Novie questions about the double-slit experiment

In summary, the conversation discusses the double-slit experiment and the role of measurement in determining the behavior of quantum particles. The speaker is seeking clarification on how the detection at the slits differs from the detection at the screen and how it affects the interference patterns. They also question the concept of "observing" changing the behavior of particles and whether the timing of detection plays a role. The expert summarizes that knowing which slit the particle passes through leads to a single-slit diffraction pattern, but questions remain about the role of detection in determining the particle's behavior.
  • #36
there is more chance of this... P.S. To have a cat's chance in hell of coming up with a valid theory of your own
than me doing an experiment as i wouldn't no where to start and as I've said the tools are not at my disposal ...
but many thanks for your words. i will take them on board in my mind as it is my only tool on this.. abit like Newtons head with the apple...

as I've said i can only ask questions . the answers i receive i process's into pictures which lead to experiments in mind which lead to more question.this is where you come in.
so
can i ask again please.
the two slit experiment with the " spying eye".
has it been done with the "spy" behind the slit?
so the wave does not know its being looked at until its gone through the slit?
ive looked on line but can't find anything to say this as been done.
im sure it must have and just wanted to know if the outcome was the same as if the "spy" was at the front.

peace
 
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  • #37
I have said exactly what happens with the "spying eye." You can use any detector you want and place it where you want. If you like, you can use a very low level of light and a photomultiplier, which will react to every individual photon. However, the only way to be sure of having detected all of the photons 'going through' one slit is to put a detector over it. It will react to every photon that lands on it. Unfortunately, as the only source of photons to land on the projection screen is then the 'other slit' you will get no interference pattern. There is no way of determining which of the photons that form the interference pattern went through which slit. As I said, the question is, in fact, meaningless.

This form of 'question and answer learning' is very inefficient. You need to read a lot and assemble the facts and ideas in your own head first. You can then post individual questions on forums like this one and you are more likely to get good and useful responses.
 
  • #38
thanks again sophiecentaur.
but you have left me as frustrated as a man in a room full of naked lesbians.
i do like your reply but I am still none the wiser of the outcome of the spying eye behind the slit.
are you a politician ?
is the outcome the same as when the spy is at the front or the same as when there is no spy at all,or a totally different outcome?
or you don't know if it has been done?
i can't do experiments ...no tools .
the sun is shining its a photontastic day .i do feel bad putting these question onto you.
ive only been into this subject for about 6days

8)
 
  • #39
This "spy" of yours is a Detector?
You put it in the places I have described. As I said, it could be a photomultiplier, to observe individual photons. BUT, once detected, the photon is no longer part of the experiment - wherever you happen to detect it.
You really must read around this - it's described in about a million different web pages.

I have to go now for a day or two.
 
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  • #40
ok.
i,d like to ask a simple question please.
did or has anyone every checked the first screen with the slit in it (the single slit screen not the double one and not the screen the photon hits at the back) to see if there is any sign either side of the slit, that a photon has past through it?

many thanks
peace
 
  • #41
lostprophets said:
ok.
i,d like to ask a simple question please.
did or has anyone every checked the first screen with the slit in it (the single slit screen not the double one and not the screen the photon hits at the back) to see if there is any sign either side of the slit, that a photon has past through it?

many thanks
peace

If you detect the photon BEFORE the slit, then the photon never passed through it. If you detect the photon AFTER the slit, then the photon went through it. A photon cannot be detected before the slit AND pass through it, as it has already been detected.
 
