Thread: The Copenhagen Interpretation: Double slit experiment

This is one of those topics that is often discussed on science forums and almost always- It's disgust... I mean discussed while the posters are waxing philosophically.

Philosophy is all fine and good if you want to sit on your butt and not really put any actual effort into enhancing knowledge. And had I placed this thread in ATM, I'd be all for philosophy and speculation.

As it is, I'm placing it here- in hopes I might learn something and others might, as well.
I think this is the wrong Board to put it on, with relatively few members... But even so, I'm banned from the other with no intention of appeal. If I had the ability- I'd run to the nearest (Several hundred miles away) University and try this properly. But for the sake of the internet- I'll try it here. 'Cuz I'm a dumbass like that.

So; The Double Slit Experiment, wave/particle duality and the Copenhagen Interpretation.
The Copenhagen Interpretation
It's purpose and fundamentals can be summarized as follows:

A system is completely described by a wave function ψ, representing an observer's subjective knowledge of the system. (Heisenberg)

The Heisenberg Uncertainty Principle is Crucial to observation.

The description of nature is essentially probabilistic, with the probability of an event related to the square of the amplitude of the wave function related to it. (The Born rule, after Max Born)

So, the average behavior given by the group and the ability to predict by the probability law defines the State Vector.

Matter exhibits a wave–particle duality. An experiment can show the particle-like properties of matter, or the wave-like properties; in some experiments both of these complementary viewpoints must be invoked to explain the results, according to the complementarity principle of Niels Bohr.

So, tie in that we are using macroscopic measurements of a microscopic system invoking the Uncertainty Principle on wave/particle duality. This concept is taken as a whole in order to avoid Paradoxes.

Measuring devices are essentially classical devices, and measure only classical properties such as position and momentum.

To eliminate simple nonlocality problems...

The quantum mechanical description of large systems will closely approximate the classical description. (The correspondence principle of Bohr and Heisenberg.)

And where our confusion begins...
Fire a beam of electrons single file at a board with a double slit. Behind the board is a film that will document where the electron hits.
The film will show a Wave Interference pattern where the amplitudes cancel eachother out.
But suppose you place a detector near one of the slits, to try to determine which slit a singly fired electron will pass through.
The film will not display the interference pattern, rather it will show two lines of hits parallel to each other.

It's as if direct observation of the event changes the state vector rather than properties of the wave.

I'd like input on the Copenhagen interpretation of the experiment.

Please, no absurdities. We all are aware that the electrons are not consciously choosing where to go.

Originally Posted by Neverfly

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Please, no absurdities. We all are aware that the electrons are not consciously choosing where to go.

Your question is predicated on something that is not true despite the fact that many very well educated people pretend that it is. To be specific, we talk about the dichotomy between classic and quantum physics as though these are equally valid explanations of nature. Classical physics is the physics of the "large"; quantum physics is the physics of the small. Simply not true. Quantum physics explains nature on all scales. Classical physics is a useful approximation, but only when it works. There is no rule that requires classical physics to work on any scale.

You should read the June 2011 issue of Scientific American. The cover story is entitled "Living in a Quantum World." It deals with this very issue. It includes a graph of macroscopic magnetism. This graph shows the classical predictions, quantum predictions, and empirical data. At high temperature the classical and quantum predictions closely agree. At lower temperatures, they diverge. The data agree with the quantum prediction. The strictly macroscopic branch of physics known as thermodynamics cannot be formulated as a self-consistent branch of classical physics. Thermodynamics must be formulated using quantum physics.

Things like the Copenhagen Interpretation are artifacts of the era when quantum mechanics was new. It helped to educate professionals and the masses alike on how to deal with the puzzling new physics called "quantum mechanics." Today, physics research is overwhelmingly in quantum mechanics. In 2011, it makes no more sense to explain quantum mechanics in terms of waves and particles than it does to explain the horizon in terms of a round Earth.

