Do I Misunderstand The Double Slit Experiment

[David Sklansky]

What I think I know about it comes from a couple of forty year old books. And what I remember reading is so spooky that it gives one pause about whether some supernatural entity could have something to do with it. But every time I mention it the scientists pooh pooh me. Which makes me think that I am thinking things about the experiment, and related exoeriments that aren't true.

So without going into detail, are the following things true?

1. If we watch individual photons as they are going through the slit(s) they make patterns on the screen like they are particles. If we don't watch them, the patterns are those of a wave.

2. If we aren't watching, but we have a movie camera pointed at the slits, the pattern is of particles.

3. If the movie camera has no film the pattern will be waves.

4. IF THE CAMERA HAS FILM AND WE DON'T LOOK AT THE SCREEN UNTIL AFTER WE LOOK AT THE PICTURES, AND ON THE WAY TO THE DRUGSTORE WE FALL AND RUIN THE FILM, WE WILL SEE WAVES ON THE SCREEN. In other words the photons "know" that we will not be able to see them go through the slits, even though our inability to do that is because of an event in the future!

Am I wrong?

[gumpzilla]

Well, if individual photons are coming through the slits, if they make it to the camera, that means they scattered off something and didn't get to the screen. So to be pedantic, they shouldn't tell you anything about the interference pattern, meaning you'll see interference behaviors.

There are ways in which you can do experiments similar to your case 4. They tend to go by the name "delayed choice quantum eraser," and it's been a while since I've read about them, so I can't say offhand if your impressions are exactly correct. It's a pretty subtle issue, obviously.

EDIT: From the Wikipedia on delayed choice quantum eraser,

[ QUOTE ]
In the double slit experiment, a photon passes through one of two slits in a double slit apparatus, and then registers on a detector. The detector shows where the photon hit it, like an image projected on a screen. If many photons individually pass through the double slit apparatus, and nothing observes which slit a given photon travels through, an interference pattern emerges on the detector. The interference pattern indicates that the light beam is in fact made up of waves. However, if someone observes which of the two slits each photon passes through, a different result will be obtained. In this case, each photon hits the detector after going through only one slit and a single concentration of hits in the middle of the detection field. This result is consistent with light behaving as individual particles, like tiny bullets. It is counterintuitive that a different outcome results based on whether or not the photon is observed after it goes through the slit but before it hits the detector.

In a quantum eraser experiment, one arranges to detect which one of the slits the photon passes through, but also construct the experiment in such a way that this information can be "erased" after the fact. It turns out that if one observes which slit the photon passes through, the "no interference" or particle behavior will result, which is what quantum mechanics predicts, but if the quantum information is "erased" regarding which slit the photon passed through, a wavelike interference pattern can be observed.

However, Kim, et al. have shown that it is possible to delay the choice to erase the quantum information until after the photon has actually hit the target. But, again, if the information is "erased," an interference pattern can be recovered in a certain subset of the photons which reach the detector, even if the information is erased after the photons have hit the detector

[/ QUOTE ]

[Borodog]

[ QUOTE ]
What I think I know about it comes from a couple of forty year old books. And what I remember reading is so spooky that it gives one pause about whether some supernatural entity could have something to do with it. But every time I mention it the scientists pooh pooh me. Which makes me think that I am thinking things about the experiment, and related exoeriments that aren't true.

So without going into detail, are the following things true?

1. If we watch individual photons as they are going through the slit(s) they make patterns on the screen like they are particles. If we don't watch them, the patterns are those of a wave.

2. If we aren't watching, but we have a movie camera pointed at the slits, the pattern is of particles.

3. If the movie camera has no film the pattern will be waves.

4. IF THE CAMERA HAS FILM AND WE DON'T LOOK AT THE SCREEN UNTIL AFTER WE LOOK AT THE PICTURES, AND ON THE WAY TO THE DRUGSTORE WE FALL AND RUIN THE FILM, WE WILL SEE WAVES ON THE SCREEN. In other words the photons "know" that we will not be able to see them go through the slits, even though our inability to do that is because of an event in the future!

Am I wrong?

[/ QUOTE ]

This is essentially correct, barring the fact that you can't just use a "movie camera". After all, you can see the interference pattern while *looking* at the beam hitting the slits. You have to actually be able to *detect* which slit an individual photon passes through, which requires interacting with it, and localizing it, which is what destroys the interference pattern. But my understanding is that if you do as you say, that is, not observe the screen and wipe out the data of which slit each photon went through, and then observe the screen, you will observe an interference pattern.

Edit: Er, what gump said.

[Schweitzer]

This is another example of a paradox that I have been wondering about for awhile.

Apparent Paradox:

I run the double-slit experiment but do not observe the slit the electrons travel through. Someone a light-minute away with a powerful telescope flips a coin to decide whether to observe them. Will I see an interference pattern or not?

If I see an interference pattern then the observer should be able to see which slit each electron went through and find a contradiction.

If I do not see interference then I know that the observer will not observe the experiment one minute from now and in effect know the future result of his coin toss. I have observed an effect before the cause.

I am about to earn a B.S. in Physics and yet I don't really understand what will happen in this situation.

[David Sklansky]

Hey Not Ready come back! Did you know about this stuff?

[Schweitzer]

[ QUOTE ]
This is essentially correct, barring the fact that you can't just use a "movie camera". After all, you can see the interference pattern while *looking* at the beam hitting the slits. You have to actually be able to *detect* which slit an individual photon passes through, which requires interacting with it, and localizing it, which is what destroys the interference pattern. But my understanding is that if you do as you say, that is, not observe the screen and wipe out the data of which slit each photon went through, and then observe the screen, you will observe an interference pattern.

Edit: Er, what gump said.


[/ QUOTE ]

So what you are saying is if light hits the particles they become localized and no interfence pattern is observed whether or not the light is observed?
I was under the impression that if light interacts with the particles, but the light is not observed, that an interfence pattern would be observed.

[dknightx]

so ... what happens if we set up the cameras to watch the slits, and we bring two people into the room.

Person A does not know the cameras are set up and can see the screen. What does he see?

Person B knows the cameras are set up, but can't see the screen. Afterwards, he takes the camera, falls down and the film is destroyed. He returns to the screen, what does he see?

At this point in time, Person A returns, does what he see differ than what he saw earlier?

[David Steele]

[ QUOTE ]
so spooky that it gives one pause about whether some supernatural entity could have something to do with it.

[/ QUOTE ]

What would the entity do?

[Phil153]

There's an excellent chance that you do.

[Borodog]

[ QUOTE ]
[ QUOTE ]
This is essentially correct, barring the fact that you can't just use a "movie camera". After all, you can see the interference pattern while *looking* at the beam hitting the slits. You have to actually be able to *detect* which slit an individual photon passes through, which requires interacting with it, and localizing it, which is what destroys the interference pattern. But my understanding is that if you do as you say, that is, not observe the screen and wipe out the data of which slit each photon went through, and then observe the screen, you will observe an interference pattern.

Edit: Er, what gump said.


[/ QUOTE ]

So what you are saying is if light hits the particles they become localized and no interfence pattern is observed whether or not the light is observed?
I was under the impression that if light interacts with the particles, but the light is not observed, that an interfence pattern would be observed.

[/ QUOTE ]

Both are correct.

[Borodog]

[ QUOTE ]
so ... what happens if we set up the cameras to watch the slits, and we bring two people into the room.

Person A does not know the cameras are set up and can see the screen. What does he see?

Person B knows the cameras are set up, but can't see the screen. Afterwards, he takes the camera, falls down and the film is destroyed. He returns to the screen, what does he see?

[/ QUOTE ]

Do A and B ever communicate with each other?

[ QUOTE ]
At this point in time, Person A returns, does what he see differ than what he saw earlier?

[/ QUOTE ]

I didn't know A ever left? What difference would that make? The screen cannot magically change from what he has previously seen.

[dknightx]

[ QUOTE ]
[ QUOTE ]
so ... what happens if we set up the cameras to watch the slits, and we bring two people into the room.

Person A does not know the cameras are set up and can see the screen. What does he see?

Person B knows the cameras are set up, but can't see the screen. Afterwards, he takes the camera, falls down and the film is destroyed. He returns to the screen, what does he see?

[/ QUOTE ]

Do A and B ever communicate with each other?


[/ QUOTE ]

no they never communicate with each other (nor do they even know someone else is in the room) until after they have both seen the screen for the first time.

[ QUOTE ]

[ QUOTE ]
At this point in time, Person A returns, does what he see differ than what he saw earlier?

[/ QUOTE ]

I didn't know A ever left? What difference would that make? The screen cannot magically change from what he has previously seen.

[/ QUOTE ]

Ok well this question isn't that important, but the question is if A will observe the particle pattern even if he does not know the slit is being observed AND the film is destroyed in the future (but before the film is actually destroyed).

[DougShrapnel]

From wiki as well "the total pattern of signal photons never shows interference, and it is only when one looks at a subset of signal photons whose idlers were seen at a particular detector that an interference pattern can be recovered. So, the experiment would certainly not allow one to send a message back in time, and whether the experiment requires any sort of backwards causality to understand it would depend on one's interpretation of quantum mechanics." So why is this spooky again?

[KikoSanchez]

I don't know much about Quantum physics nor photons, but it seems if a person or a light recording decive is viewing the photon experiment as it occurs that it will interfere with it. Photons would inevitably be refracted off the eye or camera lens and 'ruin' the experiment compared to an unobserved experiment.

Just curious, how the hell do they only send one photon at a time toward a plate?

[Borodog]

[ QUOTE ]
[ QUOTE ]
[ QUOTE ]
so ... what happens if we set up the cameras to watch the slits, and we bring two people into the room.

Person A does not know the cameras are set up and can see the screen. What does he see?