  • #42
Drakkith said:
If you detect the photon BEFORE the slit, then the photon never passed through it. If you detect the photon AFTER the slit, then the photon went through it. A photon cannot be detected before the slit AND pass through it, as it has already been detected.

sorry i think you miss understood me.
once the photon has gone through the slit and hit the back screen. can we check for any hint in the first screen that a photon has passed by/through the slit...does it leave any evidence/trail that it went through the slit..?
i guess anything coming off it would be very small indeed so maybe after a period of time firing one at a time would be the best time to check for a trail.
when i say either side of the slit i do mean either side on the front face of the screen or the internal edges of the slit

the other question i have is
when i see the results on the back screen i notice the line starts off as a dot then grows into a vertical line.
so
does the position of the "gun" "laser" that fires the photon get changed?

if not then does this not show that the photon was a wave to begin with ,or at least when it came out of the laser/gun thingy?
i don't mind being know where near here, but I am just trying to make sense of why
 
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  • #43
lostprophets said:
sorry i think you miss understood me.
once the photon has gone through the slit and hit the back screen. can we check for any hint in the first screen that a photon has passed by/through the slit...does it leave any evidence/trail that it went by..?

To my knowledge there is no "trail" left by a photon and no way to detect the photon without interacting with it and absorbing its energy.

the other question i have is
when i see the results on the back screen i notice the line starts off as a dot then grows into a vertical line.
so
does the position of the "gun" "laser" that fires the photon get changed?

No, the slit itself is rectangular, so the resulting pattern is also a rectangular.

if not then does this not show that the photon was a wave to begin with ,or at least when it came out of the laser/gun thingy?
i don't mind being know where near here, but I am just trying to make sense of why

I don't know what you mean. If you fire actual bullets through a rectangular slit, the pattern on a target behind the slit will be rectangular. If the slit is circular, then the pattern will be circular. It is the same with a wave.
 
  • #44
Drakkith said:
To my knowledge there is no "trail" left by a photon and no way to detect the photon without interacting with it and absorbing its energy.



No, the slit itself is rectangular, so the resulting pattern is also a rectangular.



I don't know what you mean. If you fire actual bullets through a rectangular slit, the pattern on a target behind the slit will be rectangular. If the slit is circular, then the pattern will be circular. It is the same with a wave.

oh my.my head is wobbling now.
so
why does a bullet not hit the back screen in the same place every time without moving the gun up or down?
 
  • #45
lostprophets said:
oh my.my head is wobbling now.
so
why does a bullet not hit the back screen in the same place every time without moving the gun up or down?

It's just an analogy. Imagine it's a machine gun that isn't stable enough and each shot is off slightly due to the kick.
The random pattern of the bullets will look similar to the shape of the slit.
 
  • #46
ok. is there any video anywhere that shows the actual experiment inits entirey and not some cartoon hero.
there seems to be very many videos that are misleading as to what actually is what..
i don't know the dimensions of the slit or anything and have many questions because of this.
its like someone telling me that a football pitch is green rectangle that humans kick a ball on into a goal,when in fact i need to how big the pitch is,what is made of ,the size of the ball,what the ball is made of and so on and on and on...
if what you say is true about the movement of the machine then i imagine these slits are very very small in length, it must be a wobbly machine ,as the size of the dots to the size of the lines are indeed very way out.so much so that if i were to compare it to scale with something else i imagine i,d be very surprised...i can imagine a beam of photons doing this but i have to say I am surprised one at a time they move so much.

im sure technology will improve with time
 
  • #47
lostprophets said:
if what you say is true about the movement of the machine then i imagine these slits are very very small in length, it must be a wobbly machine ,as the size of the dots to the size of the lines are indeed very way out.so much so that if i were to compare it to scale with something else i imagine i,d be very surprised...i can imagine a beam of photons doing this but i have to say I am surprised one at a time they move so much.

im sure technology will improve with time

Whatever the source for photons is, a light or laser or whatever, it is not designed to shoot them through a specific slit, nor does it move around during the experiment like a machine gun would. Again, that was just an analogy. Doing so would defeat the whole purpose of the experiment. Instead the size of the slits and their spacing is designed to show that photons interfere and create an interference pattern at the detector.

See this page: http://en.wikipedia.org/wiki/Double_slit_experiment
There are plenty of references in the article that should explain most of what you are asking about the setup of the experiments.
 
