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Observing the double slit experiment

by TheRealTL
Tags: double, experiment, observing, slit
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TheRealTL
#1
Aug30-10, 12:56 PM
P: 15
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?
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arkajad
#2
Aug30-10, 04:53 PM
P: 1,411
Quote Quote by TheRealTL View Post
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
#3
Aug30-10, 04:58 PM
P: 15
Quote Quote by arkajad View Post
"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
#4
Aug30-10, 05:04 PM
P: 1,411
Observing the double slit experiment

Quote Quote by TheRealTL View Post
Ok, anyone got some examples of detectors that influence the system?
Photographic plate, Geiger counter, cloud chamber, fluorescent screen. Eye of a fly.
arkajad
#5
Aug30-10, 05:11 PM
P: 1,411
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
#6
Aug30-10, 05:14 PM
P: 419
Quote Quote by arkajad View Post
Photographic plate, Geiger counter, cloud chamber, fluorescent screen. Eye of a fly.

How about ear?
arkajad
#7
Aug30-10, 05:19 PM
P: 1,411
Quote Quote by GeorgCantor View Post
How about ear?
Ear is not that sensitive to individual quanta. Not a good detector for quantum events.
GeorgCantor
#8
Aug30-10, 05:37 PM
P: 419
Quote Quote by arkajad View Post
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
#9
Aug30-10, 10:36 PM
P: 128
Quote Quote by TheRealTL View Post
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
#10
Aug31-10, 01:39 AM
P: 1,411
Quote Quote by GeorgCantor View Post
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
#11
Aug31-10, 01:49 AM
P: 1,411
Quote Quote by eaglelake View Post
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.
questions,yes
#12
Aug31-10, 02:53 AM
P: 11
Quote Quote by eaglelake View Post
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
#13
Aug31-10, 03:11 AM
P: 1,411
Quote Quote by questions,yes View Post
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.
questions,yes
#14
Aug31-10, 03:19 AM
P: 11
Quote Quote by arkajad View Post
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
#15
Aug31-10, 03:21 AM
P: 1,411
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.
questions,yes
#16
Aug31-10, 03:24 AM
P: 11
Quote Quote by arkajad View Post
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
#17
Aug31-10, 03:47 AM
P: 1,411
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
#18
Aug31-10, 04:27 AM
P: 1,411
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.


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