schroedenger's iCat:
* A bunch of detectors D1...Dn
* A Turing machine TM executing some program and taking inputs from D1...Dn
* External environment observing the above and providing a "sink" for decoherence to work
The idea is: it might be easier to analyze the behaviour of TM than that of a cat and it might even be possible to provide a full quantum description of it without invoking the mystical "observation" (one can always hope).

Now, if a particle in pure state |A0> hits detectors Di (note: pure state in einselected basis of Di, assuming they all have the same basis, i.e. designed to measure the same thing), each detector coming into contact with particle will go into state |Ai> and the whole thing ends in state |A> = |A0>|A1>|A2>...|An> - state of all subsystems corresponding to seeing outcome A. The same goes for |B>.

If the particle is in superposition of |A0> + |B0>, each individual detector coming into contact with the particle will initially be in superposition |A0>|Ai> + |B0>|Bi> and a whole thing will be a mixture of all sorts of combinations of terms. Decoherence tells us that mixed terms like |A0>|B1>|A2>... will quickly dissipate into the environment and will soon have vanishingly small amplitude (0 for all practical purposes) and the whole thing will settle in state |A> + |B>.

Components |A> and |B> will evolve separately, after some time each one will reach a state where TM has halted and a result of computation is stored on tape. If we look at these results we'll see that each of them is consistent with all D1..Dn reporting the same value. We will also note that evolution of state |A> will have no effect of state |B> and vice versa. According to the results produced by TM in state |A> everything indicates that the incoming particle's wavefunction has collapsed into state |A0> immediately upon the first detection. Same goes for TM in state |B>.

Well, this example is supposed to tell us something, I'm just not sure exactly what is it. I guess it shows that a) observer does not have to be conscious to cause apparent collapse and b) many-worlds comes out naturally and some extra effort is required to "prune" the branches that did not come to pass for a particular observer state.

DK
(disclaimer: I might be wrong about this. I have been wrong before)

 

[CJames]

This is quite a post, -dove. I'm amazed how much you were able to summarize here. I have a question.

There is also the concept of decoherence which does away with collapse and instead predicts a continuous process by which states apparently collapse and superpositions decay into mixtures. This is more or less inherent in QM already if you accept the fact that systems are getting entangled with the environment and that when we make observations we are looking at a marginal state (i.e. a subsystem that doesn't include every single particle that interacted with the system). But, this doesn't solve the actual problem of what happens when we observe a system and how we actually see randomness. In fact, decoherence doesn't even really try to explain measurement in the first place.

Is this true of quantum Darwinism? I thought the whole idea was that pointer states contained the information that we measure, while the other states decay into unmeasurable noise.

 

[-dove]

This is quite a post, -dove. I'm amazed how much you were able to summarize here.

Thanks! It missed a lot of the details I'd preferred it to have, but there is only so long you can make a forum post and expect anyone to read it. So I summarized it enough that the OP could read it, but hopefully left enough so that they could understand the true nature of the beast without being misled.

Is this true of quantum Darwinism? I thought the whole idea was that pointer states contained the information that we measure, while the other states decay into unmeasurable noise.

I'll have to admit here that I don't know much about quantum Darwinism other than the name. That said, having read the wiki article and skimmed Zurek's paper (http://arxiv.org/abs/quant-ph/0308163) it seems very interesting, and I intend on reading the paper in full soon. So I can't answer that question in full right now.

However, from what I understand about it right now...it sounds like the short answer is no on a few accounts:

-Zurek's theory is explicit about NOT having to do with reduced density matrices (marginal states) which is the key to the decoherence concept (you trace out over the parts of the environment that float away or are left unobserved): "We close this part of our discussion by calling reader’s attention to the fact that the
above derivation did not rely on – or even invoke – reduced density matrices, which are
at the very foundation of the decoherence program."

-It sounds like Zurek is claiming to solve the measurement problem. In which case, he ought to have an answer as to how single pointer states get apparently stochastically chosen. On the contrary, the decoherence picture would explain how we get from a superposition state to a large entangled state whose local observed marginal is a mixture of pointer states, but it doesn't actually do the choosing of a single pointer state.