  • #48
If the light is only allowed to pass through one slit then all you will get is the broad diffraction for a single slit.

The whole point of QM is to tell us that, once you have detected the presence of a photon or electron in one slit, it can no longer contribute to any diffraction pattern beyond.
This is a NEW IDEA which you need to take on board before going a single step further.
 
  • #49
No one seems to want to talk to me, so ill just wade in here..

SophieCentaur, do you know what would happen if you had two slits that were being monitored, but then you had another set of unmonitored slits behind the first set (a double double slit set up) that were for instance 1.61803399 times further from the emitter than the first set?
 
  • #50
VCortex said:
No one seems to want to talk to me, so ill just wade in here..

SophieCentaur, do you know what would happen if you had two slits that were being monitored, but then you had another set of unmonitored slits behind the first set (a double double slit set up) that were for instance 1.61803399 times further from the emitter than the first set?

You don't seem to understand that the act of monitoring will destroy any photon it detects. That photon can no longer be a part of your experiment. It's not like cars going past on the road. Until you 'monitor ' any photon, its energy is part of the wave and could be anywhere. Sheer chance allowed you to find it where you found it - same as sheer chance made it part of the fringe pattern if you didn't find it earlier.
You have to start thinking differently. It's QM.
 
  • #51
good mornings
hi sophiecentaur
i have another question.
does the spyin eye spy the slit from top to bottom?
if so
what would happen if the spying eye only measured from the middle down wards or middle to top or from a third from the bottom to a third from the top?
if taken it that they have used the "spy" on a single slit experiment also yes?
and if so did the back screen give the same pattern as the one without the "spy"
 
  • #52
But if you can't detect a photon without destroying it, surely then particle-wave duality is moot? How do you even get any change in the interference pattern from observation?
Wouldn't you get an interference pattern build up from the unmonitored photons through the slits, and a blank from the monitored slits, as sure as if the intervening obstruction had no slits at all? Your reply (without a statistical qualifier on detection rate for the monitored slits) seems contrary to every demonstration & explanation of the test that I have seen (& the law of energy conservation?!), unless I'm completely misunderstanding something obvious (hence the questions :)
 
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  • #53
I've been trying to get answers from Yahoo! Answers, but I haven't really been getting them. Can the double slit experiment be done with bigger objects, say grains of sand, or more? Would there be any difference in the results? I'm already aware that C60 was used, but I don't know if the results were identical to that of a photon or electron, or if there was any differentiation.
 
  • #54
lostprophets said:
good mornings
hi sophiecentaur
i have another question.
does the spyin eye spy the slit from top to bottom?
if so
what would happen if the spying eye only measured from the middle down wards or middle to top or from a third from the bottom to a third from the top?
if taken it that they have used the "spy" on a single slit experiment also yes?
and if so did the back screen give the same pattern as the one without the "spy"
You would have two different experiments - one for the top half and one for the bottom half. The unmonitored half would give a good pattern with a big contrast between light and dark fringes. The half with monitoring would show weak or no fringes
 
  • #55
VCortex said:
But if you can't detect a photon without destroying it, surely then particle-wave duality is moot? How do you even get any change in the interference pattern from observation?
Wouldn't you get an interference pattern build up from the unmonitored photons through the slits, and a blank from the monitored slits, as sure as if the intervening obstruction had no slits at all? Your reply (without a statistical qualifier on detection rate for the monitored slits) seems contrary to every demonstration & explanation of the test that I have seen (& the law of energy conservation?!), unless I'm completely misunderstanding something obvious (hence the questions :)

All the demonstrations behave as expected from the theory.
 
  • #56
sophiecentaur said:
You would have two different experiments - one for the top half and one for the bottom half. The unmonitored half would give a good pattern with a big contrast between light and dark fringes. The half with monitoring would show weak or no fringes

Ok, so from this can we say that both halves are exhibiting a wave pattern, with the monitored half showing decreased intensity due to interaction with an 'observation field' of the same intensity & 'material' as the measured unit, that has a statistical detection/destruction(/uncertainty?) threshold which precludes the destruction of all photons through the slit? Is that a sensible way to interpret the result?
 
