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DonGar
2008-Mar-08, 03:54 AM
I've had this question for a really long time, but never found a good answer. It's a physics question, not astronomy, but quantum physics is often a part of the show.

In quantum physics, things remain in an undetermined state until they are observed. However, I've never heard a more meaningful answer about what an observer is than "something which causes quantum states to become determinate".

Example answers that I've heard in various pop-physics venues:

1) A human brain (if a person doesn't see it, it doesn't count)
2) A living brain (cat, dog, etc)
3) A camera (even if the film is never developed)
4) A large molecule

So, in practical terms, what is an observer? And, of course, how do we know?

grant hutchison
2008-Mar-08, 06:06 PM
Yeah, that word "observation" has caused a lot of trouble.
Let me cut and paste something I wrote recently on another thread.

Bohr was clear that:
The entire formalism is to be regarded as a tool for deriving predictions, of definite or statistical character, as regards information obtainable under experimental conditions described in classical terms.We can't know anything about the Universe without doing experiments: making "observations". Under [the Copenhagen Interpretation], as described above, there is a line of demarcation somewhere between the quantum objects being observed, and the "classical" world perceived by the observers. This line is sometimes referred to as the "Heisenberg split".
Now, Bohr was also very clear that the instruments themselves are on the classical side of the divide:
In actual experimental arrangements, the fulfillment of such requirements is secured by the use, as measuring instruments, of rigid bodies sufficiently heavy to allow a completely classical account of their relative positions and velocities.Others, including von Neumann, have reasoned in various ways to move Heisenberg's split all the way to the level of consciousness: under that interpretation of the Copenhagen Interpretation, the wavefunction of the radioactive source, Geiger counter, poison and cat is only ever "collapsed" when perceived by a conscious observer.So you can take your pick of the interpretation you choose to use: quantum mechanics itself has nothing to say on the matter.

Grant Hutchison

EvilEye
2008-Mar-08, 09:45 PM
It isn't that what is there isn't true until you observe it. It is that you must observe it to know what state it is in.

True quantum physics just make predictions that are much broader than yes or no.

On large scales, I can throw a baseball and there is a 99.99999~% chance that it will end up in the direction I throw it.

In the quantum world, if throw a particle in one direction, it has a x chance of going here, and y chance of ending up over here, or z chance of being somewhere else.

Then you pick the highest number and hope that's where is goes.

Except... it may end up in both places or nowhere near where I was looking for it.

Ken G
2008-Mar-09, 04:34 PM
There are a number of interesting points to add to that "Heisenberg split" idea. First of all, it existed in classical mechanics also, it just never mattered to science. In other words, we never had a way to describe what happens to a system that is not observed, but we never found any evidence that what happens was different, so we simply made the simplifying assumption that it was not. It is perfectly good science to make such simplifying working assumptions, the only difference with quantum mechanics is that the targeted precision of the measurements is so spectacularly higher that we discovered the principle of "non-commuting measurements", which means that if you prepare a system in a state with a known value of some measurable, you might not simultaneously be able to know the value of some other measurable. In that light, we see that "measurement" happens at both ends of a scientific prediction-- it happens when you prepare the experiment, and again when you test the result.

This was unknown in classical physics, where it was thought that objects "carried with them" complete information about everything you could measure, but note that was only pure assumption in classical physics-- we simply did not have precise enough measurements to ever test if it was true. Physics made the simplifying assumption, but it should never have taken that assumption as seriously as it did for centuries (it was "magical thinking" to extrapolate a successful hypothesis to a level of precision that was untested). Ironically, many people see quantum mechanics as having a kind of "magical" quality not present in classical physics, but I argue that QM actually represents jettisoning a magical aspect of classical physics in a regime where it could actually be tested.

