Nobody likes to be called a dummy by a dummy.

The quantum observer

Taken from a thread yesterday...

Those who have an interest in quantum theory, what is your take on the idea of an "observer"?

In the Schrodinger's cat experiment, the cat is in an alive/dead state until the box is opened, collapsing the wave function - a human researcher is "making an observation".

Here's a wikipedia link:
http://en.wikipedia.org/wiki/Schrodinger's_Cat

The point of the experiment is to highlight the lack of definition (in the Copenhagen interpretation) of what an observer is in the quantum world.

Currently, the Goodwin interpretation is that the detector in the box qualifies as an observer and the cat never has a chance of being in a superposed alive/dead state. Which is good, because I saw what happened to that monkey in The Fly, and that is the only way I can visualise quantum superposition early in the morning.
Permalink Joel Goodwin 
August 10th, 2005
The fundamental point about Schrodinger's Cat is that it is an analogy designed purely to explain the effects of quantum probability in a dramatic way. As soon as you treat it as real you begin to tear the analogy apart.

Any mechanism that detects and reports that detection or makes use of it is an observer. If it doesn't use it or pass on some state of information then it itself has its own probability wave which collapses when interrogated.
Permalink Simon Lucy 
August 10th, 2005
The mechanism of wavefunction collapse on observation is still unclear.

It isn't _in_ quantum mechanics, it is outside, a boundary condition, the end of a state.

It is clear from experiment that macroscopic makes microscopic collapse. But some quantum effects are macroscopic.

Research is beeing done in the intermediate region, where clusters of atoms react with smaller entities, and one investigates how long there will be superposition of states in the larger entities. Here temperature comes into play, as positive temperature will kill the coherence of states anyway.

So the nice 'quantum transporter technology' will principally fail for humans because of size and temperature. Only relatively simple states at absolute zero can be 'transported'.

Apart from temperature, what is it that size makes a wavefunction collapse? We don't know. So much so that some physicists, and not crackpots, can suggest that when gravity becomes noticeable that wavefunctions will collapse.

I have seen one describe an experiment that would test that hypothesis, but accuracy-requirements would take the researchgroup several years before the experiment could be successfull.

So this is still a mystery and subject of current investigation.
Permalink Erik Springelkamp 
August 10th, 2005
It's difficult to observe continuously!

Anyway, my take is that when there is [by definition] no observer then the state is [by definition] uknown/unknowable/undefined.

- Q: Does a dog have Buddha-nature?
- A: There is no-one to ask that question, nor to answer it.

I reckon that the cat, being sentient, is an observer (that's an axiom on my part, extrapolated from my being taught to be nice to the cat, to respect its feelings, when I was young). The cat's awareness of its own state seems to me to be related to the question:

- Q: What is the probability of intelligent life existing in this universe?
- A: The probability is 100% ... because if intelligent life didn't exist in the universe, then there would be nothing to observe the universe's existence ... any/every observed universe implies the existence of an observer.

I reckon that the detector, because it's sealed in a box, makes no observation that we/you/I outside the box can know of until after we/you/I unseal the box.
Permalink Christopher Wells 
August 10th, 2005
Christofer,

You are talking about the philosofical aspects, not the physical ones.

Your reasoning is true, but not scientific because it doesn't predict anything, and cannot be falsified.

It is also true regardless of quantum mechanics.
Permalink Erik Springelkamp 
August 10th, 2005
(a) quantum physics is a model describing the physical universe. It is not the universe.
(b) At the quantum level to deal with things you can't observe you have to deal with all the possibilities at once
(c) One interpretation (the copenhagen interpretation) considers this "real".
(d) Schrodinger thought this was bloody silly and gave us the "cat in the box" example in order to take the piss out of it.
(e) Silly or not it fits the experimental results. Which is a bit of a pain in the arse frankly.
Permalink a cynic writes... 
August 10th, 2005
> philosophical not physical

Yes Erik, that's true: the quantum mechanics that I learned was nothing but Mathematics -- differential equations, not physics. The philosophy-of-science associated with this applied Mathematics was like "here we have an equation ... from which we derive another equation ... is this a *useful* equation, i.e. can we find any way in which this equation corresponds to the real [observed] world?" Perhaps it was this way because the equations themselves could not be falsified ... they could only be more or less useful/applicable.

The only even slightly related (to quantum mechanics) physical experiment that I know of (that I can narrate) is the one where a beam of light is shone at a barrier in which there are two slits, and behind which there's a photographic film. The film will register an interference pattern from the light passing through the two slits ... and this continues to be true, even when the intensity of the light beam is reduced to the point where there's only one photon at a time (it looks as if each photon travels through both slits simultaneously and then interferes with itself on the other side).