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  • #57
VCortex said:
But if you can't detect a photon without destroying it, surely then particle-wave duality is moot? How do you even get any change in the interference pattern from observation?
Wouldn't you get an interference pattern build up from the unmonitored photons through the slits, and a blank from the monitored slits, as sure as if the intervening obstruction had no slits at all? Your reply (without a statistical qualifier on detection rate for the monitored slits) seems contrary to every demonstration & explanation of the test that I have seen (& the law of energy conservation?!), unless I'm completely misunderstanding something obvious (hence the questions :)

You can place polarizers behind the slits. A polarizer won't destroy the photon, but any photon which passes through it is now polarized in a certain direction. So, in theory, you could later inspect the polarization of the photon to determine which slit it passed through. The fact that this information is available in principle can be enough to destroy the interference pattern.

Meta14 said:
I've been trying to get answers from Yahoo! Answers, but I haven't really been getting them. Can the double slit experiment be done with bigger objects, say grains of sand, or more? Would there be any difference in the results? I'm already aware that C60 was used, but I don't know if the results were identical to that of a photon or electron, or if there was any differentiation.

I believe the Zeilinger group have demonstrated diffraction by adding 48 fluorine atoms to a C60 molecule, I can't find a reference for this though. As for a grain of sand - I doubt it. The problem is that, the more massive an object gets, the larger it's momentum is and therefore smaller the wavelength - meaning less chance of seeing any wave effects.

Some drivers (usually drunk) have apparently attempted to diffract their cars around lamp posts, but none have been successful ... :biggrin:
 
  • #58
Joncon said:
Some drivers (usually drunk) have apparently attempted to diffract their cars around lamp posts, but none have been successful ... :biggrin:
this is true.but the difference there is the car is hitting the tree and not either side of the tree.
if it were to go by the side of the tree it wouldn't hit the tree .
but
everything traveling with it would hit the tree and go around the other/both sides of the tree.
so if it was emitting a wave the wave would go with the car ,hit the tree and go around the other side of the tree opposite to the side the car went.
so if the car was a photon the same thing would happen yes?
 
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  • #59
VCortex said:
Ok, so from this can we say that both halves are exhibiting a wave pattern, with the monitored half showing decreased intensity due to interaction with an 'observation field' of the same intensity & 'material' as the measured unit, that has a statistical detection/destruction(/uncertainty?) threshold which precludes the destruction of all photons through the slit? Is that a sensible way to interpret the result?
that sums it up, I think. The pattern for the monitored path would be built up with 'resolved' photons from the other slit (no interference) which dilutes the interference pattern due to unresolved photons from both slits.
 
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  • #60
Joncon said:
I believe the Zeilinger group have demonstrated diffraction by adding 48 fluorine atoms to a C60 molecule,

I'm not too proficient in technical terms, but by diffraction, are you referring to the interference pattern?
 
  • #61
'Diffraction' covers all these phenomena, aamof
 
  • #62
lostprophets said:
so if it was emitting a wave the wave would go with the car ,hit the tree and go around the other side of the tree opposite to the side the car went.
so if the car was a photon the same thing would happen yes?

No, the photon would either hit the tree and be absorbed, or it would diffract around it and go off in a random direction that we can calculate the probabilities for. Honestly, thinking about the experiment as one photon doing something is going to be confusing. Instead, think of it as a wave propagates through the slits, interferes with itself as it passes through, and impacts the screen behind the slits. Because energy is only transferred in quanta, aka photons, you will only measure the energy of the wave in specific locations. The probability of detecting this wave at a specific point is random, but follows a pattern determined by the properties of the wave. Where the two waves constructively interfere you will see more detections over time, and where they destructively interfere you will see fewer or no detections over time.
 