Person B knows the cameras are set up, but can't see the screen. Afterwards, he takes the camera, falls down and the film is destroyed. He returns to the screen, what does he see?

[/ QUOTE ]

Do A and B ever communicate with each other?


[/ QUOTE ]

no they never communicate with each other (nor do they even know someone else is in the room) until after they have both seen the screen for the first time.

[/ QUOTE ]

Well then they communicate. I said "ever".

Still thinking about my response though.

[Borodog]

[ QUOTE ]
From wiki as well "the total pattern of signal photons never shows interference, and it is only when one looks at a subset of signal photons whose idlers were seen at a particular detector that an interference pattern can be recovered. So, the experiment would certainly not allow one to send a message back in time, and whether the experiment requires any sort of backwards causality to understand it would depend on one's interpretation of quantum mechanics." So why is this spooky again?

[/ QUOTE ]

Hmm. This is news to me. Also, it doesn't quite make sense. How could you look at a subset of photons that were seen at a particular detector if you have destroyed the information from the detectors? /images/graemlins/confused.gif

[dknightx]

[ QUOTE ]
[ QUOTE ]
[ QUOTE ]
[ QUOTE ]
so ... what happens if we set up the cameras to watch the slits, and we bring two people into the room.

Person A does not know the cameras are set up and can see the screen. What does he see?

Person B knows the cameras are set up, but can't see the screen. Afterwards, he takes the camera, falls down and the film is destroyed. He returns to the screen, what does he see?

[/ QUOTE ]

Do A and B ever communicate with each other?


[/ QUOTE ]

no they never communicate with each other (nor do they even know someone else is in the room) until after they have both seen the screen for the first time.

[/ QUOTE ]

Well then they communicate. I said "ever".

Still thinking about my response though.

[/ QUOTE ]

does the answer differ if A and B never communicated (ever), or if they only communicate after they have both seen the screen?

does the answer differ if A tells B what he saw before B sees the screen (but after the film is destroyed)?

but i guess this also depends on what A actually sees and if its even possible for A and B to see different things.

[PLOlover]

what about ebr, action at distnance thingee, einstein-bohr-(rosenberg?) pair.

[Borodog]

If A & B communicate, then obviously they will have observed the same thing on the screen (whatever that might be).

IF A & B never communicate, then I believe they can have seen different things.

[DougShrapnel]

[ QUOTE ]
[ QUOTE ]
[ QUOTE ]
[ QUOTE ]
so ... what happens if we set up the cameras to watch the slits, and we bring two people into the room.

Person A does not know the cameras are set up and can see the screen. What does he see?

Person B knows the cameras are set up, but can't see the screen. Afterwards, he takes the camera, falls down and the film is destroyed. He returns to the screen, what does he see?

[/ QUOTE ]

Do A and B ever communicate with each other?


[/ QUOTE ]

no they never communicate with each other (nor do they even know someone else is in the room) until after they have both seen the screen for the first time.

[/ QUOTE ]

Well then they communicate. I said "ever".

Still thinking about my response though.

[/ QUOTE ]If the camera measures which slot each photon went through, it's the same pattern on the screen for all.

[DougShrapnel]

[ QUOTE ]
[ QUOTE ]
From wiki as well "the total pattern of signal photons never shows interference, and it is only when one looks at a subset of signal photons whose idlers were seen at a particular detector that an interference pattern can be recovered. So, the experiment would certainly not allow one to send a message back in time, and whether the experiment requires any sort of backwards causality to understand it would depend on one's interpretation of quantum mechanics." So why is this spooky again?

[/ QUOTE ]

Hmm. This is news to me. Also, it doesn't quite make sense. How could you look at a subset of photons that were seen at a particular detector if you have destroyed the information from the detectors? /images/graemlins/confused.gif

[/ QUOTE ]It's all there in the wiki article they use a beem spliter on entagled particles. And test only a subset. I'm not an expert on this stuff, so grain of salt.

[UprightCreature]

In my experience the biggest problem people have when trying to understand these kind of experiments is not really understanding what it means to observe something.

People feel like, based on everyday interactions with the macroscopic world, that they can passively observe things without disturbing or interacting with them. In reality this isn't the case in either the macro or quantum world. When you see a person in a telescope you are detecting many photons that are being emitted or bouncing off of them. You couldn’t see the person if these photons were not interacting with the person.

This has already been said in this thread, but, you can not observe a photon without interacting with it. That interaction fundamentally changes the quantum state of the photon.

To further complicate matters you can have a quantum system of entangled particles where the state of one particle depends on the state of the other particle. By observing one of the entangled particles you know something about the other particle in the system, thus collapsing the wave function of both particles. Without explaining in great detail this is the fundamental concept of observing a photon but not developing the film... that is never observing the particle that was entangled with the photon.

It turns out that even though at first glance people think you can use this to send information back in time or faster than light, you actually can't.

[PairTheBoard]

In the delayed choice quantum eraser experiments which are suppose to do something like what you describe in #4 the effect is not quite as dramatic as you describe it. At least according to my understanding when I last read about it. I believe a system of photon splitters is set up which allow photons to continue to the screen normally and produce duplicate photons which can then be directed elsewhere for study. I'm pretty fuzzy on the details, but when the erasure is done you don't actually see a change in the pattern on the screen. You use the duplicate photons with slit information erased to produce or deduce some kind of wavy subpattern of what you see on the screen. If you're really interested you should read up on it yourself. I think Wiki describes it in detail or at least links to something that does.

It's still spooky, just not as dramatic as in your OP #4.

PairTheBoard

[carlo]

I know it can be very complicated but it seems that if this is a true experiment the interference pattern speaks for itself.Simply put, the interaction of light with light breeds darkness. Following the light after the darkness reveals that light leeches through until another moment of interference. This is what the experiment reveals and no more.

Now, to assume that light is particles(photons) is consequent to the Newtonian look at light and of course the Wave theory is around the corner. To deal with light as both particle and wave is a preconceived notion because of our dependence on particularity(matter broken into parts and pieces)and the consequence or retort is the wave theory. The idea of particles(photons) in no way is brought to life by this experiment.

As a follow up on this conceive that light and darkness are realities(i.e. darkness is not the absence of light but a reality of its own.

[Metric]

[ QUOTE ]
1. If we watch individual photons as they are going through the slit(s) they make patterns on the screen like they are particles. If we don't watch them, the patterns are those of a wave.

[/ QUOTE ]
If by "watch" you mean "entangle the photon with some system in such a way that information on the path is stored in that system", then yes.

[ QUOTE ]
2. If we aren't watching, but we have a movie camera pointed at the slits, the pattern is of particles.

[/ QUOTE ]
Again, this is true as long as the state of the movie camera is being entangled with the state of the photon.

[ QUOTE ]
3. If the movie camera has no film the pattern will be waves.

[/ QUOTE ]
I.E. if the state of the movie camera (and everything else in the room) does not become entangled with the photon, then we will see waves.

[ QUOTE ]
4. IF THE CAMERA HAS FILM AND WE DON'T LOOK AT THE SCREEN UNTIL AFTER WE LOOK AT THE PICTURES, AND ON THE WAY TO THE DRUGSTORE WE FALL AND RUIN THE FILM, WE WILL SEE WAVES ON THE SCREEN. In other words the photons "know" that we will not be able to see them go through the slits, even though our inability to do that is because of an event in the future!

[/ QUOTE ]
If by "destroy the film" you mean that you disentangle the photon/screen state from everything else (including the camera film), then this is right.

This seems shocking at first, but these are all subtly the same phenomenon at work. If the photon/screen state is entangled with anything else, interference will not be observed. It doesn't matter if it was or will be entangled -- the only thing that matters as to what you will see right now is whether path-information is held by some other system via entanglemet right now.

[Borodog]

I defer to Metric on all this voodoo [censored].

[jogsxyz]

There's a disclaimer in Wikipedia.

[ QUOTE ]
This article may require cleanup to meet Wikipedia's quality standards.

[/ QUOTE ]

[DougShrapnel]

Metric, is the eraser experiment similar to a double split experiment with a moving detector? Let's say you have a moving detector between the slits and the screen. When the detector is very close to the slits, close enough to determine which slit a photon went thru, the interference pattern disappears. If you move the detector further back toward the screen, to a point where it becomes impossible to answer a which slit question, the interference pattern is displayed.

[Arp220]

Metric gave a good answer. Here is a different take on your questions:

[ QUOTE ]

1. If we watch individual photons as they are going through the slit(s) they make patterns on the screen like they are particles. If we don't watch them, the patterns are those of a wave.

[/ QUOTE ]

Correct, sort of. A better phrasing would be:

If you determine which slit each individual photon goes through, then you will see two bright spots on the screen in front of each slit, as if you shot a stream of particles straight at each slit. If you do not determine which slit each photon goes through, then you'll see an interference pattern on the screen, with a bight blob in the middle, between the slits, accompanied by 'fringes' as if you'd fired one big wave at the slits.

[ QUOTE ]

2. If we aren't watching, but we have a movie camera pointed at the slits, the pattern is of particles.

[/ QUOTE ]

Correct, as long as the movie camera is measuring which slit each individual photon goes through.

[ QUOTE ]

3. If the movie camera has no film the pattern will be waves.

[/ QUOTE ]

I would say this is incorrect. This would be taking the measurement, but not writing the result down /images/graemlins/wink.gif

[ QUOTE ]

4. IF THE CAMERA HAS FILM AND WE DON'T LOOK AT THE SCREEN UNTIL AFTER WE LOOK AT THE PICTURES, AND ON THE WAY TO THE DRUGSTORE WE FALL AND RUIN THE FILM, WE WILL SEE WAVES ON THE SCREEN. In other words the photons "know" that we will not be able to see them go through the slits, even though our inability to do that is because of an event in the future!