The second thing about the "Heisenberg split" I'd like to point out is that measurements applied from one side of the divide to quantum systems on the other side do not have some kind of "coincidental" effect of replacing the uncertainty of the possible outcomes with a particular one. Instead, the act of measurement is expressly set up to accomplish precisely that physical influence. So it's not a byproduct of a measurement that a quantum system goes from a "superposition state" to an "eigenstate" of the measurement-- the measurement is designed to create decoherence between the different eigenstates so that the system will behave as if "one or the other actually happened", which is just how classical systems behave. In short, measurement is the act of coupling quantum systems to classical systems so that they will behave classically and we can apply our standard scientific norms. Ironically, this is exactly the opposite from what many people (not Schrodinger, by the way) think happens when you connect a cat to a quantum system that can be used to kill the cat-- they think this puts the cat into a quantum state, when in fact the whole point of measurement is to get a quantum system to behave classically! If you could really put a cat in a quantum state that way, then measurement no longer serves its purpose, and suddenly we are awash in an ephemeral domain where science's norms fail and we have no idea what we are doing any more. We should only go there kicking and screaming, and so far there just isn't any good reason to.

damian1727
2008-Mar-10, 11:44 AM
as i understand it the modern view solves the observer problem with

decoherence....(you will find a better explanation than mine if you google it)

a quantum supposition is lost when an object interacts with its enviroment... it does not have to be a human observer..

if you could isolate a big object from its enviroment it would display quantum weirdness..so far some guy in vienna is up to a 60 atom buckeyball!
they are aiming at a virus next..(wtf!?)

quantum computers would take advantage of supposition to do many things at once...but the isolation thing is hard..

i dont understand this but things deconhere ....like this...

an overlap of 2 particals = 1/2x1/2= 1/4

3 particals 1/2x1/2x1/2=1/8

a water drop contains millions of particals ..the overlap between there combined waves is the sum above a million times....basically ZERO

so essentially there is no overlap in their quantum waves and hence no interference...and maybe no observer...

the world becomes the world we know when huge amounts of particals interact with themselves...

?

lol:p

damian1727
2008-Mar-11, 04:45 PM
evil said.....It isn't that what is there isn't true until you observe it. It is that you must observe it to know what state it is in....

if only that was the case....it is in all states until the wave collapses...there are trickey experiments with lots of mirrors that show this ...thats what freaked everyone out ....

its not that is in a certain spin state that you just dont know...it isnt

hence the whole problem with an objective underlying reality..

Ken G
2008-Mar-12, 11:29 PM
A lot of people think quantum indeterminacy is an obstacle to the question of "objective reality", but frankly I just don't see it. I think it comes from an overinterpretation of classical physics, the idea of determinism. There was never any evidence that classical physics is completely deterministic, because classical physics does not use sufficient precision to address the issue. Furthermore, we have sensitivity to initial conditions, and the "butterfly effect" in weather forecasting. These are all perfectly classical-- why doesn't anyone seem to think these compromise the notion of "objective reality"? In fact there is no connection-- determinism messes with objective reality just as much as indeterminism does. If we say we can predict the future using some algorithm, how do we include our making of that prediction into the algorithm? This implies that science could never, in the context of an objective reality, provide a complete description of a truly deterministic universe-- so what sense does it make to try and use science to argue that ours is? The acceptance of indeterminacy is a sigh of relief for science, it means we don't have to base our concept of objective reality on a requirement for completeness. Many of the ancient philosophers already understood that, and quantum indeterminacy adds nothing fundamental to this state of affairs. I've never understood why so many claim otherwise.

damian1727
2008-Mar-13, 09:49 AM
well i kinda agree with you but i think the problem came about because of the observer problem stated earlier....if by objective reality you mean....

an underlying reality which exists independently of our perceptions and thoughts.

are you saying that you can define an electron in its uncollapsed state as objective reality?

dont ask me!!

i think by no objective reality people were recognizing that evils statement..

''It isn't that what is there isn't true until you observe it. It is that you must observe it to know what state it is in.''

is not true...

damian1727
2008-Mar-13, 09:50 AM
ps i think deconherence solves this problem as things do exist (collapse) when we are not looking....

Ken G
2008-Mar-13, 03:25 PM
are you saying that you can define an electron in its uncollapsed state as objective reality?
Yes that's right, and in fact we already do that-- the definition of "objective" is satisfied by an electron in an "uncollapsed state" (to wit, different observers will get the same results from experiments on them). So I'm saying an electron in its "uncollapsed state" is no less a part of objective reality than one in a collapsed state. It is we who demand that objective reality have certain properties, based on our own interpretation of our experiences with it. That's not a very "objective" approach to demand reality conform to our requirements, rather than to modify our requirements to conform to reality. We get to define what "objective" means, but reality decides how it will interact with our definitions.