  • #63
Drakkith said:
No, the photon would either hit the tree and be absorbed, or it would diffract around it and go off in a random direction that we can calculate the probabilities for. Honestly, thinking about the experiment as one photon doing something is going to be confusing. Instead, think of it as a wave propagates through the slits, interferes with itself as it passes through, and impacts the screen behind the slits. Because energy is only transferred in quanta, aka photons, you will only measure the energy of the wave in specific locations. The probability of detecting this wave at a specific point is random, but follows a pattern determined by the properties of the wave. Where the two waves constructively interfere you will see more detections over time, and where they destructively interfere you will see fewer or no detections over time.
i do here you.
i kind of imagine the photon , much like a sun and all its light/energy coming of it in every direction.this light/energy i see as the wave and the sun/photon as the particle...so to me the sun/photon is a wave and a particle at the same time.
what i then do is to imagine doing the two slit experiment with the sun.
i imagine it all to scale including the spying eye and i ask myself, would the eye be able to to some how hold the light/energy coming of the sun back from going through the slit,but the sun itself was able to penetrate this and go through.
now obviously the sun and a photon are different.but my point is the photon must be emitting something off itself and this something is being blocked by the eyes energy coming from it.like an aura..
i have a wild imagination
 
  • #64
lostprophets said:
now obviously the sun and a photon are different.but my point is the photon must be emitting something off itself and this something is being blocked by the eyes energy coming from it.like an aura..
i have a wild imagination

I assure you, photons do not emit anything. Our eyes, as well as all other light sensors, work by detecting photons, which requires that they be absorbed and disappear. So if the photon is absorbed it is gone. Forever. Thus you cannot interact with a photon and measure it, AND have it continue on in your experiment. Furthermore, we cannot use light to "see" other light. IE light does not bounce off of other light back to us. So we have to place something physically in the way of the light to detect it, such as a CCD or CMOS sensor.
 
  • #65
lostprophets said:
i do here you.
i kind of imagine the photon , much like a sun and all its light/energy coming of it in every direction.this light/energy i see as the wave and the sun/photon as the particle...so to me the sun/photon is a wave and a particle at the same time.
what i then do is to imagine doing the two slit experiment with the sun.
i imagine it all to scale including the spying eye and i ask myself, would the eye be able to to some how hold the light/energy coming of the sun back from going through the slit,but the sun itself was able to penetrate this and go through.
now obviously the sun and a photon are different.but my point is the photon must be emitting something off itself and this something is being blocked by the eyes energy coming from it.like an aura..
i have a wild imagination
Your "wild imagination" may need a bit of taming if you really want to have a better understanding about this 'duality' thing. Your mental picture of a photon is just not viable, I'm afraid.
'Imagination' is certainly needed if you want to avoid being tied to a purely classical model (which means you will never 'get' QM) but the imagination still needs to take into account the evidence.
 
  • #66
sophiecentaur said:
that sums it up, I think. The pattern for the monitored path would be built up with 'resolved' photons from the other slit (no interference) which dilutes the interference pattern due to unresolved photons from both slits.

I'm not sure I understand this interpretation, as it relates to the situation we were discussing (with the two slits simultaneously being partially monitored at the top of each).
It seems like you're trying to say that the monitored halves are interacting with the unmonitored halves somehow? Maybe your wording just seems vague to me.

lostprophets said:
i do here you.
i kind of imagine the photon , much like a sun and all its light/energy coming of it in every direction.this light/energy i see as the wave and the sun/photon as the particle...so to me the sun/photon is a wave and a particle at the same time.
what i then do is to imagine doing the two slit experiment with the sun.
i imagine it all to scale including the spying eye and i ask myself, would the eye be able to to some how hold the light/energy coming of the sun back from going through the slit,but the sun itself was able to penetrate this and go through.
now obviously the sun and a photon are different.but my point is the photon must be emitting something off itself and this something is being blocked by the eyes energy coming from it.like an aura..
i have a wild imagination

I was trying to think about it like that as well, with little suns gong through the slits, but since on that scale the energy measurements are unquantifiable (if they even exist.. Which I think is possible but not practically measurable right now) it seems like that metaphor is a bit stretched.