[/ QUOTE ]

This is wrong. You will see particles. If you measure which slit the photons go through then you wont see an interference pattern on the screen. It doesn't matter if you record the result on film or not. Its the action of measurement that is important.

I'll end with something spooky. Lets say you set up the experiment and dont measure which slit the photons go through. You'll see a wave pattern on the screen. Now, if you replace the screen with a very sensitive potodetector that can in principle show where individual photons are arriving... then you'll see individual photons arriving... BUT with many more photons arriving in the bright fringes, and very few arriving in the dark fringes. In other words... you see individual photons, but arriving in the intensity pattern expected from a wave going through the slits and interfering with itself!

Spooky, isnt it?

[Arp220]

And to add something - if you set up apparatus to measure which slit each photon goes through, and then look at the screen, but not the film, you are in effect looking at the film. By looking at the screen you become 'entangled' with the screen/film/slit/photon system.

[ZeeJustin]

Metric, could you clarify what you mean by "being entangled with the state of the photon."

Are you saying that we only get the "weird" results when observing to such a degree that we can determine what slit(s) was entered by the photon?

That would imply that watching the experiment, or pointing a normal camera at it would have no effect on it, but using some kind of super camera would instead produce the "weird" results.

Is that understanding correct?

[Metric]

[ QUOTE ]
Metric, could you clarify what you mean by "being entangled with the state of the photon."

[/ QUOTE ]
The photon P is in an entangled state with some system A if the state of the combined system PA cannot be factored into a state of the form |Psi_P> (x) |Psi_A>. Most states of composite systems are entangled.

[ QUOTE ]
Are you saying that we only get the "weird" results when observing to such a degree that we can determine what slit(s) was entered by the photon?

[/ QUOTE ]
You don't necessarily have to perform the measurement yourself -- if the photon becomes entangled with anything that potentially holds information about "which slit," the interference pattern will vanish.

[ QUOTE ]
That would imply that watching the experiment, or pointing a normal camera at it would have no effect on it, but using some kind of super camera would instead produce the "weird" results.

Is that understanding correct?

[/ QUOTE ]
See above.

[Metric]

[ QUOTE ]
Metric, is the eraser experiment similar to a double split experiment with a moving detector? Let's say you have a moving detector between the slits and the screen. When the detector is very close to the slits, close enough to determine which slit a photon went thru, the interference pattern disappears. If you move the detector further back toward the screen, to a point where it becomes impossible to answer a which slit question, the interference pattern is displayed.

[/ QUOTE ]
I'm not sure I understand the question -- it's true that in a "close up" measurement, it will be hard to see the interference fringes, and that the position of detection of the individual photons will hold a good deal of "which path" information.

[Max Raker]

[ QUOTE ]
3. If the movie camera has no film the pattern will be waves.

4. IF THE CAMERA HAS FILM AND WE DON'T LOOK AT THE SCREEN UNTIL AFTER WE LOOK AT THE PICTURES, AND ON THE WAY TO THE DRUGSTORE WE FALL AND RUIN THE FILM, WE WILL SEE WAVES ON THE SCREEN. In other words the photons "know" that we will not be able to see them go through the slits, even though our inability to do that is because of an event in the future!

Am I wrong?

[/ QUOTE ]

I think you don't fully get what constitutes a measurement. Like when you say "we don't look at the screen", the measurement takes place not when a person looks at it but when the screen interacts with the photon. And if 4 was true, you could use it to send information faster than the speed of light. DO you see why?

[Max Raker]

[ QUOTE ]
I'll end with something spooky. Lets say you set up the experiment and dont measure which slit the photons go through. You'll see a wave pattern on the screen. Now, if you replace the screen with a very sensitive potodetector that can in principle show where individual photons are arriving... then you'll see individual photons arriving... BUT with many more photons arriving in the bright fringes, and very few arriving in the dark fringes. In other words... you see individual photons, but arriving in the intensity pattern expected from a wave going through the slits and interfering with itself!

Spooky, isnt it?

[/ QUOTE ]

This is really the only spooky part of this. It is even weirder to think that you can slow down the rate at which you emit the photons to something like 1 per hour and you will still get an interference pattern. So it has nothing to do with 2 different photons interacting with each other.

So though an individual photon can only go through one slit, it "knows" that the other one is there. The standard explanation is it doesn't make sense to talk about photons until a measurement forces localization. Others claim that the many worlds interpretation of QM is needed to explain this.

[NotReady]

[ QUOTE ]

Hey Not Ready come back! Did you know about this stuff?


[/ QUOTE ]

Very flattering but you have more than one expert explaining it in this thread. My only take on it is that we change the quantum world by observing it. If you try to grab something very light that's floating in water the object will move because of the action of your hand causing waves which move the object. I think something like that is what happens when we try to "grab" the quantum world by observation. Just a total layman's view.

[Max Raker]

[ QUOTE ]
This is another example of a paradox that I have been wondering about for awhile.

Apparent Paradox:

I run the double-slit experiment but do not observe the slit the electrons travel through. Someone a light-minute away with a powerful telescope flips a coin to decide whether to observe them. Will I see an interference pattern or not?

If I see an interference pattern then the observer should be able to see which slit each electron went through and find a contradiction.

If I do not see interference then I know that the observer will not observe the experiment one minute from now and in effect know the future result of his coin toss. I have observed an effect before the cause.

I am about to earn a B.S. in Physics and yet I don't really understand what will happen in this situation.

[/ QUOTE ]

After the guy flips the coin, it will take him 1 minute to be able to determine which slits the photons are going through. So you will know the result of his flip but only after a time of distance/c from the flip. Does that seem right to you?

[teampursuit]

Do you mean the Feynman Lectures? There's a really good discussion of this there. Where you're gettng bogged down is in the definition of 'observed'.

[PairTheBoard]

We already understand light to be a self propagating electromagnetic wave. That's what a photon of light is. Electric and Magnetic Forces fluxing back and forth against each other and propagating forward as a result. This Electromagnetic Fluxing Field of forces constituting a photon in travel is spread out in space. I don't think it's well understood what happens when that spread out travelling fluxing field of EM forces gets its energy absorbed when it makes contact with something like a Film. The Field of Forces is spread out in space, but the energy doesn't get absorbed in the same smeared out way. It somehow all gets pulled down into a single "point". That's what we see on the Film when we interpret it as a "particle" hitting the screen. But it's not really a particle hitting the screen. What we see is the result of a spread out self propagating wave of Fluxing EM forces getting the spread out energy pulled into a single "point" of absorption.

With such a view it's not so hard to see why a single self propagating photon "wave" might pass through both slits and thereby have it's structure of electromagnetic flux lines altered so that the way the altered wave has it's energy pulled together into a point of absorption is also altered in a way that can be measured by looking at the statistical pattern of absorption points on the Film for a number of such photons.

So it's our mistaken notion that because a photon looks like a particle at the Film it must have gone through one slit or the other. It's only when we take a measurement to observe it going through one of the slits that this is really the case. What happens then is that we alter the spread out EM Flux lines with a kind of Partial Absorption, forcing the the spread out energy to get pulled into the slit local, but without complete absorption into a point. The structure of the EM flux lines is then altered in a way that the new structure is absorbed at the Film with the same statistical earmarks as if the slit were the origin of the photon.

I don't know how well this explanation holds up against all the experiments they've done. But if it does, then the spooky thing is not so much that a photon of light - which we already model as a self propagating EM wave - behaves this way. But that all so called "particles" do as well. Not all "particles" are as easily understood as smeared out distributions of self interacting Forces of some kind. If that's what they are then I don't think they've identified the "Forces".

PairTheBoard

[hexag1]

the explanation given by Feynaman in "The Character of Physical Law" sums it up best:

first we must keep in mind the following:
When we look at anything under a microscope, our smallest resolution is given by the frequency of the light we use too look. In other words, if we have two dots, we can only distinguish them from each other if the light we use to look has a shorter wavelength than the distance between the two dots. Anything shorter and they look like one dot.

Now, with that in mind:

If we let the electron pass through the two slits we will get a pattern that indicates that that electron behaves like a wave.

If the intensity of the electron beam is turned down low enough, then we can see that they come in lumps; individual units. The probability of us catching a lump at any point after the two slits is given by a sinusoidal wave function. When all the probilities are mapped, the pattern of electron arrival looks like a ripple.

If we try too 'look' at the electrons by shooting light at the electrons before they hit, it will seem like the electrons definitely pass through one slit or another. The pattern of arrival for the electrons on the other side of the slits will look like electrons obey ballistic mechanics.

We can try to look at the electrons before they pass through the slits. We do this by shooting light at them. But the light affects the path of the electrons. When we shine a light, the path of the electrons is drastically affected. They no longer behave like waves, but instead like ballistic particles.

We can try to turn down the energy of the light we use to look at them. If we turn it down low enough, the light no longer affects the electrons enough, and they behave like waves again. However, a new problem arises. Now that we have decreased the energy of the light (and therefore the wavelength of the light) we shine on the electrons, we can no longer distinguish between the two slits the electrons pass through. The wavelength that equals the distance between the two slits, equals the wavelength that no longer affects the path of the electrons.

Therefore it is IN PRINCIPLE impossible to tell through which slit the electron will pass. Nature is rigged in just such a way that we can never tell what happens. Some say that nature herself doesnt know through which slit the electron will pass.