''It isn't that what is there isn't true until you observe it. It is that you must observe it to know what state it is in.''
A truer version is, "the idea that the electron is in a 'state' is a requirement that we created for it, so it is up to us to gather the information to be able to describe that state".

damian1727
2008-Mar-13, 03:47 PM
yup i agree ...but i guess its a modern way to look at it .. the old days an object was meant to be an object?

i for one am very happy to believe that the universe would still be there if we were not...

EvilEye
2008-Mar-13, 03:56 PM
yup i agree ...but i guess its a modern way to look at it .. the old days an object was ment to be an object?

i for one am very happy to believe that the universe would still be there if we were not...

That was precicely what I meant when you said I was wrong.

Quantum actions only take place at the subatomic level.

My wife is not in a dual-state when I can't see her. She is not both alive and dead. She is most certainly in one state or the other. If she were, she would have memories of both when I next saw her.

damian1727
2008-Mar-13, 05:02 PM
:)

your wife is a Macroscopic object who is fully deconhered so yes

but an electron in a superstition is not the same....it is not that it is say spin up and then you look and say oh its spin up

its not spin up till you look...it is all possible states till its waveform collapses

hence it can go thro both slits...or bounce off a mirror..(light takes all paths thro a mirror)


''The conclusion of all this is that there is no experiment that can tell us what the electrons are doing at the slits that does not also destroy the interference pattern. This seems to imply that there is no answer to the question of what is going on at the slits when we see the interference pattern. The path of the electron from the electron gun to the screen is not knowable when we see the interference pattern. As Heisenberg said, "The path [of the electron] comes into existence only when we observe it."

?


dont ask me but thats the way it is

sorry if i misunderstood you....its coz you put state at the end and that only happens when the waveform collapses...*brain melt*

Steve Limpus
2008-Mar-13, 07:01 PM
I find wives are most definitely dual state, at least, even when we do observe them.

There's a chance I will understand Quantum Mechanics one day. Wives, I dunno...

(Honey, I love you if you read this when I'm not looking!)

damian1727
2008-Mar-13, 07:36 PM
hey steve hows it going down under?

hear you on that last post !

(if your not looking she aint there !!)....like my 2 year old... if she cant see you you cant see her..lol

damian1727
2008-Mar-13, 07:36 PM
my wifes got one state....RIGHT

:/ *gulp*

Steve Limpus
2008-Mar-13, 09:34 PM
Hey Damian

Life is good, Rugby season is starting. :dance:

My wife dislikes Rugby as much as Astronomy.

But less than Cricket. :shhh:

But she does love our boys, so she manages our team in spite of.

(...and you do a great job princess!)

Steve Limpus
2008-Mar-13, 10:12 PM
Damien, did you hear any more about that Garrett Lisi deal? I followed it for a while but it seemed to die... you were sceptical all along right?

I'm picking you're counting the days to LHC light off! I've listened to most of their podcasts - those guys rock. John Barrowman was a laugh (you could never accuse him of being in the closet!).

Here's the link if anyone has missed them.

http://www.cernpodcast.com/

Ken G
2008-Mar-14, 06:04 PM
yup i agree ...but i guess its a modern way to look at it .. the old days an object was meant to be an object?
In the old days they tended to overestimate their ability to conceptualize reality, some even thought what was in their minds was closer to reality than what was accessible to their senses. I think there are three things: what is accessible to our minds, what is accessible to our senses, and what is real.


i for one am very happy to believe that the universe would still be there if we were not...Yes, I agree, and no experiment indicates otherwise. But what would clearly not be there without us is the way we think about the universe-- what we think is real.

EvilEye
2008-Mar-14, 06:32 PM
way we think about the universe-- what we think is real.

There's only one real problem with this statement.

When I thought I could fly... I fell and bustedededed my noggin.

damian1727
2008-Mar-14, 06:53 PM
evil lol :)

steve yeah baby yeah !! (LHC)...as for lisi....read a few quite serious problems with his ideas ...treating fermons as bosons or sum such...it did not seem to actually say anything....pretty tho :)

damian1727
2008-Mar-14, 06:57 PM
cricket is real :)

Ken G
2008-Mar-15, 05:14 AM
There's only one real problem with this statement.

When I thought I could fly... I fell and bustedededed my noggin.