> Your reasoning is ... not scientific because it doesn't predict

That's is the nature of Schrödinger's thought experiment itself, isn't it? The associated "prediction" is merely that you *cannot* know (cannot predict) the state of the cat until after you observe it. The only way to falsify that statement or that thought-experiment, that I can see, is the route which the OP took: for example to ask whether there's a universal observer, like asking whether there's a cosmic conciousness or God who knows the state of the cat even if we don't?
Permalink Christopher Wells 
August 10th, 2005
(f) My take: it's a construct of the model not a construct of the universe. Repeat out loud - description!=reality.

Think of the London Underground map. This accuratly describes the relationship between London underground stations. It does not show their physical position and although you can infer that you're likely to find yourself horribly wrong (Queensway to Bayswater springs to mind).
Permalink a cynic writes... 
August 10th, 2005
> At the quantum level to deal with things you can't observe you have to deal with all the possibilities at once

Fuzzy logic diagnostic trees do something like this: "Before we observe him at all, the patient has a 30% probability of being tall ..."
Permalink Christopher Wells 
August 10th, 2005
Cynic, I agree with you that it is just a model and as long as gives us answers that allow us to predict reality that's fine and dandy (hmm, shades of yesterday's thread). I wouldn't want to reject the model just based on the inability to understand it in human terms.

It's still interesting to try to draw out a picture of the universe from the equations - as we naturally do in physical models closer to home. I suspect the "observer" issue is a red herring and it is not possible to blow up quantum effects to the macroscopic level - at least not like this.

Your point (e) is priceless.
Permalink Joel Goodwin 
August 10th, 2005
"Schrodinger thought this was bloody silly and gave us the "cat in the box" example in order to take the piss out of it."

I've never, ever seen a cat take piss out of a box.

The reverse... I can see that any day I want.
Permalink MarkTAW 
August 10th, 2005
Either you're taking the piss or we are once again devided by our common language. In the unlikely event it's the latter "taking the piss"="making fun of".
Permalink a cynic writes... 
August 10th, 2005
No. Schroedinger left the box on the ground behind the car because he forgot to put it in the trunk. Then he backed over it. So the cat is most definately dead.
Permalink Peter 
August 10th, 2005
"Taking a piss" means you're relieving yourself.

"Taking the piss" means there is a specific piss in the world that you're trying to obtain.
Permalink MarkTAW 
August 10th, 2005
At least, in my version of the universe. Your particular obsveration of reality may be different.
Permalink MarkTAW 
August 10th, 2005
"As soon as you treat it as real you begin to tear the analogy apart."

This is so pertinent, and true, and needs to be mentioned everytime someone mentions the damn cat in the box. I think the cat in the box analogy distracts from the point it is trying to make more than clarifies anything.
Permalink Dennis Forbes 
August 10th, 2005
Dennis sez : "I think the cat in the box analogy distracts from the point it is trying to make more than clarifies anything."

I agree. It's unfortunate in many ways, particularly as it's laden with extraneous issues that muddle the question -- is the detector aware? is the cat aware? if one, why not the other? how smart does the cat have to be to be an observer, etc. etc. etc.

As far as experiments in quantum physics go, the simple and elegant double-slit experiment is, in my opinion, unrivalled. Anyway.
Permalink Snark 
August 10th, 2005
The reason folks have so many issues with the "cat in a box" is because they are wed to Aristotle's Law of the Excluded Middle. The cat is *both* dead *and* alive until the box is opened. Yet ALotEM claims that it cannot be.

A contradiction exists only because one or more premises is false. In this case, ALotEM is false. Since ALotEM is one of those unexamined axioms that people use and won't look at, they flip out rather than examine it for validity. That worship of ALotEM is also why many engineers/scientists wig out about Fuzzy Logic.
Permalink Peter 
August 10th, 2005
> Q: Does a dog have Buddha-nature?
> A: There is no-one to ask that question, nor to answer it.

I don't think that's the right answer.
Permalink son of parnas 
August 10th, 2005
> The reason folks have so many issues with the
>"cat in a box" is because they are wed to
>Aristotle's Law of the Excluded Middle.

I'll use a fuzzy measure and say the cat is .5 alive.
Permalink son of parnas 
August 10th, 2005
A thing does not need to have sentience to be an observer.
Permalink Aaron F Stanton 
August 10th, 2005
> I don't think that's the right answer.

The canonical answer to that question is "mu" -- and much has been written on that question+answer.

In this case (i.e. above) I gave a different (non-canonical) answer ... after all the question was being asked in a different context.

In what way don't you think that's the right answer?
Permalink Christopher Wells 
August 10th, 2005
Peter, does this really "invalidate" the law of the excluded middle?