/images/graemlins/confused.gif /images/graemlins/confused.gif /images/graemlins/confused.gif /images/graemlins/confused.gif /images/graemlins/confused.gif /images/graemlins/confused.gif /images/graemlins/confused.gif /images/graemlins/confused.gif /images/graemlins/confused.gif /images/graemlins/confused.gif /images/graemlins/confused.gif /images/graemlins/confused.gif /images/graemlins/confused.gif /images/graemlins/confused.gif /images/graemlins/confused.gif /images/graemlins/confused.gif /images/graemlins/confused.gif /images/graemlins/confused.gif /images/graemlins/confused.gif /images/graemlins/confused.gif

[ILOVEPOKER929]

Hi David, There's nothing that I can add to this thread that hasnt already been said. I just wanted to mention two excellent books that have helped me understand what's going on here:

1) "The Elegant Universe" written by Brian Green
2) "The Fabric of the Cosmos" also by Brian Green

Both books cover the infamous double slit experiment, and "The Fabric of the Cosmos" talks about other interesting experiments in quantum physics such as the Beam-splitter experiment and the Delayed-choice quantum eraser experiment.

These books are easy to read becuz Green assumes from the outset that the reader knows nothing about quantum physics.

[TheMuppet]

[ QUOTE ]
1. If we watch individual photons as they are going through the slit(s) they make patterns on the screen like they are particles. If we don't watch them, the patterns are those of a wave.

[/ QUOTE ]

True. The pattern vanishes when you disturb the photon(s).

[ QUOTE ]
2. If we aren't watching, but we have a movie camera pointed at the slits, the pattern is of particles.

[/ QUOTE ]

Depends an what you actually mean here. Once the photon hits the camera film, its gone, and you cant make it magically reapper inorder to make an interference pattern or a point particle pattern.

Basically its the same a detection it when it passes through the slits, if you do that the pattern vanishes.

[ QUOTE ]
3. If the movie camera has no film the pattern will be waves.

[/ QUOTE ]

If you dont look at them when passing (disturb) then will make an interference pattern.

[ QUOTE ]
4. IF THE CAMERA HAS FILM AND WE DON'T LOOK AT THE SCREEN UNTIL AFTER WE LOOK AT THE PICTURES, AND ON THE WAY TO THE DRUGSTORE WE FALL AND RUIN THE FILM, WE WILL SEE WAVES ON THE SCREEN. In other words the photons "know" that we will not be able to see them go through the slits, even though our inability to do that is because of an event in the future!

[/ QUOTE ]

Not resolved as of yet.

Shahriar Afshar did an experiment that does this. And according to his experiment you can actually look (after the fact) which slot it passed and you still get the interference pattern.

However this experiment is not conclusive, and might actually point to something completly different going on (new physics).

[ILOVEPOKER929]

[ QUOTE ]


[ QUOTE ]
4. IF THE CAMERA HAS FILM AND WE DON'T LOOK AT THE SCREEN UNTIL AFTER WE LOOK AT THE PICTURES, AND ON THE WAY TO THE DRUGSTORE WE FALL AND RUIN THE FILM, WE WILL SEE WAVES ON THE SCREEN. In other words the photons "know" that we will not be able to see them go through the slits, even though our inability to do that is because of an event in the future!

[/ QUOTE ]

Not resolved as of yet.

Shahriar Afshar did an experiment that does this. And according to his experiment you can actually look (after the fact) which slot it passed and you still get the interference pattern.

However this experiment is not conclusive, and might actually point to something completly different going on (new physics).

[/ QUOTE ]

About Scenaro #4: As has already been mentioned in this thread by many posters. In order for the camera to observe which slit the photons moves through it has to use other photons to see that photon. This process disturbs the photons in question and gives us "which path" information which leads to the partical pattern on the back screen.

So if the camera "disrupts" the passing photons. It doesnt matter if humans arent looking at the screen. It will always be a particle pattern. Furthermore, even if we lose the film before we look at the screen, a particle pattern will still be there.

Bottom line is this: Once the photons hit the screen its all over. There's nothing we can do to change the pattern on that screen.

How bout this: What if we use some kind of tagging device to see which slit each photon goes through and then "erase" the mark imprinted by the tagging device just before the photons hit the screen. Will there still be a particle pattern on the screen or an interference pattern revealing a wave? The answer is we will see an interference pattern. this in a nut shell is the quantum eraser experiment.

One of the keys to understanding the quantum eraser experiment is the nature in which we "tag" the photons to know which slit each one passes through. We have to be able to "tag" each photon in such a way that "which path" information can be erased before each photon hits the screen. For instance, if we placed a photon detector in front of each slit, the detector's readout would establish with certainty whether the photon went through the left slit or through the right slit and there would now be no way to erase this information so there would be no way to recover the interference pattern. So the quantum eraser experiment is directly dependent on exactly how we figure out which slit each photon goes through. Here's a passage from Brian Green's book "The Fabric of the Cosmos" that explains this idea:

"The tagging devices are different (from a photon detector) because they provide only the potential for which-path information to be determined-and potentialities are just the kinds of things that can be erased."

BTW, everything Ive talked about basically comes from pages 192-194 of Green's book.

To sum things up again, Sklansky's scenario 4) cannot happen becuz the photons have already hit the screen, and since the camera used other photons to see which slit each passing photon went through, thus eastablishing which path information, the pattern on the screen will always be a particle pattern whether we lose the film or not. These are the conclusions I have come to based on my limited understanding of quantum mechanics.

[gumpzilla]

[ QUOTE ]

To sum things up again, Sklansky's scenario 4) cannot happen becuz the photons have already hit the screen, and since the camera used other photons to see which slit each passing photon went through, thus eastablishing which path information, the pattern on the screen will always be a particle pattern whether we lose the film or not. These are the conclusions I have come to based on my limited understanding of quantum mechanics.

[/ QUOTE ]

Not exactly. I could be wrong, but I'm pretty sure that in vacuum photons do not interact (or if they do because of some weird vacuum fluctuation / quantum field theory reasons that I don't understand, it certainly doesn't have a big cross section.) So the issue isn't that you're measuring one photon with another, but that any photons that get to the camera represent ones that did not hit the screen, and so you don't know anything about what's going on with the things that are hitting the screen.

Looking at the Wiki article (and I should read the paper at some point), the way that real quantum eraser experiments are done usually involves parametric down conversion, which is a nonlinear process in a medium where an incoming photon of frequency 2f gets changed into two entangled photons of frequency f. One of these photons gets sent to the "screen," and the other ends up going into an interferometer, where through some cleverness in design you can extract which way information for some fraction of the photons that make it through. So the trick is that you turn your single photon into two photons, and then use their entanglement so that measurements on one photon tell you something about the other.

[TheMuppet]

[ QUOTE ]
[ QUOTE ]


[ QUOTE ]
4. IF THE CAMERA HAS FILM AND WE DON'T LOOK AT THE SCREEN UNTIL AFTER WE LOOK AT THE PICTURES, AND ON THE WAY TO THE DRUGSTORE WE FALL AND RUIN THE FILM, WE WILL SEE WAVES ON THE SCREEN. In other words the photons "know" that we will not be able to see them go through the slits, even though our inability to do that is because of an event in the future!

[/ QUOTE ]

Not resolved as of yet.

Shahriar Afshar did an experiment that does this. And according to his experiment you can actually look (after the fact) which slot it passed and you still get the interference pattern.

However this experiment is not conclusive, and might actually point to something completly different going on (new physics).

[/ QUOTE ]

About Scenaro #4: As has already been mentioned in this thread by many posters. In order for the camera to observe which slit the photons moves through it has to use other photons to see that photon. This process disturbs the photons in question and gives us "which path" information which leads to the partical pattern on the back screen.

So if the camera "disrupts" the passing photons. It doesnt matter if humans arent looking at the screen. It will always be a particle pattern. Furthermore, even if we lose the film before we look at the screen, a particle pattern will still be there.

Bottom line is this: Once the photons hit the screen its all over. There's nothing we can do to change the pattern on that screen.

How bout this: What if we use some kind of tagging device to see which slit each photon goes through and then "erase" the mark imprinted by the tagging device just before the photons hit the screen. Will there still be a particle pattern on the screen or an interference pattern revealing a wave? The answer is we will see an interference pattern. this in a nut shell is the quantum eraser experiment.

One of the keys to understanding the quantum eraser experiment is the nature in which we "tag" the photons to know which slit each one passes through. We have to be able to "tag" each photon in such a way that "which path" information can be erased before each photon hits the screen. For instance, if we placed a photon detector in front of each slit, the detector's readout would establish with certainty whether the photon went through the left slit or through the right slit and there would now be no way to erase this information so there would be no way to recover the interference pattern. So the quantum eraser experiment is directly dependent on exactly how we figure out which slit each photon goes through. Here's a passage from Brian Green's book "The Fabric of the Cosmos" that explains this idea:

"The tagging devices are different (from a photon detector) because they provide only the potential for which-path information to be determined-and potentialities are just the kinds of things that can be erased."

BTW, everything Ive talked about basically comes from pages 192-194 of Green's book.

To sum things up again, Sklansky's scenario 4) cannot happen becuz the photons have already hit the screen, and since the camera used other photons to see which slit each passing photon went through, thus eastablishing which path information, the pattern on the screen will always be a particle pattern whether we lose the film or not. These are the conclusions I have come to based on my limited understanding of quantum mechanics.

[/ QUOTE ]

I know I know. But the experiment that Shahriar Afshar performed, actually "looked" without looking.

You will have to look it up yourself to understand it.

But in principle he actually did this:
- Send photons through slits
- Look what slit the photon came through (without actually looking). (hint, this is the clever part)
- Observe if they make a point particle pattern or an interference pattern.

And he still got an interference pattern.

[ILOVEPOKER929]

"Not exactly. I could be wrong, but I'm pretty sure that in vacuum photons do not interact (or if they do because of some weird vacuum fluctuation / quantum field theory reasons that I don't understand, it certainly doesn't have a big cross section.) So the issue isn't that you're measuring one photon with another, but that any photons that get to the camera represent ones that did not hit the screen, and so you don't know anything about what's going on with the things that are hitting the screen."