You misunderstand what I meant-- I was not saying that what we think is real, I was saying that what we think is happening, what we think is real, may be distinguished from what is actually happening-- but science deals with the former. So I'm actually saying what you are saying-- it matters not what you think is real if you are smacking your head on the ground, but that just means science isn't the final arbiter of reality.

damian1727
2008-Mar-15, 11:57 AM
it is the best we have tho

damian1727
2008-Mar-15, 12:07 PM
http://www.youtube.com/watch?v=qjGRySVyTDk&feature=related


:whistle:



cant we put up u tube ?

EvilEye
2008-Mar-15, 12:49 PM
You misunderstand what I meant-- I was not saying that what we think is real, I was saying that what we think is happening, what we think is real, may be distinguished from what is actually happening-- but science deals with the former. So I'm actually saying what you are saying-- it matters not what you think is real if you are smacking your head on the ground, but that just means science isn't the final arbiter of reality.


Sorry. I was just taking the opportunity to make the joke.

I know what you mean.

But we aren't the final arbiters of reality either. The universe was here before us. Before thought. The wave didn't collapse into reality the moment someone questioned it. We didn't create the universe around us. We are just beginning to understand it. If anything.. the universe itself wanted to know, and allowed for us to explore it, and explain it. The universe may indeed be, curious.

Just as we ask "What is my purpose?", so may the universe have that question built in for itself.

(This is more philosophy than science)

Scientifically... True Reality is what happens regardless of what we think. Our own reality is created and destroyed by experience.

My reality last night was that when I woke up this morning, the sun would come up in the east. It did. But if it hadn't, then my reality would be altered, but that doesn't change true reality. It just changes what we know about what's going on around us.

EvilEye
2008-Mar-15, 12:58 PM
Back to the original question.. yes. A camera with sound is a perfect example.

If a tree falls in the forrest and there is ONLY a camera around to hear it, does it make a sound.

Yes. In a sense. It makes the sound waves. Sound is what we call our own interpretation of those waves.

If the sun rises and there is no-one alive to watch it, is it dark?

damian1727
2008-Mar-15, 01:32 PM
no

EvilEye
2008-Mar-15, 09:14 PM
no

OK...

I guess you'll have to be sentient non-existant entity to ever answer the question then.

My video camera has shown me things I didn't hear or see when they actually happened. I guess someone put them there.

damian1727
2008-Mar-15, 11:06 PM
huh?

EvilEye
2008-Mar-16, 12:10 AM
huh?

The question was about the observer. If you aren't there, then it doesn't mean it doesn't happen. There is no wave to collapse just by your god-like observation of it.

If the cat is in the box.. it is alive or dead.... period...whether you look or not.

Ken G
2008-Mar-16, 12:10 AM
But we aren't the final arbiters of reality either.Sure we are. "Reality" is our word, after all. There is nothing you and I can discuss that we are not the "final arbiters" of.


Scientifically... True Reality is what happens regardless of what we think. Our own reality is created and destroyed by experience.But science is ours, so scientifically, true reality is whatever we define it to be. A useful definition will require that we not be tyrants, however, I'll grant you that.

KaiYeves
2008-Mar-16, 12:12 AM
(Title)
Somebody who observes quantums, duh! ;-)

EvilEye
2008-Mar-16, 01:38 AM
Sure we are. "Reality" is our word, after all. There is nothing you and I can discuss that we are not the "final arbiters" of.

But science is ours, so scientifically, true reality is whatever we define it to be. A useful definition will require that we not be tyrants, however, I'll grant you that.

That is philosophy too.

Does the world end when I die?

Ask George Washington.

Ken G
2008-Mar-16, 02:14 AM
That is philosophy too. Actually, it isn't. It's just applying the definitions of the words.


Does the world end when I die?
That's irrelevant, we are not talking about you, we are talking about science and reality. And yes, human science would end if all humans and all traces of our writings on science die, as would whatever have been all our concepts of what reality is. If you are asking about real reality, rather than our concept of reality, then you are talking nonsense, because the only thing we can have a conversation about is our concept of reality-- and that's not philosophy, it's fact.

I think what you are actually saying is that our concept of reality is connected with our ability to imagine something that exists outside of our imagining it. This model of reality works great, passes most of the tests we give it, and will be gone with us-- unless some nonhuman intelligence is also using it (which they likely are).

