Observing the double slit experiment

[TheRealTL]

In this experiment wave particle duality is shown. Without observation the wave function is used. With observation the particle function is used.

My question is what is the definition of observation? Specifically in the case of an electron gun is the observer a conductive piece of material in and around the electron path?

 

[arkajad]

In this experiment wave particle duality is shown. Without observation the wave function is used. With observation the particle function is used.

My question is what is the definition of observation? Specifically in the case of an electron gun is the observer a conductive piece of material in and around the electron path?

"Observation" is not a very good concept. "Detection" is better (presence of human "observers" is irrelevant for the detection to take place). You have a detection when you have a detector (or several of them) coupled to your quantum system.

 

[TheRealTL]

"Observation" is not a very good concept. "Detection" is better. You have a detection when you have a detector (or several of them) coupled to your quantum system.

Ok, anyone got some examples of detectors that influence the system?

 

[arkajad]

Ok, anyone got some examples of detectors that influence the system?

Photographic plate, Geiger counter, cloud chamber, fluorescent screen. Eye of a fly.

 

[arkajad]

I should add that in "Bohmian mechanics" the philosophy is different. But I do not think you want to know about Bohmian mechanics - it is a separate subject.

 

[GeorgCantor]

Photographic plate, Geiger counter, cloud chamber, fluorescent screen. Eye of a fly.

How about ear?

 

[arkajad]

How about ear?

Ear is not that sensitive to individual quanta. Not a good detector for quantum events.

 

[GeorgCantor]

Ear is not that sensitive to individual quanta. Not a good detector for quantum events.

Detection clicks are audiable. But my focus was on the "fly's ear" not just ear, or just 'eye'.

 

[eaglelake]

In this experiment wave particle duality is shown. Without observation the wave function is used. With observation the particle function is used.

My question is what is the definition of observation? Specifically in the case of an electron gun is the observer a conductive piece of material in and around the electron path?

Without observation, what is the wave function used for?? What is the "particle function"??
A quantum experiment must include a measurement result that is obtained when the particle is detected. I think this is what you mean by observation; observation is the measurement result. This result is a necessary part of the experiment. (Bohr) Without a result (observation) there is no experiment to discuss. The wavefunction is used to calculate the probability of obtaining that result. Without observation, there is no wave function.
Neither the theory nor the experiment describe what the particle is doing before it is detected. Quantum mechanics predicts only the possible results of a measurement and the statistical distribution of those results. We have no idea what the particle is doing before detection. (Wheeler)
The particle is always detected as a particle. It is the statistical distribution of the results that we identify as an interference pattern, which is characteristic of classical waves. Thus, we see "a particle" when the individual particle hits a detection screen. We see an "interference pattern" (caused ?? by "a wave") when a large number of particles have hit the screen one at a time.
An observation is a measurement result that gives a value for a specified observable, such as energy, momentum, spin, etc. The particle detector is part of the measuring apparatus, which is the observer. As noted by others, the experiment does not require a human observer.
What are you trying to measure with " a conductive piece of material in and around the electron path?"

 

[arkajad]

Detection clicks are audiable. But my focus was on the "fly's ear" not just ear, or just 'eye'.

Ear is not necessary. Irreversible recording of whatever kind is.

 

[arkajad]

Neither the theory nor the experiment describe what the particle is doing before it is detected. Quantum mechanics predicts only the possible results of a measurement and the statistical distribution of those results. We have no idea what the particle is doing before detection. (Wheeler)

That depends on which "theory". If your theory does not bother - then it does not describe. If it bothers - then it describes. Some people do not have an idea and do not care, some other people have an idea (right or wrong) and describe. Some theories bother only with the statistics, some with description of individual detection processes.

