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In the Double-Slit experiment aren't we monitoring the end result even when we are not monitoring which slit the photons are going through?
Why doesn't the monitoring of the end result collapse the wave?
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Follow Ups:
I noticed this topic recently, as I do not hit this forum often. I know there is a long string of acrimony below, but I wanted to attempt a clear answer.
The strange finding of quantum mechanics is that a quanta does not behave either as a particle or as a wave, but has characteristics of both. A quanta could be a photon of light or an electron, or something else small, either with or without mass.
Predicting quantum behavior involves summing over all possible paths. The double slit experiment is the most simple example, as there are only 2 paths, both of 50% probability.
Here is where it starts to get strange. A single particle in the quantum world must be visualized as taking both paths. Now of course it cannot take both paths, but the probability of both paths is seen as a real thing, a "probability wave." When you project separate particles, even minutes apart, the probability waves are seen to interfere. They create interference patterns, just as light waves interfere through a grating.
How can separate particles interfere? Well they cannot. So it is wrong to visualize an electron as a tiny particle, like a little rock. It is something else much harder to visualize, a wave of probability.
Now comes the trickiest part, and the part relevant to your question. When an observable quantity must be measured, the wave of probability is said to collapse to a single value. So for example, the position of an electron, rather than being 50% maybe in one place, and 50% maybe in another, is found to be 100% in one of the two possible locations.
This part of quantum theory, collapse of the wave function, is the most mysterious and the least understood. There are many theories, none of them particularly satisfying. Most scientists would say this occurs at the moment the particle interacts with a macroscopic detector, while others say it must reach consciousness. Who can know what happens before things reach consciousness anyway? And is a dog conscious enough? There are a lot of unanswerable questions.
I would recommend The Road to Reality by Roger Penrose in this area. It is an ambitious book, and in my opinion, not completely successful, Many of the topics he tries to cover seem to be pitched way above the level that a layman will understand without extensive background. But in this one area, I think he writes at a level most people can follow.
Now, to get back to your specific question. The probability wave is seen to collapse at the point of measuremnt. So if you measure it at the slit itself, the probabilities are gone and there is a localized particle. There can be no interference after the slit in this case. If you measure it somewhere behind the slit, interference will be seen. The quantum thing acts as a wave until the very moment of measurement.
You wrote,
"The strange finding of quantum mechanics is that a quanta does not behave either as a particle or as a wave, but has characteristics of both. A quanta could be a photon of light or an electron, or something else small, either with or without mass."
Actually that's not true. Case in point, quantum dots. When the electrons are confined in 3D space that is smaller than the de Broglie wavelength (I.e., nanoscale) the photons (emitted) can ONLY be waves, not particles.
Cheers
Not following you. Yes photons at emitted. AFAIK these photons are exhibit the photoelectric effect as well as all the wave effects of light. This was the original effect that required a suggestion of quantization or a sort of particle nature to light. I would be glad to examine evidence to the contrary.
Once electrons are confined to spaces with dimensions below the DeBroglie wavelength the emitted photons cannot act as particles, only as waves. Ref Quantum Confinement. Same idea applies to the ubiquitous CD laser. Ref Quantum Well. That's why the photons from the CD laser form a beam of coherent light. Ref Coherent Light.
Well I know about quantum confinement and coherent light. This light exhibits quantization into photons which is the "particle" part of its quantum nature, just like any other light. When you state these cannot act as particles, you are incorrect. When they interact with a photo detector, they act like discrete particles. If you have evidence to the contrary, I would be glad to examine it.
I actually disagree that the photodector detects photons as particles. A photodetector detects energy. it doesn't count the particles, if that's what you were thinking. In this case specifically electromagnetic energy. The "energy" of the laser is actually specified as 5 mW or whatever. If the power of the light falls below a pre-determined level the light fails to be detected, thus attempting to prevent reflected stray light from affecting results. Besides both quantum dots and CD lasers emit coherent light and coherence is a property of waves, not particles, no?
Edits: 10/08/15
Certainly coherence is a wave phenomena. Light certainly acts as a wave and was long visualized as a purely wave phenomena.
The interaction of light with photosensitive metals led to a puzzle, the photoelectric effect (see link). The eventual explanation was that light, previously considered a wave, exhibited a quantized particulate nature, each particle being labelled a photon.