EvilEye
2008-Mar-16, 02:49 AM
Actually, it isn't. It's just applying the definitions of the words.
That's irrelevant, we are not talking about you, we are talking about science and reality. And yes, human science would end if all humans and all traces of our writings on science die, as would whatever have been all our concepts of what reality is. If you are asking about real reality, rather than our concept of reality, then you are talking nonsense, because the only thing we can have a conversation about is our concept of reality-- and that's not philosophy, it's fact.

I think what you are actually saying is that our concept of reality is connected with our ability to imagine something that exists outside of our imagining it. This model of reality works great, passes most of the tests we give it, and will be gone with us-- unless some nonhuman intelligence is also using it (which they likely are).



I'm sorry. But I have a problem with injecting myself into reality.

**** happens whether I am there or not.

damian1727
2008-Mar-16, 12:37 PM
he's got it on camera....

Ken G
2008-Mar-16, 12:40 PM
I'm sorry. But I have a problem with injecting myself into reality.

**** happens whether I am there or not.

That is certainly the standard for our model of reality, to within certain "probability" related nuances.

damian1727
2008-Mar-16, 12:52 PM
in the double slit experiment tho very DIFFERENT **** happens if you are not there....

ie you get an interference pattern and the photons seem to go thro both slits..

even if you measure AFTER the slits it effects what the photon does at the slit...

as for the cat (even tho i think dechonherence explains why it is one or the other)
it is not something that can just be easily swept under the carpet as obvious..

damian1727
2008-Mar-16, 12:53 PM
:boohoo:electrons never ''jump'' energy levels whilst observed.....a watched kettle really does never boil...


lol

EvilEye
2008-Mar-16, 04:47 PM
Then the original question should be what happens to an obsrever of quantum physics.

Because the quatum world doesn't work the same way at our scale.

I will never, by chance, fall up out of bed.

damian1727
2008-Mar-16, 07:28 PM
or at least it very unlikely ;)

Steve Limpus
2008-Mar-16, 09:32 PM
Down Under, we fall up out of bed all the time. :think:

EvilEye
2008-Mar-17, 02:29 AM
oof... my typing was horrible up there.

Sorry.

damian1727
2008-Mar-17, 08:55 AM
don t worry mine is always awful i cant speel atall :)

clint
2008-Mar-18, 02:21 PM
That is philosophy too.

Here's what wikipedia (http://en.wikipedia.org/wiki/Reality) has to say about reality:


In the strict sense of philosophy, there are levels or gradation to the nature and conception of reality. These levels include, from the most subjective to the most rigorous: phenomenological reality, truth, fact, and axiom.

Imagination (http://en.wikipedia.org/wiki/Imagination), on the other hand, is part of how we make sense of what we perceive:


Imagination is the ability to form mental images, or the ability to spontaneously generate images within one's own mind. It helps provide meaning to experience and understanding to knowledge; it is a fundamental facility through which people make sense of the world


...it also plays a key role in the learning process.

Ken G
2008-Mar-18, 02:53 PM
in the double slit experiment tho very DIFFERENT **** happens if you are not there....
This is a common misconception about quantum mechanics. But if you look at the theory, the predictions depend only on the experimental setup, and are obtained entirely in a scheme that does not require my presence in the equations-- it only needs to me to see if I was right.


ie you get an interference pattern and the photons seem to go thro both slits..That is controlled by the experimental setup, not my presence.


even if you measure AFTER the slits it effects what the photon does at the slit...
That statement may or may not be correct depending on how certain key words are intepreted, but taken at face value it sounds like a common misconception about "delayed choice quantum erasure". Half the articles I see on that topic make steam come out of my ears, because I know they are feeding that false impression. Nothing that an experimental setup does later can alter the correct prediction of a prior outcome. It is only our interpretation of when things happen that tends to be faulty-- our intuition about causality, not causality itself.


as for the cat (even tho i think dechonherence explains why it is one or the other)
it is not something that can just be easily swept under the carpet as obvious..Certainly there is nothing obvious about it. But the role of the observer in quantum mechanics is way oversold-- the real issue is the role of the observer in all of science. Science is manifestly an intellectual organization of the interaction between an observer and his/her environment, and that is as true in Newtonian mechanics as in quantum physics. It is only the people who mistake their science for "what is really happening" that run into philosophical conundrums, and not surprisingly-- logically, the use of a false premise will tend to do that.