I never looked at it this way before. My understanding of quantum mechanics is not deep enough to know if what youre saying is true or not. I will assume for now that what you said is true though. However I do think it would be better for didactic purposes to assume that the camera is using other photons to observe the photons passing through the slits even if this is impossible.

"Looking at the Wiki article (and I should read the paper at some point), the way that real quantum eraser experiments are done usually involves parametric down conversion, which is a nonlinear process in a medium where an incoming photon of frequency 2f gets changed into two entangled photons of frequency f. One of these photons gets sent to the "screen," and the other ends up going into an interferometer, where through some cleverness in design you can extract which way information for some fraction of the photons that make it through. So the trick is that you turn your single photon into two photons, and then use their entanglement so that measurements on one photon tell you something about the other."

What youre talking about here is called the "Delayed-Choice Quantum Eraser" experiment. This is an extention of the beam-splitter experiment. Since we are talking about a double slit experiment in this thread, a simple version of the quantum eraser experiment is all that is necessary to convey my point. Both the eraser experiment you mentioned and the one I delineated are valid in explaining this counterintuitive phenomena.

Again the main point I was trying to illustrate is that once "which path" information on the photon has been established, and these photons have already hit the screen, nothing in the future can change the particle pattern on the screen for these photons, so Sklansky's scenario 4) cannot happen. Again this is based on what little I know about quantum mechanics.

[ILOVEPOKER929]

[ QUOTE ]


I know I know. But the experiment that Shahriar Afshar performed, actually "looked" without looking.

You will have to look it up yourself to understand it.

But in principle he actually did this:
- Send photons through slits
- Look what slit the photon came through (without actually looking). (hint, this is the clever part)
- Observe if they make a point particle pattern or an interference pattern.

And he still got an interference pattern.

[/ QUOTE ]

I will look this up. Thank you for this information Muppet.

[Max Raker]

[ QUOTE ]
[ QUOTE ]
[ QUOTE ]


[ QUOTE ]
4. IF THE CAMERA HAS FILM AND WE DON'T LOOK AT THE SCREEN UNTIL AFTER WE LOOK AT THE PICTURES, AND ON THE WAY TO THE DRUGSTORE WE FALL AND RUIN THE FILM, WE WILL SEE WAVES ON THE SCREEN. In other words the photons "know" that we will not be able to see them go through the slits, even though our inability to do that is because of an event in the future!

[/ QUOTE ]

Not resolved as of yet.

Shahriar Afshar did an experiment that does this. And according to his experiment you can actually look (after the fact) which slot it passed and you still get the interference pattern.

However this experiment is not conclusive, and might actually point to something completly different going on (new physics).

[/ QUOTE ]

About Scenaro #4: As has already been mentioned in this thread by many posters. In order for the camera to observe which slit the photons moves through it has to use other photons to see that photon. This process disturbs the photons in question and gives us "which path" information which leads to the partical pattern on the back screen.

So if the camera "disrupts" the passing photons. It doesnt matter if humans arent looking at the screen. It will always be a particle pattern. Furthermore, even if we lose the film before we look at the screen, a particle pattern will still be there.

Bottom line is this: Once the photons hit the screen its all over. There's nothing we can do to change the pattern on that screen.

How bout this: What if we use some kind of tagging device to see which slit each photon goes through and then "erase" the mark imprinted by the tagging device just before the photons hit the screen. Will there still be a particle pattern on the screen or an interference pattern revealing a wave? The answer is we will see an interference pattern. this in a nut shell is the quantum eraser experiment.

One of the keys to understanding the quantum eraser experiment is the nature in which we "tag" the photons to know which slit each one passes through. We have to be able to "tag" each photon in such a way that "which path" information can be erased before each photon hits the screen. For instance, if we placed a photon detector in front of each slit, the detector's readout would establish with certainty whether the photon went through the left slit or through the right slit and there would now be no way to erase this information so there would be no way to recover the interference pattern. So the quantum eraser experiment is directly dependent on exactly how we figure out which slit each photon goes through. Here's a passage from Brian Green's book "The Fabric of the Cosmos" that explains this idea:

"The tagging devices are different (from a photon detector) because they provide only the potential for which-path information to be determined-and potentialities are just the kinds of things that can be erased."

BTW, everything Ive talked about basically comes from pages 192-194 of Green's book.

To sum things up again, Sklansky's scenario 4) cannot happen becuz the photons have already hit the screen, and since the camera used other photons to see which slit each passing photon went through, thus eastablishing which path information, the pattern on the screen will always be a particle pattern whether we lose the film or not. These are the conclusions I have come to based on my limited understanding of quantum mechanics.

[/ QUOTE ]

I know I know. But the experiment that Shahriar Afshar performed, actually "looked" without looking.

You will have to look it up yourself to understand it.

But in principle he actually did this:
- Send photons through slits
- Look what slit the photon came through (without actually looking). (hint, this is the clever part)
- Observe if they make a point particle pattern or an interference pattern.

And he still got an interference pattern.

[/ QUOTE ]

For this thread we probably shouldn't mention the Afshar experiment. Most people I've talked to have serious doubts about the setup and conclusion. Even if the Afshar experiment is correct I still think 4 would be wrong since it could be used to send information faster than C.

[TheMuppet]

[ QUOTE ]
[ QUOTE ]


I know I know. But the experiment that Shahriar Afshar performed, actually "looked" without looking.

You will have to look it up yourself to understand it.

But in principle he actually did this:
- Send photons through slits
- Look what slit the photon came through (without actually looking). (hint, this is the clever part)
- Observe if they make a point particle pattern or an interference pattern.

And he still got an interference pattern.

[/ QUOTE ]

I will look this up. Thank you for this information Muppet.

[/ QUOTE ]

Good idea /images/graemlins/smile.gif But its somewhat of a mess, as it stands they are still discussing if what he did is actually right or not. You would think its simple to resolve, but apparently its not.

Personally I think all of QM is an enormous mess, its a good theory, but there is definitely something missing. And its most likely a very good approximation of some other more fundamental theory.

So as it stand, resolving this wont be easy.

[TheMuppet]

[ QUOTE ]

For this thread we probably shouldn't mention the Afshar experiment. Most people I've talked to have serious doubts about the setup and conclusion. Even if the Afshar experiment is correct I still think 4 would be wrong since it could be used to send information faster than C.

[/ QUOTE ]

I'm actually inclined to agree /images/graemlins/ooo.gif I only really brought it up, because as it is you cant say for sure that its invalid or for that matter that it is valid.

And sending information faster than C is totally ok, as long as its not classical information (spooky action at a distance already says that information can travel faster than C - unless you wanna bring hidden variables into this, and I think your more likely to start worshiping green tea pots).

[Max Raker]

[ QUOTE ]
[ QUOTE ]

For this thread we probably shouldn't mention the Afshar experiment. Most people I've talked to have serious doubts about the setup and conclusion. Even if the Afshar experiment is correct I still think 4 would be wrong since it could be used to send information faster than C.

[/ QUOTE ]

I'm actually inclined to agree /images/graemlins/ooo.gif I only really brought it up, because as it is you cant say for sure that its invalid or for that matter that it is.

And sending information faster than C is totally ok, as long as its not classical information (spooky action at a distance already says that information can travel faster than C).

[/ QUOTE ]

The way it is worded now, it seems that I could send information. In the EPR paradox you can't send information so it is not a problem.

In 4, i could take the pictures far away and flip a coin. Heads I destroy them, tails I look at them. You can look at the screen after some time has passed and you will know if I flipped heads or tails. Am I wrong or does this make sense?

[gumpzilla]

[ QUOTE ]

What youre talking about here is called the "Delayed-Choice Quantum Eraser" experiment. This is an extention of the beam-splitter experiment. Since we are talking about a double slit experiment in this thread, a simple version of the quantum eraser experiment is all that is necessary to convey my point. Both the eraser experiment you mentioned and the one I delineated are valid in explaining this counterintuitive phenomena.

[/ QUOTE ]

Except I believe yours is not physically possible, and mine is. This seems like nittiness, but if there were no way to actually set up an experiment that would measure something like this then it would be a worthless subject to argue. Even in the Bohr-Einstein style thought experiments to try and hash out whether the uncertainty principle made sense, a key point was that they were always talking about real physical systems and behavior.

[luckyme]

[ QUOTE ]

And sending information faster than C is totally ok, as long as its not classical information (spooky action at a distance already says that information can travel faster than C).

[/ QUOTE ]

It's unfortunate that Einstein used that phrase. There is nothing spooky about an observation unless we go into it with an expectation of how nature 'should' be. If we go in with 'nature is how we find it' then it wouldn't occur to us to label it spooky. A mystery, since we don't have a grasp of the situation, but nothing more.

Tribesmen attribute thunder/lightening to spooks and DS keeps up our innate animism with the latest mystery. Iow, the OP is nothing more than our 40,000 year old habit showing it's still part of our makeup. There is no sense in which the slit experiment 'violates' any part of reality, merely our preconceptions of it.

luckyme

[TheMuppet]

[ QUOTE ]

In 4, i could take the pictures far away and flip a coin. Heads I destroy them, tails I look at them. You can look at the screen after some time has passed and you will know if I flipped heads or tails. Am I wrong or does this make sense?

[/ QUOTE ]

Makes sense, except in this experiment there is no picture to destroy.

The setup David suggested will always produce point particle patterns. No matter what happens to the film, we looked so the interference got destroyed.

The Afshar experiment should always produce interference patterns, no matter what. But then again he is not really looking (which is the big point of contention afaik).

I think David is confuses about observing. Its not about who, its about the act (be it a film, a conscious observer, a photon detector or whatever).

[Max Raker]

[ QUOTE ]

Not exactly. I could be wrong, but I'm pretty sure that in vacuum photons do not interact (or if they do because of some weird vacuum fluctuation / quantum field theory reasons that I don't understand,

[/ QUOTE ]

This is second quantization and is where quantum field theory begins. For just the double slit you don't really need it though.