Would it be more beneficial to think about the situation like a whistle, where the quantized photon is the whistle ball, the slits are the whistle body & blowing it can represent the photon emitter/uncertainty of photon path (& maybe hypothetical further quantized energy states) through a medium?

So, we blow the whistle, and the ball vibrates within the body. The pitch of the sound we get represents the interference pattern we get (which is a combination of degrees of freedom available to the ball inside the body, and energy imparted to the ball by blowing, and as it represents light we will blow the whistle at a constant pressure :).

Now to describe the quantized photon we must either split the whistle open mid-blow and see where the ball flies, and this would subsequently destroy the interference pattern (or 'pitch' of the whistle) & the photon ball would be scattered randomly wherever its' last bounce within the body sent it;
Or, we could try being less intrusive and try to find out where the photon is without losing it. So we try blowing back into the whistle's exhaust hole and peeping through at the same time, hoping that the ball still has enough energy to sound the whistle (this would be like an 'observation field' parallel to the slits that has a percentage chance of intercepting a photon).
Now, although we can still hear the whistle, the degrees of freedom for the ball are significantly reduced. The higher energy states of freedom that were available before are taken up by our blow-back, and so the ball is more likely to vibrate at the bottom of the whistle body, so although we can hear the whistle and the pitch is the same, the volume is much lower (and so in the real experiment, there is little to no wavelike interference).

Sound ok, anyone?
 
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  • #67
VCortex said:
I'm not sure I understand this interpretation, as it relates to the situation we were discussing (with the two slits simultaneously being partially monitored at the top of each).
It seems like you're trying to say that the monitored halves are interacting with the unmonitored halves somehow? Maybe your wording just seems vague to me.

You aren't interacting with the slits, but with the photons. I think what he means is that if a photon would have gone through the top of a slit and interfere with itself, but you are monitoring the top half of one slit, it can no longer interfere with itself if it goes through the top of the unmonitored slit, and passed through as if there was only one slit. If it went through the bottom then it can still interfere and will produce an interference pattern.



I was trying to think about it like that as well, with little suns gong through the slits, but since on that scale the energy measurements are unquantifiable (if they even exist.. Which I think is possible but not practically measurable right now) it seems like that metaphor is a bit stretched.

I don't know what you mean here. What energy are you measuring? We have detectors capable of detecing single photons, electrons, etc.

Would it be more beneficial to think about the situation like a whistle, where the quantized photon is the whistle ball, the slits are the whistle body & blowing it can represent the photon emitter/uncertainty of photon path (& maybe hypothetical further quantized energy states) through a medium?

No. There is no way to classically think about this. The photon or electron or whatever you are shooting through the slits travels like a wave and is detected like a particle. Because it travels like a wave it can interfere with itself (like any wave does). If you image it as a little "ball" or "sun" or anything like that it will NOT make sense and you will not understand it.

But if you can't detect a photon without destroying it, surely then particle-wave duality is moot? How do you even get any change in the interference pattern from observation?
Wouldn't you get an interference pattern build up from the unmonitored photons through the slits, and a blank from the monitored slits, as sure as if the intervening obstruction had no slits at all? Your reply (without a statistical qualifier on detection rate for the monitored slits) seems contrary to every demonstration & explanation of the test that I have seen (& the law of energy conservation?!), unless I'm completely misunderstanding something obvious (hence the questions :)

A few things here. If we use electrons instead of photons we CAN bounce light off of them to see where they are at. If we set up our experiment so that we see which slit the electron went through it will NOT produce an interference pattern even though the electrons get through the slits just fine and aren't destroyed. This also works with excited atoms. We can excite them and have them emit light before or after the slits so that we can see which one they went through. Again we find that if we know which slit they pass through then they do not produce an interference pattern. The same atoms, not excited, DO produce an interference pattern.
 