damian1727
2008-Mar-18, 06:57 PM
That statement may or may not be correct depending on how certain key words are intepreted, but taken at face value it sounds like a common misconception about "delayed choice quantum erasure". Half the articles I see on that topic make steam come out of my ears, because I know they are feeding that false impression. Nothing that an experimental setup does later can alter the correct prediction of a prior outcome. It is only our interpretation of when things happen that tends to be faulty-- our intuition about causality, not causality itself.
Quote:



could you explain a bit?

as i understand it if you know the path the pattern goes....

if you measure after the slits ie know the path the pattern goes...seeming to suggest that the photon took one slit or the other....tho it does hit the detector after...

i get very confused with all those mirrors...

please dont misunderstand me i am not into this whole observer thing and completly agree that it depends on the experimental set up...

tho why the 2 different results exist?

i must also admit to not being smart enough to have a problem with the role of observers in science...i'll leaver that to philosophers....nmp ;)

damian1727
2008-Mar-18, 07:09 PM
http://arxiv.org/pdf/quant-ph/0008036


???!??

Ken G
2008-Mar-18, 10:26 PM
as i understand it if you know the path the pattern goes....
Correct.


tho why the 2 different results exist?
It's all about interference. Basically, the things that happen receive contribution from all the ways they can happen, and the different ways don't add normally, they don't simply accumulate they interfere. Your knowledge of the situation can allow you to rule out certain contributions, thereby destroying the interference. The interaction is physical, so occurs even if you don't use the information, that's where the setup comes in. But there's no need for any backward causality in time, and efforts to include it usually are more ungainly than the classical notions they attempt to resuscitate.

damian1727
2008-Mar-18, 10:48 PM
mmm

thanks
:D

Clegrand
2008-Mar-21, 11:23 AM
From what I have read, at the quantum level, the smaller particles (I use this term loosely) when observed (ie electrons) are affected by the interaction of the particles used (ie photons) so that the whole experiment is pretty much stuffed :) from the very beginning. As the electrons, in theory, will act differently when not "watched" then when they are observed. Also, hasn't it been theorised that the more you confine your region of observation the more energetic the particles become which again changes the whole outcome.

Therefore, doesn't the observer change the outcome?

EvilEye
2008-Mar-21, 11:52 AM
From what I have read, at the quantum level, the smaller particles (I use this term loosely) when observed (ie electrons) are affected by the interaction of the particles used (ie photons) so that the whole experiment is pretty much stuffed :) from the very beginning. As the electrons, in theory, will act differently when not "watched" then when they are observed. Also, hasn't it been theorised that the more you confine your region of observation the more energetic the particles become which again changes the whole outcome.

Therefore, doesn't the observer change the outcome?

For some reason this whole idea reminds me of the Gary Larson (Far Side) comic, where the cows are all standing around smoking cigarettes, until a car comes over the hill, and they all drop down and start eating grass.

Clegrand
2008-Mar-21, 12:20 PM
LOL
Nah, a better analogy is the movie Cats and Dogs where they are actually special agents that just act like regular cats and dogs when a poor unsuspecting human comes by:p

Ken G
2008-Mar-23, 09:54 PM
From what I have read, at the quantum level, the smaller particles (I use this term loosely) when observed (ie electrons) are affected by the interaction of the particles used (ie photons) so that the whole experiment is pretty much stuffed :) from the very beginning.This is true, but it is often said in very misleading ways. The whole point of a measurement is to bring a quantum system into contact with something we already understand, and that always means a system we can rely on to behave classically. So we are intentionally mucking with the quantum system when we measure it, it's not surprising at all. It is like translating a poem from a language we don't understand to one we do-- and then being surprised the translation has a somewhat different impact than the original.

As the electrons, in theory, will act differently when not "watched" then when they are observed.We have no idea how electrons behave when "not watched", what we do is figure out what they do by watching them. We have no language to even discuss what they do if we can't watch them-- the watching can be (and often is) hypothetical, but the very language we use presumes said "watching". That's where a lot of people get hung up on "tree falling in the woods" issues, but the interesting issues persist even if you imagine a hypothetical observer. What language will you use to describe such a hypothetical interaction, other than the same language you use for the "real" one?