This was the very beginning of quantum theory. Which has been extensively tested and verified in the century since. There is nothing peculiar to lasers or quantum dots that changes this picture of the light they generate. In fact, you can read references to photon generation in many quantum dot papers.
Well, anyway, you can have the last word on this, I fear that if we do not have an agreement at this point, we never will. See you on a more populated forum like film.
The photoelectric effect has to do with the emission of electrons from a metal surface due to application of light to the surface. Quantum dots and laser emit photons due to the stimulation of electrons by external light or other energy. In the case of the quantum dot the (artificial) atoms actually do not contain nuclei only an empty hole. It is because the quantum dot is nanoscale on the order of the Bohr radius or smaller that the emitted light is wave onlly.
In the case of the audio signal as an electromagnetic wave, like any electromagnetic wave, the wave comprises photons, just not photons in the visible light spectrum. Now are they particles AND waves? You decide.Nice chatting with you.
Edits: 10/09/15
Tre'
Electricity creates magnetism, and magnetism creates electricity. Light is an electro-magnetic phenomena, and it can be conceptualized as an electrical wave which collapses into a magnetic wave which is at a right angle to the electrical wave, and then the magnetic wave collapses into an electrical wave which is at a right angle to the previous magnetic wave, and so forth on and on. If you are observing just the electrical aspect of the light wave, then you don't see the magnetic aspect, and the electrons will behave as particles. If you are observing the magnetic aspect of the light wave, then what is observed will appear as magnetic particles. The light we see is a combination of these electro-magnetic waves. Planck referred to the photons he was studying as "quanta", or small bundles of energy which behaved like particles. As regarding the video which the present discussion revolves around, the "sensors" are not described in any detail. It can be safely assumed (I hope) that these sensors involve some form of electromagnetic functionality, and are therefore part of the experiment when they are added to the double slit experiment. Whether the tape recorder the sensors feed is on or not is a red herring. While light can behave as a particulate phenomena, in totality it's actually a wave phenomena. The paradoxes arising from the double slit experiment are actually not all that strange compared to some of the other stuff surrounding quantum weirdness.
Paul
"Whether the tape recorder the sensors feed is on or not is a red herring. While light can behave as a particulate phenomena, in totality it's actually a wave phenomena"
I researched more than just that one video.
When the data from the sensors (which are on and functioning) is not being recorded the photons behave like a wave. When the data is being recorded the photons act like particles.
This proves that the sensors are not part of the experiment but human observation (or the possibility of human observation) is what makes the change.
At least that's the way I read it.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
At 3:54 in the video it's mentioned that a "measuring device" is placed "by one slit". This is a singular device not described, and it's located near just one slit. The video is entertaining, and it describes the paradoxical data the scientists were confronted with when this experiment was first done. However it is stuck with the outdated conception of the electron as an indivisible and discreet "ball of matter". If an observation could actually collapse the wave function of the experiment as it's described, then a person looking at the experiment, or not, should have the same effect in a movie of the experiment. Anyway, let's switch to still photography.
Imagine you're sitting in an arm chair, and there's a butterfly flying around the room in a circle above and in front of you. Lets's say this is an electric butterfly which is tethered to the ceiling on a string and nail, and there's enough power in the battery so that the butterfly maintains a constant speed. As the butterfly comes around you snap a photo with a camera with a slow lens and slow film. When you develop the film you see the butterfly as a blurry grey rod about one foot long, and the wing beats as a blurry wave pattern on both sides of the rod. You can tell exactly how fast the butterfly was flying by the length of the blurry rod compared to the shutter speed of the camera. However you can't tell exactly where the butterfly was located, as it was everywhere in the blurry rod.
Next you snap a photo of the butterfly with a camera with very fast lens and film. When you develop this shot you see the butterfly frozen in space time. You can tell exactly where the butterfly was in the room, but you can't tell from the photo how fast it was flying, you can only estimate it's speed by the speed of the shutter, as at a certain high rate of speed the butterfly would start to blur. An observer looking at just the photo could'nt tell if the butterfly was moving or standing still in one place, as the image is frozen in space and time. In a manner of speaking you could say that the photo with the fast film and lens had collapsed the wave function, however this is a rather one dimensional view of the event of the butterfly flying around the room.