In the cat situation, the alive/dead is NOT a single state e.g. half and half. The ratio of dead cat and alive cat varies with time approaching much more dead cat as we go to infinity.

(this is not a conversation I ever thought I would have)

So what was "wrong" was our assertion that a cat has only two states ALIVE or DEAD.

The law of the excluded middle is one of logic; a statement is either TRUE or NOT TRUE. (this is actually a statement of the Law of Bivalence, but it's pretty much for the same for us)

What is our logical statement? Take Felix is ALIVE. In the pre-quantum days, we'd say the opposite of the statement is Felix is DEAD, and I am in tears because he was a joyous companion.

In the quantum world, the opposite of this statement is *not* Felix is DEAD, it is "Felix is either DEAD or in a superposed ALIVE/DEAD state with a ratio of 0<p<1".

Now that is rather a mouthful, not to say unfortunate for Felix, but the Law of the Excluded Middle still applies. What was invalid was our assumption that there were only two possible states.
Permalink Joel Goodwin 
August 10th, 2005
Aaron, are you trying to say some of the observers on this group aren't sentient? =)
Permalink Joel Goodwin 
August 10th, 2005
No comment, but I'm just gonna sit back and mindlessly watch the fallout from the implications.

:)
Permalink Aaron F Stanton 
August 10th, 2005
In this case, ALotEM is the false premise. ALotEM does not always hold true, but logicians love to believe that it is always true in every case.

2 simple experiments that can show why ALotEM is not true at all times:

1 - get a room full of people. Ask them individually if the room is hot or cold. Change the temperature, at each temperature point ask them individually if they are hot or cold. You will end up with an S shaped curve when plotting Hottness vs temperature. Is the room hot or cold? Yes.

2 - get 3 large bowls of water. One has ice added to the water. One is hot (not scalding) and the third is room temperature. Place the bowls so that the hot is at one end, the cold at the other end, and the room temperature one is in the middle.
Place one hand in the hot water.
Place the other hand in the cold water.
Leave them there for 5 minutes.
Place both hands in the room temperature water.
The hand that was in cold water claims the water is hot.
The hand that was in hot water claims that the water is cold.
Both hands are in the same water, is one hand lieing? Are they both lieing? No. Your body uses differences to send information. Yet if you worship ALotEM, you have a hard time reconcilling the different signals that your hands are transmitting to your brain. Damned relativist hands!

Experiment 1 points out part of the difficulty that some people have with Fuzzy Logic. FL is an attempt to turn human requirements into something a computer can process. Since humans aren't always consistant, nor do those bags of meat and bones all act the same, or even speak clearly, you have to reconcile that with odd terms like "membership functions."

<voice="Ross Perot">
Is that person short or tall? That's a simple question! Yes or No! Anyone with the IQ of an ashtray can answer that question. Are they short or tall? Don't give me that "a person 5'6" has a 65% membership in tall" baloney. Answer the question.
</voice>
Permalink Peter 
August 10th, 2005
> In what way don't you think that's the right answer?

The answer I prefer is to consider the dog as representing the animal nature, which can not see beyond samsara, whereas a human can. Thus a dog can not have buddha nature.
Permalink son of parnas 
August 10th, 2005
So we were devided by our common language;-)

http://www.peevish.co.uk/slang/t.htm
Permalink a cynic writes... 
August 10th, 2005
Ah, but the buddha nature beyond buddha nature is not buddha nature - it cannot be.

Does a dog have buddha nature beyond buddha nature?
Permalink Aaron F Stanton 
August 10th, 2005
Peter, I'm not well-read in the discipline of fuzzy logic, but if I had to read up on everything before I could comment I would probably be quiet all of the time. =)

1) I agree that fuzzy logic appears extremely suitable for "human measurements" where there is no clear definition. "Is my hand cold?" lies in the area of imprecision - prime fuzzy logic territory. Standard logic requires a universally accepted definition of cold, or to go out and find the "statistical definition" of cold.

2) In the cat example, the cat state is not a human approximation but actually something that can be calculated exactly. We know exactly the probabilities involved - I don't see the need to use fuzzy logic when probability and bog-standard logic works fine.

3) Our tortured cat thought experiement does not break the law of the excluded middle. If we start off with an axiom that there are just two states to choose from then we are going to have logic problems, but the quantum world forces us to give up these fixed states "until the wave function collapses". We can build a perfectly logical framework if we give up these absolutes. (which is quite bizarre, considering that a lot of quantum theory forces us INTO using different states, quanta of energy etc.)

I'm not dissing the use of fuzzy logic, I don't know enough about it to do that, I'm just saying it's not essential here.