 

[questionsyes]

Without observation, what is the wave function used for?? What is the "particle function"??
A quantum experiment must include a measurement result that is obtained when the particle is detected. I think this is what you mean by observation; observation is the measurement result. This result is a necessary part of the experiment. (Bohr) Without a result (observation) there is no experiment to discuss. The wavefunction is used to calculate the probability of obtaining that result. Without observation, there is no wave function.
Neither the theory nor the experiment describe what the particle is doing before it is detected. Quantum mechanics predicts only the possible results of a measurement and the statistical distribution of those results. We have no idea what the particle is doing before detection. (Wheeler)
The particle is always detected as a particle. It is the statistical distribution of the results that we identify as an interference pattern, which is characteristic of classical waves. Thus, we see "a particle" when the individual particle hits a detection screen. We see an "interference pattern" (caused ?? by "a wave") when a large number of particles have hit the screen one at a time.
An observation is a measurement result that gives a value for a specified observable, such as energy, momentum, spin, etc. The particle detector is part of the measuring apparatus, which is the observer. As noted by others, the experiment does not require a human observer.
What are you trying to measure with " a conductive piece of material in and around the electron path?"

If there is no "human observer", how does one acquire knowledge of the experimental results?

 

[arkajad]

If there is no "human observer", how does one acquire knowledge of the experimental results?

Acquisition of knowledge is a separate branch of science. It is not needed if you want to discuss the behavior of detectors, interference, double slit experiments etc. For this you need physics, dynamics, evolution equation, a little bit of probability theory.

 

[questionsyes]

Acquisition of knowledge is a separate branch of science. It is not needed if you want to discuss the behavior of detectors, interference, double slit experiments etc. For this you need physics, dynamics, evolution equation, a little bit of probability theory.

But in order for such a discussion to take place, doesn't there at some point have to be "human observation"?

 

[arkajad]

Are you interested in human beings or are you interested in physics. Human beings, their psychology, neurobiology, etc. is a different branch. Of course quantum processes, in particular detection processes take also place in neural activities. But that does not influence the laws physics.

 

[questionsyes]

Are you interested in human beings or are you interested in physics. Human beings, their psychology, neurobiology, etc. is a different branch. Of course quantum processes, in particular detection processes take also place in neural activities. But that does not influence the laws physics.

But you agree that "human observation" is required for completion of the exercise?

 

[arkajad]

It depends on the exercise. Rats also exercise, frogs do, and birds exercise as well. Perahps the whole Nature exercises, one way or another. Physics is about making the patterns. Recognition of patterns is another thing.

 

[arkajad]

Quoting from J. A. Wheeler ("Geons, Black Holes & Quantum Foam", p. 343):

"I wanted to emphasize in this talk that the essential feature of act of 'measurement' is amplification from the quantum thing observed to the classical thing doing the observing, which need have nothing to do with human intervention or human consciousness"

Notice that "measurement" is in quotation marks. Means: be careful even with this concept.

 

[questionsyes]

Quoting from J. A. Wheeler ("Geons, Black Holes & Quantum Foam", p. 343):

"I wanted to emphasize in this talk that the essential feature of act of 'measurement' is amplification from the quantum thing observed to the classical thing doing the observing, which need have nothing to do with human intervention or human consciousness"

Notice that "measurement" is in quotation marks. Means: be careful even with this concept.

My question wasn't to imply observation was necessarily an act of measurement, merely that "human observation" was a conclusive requirement of experimentation.

 

[arkajad]

My question wasn't to imply observation was necessarily an act of measurement, merely that "human observation" was a conclusive requirement of experimentation.

Human observation may be right or wrong. Some people see things that do not exist. Some see wrong colors. You would have to define the terms you are using. But this will take you out of the domain of physics. These forums are called "physicsforums", and this part of the forums is called "Quantum physics". You need to distinguish physics from philosophy, psychology etc.

You do need to know anything about philosophy and psychology to study and analyze physics phenomena. Just learn physics and mathematics and how to apply them in real world.

 

[questionsyes]

Human observation may be right or wrong. Some people see things that do not exist. Some see wrong colors. You would have to define the terms you are using. But this will take you out of the domain of physics. These forums are called "physicsforums", and this part of the forums is called "Quantum physics". You need to distinguish physics from philosophy, psychology etc.