Originally Posted by MisterMe

Your question is predicated on something that is not true despite the fact that many very well educated people pretend that it is. To be specific, we talk about the dichotomy between classic and quantum physics as though these are equally valid explanations of nature. Classical physics is the physics of the "large"; quantum physics is the physics of the small. Simply not true. Quantum physics explains nature on all scales. Classical physics is a useful approximation, but only when it works. There is no rule that requires classical physics to work on any scale.

You should read the June 2011 issue of Scientific American. The cover story is entitled "Living in a Quantum World." It deals with this very issue. It includes a graph of macroscopic magnetism. This graph shows the classical predictions, quantum predictions, and empirical data. At high temperature the classical and quantum predictions closely agree. At lower temperatures, they diverge. The data agree with the quantum prediction. The strictly macroscopic branch of physics known as thermodynamics cannot be formulated as a self-consistent branch of classical physics. Thermodynamics must be formulated using quantum physics.

Things like the Copenhagen Interpretation are artifacts of the era when quantum mechanics was new. It helped to educate professionals and the masses alike on how to deal with the puzzling new physics called "quantum mechanics." Today, physics research is overwhelmingly in quantum mechanics. In 2011, it makes no more sense to explain quantum mechanics in terms of waves and particles than it does to explain the horizon in terms of a round Earth.

Thank you for the reading suggestion.

I'll admit- I am quite old fashioned (and possibly out of date) in how I look at this topic. I prefer the marble to the wood.
Living in a Quantum World: Scientific American

My points: I agree that Understanding Quantum mechanics should explain the macroscopic world to greater accuracy. It's also more tedious and I see no harm in falling back on Classical Physics if you want a little less accuracy for simplified work. However, the problem remains in being able to measure, observe and document that which is smaller than any instrument.

We must experiment, measure and observe- Indirectly.

Take a cube made of glass and shine a light through it to your desktop. You will see, on the desktop, a shadow of the cube. It will look flat. Depending on the angle, maybe square.
Do the same thing with (using magic) a Hypercube. If you look at the shadow of the hypercube, you will see what looks like a cube to our 3D minds.

In Quantum Mechanics, we are looking at shadows.

In the double slit experiment- a shadow of a shadow. We display the results of a 4D experiment using 3D equipment on a 2D film.

You gave an opinion, but no real answers.

What are your thoughts on Decoherence?
Do you think that we are creating the shadow cast, seeing the illusion of measurement?

Originally Posted by Neverfly

...

What are your thoughts on Decoherence?
Do you think that we are creating the shadow cast, seeing the illusion of measurement?

It appears to me that decoherence is simply the name given by some to a well-known feature of wave functions. Specifically, the wave functions of pure quantum states are indeterminate. Only the wave functions of mixed states can be determined. Terms like this tend to leave me a bit cold because they are a bit too much like contemplating our navels. Without decoherence, we can't perform measurements on physical systems.

Quantum mechanics is not just the best that we have; it is all that we have. We don't know if a classical measurement is accurate until quantum mechanics says that it is accurate. Calling the double-slit experiment a shadow appears to an attempt to live in denial of the fact that we live in a quantum universe. The wave properties of matter are inescapable element of this universe. Scientists and engineers must deal with these properties everyday. To the Intel engineer whose bread an butter depends on reducing the traces in the company's new microprocessors to ever narrower widths, matter waves are a nemesis, not an illusion.

Originally Posted by MisterMe

Terms like this tend to leave me a bit cold because they are a bit too much like contemplating our navels.

Full agreement there. A bit like the Spooky Action at a distance problem, in hindsight. Although, Mathematically, Einstein was able to contend with that with General Relativity.
Which is odd because this next statement implies that you did not understand my meaning.

Originally Posted by MisterMe

Calling the double-slit experiment a shadow appears to an attempt to live in denial of the fact that we live in a quantum universe. To the Intel engineer whose bread an butter depends on reducing the traces in the company's new microprocessors to ever narrower widths, matter waves are a nemesis, not an illusion.