Also, hasn't it been theorised that the more you confine your region of observation the more energetic the particles become which again changes the whole outcome.
Yes, that's the "Heisenberg uncertainty principle" and is well established. What is not well established is how to interpret this effect.


Therefore, doesn't the observer change the outcome?I would not so much say the observer "changes" the outcome, as the observer defines the outcome. Observation is a very purposeful classical intervention into quantum behavior, there are no observations that are counterexamples. I believe this is more or less what Bohr called "complementarity" between quantum and classical realms.

Ken G
2008-Mar-23, 09:59 PM
For some reason this whole idea reminds me of the Gary Larson (Far Side) comic, where the cows are all standing around smoking cigarettes, until a car comes over the hill, and they all drop down and start eating grass.I believe that's the lighter side of the "principle of complementarity" in a nutshell!

EvilEye
2008-Mar-24, 02:46 AM
I believe that's the lighter side of the "principle of complementarity" in a nutshell!

Just for the un-schooled -
complementarity principle
From: The Columbia Encyclopedia, Sixth Edition | Date: 2007
The Columbia Encyclopedia, Sixth Edition

complementarity principle physical principle enunciated by Niels Bohr in 1928 stating that certain physical concepts are complementary. If two concepts are complementary, an experiment that clearly illustrates one concept will obscure the other complementary one. For example, an experiment that illustrates the particle properties of light will not show any of the wave properties of light. This principle also implies that only certain kinds of information can be gained in a particular experiment. Some other information that is equally important cannot be measured simultaneously and is lost.

Bibliography: See W. Heisenberg, The Physical Principles of the Quantum Theory (1930, repr. 1949); N. Bohr, Atomic Physics and Human Knowledge (1958); B. L. Cline, Men Who Made a New Physics: Physicists and the Quantum Theory (1987).

Clegrand
2008-Mar-25, 10:39 AM
Thanks for your refinement of my previous posting Ken G and Evil Eye,

I particularly liked the "observer defines the outcome" point that Ken G made.

One wonder's that when the notions of today are "translated" as Ken G's poetry, by future scientists, will they also have a misleading impact?

Ken G
2008-Mar-26, 01:45 AM
One wonder's that when the notions of today are "translated" as Ken G's poetry, by future scientists, will they also have a misleading impact?I suppose that depends on if our science has reached a level that is qualitatively different from the science of the ancients that we sometimes dismiss as naive and lacking in modern sophistication. I don't know, but frankly I wouldn't be surprised if science a thousand years from now wrinkles its nose at us in a very similar way. To some degree, I'd like to believe that-- but not as much as I'd like to be a fly on that wall.

dcl
2008-Apr-24, 02:08 AM
Lot's of words are being bandied around on the question of what a quantum obserever is. There's a simple answer that some of the contributors to this thread have offered, but they're mixed in with a lot of distracting and somewhat misguided efforts. I'll offer my own, which I believe has merit because it's as basic as possible. It's also concise, dispensing with a lot of distracting details:

In quantum mechanics, the positions of material objects are represented by mathematical expressions called "wave functons." A wave function has a numerical value at every point in the region of space in which the object has any chance of being found. That valueis a measure of the probability that an observation will find the object at that point. That region of space is called the "configuration space" for that object. The quantum observer is the hypothetical person who looks for the object.

R_H_W
2009-Jan-26, 01:47 AM
This idea of 'observer' is difficult not to misrepresent, I think. It's a bad choice of word. In a strict sense, even _we_ aren't 'observers' in the common sense of 'conscious oberver' at the quantum level, since what we actually perceive as what we call an observation is clearly only a construct of our own brains (see Epistemology 101). The initial act of a human-scale visual observation by us starts when a group of photons strikes the photoreceptors at the back of our eye(s). Coded neural messages are sent to the visual cortex, etc. etc.

This is what we colloquially call an 'observation' in visual terms. Of course there are other kinds of observations using different senses however visual observations are more prone to this misunderstanding because of the quantum nature of the stimulus involved - i.e. photons.

We are then no different to a piece of machinery that might intercept the same photons and do something to them (like scatter them - i.e. the atmosphere). Any interaction between a quantum entity and something that is separate from it must constitute an 'observation'.

The idea that somehow consciousness must be involved in the 'observation' is a misunderstanding brought about by the misuse of the word.