[TheMuppet]

[ QUOTE ]

It's unfortunate that Einstein used that phrase. There is nothing spooky about an observation unless we go into it with an expectation of how nature 'should' be. If we go in with 'nature is how we find it' then it wouldn't occur to us to label it spooky. A mystery, since we don't have a grasp of the situation, but nothing more.

Tribesmen attribute thunder/lightening to spooks and DS keeps up our innate animism with the latest mystery. Iow, the OP is nothing more than our 40,000 year old habit showing it's still part of our makeup. There is no sense in which the slit experiment 'violates' any part of reality, merely our preconceptions of it.

luckyme

[/ QUOTE ]

Depends. I think you misunderstand spooky action at a distance.

Take a photon, split it in to two entangled photons. At this point their spin is in a superposition.

Move the photons some distance apart (as far as you like). Now measure the spin on one of them. You get up, the other will measure as down - instantly.

Prior to measuring you had two photons with a spin that was in a superposition, after you have two photons in distinct states up and down (not up up or down down).

Unless you believe in hidden variables, some information has to have been passed between these two photons. Otherwise you wouldn't always get up + down or down + up (you would get an equal distribution of up up / down down / up down / down up).

The information that was exchange was not classical - in other words you cannot use it to communicate, but it was still exchange, and instantly no matter the distance.

[Max Raker]

[ QUOTE ]
[ QUOTE ]

It's unfortunate that Einstein used that phrase. There is nothing spooky about an observation unless we go into it with an expectation of how nature 'should' be. If we go in with 'nature is how we find it' then it wouldn't occur to us to label it spooky. A mystery, since we don't have a grasp of the situation, but nothing more.

Tribesmen attribute thunder/lightening to spooks and DS keeps up our innate animism with the latest mystery. Iow, the OP is nothing more than our 40,000 year old habit showing it's still part of our makeup. There is no sense in which the slit experiment 'violates' any part of reality, merely our preconceptions of it.

luckyme

[/ QUOTE ]

Depends. I think you misunderstand spooky action at a distance.

Take a photon, split it in to two entangled photons. At this point their spin is in a superposition.

Move the photons some distance apart (as far as you like). Now measure the spin on one of them. You get up, the other will measure as down - instantly.

Prior to measuring you had two photons with a spin that was in a superposition, after you have two photons in distinct states up and down (not up up or down down).

Unless you believe in hidden variables, some information has to have been passed between these two photons. Otherwise you wouldn't always get up + down or down + up (you would get an equal distribution of up up / down down / up down / down up).

The information that was exchange was not classical - in other words you cannot use it to communicate, but it was still exchange, and instantly no matter the distance.

[/ QUOTE ]

Right, but in entangled state you can not force the electron to be up or down. If you could do that then it would violate special relativity as you could use it to instantly communicate something over long distances.

[ILOVEPOKER929]

[ QUOTE ]
[ QUOTE ]

What youre talking about here is called the "Delayed-Choice Quantum Eraser" experiment. This is an extention of the beam-splitter experiment. Since we are talking about a double slit experiment in this thread, a simple version of the quantum eraser experiment is all that is necessary to convey my point. Both the eraser experiment you mentioned and the one I delineated are valid in explaining this counterintuitive phenomena.

[/ QUOTE ]

Except I believe yours is not physically possible, and mine is. This seems like nittiness, but if there were no way to actually set up an experiment that would measure something like this then it would be a worthless subject to argue. Even in the Bohr-Einstein style thought experiments to try and hash out whether the uncertainty principle made sense, a key point was that they were always talking about real physical systems and behavior.

[/ QUOTE ]

It is possible. It's been done. My source is "The Fabric of the Cosmos" page 192.

[TheMuppet]

[ QUOTE ]

Right, but in entangled state you can not force the electron to be up or down. If you could do that then it would violate special relativity as you could use it to instantly communicate something over long distances.

[/ QUOTE ]

Exactly. Hence the difference between quantum information and classical information.

But I only wrote all that to say why he used the word spooky.

And it is spooky, quantum information was exchange, yet it did so instantly.

So violating C is fine, as long as its only done with quantum information.

[ILOVEPOKER929]

[ QUOTE ]
[ QUOTE ]

It's unfortunate that Einstein used that phrase. There is nothing spooky about an observation unless we go into it with an expectation of how nature 'should' be. If we go in with 'nature is how we find it' then it wouldn't occur to us to label it spooky. A mystery, since we don't have a grasp of the situation, but nothing more.

Tribesmen attribute thunder/lightening to spooks and DS keeps up our innate animism with the latest mystery. Iow, the OP is nothing more than our 40,000 year old habit showing it's still part of our makeup. There is no sense in which the slit experiment 'violates' any part of reality, merely our preconceptions of it.

luckyme

[/ QUOTE ]

Depends. I think you misunderstand spooky action at a distance.

Take a photon, split it in to two entangled photons. At this point their spin is in a superposition.

Move the photons some distance apart (as far as you like). Now measure the spin on one of them. You get up, the other will measure as down - instantly.

Prior to measuring you had two photons with a spin that was in a superposition, after you have two photons in distinct states up and down (not up up or down down).

Unless you believe in hidden variables, some information has to have been passed between these two photons. Otherwise you wouldn't always get up + down or down + up (you would get an equal distribution of up up / down down / up down / down up).

The information that was exchange was not classical - in other words you cannot use it to communicate, but it was still exchange, and instantly no matter the distance.

[/ QUOTE ]

Yes, this data rules out the idea of a local universe. This just means that we have to update our "classical" model of reality.

[Metric]

[ QUOTE ]
[ QUOTE ]

Right, but in entangled state you can not force the electron to be up or down. If you could do that then it would violate special relativity as you could use it to instantly communicate something over long distances.

[/ QUOTE ]

Exactly. Hence the difference between quantum information and classical information.

But I only wrote all that to say why he used the word spooky.

And it is spooky, quantum information was exchange, yet it did so instantly.

So violating C is fine, as long as its only done with quantum information.

[/ QUOTE ]
The state-of-the-art understanding of this is that no information at all needs to be exchanged between separated entangled particles, and "wave function collapse" (which is supposed to take place in a quantum measurement) is a bit of a red herring.

See, e.g. section 5 of http://lanl.arxiv.org/abs/0708.3535

[gumpzilla]

[ QUOTE ]
[ QUOTE ]
[ QUOTE ]

What youre talking about here is called the "Delayed-Choice Quantum Eraser" experiment. This is an extention of the beam-splitter experiment. Since we are talking about a double slit experiment in this thread, a simple version of the quantum eraser experiment is all that is necessary to convey my point. Both the eraser experiment you mentioned and the one I delineated are valid in explaining this counterintuitive phenomena.

[/ QUOTE ]

Except I believe yours is not physically possible, and mine is. This seems like nittiness, but if there were no way to actually set up an experiment that would measure something like this then it would be a worthless subject to argue. Even in the Bohr-Einstein style thought experiments to try and hash out whether the uncertainty principle made sense, a key point was that they were always talking about real physical systems and behavior.

[/ QUOTE ]

It is possible. It's been done. My source is "The Fabric of the Cosmos" page 192.

[/ QUOTE ]

The experiment you cite is the one *I* am talking about, which did use parametric down conversion. Your previous comment regarded photons interacting and cameras.

Max, I know about second quantization. I guess you could have some kind of goofy process like virtual pair production, electron interacts with photon 2, annihilation, and then maybe you have photon-photon interaction. The spirit of my comment still stands.

[TheMuppet]

[ QUOTE ]
The state-of-the-art understanding of this is that no information at all needs to be exchanged between separated entangled particles, and "wave function collapse" (which is supposed to take place in a quantum measurement) is a bit of a red herring.

See, e.g. section 5 of http://lanl.arxiv.org/abs/0708.3535

[/ QUOTE ]

Thanks.

Very impressive. Although I must admit, its going to take me some time to actually hack my way through all the math.

[thylacine]

[ QUOTE ]

The state-of-the-art understanding of this is that no information at all needs to be exchanged between separated entangled particles, and "wave function collapse" (which is supposed to take place in a quantum measurement) is a bit of a red herring.

See, e.g. section 5 of http://lanl.arxiv.org/abs/0708.3535

[/ QUOTE ]

Do you agree with them? (Haven't had a chance to read it yet.)

Do you believe that the entire universe (all of reality) is quantum theoretic? Or do you believe that some information is not quantum information and that quantum theory is an emergent phenomenon that is not truly fundamental?

[ILOVEPOKER929]

[ QUOTE ]
[ QUOTE ]
[ QUOTE ]
[ QUOTE ]

What youre talking about here is called the "Delayed-Choice Quantum Eraser" experiment. This is an extention of the beam-splitter experiment. Since we are talking about a double slit experiment in this thread, a simple version of the quantum eraser experiment is all that is necessary to convey my point. Both the eraser experiment you mentioned and the one I delineated are valid in explaining this counterintuitive phenomena.

[/ QUOTE ]

Except I believe yours is not physically possible, and mine is. This seems like nittiness, but if there were no way to actually set up an experiment that would measure something like this then it would be a worthless subject to argue. Even in the Bohr-Einstein style thought experiments to try and hash out whether the uncertainty principle made sense, a key point was that they were always talking about real physical systems and behavior.

[/ QUOTE ]

It is possible. It's been done. My source is "The Fabric of the Cosmos" page 192.

[/ QUOTE ]

The experiment you cite is the one *I* am talking about, which did use parametric down conversion. Your previous comment regarded photons interacting and cameras.



[/ QUOTE ]

Then we just had a misunderstanding. My comments regarding photons interacting with cameras simply reveals my ignorance on how photons interact with cameras. Assuming you are right, I thank you for pointing this out.