You do need to know anything about philosophy and psychology to study and analyze physics phenomena. Just learn physics and mathematics and how to apply them in real world.

I disagree that this is not the domain of physics, indeed, i would have thought it's importance to quantum physics somewhat a mute point. But I'm willing to stop posting on the subject if others wish it so.

My definition of "human observation" would be - An intelligible interpretation (whether correct or otherwise) of information.

Isn't the above an inescapable inevitability (if one desires to form and communicate a conclusion) of experimentation?

 

[arkajad]

Well, you can post, why not? Nobody seems to be disagreeing with you so far - except of me.

 

[eaglelake]

That depends on which "theory". If your theory does not bother - then it does not describe. If it bothers - then it describes. Some people do not have an idea and do not care, some other people have an idea (right or wrong) and describe. Some theories bother only with the statistics, some with description of individual detection processes.

You are confusing theory with interpretation. I am suggesting that we take quantum mechanics at face value without any interpretation.
All the different interpretations try to explain, "what is really happening". People, including Einstein, refuse to accept the purely statistical nature of quantum events. They believe that the quantum particle must be doing something before it is detected and a complete theory would describe that something. But every attempt to date that assumes a classical-like existence for the particle gives results that do not agree with actual experiments. This is why real experiments do not agree with the EPR experiment and Bell's theorem. (I think a review of delayed choice experiments would also be helpful.)

 

[arkajad]

"People, including Einstein, refuse to accept the purely statistical nature of quantum events. "

Quantum theory is not purely statistical. Schrodinger equation is deterministic.

Theory and interpretation are always mixed. What's wrong with it?

 

[IFNT]

"People, including Einstein, refuse to accept the purely statistical nature of quantum events. "

Quantum theory is not purely statistical. Schrodinger equation is deterministic.

Theory and interpretation are always mixed. What's wrong with it?

That is why the Schrodinger equation is semi-classical. More intelligent species will make no interpretations, but accept the theory and think abstractly.

 

[arkajad]

What's wrong with something being semi-classical? Is it supposed to be a an insult? The problem with the Schrodinger equation is that it does not describe the detector clicks, not that it is "semi-classical".

 

[Galap]

In this experiment wave particle duality is shown. Without observation the wave function is used. With observation the particle function is used.

My question is what is the definition of observation? Specifically in the case of an electron gun is the observer a conductive piece of material in and around the electron path?

Maybe we should define 'observation' or 'detection' as those actions that 'collapse' wavefunctions.

 

[IFNT]

What's wrong with something being semi-classical? Is it supposed to be a an insult? The problem with the Schrodinger equation is that it does not describe the detector clicks, not that it is "semi-classical".

I am merely saying that there is no need to interpret a physical theory other than helping the human mind comprehend it.

 

[arkajad]

Maybe we should define 'observation' or 'detection' as those actions that 'collapse' wavefunctions.

Detector may help to collapse the wave function, but does not have to collapse it, since there is a random element in it. What detector does is: it introduces additional element to the evolution equation of the wavefunction making it non-unitary.

I am not sure about is whether the above is a theory or its interpretation. I would say: it is a hypothesis.

 

[zonde]

I am merely saying that there is no need to interpret a physical theory other than helping the human mind comprehend it.

You have to establish unambiguous correspondence between abstract theory and physical reality. Otherwise predictions made by theory would be at the same level as Nostradamus prophecies.
If interpretations are helping with that then they are essential to theory.

 

[arkajad]

You have to establish unambiguous correspondence between abstract theory and physical reality. Otherwise predictions made by theory would be at the same level as Nostradamus prophecies.
If interpretations are helping with that then they are essential to theory.

Agree. A part of some theory may look like this

x=yz^2

But our theorist writes it as

E=mc^2

in order to set the recipient minds into certain mindset that points toward its interpretation.

 

[Galap]

Agree. A part of some theory may look like this

x=yz^2

But our theorist writes it as

E=mc^2

in order to set the recipient minds into certain mindset that points toward its interpretation.

Context, in other words.