I would expect that Zurek's theory invokes something post-quantum, as even he notes:

"Hence, any conceivable superposition (including the counterintuitive “Schrödinger cat” states) should have an equal right to be a valid description of a real apparatus (or a real cat) in a completely quantum Universe."

But I'm not so sure because he also says:

"I review key ideas of quantum Darwinism and investigate its connections with the environment – assisted invariance or envariance, a recently identified symmetry exhibited by pairs of entangled quantum systems that is responsible for the emergence of probability (allowing, in particular, a completely quantum derivation of the Born’s rule) within the wholly quantum Universe."

It would shock me if his theory is inherent in QM already unless it did the same thing that every other solution has done thus far, which is to make a lot of fuss and introduce a lot of new ideas and concepts, pretty tricks and fireworks, to give people things to read about and to impose the appearance that it has been solved while the real heart of the problem (not necessarily intentionally) gets swept under the rug.

I would be extremely surprised if there is a true solution entirely within QM-minus-the-measurement-postulate. Although I'd certainly love and hope to be surprised!

 

[-dove]

This observer issue inevitably brings up the consciousness causes collapse argument, and that warrants that I make an additional comment in this separate double post independent of the above post's topic.

As I already said in my first post, both sides of the argument are wrong since neither can even come up with a physical definition of the theory they are arguing over. But the people who instantly dismiss it because of the fact that its anthropomorphic on some level or seems skirting too close to mysticism are despicable. It's just as bad to insist that "good" theories must be special by being entirely unanthropomorphic as it is to insist on anthropomorphic principles. Moreover, consciousness is special on some level, and it is ridiculous that some scientists are so insecure about their personal level of scientific rigor that they feel the need to deny this for such a sake.

Even from an external standpoint, consciousness is astounding. Presumably (though debatably***) "unconscious" particles are essentially organizing themselves in ways that allow them to try to figure out and express what rules govern the way particles interact! It would be as if you threw a googol billiard balls on a table and they started to organize in ways that argued over the rules of billiards. On an internal level it is even more astounding, since it shows the apparently trancedent phenomenon of "thinking", which is certainly the least understood physical phenomenon yet the one we have the best evidence for. On a personal level, is there anything you have better proof for than the fact that you think? All other forms of evidence rely on it! Furthermore, if we consider the possibility of free will as part of consciousness, then there is seemingly no way to even model it in known physics and mathematics. Namely because it is not compatible with deterministic nor stochastic processes, which are mutually exclusive and are canonically treated as complements (if a process is not one then it is the other).

So no one should try to argue that there isn't something special about consciousness, because evidence seems to say there is (biased of course). Now on what level of physics it is special is debatable, and there is certainly nothing saying that it is a quantum level. But the fact that it is quite remarkable and apparently unexplainable in currently accessible means suggests that there might be something fundamentally physically unique about it, in which case it is reasonable to conjecture things like this unique process being the cause of phenomena like collapse. At the same time, it doesn't warrant people to just say "it must be consciousness that does x" when we can't even define it yet nor really prove anything wrong about it. For these reasons, though, it should be taken seriously, as it was by Von Neumann, Wigner, and many others; but we most certainly shouldn't lose sight of the fact that we need to physically define it before we start worrying about proving or disproving something about it. Finally, we shouldn't give any special treatment to other candidates for unique physical processes that cause collapse (or explain anything else for that matter) just because they don't have anything to do with consciousness; because if someone really believes that consciousness isn't special then what more is it than a physical process?, and they presumably would allow physical processes to be the cause or explanation of things.



***Conway and Kochen claim to prove that if anyone has any amount of free will, then elementary particles must too: http://arxiv.org/pdf/quant-ph/0604079v1. Which is not totally unbelievable, because it would be equally or much more unbelievable for things without any free will to combine to form something that somehow had it.

 

[Harisankar]

Thanks everyone for your replies.
Dove and Stevie have given detailed answers which have give me more insight(no,you have not confused me,Dove).
But due to my lack of acquaintance with Dirac's formalism,I have found the latter part a bit of a stretch,though I am not asking any clarification,just stating my own disabilities.

It does seem to me that the exact nature of the question and it's answer is far from a consensus.

Thank You All.

 

[Demystifier]

"Observer" of a system is anything that causes decoherence of that system.