The act of observing something creates a conceptual model of it, and this is certainly subject to change. In the 1920's Bohr and Heisenberg got together and came up with the Copenhagen Interpretation which theorized that matter propagates as waves which collapse into particles when observed. This shoved under the carpet some of the really weird stuff connected with quantum theory like the Klein-Gordon Equation which theorized backward and forward time causality! Anyway, some were attracted by the implication of the Copenhagen Interpretation that human observation creates reality, as the creator of the video suggests.
Paul
I researched beyond that video.The sensor tracks the photons to see which slit it goes through.
The photons land on the collection plate as a wave pattern when the sensor is on and recording.
The photons land on the collector plate as particles would when the sensors are on and not recording.
It's said to be not a matter of perspective but a real change to reality.
I'm not defending it or denying it.
I just want to know, assuming the above is true, why when we observe both the movement at the slit the photons and where they land, the photons stop acting as a wave (WRT where they land on the collector plate) but when we just observe where they land on the collector plate, but not the movement at the slit, they land on the collector as a wave?
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 05/30/15 05/30/15
The video actually refers to electrons being fired one-at-a-time at the double slit plate and wave behavior is observed. Then a sensor is placed near one of the slits and particulate behavior is observed. Electrons are very small and easily influenced by electro-magnetic fields and other electrons. Any sensor would have to be drastically larger than a single electron, and as such would become a major factor in the experiment. If you put a small magnet (which is not observing anything) in place of the sensor, it's reasonable to expect that the magnet would affect the experiment. It's not mentioned in the video whether a second sensor was placed near the other slit to see how that affected the experiment, and a scientist would be expected to explore all possibilities. The experiment really just proves the wave-like nature of the electron rather than the former conception of it as a solid ball of matter orbiting a central nucleus, which is analogous to a miniature earth and sun. There are too many holes in the experiment as it's presented in the video for it to stand up as evidence that the Copenhagen Interpretation is at work and observation is creating reality. If you substitute "measurement" for "observation", then it's easy to see why it's extremely important in science to understand how a measurement can affect the experiment.
This is not to dismiss the strangeness of the quantum world. There is also a longer 12 min. version on youtube of the 9 min. video you linked to here. In that version quantum entanglement is discussed, which Einstein referred to as "spooky action at a distance". This has been discussed on this very forum a while ago.
How does this relate to audio? After all we're in an Audio Asylum. The late Richard Heyser was an audio pioneer, and he was also interested in the quantum realm. He saw parallels between our difficulty correlating our audio measurements with what we hear, and some of the measurement paradoxes in the quantum world. Heyser's unpublished papers are now available on the Columbia College of Chicago website. They are being presided over by Doug Jones who did a very interesting presentation on Heyser at the Chicago AES meeting this May. Richard Feynman (who was a teacher of Heyser's) used to say "There are two things you have to remember with science: 1. That you have to be careful you are not fooling yourself; and 2. That you are the easiest person to fool."
Paul
I have nothing intelligent enough to add to this except that oddly I just joined The Asylum and independently was watching this video and reading about the topic, and just wondering how I got started on that and what an odd coincidence it is to be reading this here
Sort of like that "monkey" effect they spoke of back in the 80s
I personally was thinking that the quantum world may finally be elementary enough to bring into focus the stark difference between our thought processes and the actual objective functioning of reality. That just like philosophy fell into epistimology and linguistics then this too could be more a descriptor of how our thought processes are maybe hopelessly based in metaphor and versions of causality that simply do not apply to fundamental reality
And, no, I cannot clarify this further...LOL
JaroTheWise
.
From what I've read you don't even have to monitor the data from the slit sensors in real time.
If that data is being recorded and there is a possibility that a human can ever look at it then the wave collapses.
The sensors can be in place and working but if no data is being stored then the wave does not collapse.
But monitoring where the photons end up (on the collector plate, as a wave pattern or a particle pattern) does not collapse the wave.
So back to the original question, why does observing the photons, at the slits, collapse the wave but observing the photons at the collector plate not?
What's the difference?
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
What's the difference?
Well, the photons you see from the target aren't the same ones. The original ones are destroyed upon impact and new ones are generated from the material. Maybe that's the deal?
Rick
The photons are acting as waves and particles. It's wave particle duality that is involved in the experiment not quantum decoherence or quantum superposition.