[Metric]

[ QUOTE ]
[ QUOTE ]

The state-of-the-art understanding of this is that no information at all needs to be exchanged between separated entangled particles, and "wave function collapse" (which is supposed to take place in a quantum measurement) is a bit of a red herring.

See, e.g. section 5 of http://lanl.arxiv.org/abs/0708.3535

[/ QUOTE ]

Do you agree with them? (Haven't had a chance to read it yet.)

Do you believe that the entire universe (all of reality) is quantum theoretic? Or do you believe that some information is not quantum information and that quantum theory is an emergent phenomenon that is not truly fundamental?

[/ QUOTE ]
Yes I do believe them, and my position is that quantum theory is self-contained -- all classical information is emergent from quantum information (which is well-behaved and evolves locally and unitarily). It is always possible that QM is wrong, but at least it is self-consistent.

[David Sklansky]

[ QUOTE ]
[ QUOTE ]

And sending information faster than C is totally ok, as long as its not classical information (spooky action at a distance already says that information can travel faster than C).

[/ QUOTE ]

It's unfortunate that Einstein used that phrase. There is nothing spooky about an observation unless we go into it with an expectation of how nature 'should' be. If we go in with 'nature is how we find it' then it wouldn't occur to us to label it spooky. A mystery, since we don't have a grasp of the situation, but nothing more.

Tribesmen attribute thunder/lightening to spooks and DS keeps up our innate animism with the latest mystery. Iow, the OP is nothing more than our 40,000 year old habit showing it's still part of our makeup. There is no sense in which the slit experiment 'violates' any part of reality, merely our preconceptions of it.

luckyme

[/ QUOTE ]

You are making a terrible analogy. As I told madnak almost all unexplained events in this day and age don't strike scientists as totally mysterious. For instance if we discovered that two people could truly communicate telepathically it wouldn't be evidence for God. The double slit experiment however, if I understand it correctly, is more than just unexplained. It seems to defy logic, not just science. And it seems to invoke human consciousness.

Also if you claim that no observation is spooky because "nature is how you find it" you are actually spouting the theistic line. Atheists believe that observations must conform to general laws. Willy nilly observations without underlying logical laws (eg the stars lining up to spell Peter 666) are strong evidence of intelligent design.

[madnak]

[ QUOTE ]
Unless you believe in hidden variables, some information has to have been passed between these two photons. Otherwise you wouldn't always get up + down or down + up (you would get an equal distribution of up up / down down / up down / down up).

[/ QUOTE ]

I don't claim to understand the math, but this doesn't make sense. Where is information being passed?

One particle becomes "down" and the other particle simultaneously becomes "up." Where is the information passage? You seem to be assuming that when you measure one particle, an "event" happens in that particular physical location, and information about that event has to propagate to the other particle's location. Do you have any justification for this assumption?

The fact that you are performing your measurement in one location seems to imply little about the event. Given that both entangled particles change states simultaneously, it seems more likely that the event is happening in both locations at once, or that the event isn't best interpreted in spatial terms (ie there is no "location" where it is "happening," we just see the effects in the locations of the two particles). Where am I going wrong here?

[madnak]

[ QUOTE ]
As I told madnak almost all unexplained events in this day and age don't strike scientists as totally mysterious.

[/ QUOTE ]

No more or less so than the double slit experiment.

[ QUOTE ]
For instance if we discovered that two people could truly communicate telepathically it wouldn't be evidence for God.

[/ QUOTE ]

More so than the double slit experiment...

[ QUOTE ]
The double slit experiment however, if I understand it correctly,

[/ QUOTE ]

This thread establishes that you do not.

[ QUOTE ]
is more than just unexplained. It seems to defy logic,

[/ QUOTE ]

It definitely doesn't seem to defy logic.

[ QUOTE ]
not just science. And it seems to invoke human consciousness.

[/ QUOTE ]

What the hell? How does it seem to invoke consciousness? Unless I've missed something very major in this thread, I don't see what consciousness has to do with anything. My suspicion is that you are taking the term "observation" much too literally. "Observation" in the physical sense doesn't mean "conscious awareness."

[luckyme]

[ QUOTE ]
[ QUOTE ]
[ QUOTE ]

And sending information faster than C is totally ok, as long as its not classical information (spooky action at a distance already says that information can travel faster than C).

[/ QUOTE ]

It's unfortunate that Einstein used that phrase. There is nothing spooky about an observation unless we go into it with an expectation of how nature 'should' be. If we go in with 'nature is how we find it' then it wouldn't occur to us to label it spooky. A mystery, since we don't have a grasp of the situation, but nothing more.

Tribesmen attribute thunder/lightening to spooks and DS keeps up our innate animism with the latest mystery. Iow, the OP is nothing more than our 40,000 year old habit showing it's still part of our makeup. There is no sense in which the slit experiment 'violates' any part of reality, merely our preconceptions of it.

luckyme

[/ QUOTE ]

You are making a terrible analogy. As I told madnak almost all unexplained events in this day and age don't strike scientists as totally mysterious. For instance if we discovered that two people could truly communicate telepathically it wouldn't be evidence for God. The double slit experiment however, if I understand it correctly, is more than just unexplained. It seems to defy logic, not just science. And it seems to invoke human consciousness.

Also if you claim that no observation is spooky because "nature is how you find it" you are actually spouting the theistic line. Atheists believe that observations must conform to general laws. Willy nilly observations without underlying logical laws (eg the stars lining up to spell Peter 666) are strong evidence of intelligent design.

[/ QUOTE ]

wow.
"defies logic" ! how does it do that?
Human logic determines how the universe operates? Isn't it the other way around? Isn't your claim that it should do what we expect the main stumbling block for science over the years? Isn't that what even einstein chocked on?

"Atheists believe..." what silliness is that? There is no belief you can claim if all the info you have is "george is an atheist". Atheism is a statement of one fact and one fact only "george does not believe a (theistic)god exists". There is no reason somebody can't be an atheist and think his dead grandmother makes the wind ... some may actually fit that.

Your 'atheists believe' claim may be confusing the scientific approach of looking for natural explanations.

When the stars line up for the scrabble tournament we can have another chat, but the universe acting at the quantum level differently than what we understand from our rabbit-hunting level perspective sure doesn't factor into deductions we can draw from it.

String theory or branes may move the discussion into new territory, reframing this slit situation out of existence in a sense.

luckyme

[David Sklansky]

If we take your stance to its extreme one could say that seeing a man crucified and than coming back to life is simply an observation that, though mysterious, is just the way nature works. Same with observing that people who wear yamulkes get their prayers answered.

As for the double slit experiment, it is my understanding that one of the explanations proposed seriously by physicists is that every time a measurement is made the whole universe breaks in two. Or something like that. Are you OK with that but not OK with the explanation that there was some sort of intelligent design regarding quantum theory?

[DougShrapnel]

David, perhaps another explaination might help with regard to the double slit experiement. Light travels as a wave from point a to point b. Even thru slits. When you locate the light you create a new point. So the light now travels as a wave from point a to the new point near a slit, and then continues on it's way to the point b as a wave. There is no wave of light at the slits, hence the interference pattern disappears when we observe light with slit information. A major problem in the 40 year old books was that things couldn't be both a wave and a particle. It's now thought by many that everything is on a wave-particle duality, very similar to how location and speed are complementary.

[madnak]

[ QUOTE ]
As for the double slit experiment, it is my understanding that one of the explanations proposed seriously by physicists is that every time a measurement is made the whole universe breaks in two. Or something like that.

[/ QUOTE ]

Yes, but that's incomplete. Measurement per se is irrelevant. According to the Many Worlds interpretation, every time particles interact the universe splits. Measuring particles necessitates interacting with them, so measurement does "split the universe," but most of the "universe splits" are unrelated to measurement (and certainly unrelated to consciousness). This hardly implies any intelligent design - certainly no more than anything else does. What it implies is that the universe is a complex sort of thing that isn't ripe for analogy. It's not a "big dark room" like most people seem to intuitively think.

Measurement is a big deal because everything we know about the universe comes from our measurements. Not because measurement appears to have some special properties.

Also, keep in mind that physicists as a group are particularly likely to be atheists. That is, the people who do understand the double-slit experiment are likely to disbelieve in intelligent design. This wouldn't make much sense if the DSE implies ID.

[luckyme]

[ QUOTE ]
As for the double slit experiment, it is my understanding that one of the explanations proposed seriously by physicists is that every time a measurement is made the whole universe breaks in two. Or something like that. Are you OK with that but not OK with the explanation that there was some sort of intelligent design regarding quantum theory?

[/ QUOTE ]

I'm ok with any conjecture, even theistic ones. I just don't take it as useful until something testable comes out of it with measurable predictions, etc.

If the universe splits in two at each option, so be it. What am I supposed to do, start spraying everything with Crazee Glue?

ID isn't an explanation in the same class. It's essentially a non-explanation, an explanatory dead-end. Even if it were true, there is no way to know when we reach that throwing-up-hands limit, track record is that some genius comes along and gives us a non-ID explanation.

[ QUOTE ]
If we take your stance to its extreme one could say that seeing a man crucified and than coming back to life is simply an observation that, though mysterious, is just the way nature works.

[/ QUOTE ]

Of course. If men are trapped under ice for an hour and come 'back to life' then that's the way our species performs. If we do it after crucifixion it'd be an interesting discovery and I can't think of a reason to say, " hey, we can't do that... it defies logic". So far, people crucified properly have done the right thing and stayed dead.
The universe doesn't run on logic, it does what it does and we try to understand it logically. It's not the same thing.

luckyme

[David Sklansky]

"Measuring particles necessitates interacting with them, so measurement does "split the universe," but most of the "universe splits" are unrelated to measurement (and certainly unrelated to consciousness). This hardly implies any intelligent design -"

I wasn't saying that at all. I was simply wondering luckyme would be so sceptical of an intelligent design theory but not of an equally crazy sounding many worlds theory.