I did not call the double slit experiment a shadow.
I called the Results a Shadow and I gave an example to explain my use of that word.
We cannot see the results directly- as if we are looking at the shadow cast by the results and then trying to piece together what the results might have looked like from that shadow.
And it seems likely to me that at times, the shadow would be too incomplete to make an accurate picture.

I never claimed that matter waves were an illusion at all.

MisterMe, since you seem to be quite educated, I had hoped you would contribute to this thread.

But your contributions will be useless if you completely distort and misread what I asked.

I do not care about your personal opinions as much as I do something tangible. If you think that the Copenhagen Interpretation is out-moded, please detail what better line of thought has replaced it.
If you think that the Double Slit Experiment is revealing, please tell us what it reveals. If you think it is flawed, please specify what the flaws are.
Speculate even, make an educated guess (along with Everyone else in the world) as to why on Earth the Double Slit Experiment yields entirely Different Results depending on whether or not the process of the experiment is observed or not. The only thing I really ask of posters is that if they speculate on that- that they do not wax philosophically like a stoned pothead laying back on the roof of his 1983 Trans Am.
"Dude... What if like, we're the matter waves and like, we're like electrons choosing where to go, man. That's some trippy shit, man." I don't give a damn about the useless maryjane pontificating.

Originally Posted by Neverfly

...

I do not care about your personal opinions as much as I do something tangible. If you think that the Copenhagen Interpretation is out-moded, please detail what better line of thought has replaced it.
If you think that the Double Slit Experiment is revealing, please tell us what it reveals. If you think it is flawed, please specify what the flaws are.
Speculate even, make an educated guess (along with Everyone else in the world) as to why on Earth the Double Slit Experiment yields entirely Different Results depending on whether or not the process of the experiment is observed or not. The only thing I really ask of posters is that if they speculate on that- that they do not wax philosophically like a stoned pothead laying back on the roof of his 1983 Trans Am.
"Dude... What if like, we're the matter waves and like, we're like electrons choosing where to go, man. That's some trippy shit, man." I don't give a damn about the useless maryjane pontificating.

You appear to be taking offense where none is intended. Let me address the issue of the directness or indirectness of measurements. Measurements are controlled and reproducible applications of our senses. We have just five senses--sight, hearing, taste, touch, and smell. Their usefulness to scientific measurement are in the order listed. Anything that is inaccessible to our senses must be measured indirectly. This includes an overwhelming fraction of physical quantities. We can measure length directly by sight. We can can also see color and brightness. We can hear tone and volume. We can taste flavors, feel temperature, texture, and hardness, and smell odors. I may have missed some, but the list of missed direct measurables is short. However, most direct measurables cannot be measured directly in an objective manner. My blue may not be the same as your blue. In the case of some individuals, we know for a fact that their blue is not the same as my blue.

The thing that we can objectively measure directly is length. Digital instrumentation aside, most scientific instruments convert physical quantities into a length or angle. For example, a voltmeter converts electrical potential difference into the angle that a needle deflects. An automobile's speedometer is really an electric generator/voltmeter combination whose voltage is proportional to the speed of the car. Thermometer? A capillary of mercury whose length change is directly proportional to the temperature. I can give numerous additional examples. Notice that these are all "classical" examples. In the case of scientific instrumentation, most instruments convert whatever is being measured into a voltage, which is then converted to a digital signal for computer input.

The quantum mechanical properties of our subjects have little impact on how directly we can measure them. Quantum mechanics places a limit on the accuracy of measurements, not their directness.

The point that I made in my previous earlier posts in this thread is that we live in a quantum world. There is no alternative to this fact. We may use classical considerations only if they agree with quantum predictions.