Edits: 05/21/15 05/21/15
Yes, waves when we are not looking and particles when we do look.
But waves when we look at the result. That was my question.
Why don't they act as particles when we look only at the result?
What's the difference between looking at the result vs. looking at which slit they go through?
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
No. They are particles and waves all the time. Looking has nothing to do with it. Even electrons are particles and wave all the time - simultaneously. Even bowling balls are particles and waves all the time. Capish?
Did you watch the video?
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
No. It doesn't show up on my iPad. Why, does the video dispute me?
Yes.
In the experiment the photons acted like a wave as long as their movement through the slits were not being monitored.
As soon as their movement were being monitored they stopped acting like waves and started acting like particles.
My question is this. The result, of them acting like waves or particles, is/was being monitored. Why wouldn't that cause them to stop acting like a wave?
Why does only monitoring them at the slits cause the wave to "collapse" but monitoring the resultant wave patter not cause the wave to collapse?
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Well, that's odd because elsewhere on the Internet perhaps Wikipedia it mentions that when individual photons entering the slits are monitored (in a variation of The laser beam experiment the tell tale interference pattern is observed on the other side, proving that the individual photons are acting as particles when they enter the slits AND waves when they produce the interference pattern on the other side.All atomic particles including photons and electrons - and even bowling balls - act simultaneously as waves and particles. So, if you could devise an experiment to test bowling balls with slits big enough for them to go through the results would be the same: the bowling balls would act as particles and waves simultaneously. That was the big news about Young's experiment. Hel-loooo!
From Wikipedia for the double slit experiment:
"In the basic version of this experiment, a coherent light source such as a laser beam illuminates a plate pierced by two parallel slits, and the light passing through the slits is observed on a screen behind the plate.[2][3] The wave nature of light causes the light waves passing through the two slits to interfere, producing bright and dark bands on the screen-a result that would not be expected if light consisted of classical particles.[2][4] However, the light is always found to be absorbed at the screen at discrete points, as individual particles (not waves), the interference pattern appearing via the varying density of these particle hits on the screen.[5] Furthermore, versions of the experiment that include detectors at the slits find that each detected photon passes through one slit (as would a classical particle), and not through both slits (as would a wave).[6][7][8][9][10] These results demonstrate the principle of wave
Edits: 05/21/15 05/21/15 05/21/15 05/21/15 05/21/15
You are not understanding the experiment.
You need to watch the video.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
The single slit and double slit experiments are filled with mysteries and paradoxes. No bout a doubt it. If you have monitors near the slits that means you have to have light to see, right? Won't that light needed to observe the slits interfere with the experiment?
Edits: 05/21/15 05/21/15
The fact that there are measurement tools close to the slits does not change anything. And no, you don't need light to see photons.
The output of the measurement tools can be hooked up but only when recording data does it collapse the wave.
I think you need to do more research on this. You're not really up to speed.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Well, YOU DON'T KNOW. Go visit your local library.
.
Have Fun and Enjoy the Music
"Still Working the Problem"
I agree. Geoff needs to watch the video. I have the same question.
I'm glad someone else has the same question.
In almost 100 years someone must have answered (or attempted to) the question but I can't find it.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Uh, she's pulling your leg. Duh. The answer to your question I suspect is in the explanation of Schrödinger's Cat. So the answer has been known for what 80 years?
Edits: 05/21/15
Geoff, I'm serious, I have the same questions. I can think for myself. Just because I joke around doesn't mean I'm an idiot. If you don't know the answer, just say you don't know the answer.
I did watch the video. Doh. You have a question on the double slit experiment? You're so funny!
Yes I do.
Why is observing the movement of the photons at the slits different than observing where the photons land?
If observing the movement of the photons as they pass through the slits collapses the wave, why doesn't observing where the photons eventually land collapse the wave?
I really don't need an answer at this point.
At this point I would just like to know if you understand my question?
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
obtuse to admit it. He will of course have a smart ass answer to deflect his lack
of understanding your legitimate (and damn good) question, 'cause that's how he do.
You shouldn't expect more than that from him though.
Well, maybe a smart ass photo after he gets tired of typing.
Mostly I suspect he'd rather be selling his quantum tweaks that he has
trouble explaining in any sort of cohesive fashion than trying to answer
a question that you'd be better off asking that cartoon character in the video.