Q - I'm sure someone must have tried, but I have to ask, has fuzzy logic been applied to the quantum world?
Permalink Joel Goodwin 
August 10th, 2005
> Does a dog have buddha nature beyond buddha nature?

As the animal nature may already be beyond cause and effect, with a more direct understanding of the atman, I would say no.
Permalink son of parnas 
August 10th, 2005
Peter, maybe this is what you were driving at. Picked this up on a Google search (http://www.thymos.com/science/cs1996.html):

"Furthermore, Quantum Mechanics is built upon probabilities, and that choice forces a specific interpretation of the universe. The interpretation of quantum phenomena would be slightly different if Quantum Mechanics was based on Fuzzy Logic ... probabilities entail uncertainty, whereas Fuzzy Logic entails ambiguity. In a fuzzy universe a particle's position would be known at all times, except that such a position would be ambiguous (a particle would be simultaneously "here" to some degree and "there" to some other degree). Fuzzy Logic may actually provide a model of the universe that is more plausible (i.e., not random but deterministic) or at least more in line with our daily experience..."

Although, even in a fuzzy quantum world, I think we're still going to have to deal with some weird shit.
Permalink Joel Goodwin 
August 10th, 2005
One interesting thing about time dependent quatnum mechanics is that if you actually do collapse the wavefunction at a given point in time - resolve the particle - it still doesn't affect the wavefunction before or after the collapse.

That is, if you've done the math right. Done properly, the time dependent wavefunction already includes all possible collapses at all points in time.
Permalink Aaron F Stanton 
August 10th, 2005
Joel, that link isn't a good one to be relying on. He doesn't understand conductivity, so his belief in some subatomic particle of conciousness isn't going to be believable either.

http://hyperphysics.phy-astr.gsu.edu/hbase/solids/band.html
For a better explanation of conductivity.

If quantum mechanics fails to give you a headache when you think about it, then you aren't thinking about quantum mechanics.

My problems with the "abstract" you linked start with the first sentence. Conciousness is an emergent behavior. There isn't a gene for a beehive, there isn't a gene for an ant nest. The behaviors that create them emerge from simple rules of behavior. I believe that understanding emergent behavior will lead to some very different understandings in the future. As different as the understandings that quantum mechanics have lead us to, and let us manufacture. I'm going to refer you to a review of Emergence that I submitted to slashdot: http://slashdot.org/article.pl?sid=04/12/15/2142206
I like that book, and I think it is one that people should read. Go to the library if you don't want to spend a few bucks on it. But, please, read it.
Permalink Peter 
August 10th, 2005
"One interesting thing about time dependent quatnum mechanics is that if you actually do collapse the wavefunction at a given point in time - resolve the particle - it still doesn't affect the wavefunction before or after the collapse.

That is, if you've done the math right. Done properly, the time dependent wavefunction already includes all possible collapses at all points in time."

This is not true.

The collapse means that one component of the wavefunction will get amplitude 1 while all other components wil get amplitude 0. The function changes.

If it wouldn't change then the outcome would have been certain, which can happen of course. Not everything is always unsure in QM :-)
Permalink Erik Springelkamp 
August 10th, 2005
Quantum theory has always been over my head. I'm sorry if what I'm saying is off track.

Is not the Schrodinger's cat a thought experiment and there have been more thought experiments because of the reason that a normal experiment cannot be carried on?

There is something lost when we measure anything. When we use the thermometer to measure the temperature of something, the thermometer itself takes in some heat. When an observer focuses on the sun to measure any parameter he wants something is lost because of the observer involved. The tools used to measure or record something have very less effect on what is being measured and what is lost is negligible. But this is not the case when it comes to measuring some parameter of an electron. The effect of the tool is far from negligible. If something as big as a real cat is involved we wouldn't have the problem of an observer affecting what is observed. Is this not why we resort to use probabilistic account of what's happening?

No one mentioned Heisenberg's uncertainty principle. Wasn't this theory first proposed and didn&#8217;t Shrodinger later worked on the thought experiment based on the same?
Permalink Senthilnathan N.S. 
August 11th, 2005
"If it wouldn't change then the outcome would have been certain"

Are you quite sure of this? It's possible that I'm wrong, as it's been a bit over 6 years since I did any of this, and only a bit longer than that that I really stopped caring much about it, so I'm more than a bit rusty.
Permalink Aaron F Stanton 
August 11th, 2005
"The collapse means that one component of the wavefunction will get amplitude 1 while all other components wil get amplitude 0. The function changes."

I mean, this part I understand, but my fuzzy memory told me that this was already taken into account as a possibility in the wavefunction.
Permalink Aaron F Stanton 
August 11th, 2005

This topic was orginally posted to the off-topic forum of the
Joel on Software discussion board.

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