 

[DevilsAvocado]

Quoting from J. A. Wheeler ("Geons, Black Holes & Quantum Foam", p. 343):

"I wanted to emphasize in this talk that the essential feature of act of 'measurement' is amplification from the quantum thing observed to the classical thing doing the observing, which need have nothing to do with human intervention or human consciousness"

Notice that "measurement" is in quotation marks. Means: be careful even with this concept.

Could we flip the coin and say, that a quantum thing not interacting with anything ("screened off") – is not observed.

Thus, a quantum thing interacting with anything ("screened on") – is observed.

?

Why I think like this, is because of superposition and entanglement. As soon as the 'particles' are not "screened off", it’s impossible to maintain entanglement.

That’s why we seldom see entangled elephants. Not because it’s impossible, but because it’s extremely hard to "screen off" an elephant.

Correct?

 

[arkajad]

Thus, a quantum thing interacting with anything ("screened on") – is observed.

Quantum thing interacting is just interacting. Observation, measurement, monitoring are terms used for a special kind of interactions, namely those that actualize the potential, that reveal it.

The problem is that the standard quantum theory does not have a formalism for this kind of interactions, therefore is rather fuzzy about it. But if you read what non-standard people write about this question, you will understand better what these people are up to and why.

If you are interested I recommend reading

Gennaro Auletta, "Foundations and Interpretation of Quantum Mechanics". Subtitle: "in the Light of a Critical-Historical Analysis and a Synthesis of the Results", World Scientific 2001

 

[DevilsAvocado]

Quantum thing interacting is just interacting. Observation, measurement, monitoring are terms used for a special kind of interactions, namely those that actualize the potential, that reveal it.

Okay, thanks. I have to digest this some more I think... it’s something in my brain that automatically 'connects' words like observation, measurement, monitoring, reveal – to human (or intelligent) 'activities', but I know it’s wrong...

Thanks for the reading tips.

 

[arkajad]

Here is a small but relevant part from the table of content in the monograph of Auletta:

9 The measurement problem in quantum mechanics 277 9.1 Statement of the problem 278 9.2 A brief history of the problem 284 9.3 Schrödinger cats 291 9.4 Decoherence 297 9.5 Reversibility/irreversibility 308 9.6 Interaction-free measurement 315 9.7 Delayed-choice experiments 320 9.8 Quantum Zeno effect 322 9.9 Conditional measurements or postselection 325 9.10 Positive operator valued measure 327 9.11 Quantum non-demolition measurements 335 9.12 Decision and estimation theory 341 Summary 349 Problems 351 Further reading 353

Part IV Quantum information: state and correlations 14 Quantum theory of open systems 513 14.1 General considerations 514 14.2 The master equation 516 14.3 A formal generalization 523 14.4 Quantum jumps and quantum trajectories 528 14.5 Quantum optics and Schrödinger cats 533 Summary 540 Problems 541 Further reading 542 15 State measurement in quantum mechanics 544 15.1 Protective measurement of the state 544 15.2 Quantum cloning and unitarity violation 548 15.3 Measurement and reversibility 550 15.4 Quantum state reconstruction 554 15.5 The nature of quantum states 564 Summary 565 Problems 565 Further reading 566 16 Entanglement: non-separability 567 16.1 EPR 568 16.2 Bohm’s version of the EPR state 573 16.3 HV theories 577 16.4 Bell’s contribution 582 16.5 Experimental tests 595 16.6 Bell inequalities with homodyne detection 605 16.7 Bell theorem without inequalities 613 16.8 What is quantum non-locality? 619 16.9 Further developments about inequalities 623 16.10 Conclusion 625 Summary 625 Problems 626 Further reading 627 17 Entanglement: quantum information and computation 628 17.1 Information and entropy 628 17.2 Entanglement and information 631 17.3 Measurement and information 639 17.4 Qubits 642 17.5 Teleportation 643 17.6 Quantum cryptography 646 17.7 Elements of quantum computation 650 17.8 Quantum algorithms and error correction 659 Summary 671