I believe that you are in error about the results of the double-slit experiment. Indeed electrons passing through the apparatus formed an interference pattern lift that formed by electromagnetic radiation. When one slit is covered, then the pattern must be single-slit diffraction. Each electron in the double-slit experiment must be considered to pass through both slits.

Originally Posted by MisterMe

I believe that you are in error about the results of the double-slit experiment. Indeed electrons passing through the apparatus formed an interference pattern lift that formed by electromagnetic radiation. When one slit is covered, then the pattern must be single-slit diffraction. Each electron in the double-slit experiment must be considered to pass through both slits.

That may well be- I've never performed the experiment first hand.
I've had to double check this several times because I had accused others of being in error about the outcomes just as you had done to me, now.
But every last single thing I've read on the double slit experiment describes that you will have two outcomes:
You will have a wave interference pattern if you run the double slit experiment as is.
You will have two parallel lines if you run the double slit experiment with a detector to determine electron path.

The slits are not blocked or covered. One merely has more determination than the other. The outcome appears to be influenced by whether or not the electron path is observed.

From Wiki:

When electrons are fired singly through a double-slit apparatus they do not cluster around two single points directly on lines between the emitter and the two slits, but instead one by one they create an interference pattern. However, they do not arrive at the screen in any predictable order. In other words, knowing where all the previous electrons appeared on the screen and in what order tells us nothing about where any future electron will hit (although we can calculate the probability of it striking at any specified point).[39]

When a detection device is placed in front of the slits to observe incoming particles one by one, the observation collapses the wave function of the incoming electrons, and they pass through behaving like particles, creating two bands instead of an interference pattern. When no such observation is made, the wave function is not collapsed going into the slits, and the wave function potentials interfere, producing interference patterns

Originally Posted by Neverfly

...

The slits are not blocked or covered. One merely has more determination than the other. The outcome appears to be influenced by whether or not the electron path is observed.

From Wiki:

I wish that you had provided provided a link to your Wiki reference. I found this Dr. Quantum video on You Tube. It is visually makes the same claim that your Wiki does. However, it is a cartoon. I would like to see the real apparatus with at least the real images.

Without access to your sources, it appears to me that the attempt to determine which slit the electron "really" passes through blocks the slit in front of the detector, making the other slit a single slit. When the other slit is tested, it is blocked. The resulting pattern is two single-slit [Fraunhofer] diffraction patterns.

Originally Posted by MisterMe

I wish that you had provided provided a link to your Wiki reference.

Sorry about that. Yes, I should have. Here it is:
Double-slit experiment - Wikipedia, the free encyclopedia

Originally Posted by MisterMe

I found this Dr. Quantum video on You Tube. It is visually makes the same claim that your Wiki does. However, it is a cartoon. I would like to see the real apparatus with at least the real images.

Funny... that wiki link references that video in the ref. list.
I went ahead and watched it and although "Dr. Quantum" is probably not bad for beginner science, it was pissing me off with its hyped up sensationalism, up-playing the notion that the electron makes a decision all on its own. That can mislead young and malleable minds...
As if we don't have trouble unlearning all the garbage that was regurgitated by adults and we were forced to swallow in our youths enough as it is...

Originally Posted by MisterMe

Without access to your sources, it appears to me that the attempt to determine which slit the electron "really" passes through blocks the slit in front of the detector, making the other slit a single slit. When the other slit is tested, it is blocked. The resulting pattern is two single-slit [Fraunhofer] diffraction patterns.

Many of my sources are the old fashioned library book and textbooks. When I have time at home, I can check the bookshelves or check which universities use which books- so for now, wiki is the best I can do as it is fast and easy.
The measurement problem.
Sadly, you and I seem to be in error. It happens...
But neither slit, at any time, is blocked.
It seems that the experiment is based on the Born Hypothesis. Thomas Young was the first to perform the experiment using a light source.
Claus Jönsson performed the experiment in '61 using an electron beam and Pier Giorgio Merli of Italy, repeated it in '74 firing One Photon at a Time. The Merli experiment was again performed under strict laboratory conditions in 1989 by Dr. Akira Tonomura of Japan. With better equipment, Tonomura was able to duplicate the experiment of firing one single electron at a time with great accuracy but his experiment confirmed the same results as Merli's in '74.