[madnak]

[ QUOTE ]
David, perhaps another explaination might help with regard to the double slit experiement. Light travels as a wave from point a to point b. Even thru slits. When you locate the light you create a new point. So the light now travels as a wave from point a to the new point near a slit, and then continues on it's way to the point b as a wave. There is no wave of light at the slits, hence the interference pattern disappears when we observe light with slit information. A major problem in the 40 year old books was that things couldn't be both a wave and a particle. It's now thought by many that everything is on a wave-particle duality, very similar to how location and speed are complementary.

[/ QUOTE ]

I'm going to attempt a broad intuitive explanation. Someone let me know if I'm way off-base. I know I'll be off-base, I don't know that any intuitive explanation can be on-base, but I'm hoping to be "close enough." I'll use Muppet's up/down idea.

There was a time when scientists saw particles, and saw that they were either up or down. Scientists also saw waves, and believed that waves were different from particles.

Then some experiments showed strange things. Certain particles seemed to be both "up and down" at the same time. Some waves seemed to act like particles sometimes. None of this made much sense to the scientists.

But then they figured it out. There are waves. These waves have up and down properties. When one wave interacts with another wave in a certain way, the first wave turns into a particle - basically the whole wave is "pulled together" into the point at its leading edge. When the wave turns into a particle it starts behaving like one - like a little marble instead of a ripple across water.

Though the wave itself has up properties and down properties, when that wave turns into a particle it becomes either up or down, one or the other. It's completely random which way the particle will be. But it will always be either up or down, not both.

This randomness was interesting to scientists, and some possible explanations were raised. One of these explanations was the following - when a wave turns into a particle, it retains both its up properties and its down properties. In order to do this, the wave creates two universes. In one of these universes, it becomes an up particle, and in the other universe, it becomes a down particle. So whenever a wave becomes a particle, new universes are created.

WRT the double slit experiment, it's simple. Measuring a wave causes it to turn into a particle. If we let a wave move through two slits and then measure it, we see a wave. The wave will turn into a particle only after we measure it. But if we measure the wave before it goes through the slits, and then measure it again after it goes through the slits, we see a particle. The first time we measure the wave we see a wave, but then it turns into a particle, so the second time we measure we see a particle. This was confusing to scientists at first, when they thought that waves and particles were separate.

Using this explanation David, it should be easy to see why 1, 2, and 3 in your OP do happen, and 4 does not happen.

[madnak]

[ QUOTE ]
"Measuring particles necessitates interacting with them, so measurement does "split the universe," but most of the "universe splits" are unrelated to measurement (and certainly unrelated to consciousness). This hardly implies any intelligent design -"

I wasn't saying that at all. I was simply wondering luckyme would be so sceptical of an intelligent design theory but not of an equally crazy sounding many worlds theory.

[/ QUOTE ]

Ah. I see. Well, I think they're similar. Both have no real evidence going for them, and both introduce unnecessary complexities. But I guess some math is starting to be consistent with the MWI, so it's getting more popular.

[Schweitzer]

[ QUOTE ]
I run the double-slit experiment but do not observe the slit the electrons travel through. Someone a light-minute away with a powerful telescope flips a coin to decide whether to observe them. Will I see an interference pattern or not?

If I see an interference pattern then the observer should be able to see which slit each electron went through and find a contradiction.

If I do not see interference then I know that the observer will not observe the experiment one minute from now and in effect know the future result of his coin toss. I have observed an effect before the cause.

[/ QUOTE ]

Maybe I am slow but I still do not understand what will happen here. I can't see an interference pattern because the observer would be able to look at the experiment a minute later and see which slit the electrons went through. (Which would be both if there is an interference pattern)

If I see a particle-type pattern, then that would seem to indicate that the light forced a wave collapse whether or not the light was observed. I was taught that this will not happen if the light is not observed.

The only other possibility I can think of is that the observation one minute in the future caused a collapse, which seems impossible.

[luckyme]

[ QUOTE ]
I was simply wondering luckyme would be so sceptical of an intelligent design theory but not of an equally crazy sounding many worlds theory.

[/ QUOTE ]

One major problem with ID is it only applies just when it's not needed. The universe gets simpler and simpler as we drill down and the need to call in an ID'er virtually disappears.
When we couldn't figure out how blood flows or birds fly or why the plague killed us, that was the time we could call for a designer if we were so inclined ... when things were complex. Now that we understand things down to simple interactions at the quantum level, why would "some intelligence that explains this complexity" be needed ... the complexity only existed at the macro level.

luckyme

[David Sklansky]

What?

[madnak]

[ QUOTE ]
Maybe I am slow but I still do not understand what will happen here. I can't see an interference pattern because the observer would be able to look at the experiment a minute later and see which slit the electrons went through. (Which would be both if there is an interference pattern)

If I see a particle-type pattern, then that would seem to indicate that the light forced a wave collapse whether or not the light was observed. I was taught that this will not happen if the light is not observed.

The only other possibility I can think of is that the observation one minute in the future caused a collapse, which seems impossible.

[/ QUOTE ]

How are you observing the photons passing through the slit from so far away? I don't think a telescope is sufficient. Based on my understanding, you have to actively interfere with the experiment in order to observe those photons, which is the issue. If you're a light-minute away, you can't interfere with the experiment. If observation is happening then it must happen before the photons enter the slits - it might take a minute for information about the observation to reach you, but that's just "lag." If nobody is "getting their hands dirty" at the location of the experiment, I think you'll just see a wave-like interference pattern through a telescope.

[luckyme]

[ QUOTE ]
What?

[/ QUOTE ]

erhmmmm..

We can understand how the moon effects seal mating and how humans evolved from single cells.
Now I find a light wave that seems to want to act like a particle to me at times, etc ... and NOW I'm supposed to want to call in a designer?

What would that explain? when all the spin-offs (me included) are where the complexity is.
At the quantum level, god could play dice, light does it's weirdsy stuff and everything would be as it is today.. no designer need apply.

luckyme

[Schweitzer]

[ QUOTE ]
How are you observing the photons passing through the slit from so far away? I don't think a telescope is sufficient. Based on my understanding, you have to actively interfere with the experiment in order to observe those photons, which is the issue. If you're a light-minute away, you can't interfere with the experiment. If observation is happening then it must happen before the photons enter the slits - it might take a minute for information about the observation to reach you, but that's just "lag." If nobody is "getting their hands dirty" at the location of the experiment, I think you'll just see a wave-like interference pattern through a telescope.

[/ QUOTE ]

Ok, so I shine high frequency light upon the experiment. If I observe the light I should be able to detect the electrons as particles and determine which slit they went through. (I realize they were a wave before this and the measurement will collapse them to being in front of one of the slits)
In this system I will certainly see a particle pattern.

If, however, I shine the light on the experiment but the light is not observed, will I not see an interference pattern? And if that is the case, wouldn't someone with a powerful detector be able to detect the light from this experiment after the experiment has been finished?

[madnak]

If you shine the light, then you're observing. I'm pretty sure that whether you choose to look at the light is irrelevant - by shining the light you're causing the particle pattern because you're measuring (even if you aren't looking at those measurements).

It's not like the photons have a psychic awareness of whether you're paying attention. It's just that the amount of interaction necessary to take measurements happens to be exactly the amount of interaction necessary to affect the result. But I'll defer to someone with greater knowledge of the subject.

[ChrisV]

[ QUOTE ]
You are making a terrible analogy. As I told madnak almost all unexplained events in this day and age don't strike scientists as totally mysterious. For instance if we discovered that two people could truly communicate telepathically it wouldn't be evidence for God. The double slit experiment however, if I understand it correctly, is more than just unexplained. It seems to defy logic, not just science. And it seems to invoke human consciousness.

[/ QUOTE ]

David,

The idea that this invokes human consciousness is as a result of the vagueness of the Copenhagen Interpretation, which fails to properly define "observer" or even "measurement. Steven Weinberg quoted on the Wikipedia page about the Copenhagen Interpretation:

[ QUOTE ]
Bohr's version of quantum mechanics was deeply flawed, but not for the reason Einstein thought. The Copenhagen interpretation describes what happens when an observer makes a measurement, but the observer and the act of measurement are themselves treated classically. This is surely wrong: Physicists and their apparatus must be governed by the same quantum mechanical rules that govern everything else in the universe. But these rules are expressed in terms of a wave function (or, more precisely, a state vector) that evolves in a perfectly deterministic way. So where do the probabilistic rules of the Copenhagen interpretation come from?
Considerable progress has been made in recent years toward the resolution of the problem, which I cannot go into here. It is enough to say that neither Bohr nor Einstein had focused on the real problem with quantum mechanics. The Copenhagen rules clearly work, so they have to be accepted. But this leaves the task of explaining them by applying the deterministic equation for the evolution of the wave function, the Schrödinger equation, to observers and their apparatus.

[/ QUOTE ]

You should also look up the transactional interpretation, which removes the weirdness at the expense of allowing limited backwards-in-time causality (not the kind you can send messages with). Bottom line is that although the maths of quantum mechanics works, how we interpret what is happening is very much still up in the air. Schroedinger's Cat and that sort of thing is entirely a product of the Copenhagen Interpretation, which is untested (and currently untestable).

[goofball]

DS,

Nobody understands quantum mechanics.

[mrick]

[ QUOTE ]
There's a disclaimer in Wikipedia.

[ QUOTE ]
This article may require cleanup to meet Wikipedia's quality standards.

[/ QUOTE ]

[/ QUOTE ]

OK I removed the disclaimer. You can use that article now. It's safe.