HIM you can take seriously.
"Once this was all Black Plasma and Imagination" -Michael McClure
Until now, I thought I was alone in my findings.
Anyone who thinks he understands the double slit experiment is only fooling himself. I don't pretend to know everything, Mousetrap. Unlike yourself. Besides I'm the only one with attitude here so take your personality issues elsewhere.
So what is your guess?
Why doesn't observing the result collapse the wave the way observing the movement of the photons at the slit does?
Remember we already know it has nothing to do with the presents of the sensors.
I personally think you're bluffing and you really know nothing about quantum physics and the quantum wave.
Please prove me wrong and say something relevant.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
| Why doesn't observing the result collapse the wave the way observing the movement of the photons at the slit does?
The wavefunction of the particle *did* collapse on the final screen, that was an irreversible collision and the particle didn't continue to do anything else. Before the measurement on the final screen the wavefunction was distributed. After, not so.
The observation or non-observation at the slit permitted the particle to still pass through. This shows that even an observation which permits something to pass through will change the behavior of the quantum mechanical particle/wave going through.
Both kinds of observations have an effect.
"The observation or non-observation at the slit permitted the particle to still pass through. This shows that even an observation which permits something to pass through will change the behavior of the quantum mechanical particle/wave going through."
But having the physical mechanism to observe at the slit does not collapse the wave. Only HUMAN observation (or the the possibility of human observation [the recording of data from the sensor]) collapses the wave.
On the other hand, human observation of the final screen does not collapse the wave when there is no human observation at the slit (or the possibility of human observation).
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
If I was bluffing I would have offered up a reason. Guess I must not be bluffing. Duh. You see something on the internet you can't explain. Big friggin deal! Get over it.
Get over what?
I asked one question, "Why doesn't the monitoring of the end result collapse the wave?".
You either have an answer or you don't.
If you have nothing, not even a guess, I can only assume you haven't looked into quantum physics.
The thing is, I thought some of you products are supposedly based on quantum physics?
Maybe I'm wrong.
Thanks anyway.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
No need to bust my balls. Yes, I design quantum mechanics based products. But that logically doesn't mean I know everything. Any more than a thoracic surgeon knows all about brain surgery. Let me know if you find the answer. By the way just curious don't you find it strange that particles like electrons act like waves too? Or that bowling balls act like waves. Or are you too sophisticated? EVERYTHING about the double slit experiment is strange, such as firing single photons one at a time through the slits, and obtaining the interference pattern on the other side. Do you see why that is strange?
Edits: 05/22/15 05/22/15 05/22/15 05/22/15
| Do you see why that is strange?Yes it's strange, but only if you think of particles as being first. The wavefunctions are.
The duality is that in observational physical 3-d space the effects look like 3-d particles sometimes and 3-d waves sometime.
The truth is that neither is precisely right.
The laws of quantum mechanics are written as evolution operators on wave*functions* which are the true fundamental "things" {elements of state} in the theory. Of course these are much less intuitive for human brains to understand, and even less intuitive is that they are elements in a functional Hilbert space which is not physical space. And that's where all the weirdness comes from.
Particle/no-particle is a sometime thing as one can see by creation/annihilation operators on the underlying fields (which are quantum mechanical wavefunctions of functions (the field)). Just depends on your basis. You don't even need to have a definite number of particles at any time, i.e. the wavefunction needn't be in an eigenstate of the particle number operator. If you took expectation you'd have a probability distribution of particle counts.
Edits: 06/04/15
Yes, I do.
"...I design quantum mechanics based products"
But you have no opinion WRT my question?
I'm sorry but that seems strange to me.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
At this point who gives a shit?
If you really know little about QP, but you say you design QP products, your customers might give a shit.
I would think someone who knows about QP would have some kind of answer to my question.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Good luck with that one Tre'.
Geofftrait is now in defense mode and going to hang himself.
He seems to enjoy that.
"Once this was all Black Plasma and Imagination" -Michael McClure
I did. What's your point? The single slit and double slit experiments are landmark WTF science experiments.
Edits: 05/21/15
I don't think it does. But I'm more a many worlds kind of guy when it comes to QM. It's all down to decoherence imho. http://en.wikipedia.org/wiki/Quantum_decoherence
The first sentence should have said
I don't think it does regardless.
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