I may have left gaps there. That's a combo of Memory, Wiki and quickly looking up names and dates.
But this experiment is claimed to have also been performed by Wolfgang Pauli and Neils Bohr, though neither published results and from what I read, did not mess with it, much. I have no idea the veracity of that claim. Google yielded nothing on that.

I lack the means to recreate the experiment because I can't seem to hit the damned electrons with a baseball bat and get them to fire one at a time. But all peer reviewed journals attest that at no time was any slit covered, blocked or physically interfered with.
To further complicate matters, Wheeler proposed a thought experiment based on the paradox of the double slit experiment results which has since been tested and confirmed.
Wheeler's delayed choice experiment - Wikipedia, the free encyclopedia

Richard Feynman has been known to set aside his bongo drums to comment on this experiment as an example of the absolute weirdness of QM.
Personally, I disagree with Dr. Feynman, as I find weirdness a matter of perspective and I suspect that the experiment is lacking some unknown vantage point that might clarify why the electron behaves differently if its path is determined than it does if its path is described as a wave function.

Originally Posted by Neverfly

Sorry about that. Yes, I should have. Here it is:
Double-slit experiment - Wikipedia, the free encyclopedia

Thank you. I had seen that site. However, it has two major failings. 1) It does not include an image of the results of the slit-identification attempt. 1) It gives no authority for the second to last paragraph.

Originally Posted by Neverfly

I went ahead and watched it and although "Dr. Quantum" is probably not bad for beginner science, it was pissing me off with its hyped up sensationalism, up-playing the notion that the electron makes a decision all on its own. That can mislead young and malleable minds...
As if we don't have trouble unlearning all the garbage that was regurgitated by adults and we were forced to swallow in our youths enough as it is...

I agree with your sentiments. However, I am willing to give Dr. Quantum some slack. I reserve my ire for working scientists who spout absolute nonsense to popular audiences.

Originally Posted by Neverfly

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But neither slit, at any time, is blocked.

This appears to be a very restrictive definition of the word blocked. The detector cannot detect a electron [or photon] unless it is placed between the slit and imaging medium.

It appears to me that the "mystery" is that a classical question was asked of a quantum system. "Which slit did the electron passed through?" makes no sense for a quantum system. Since you started this thread, I have checked my sources to bolster my understanding of this topic. One source points out that the optics of electrons is essentially the same as that of x-ray photons.

Most people think of photons are particles of light. Well, OK sort of. However, photons are really quanta of electromagnetic fields. To really get into the weeds, they are quanta of electromagnetic field fourier components. Photons have definite energy and momentum and, thus, are completely non-localized in both time or space. The electrons in the double-slit experiments are free particles whose wave functions behave mathematically much like photon wave functions.

An attempt to measure a wave function alters its boundary conditions and initial conditions. If you change the boundary conditions or initial conditions, then you change the wave function everywhere for all time. It is to be expected that attempts to determine the path taken by an electron or by a photon from a distant source took will result in frustration.

Originally Posted by Neverfly

Claus Jönsson performed the experiment in '61 using an electron beam and Pier Giorgio Merli of Italy, repeated it in '74 firing One Photon at a Time. The Merli experiment was again performed under strict laboratory conditions in 1989 by Dr. Akira Tonomura of Japan. With better equipment, Tonomura was able to duplicate the experiment of firing one single electron at a time with great accuracy but his experiment confirmed the same results as Merli's in '74.

Understand that I am not casting doubt on whether or not the experiment was performed. To the contrary, I asked for a link to your sources so that I can see an image of the failed attempt to determine the path of the electron. I see several images of the electron double-slit interference pattern. However, I have seen no image of the failed attempt.