  • #68
VCortex said:
I'm not sure I understand this interpretation, as it relates to the situation we were discussing (with the two slits simultaneously being partially monitored at the top of each).
It seems like you're trying to say that the monitored halves are interacting with the unmonitored halves somehow? Maybe your wording just seems vague to me.

It seems to me that you are still determined to link all this back to Classical thinking. Doomed to failure, I'm afraid - which is why QM had to be introduced in the first place.
If you are "monitoring" a photon's presence then it no longer can take part in the interference. By eliminating some of the photons that go through the monitored slit, you are, in effect, reducing the number that get through and the classical wave treatment would then say that you will not get total cancellation in the nulls because the amplitudes are not the same. The QM argument would be that you have altered the statistics of the probability of where a photon happens to arrive - again producing an 'impure' interference pattern'.

As for the rest of what you write - it is just not a valid set of ideas. For instance, what is a "quantised photon" supposed to be. A photon IS a quantum of energy. All that stuff about whistles and balls is -well - idle ravings (with respect, of course). Spend some time reading what 'people who know' have to say about the topic (I do not refer to my own input, btw) and you have a chance of coming to a useful understanding. Home produced pictures are pretty much guarantee to let you down.

The idea of monitoring the presence of electrons is an interesting one - because it can be done. However, in order to monitor it, you have to disturb its path in some way. It will change its energy in some undetermined way. So its wavelength will no longer be exactly the same as its 'alternative self' and it can no longer 'interfere with itself on the way through the two slits at the same time' and its 'wave' collapses into that of a single, uniquely identified, electron going past where it was detected. I defy anyone NOT to have a bit of a problem with that but QM is like that at every twist and turn.
 
  • #69
Drakkith said:
1:You aren't interacting with the slits, but with the photons. I think what he means is that if a photon would have gone through the top of a slit and interfere with itself, but you are monitoring the top half of one slit, it can no longer interfere with itself if it goes through the top of the unmonitored slit, and passed through as if there was only one slit. If it went through the bottom then it can still interfere and will produce an interference pattern. 2:I don't know what you mean here. What energy are you measuring? We have detectors capable of detecing single photons, electrons, etc.
3:No. There is no way to classically think about this. The photon or electron or whatever you are shooting through the slits travels like a wave and is detected like a particle. Because it travels like a wave it can interfere with itself (like any wave does). If you image it as a little "ball" or "sun" or anything like that it will NOT make sense and you will not understand it.
4:A few things here. If we use electrons instead of photons we CAN bounce light off of them to see where they are at. If we set up our experiment so that we see which slit the electron went through it will NOT produce an interference pattern even though the electrons get through the slits just fine and aren't destroyed. This also works with excited atoms. We can excite them and have them emit light before or after the slits so that we can see which one they went through. Again we find that if we know which slit they pass through then they do not produce an interference pattern. The same atoms, not excited, DO produce an interference pattern.

1: This wording seems like a more coherent description although it again supposes a different set of apparatus to the one we were previously discussing. I would question whether a photon would rather 'choose' to go through the top of unmonitored slit 2 rather than monitored slit 1, as your interpretation seems to imply.

2: I'm just trying to get a handle on the implications of the experiment without a strictly defined energy unit, so as it stands I suppose anything from photons to C60 & anything inbetween.

3: My analogy took into account both particle & wave features (particle = whistle ball, wave = whistle pitch). I fail to see how trying to think logically is incompatible with a mathematical description like a wavefunction.
I also have no idea how to define a clear mental divide between whatever 'classical' & 'non-classical, contemporary(?)' modes of thinking are supposed to be, let alone accuse someone of thinking either way.

4: This is interesting. How many times can you 'sample' a collapsed path electron's (or other relevant wave/particle thing) position?

sophiecentaur said:
5:It seems to me that you are still determined to link all this back to Classical thinking. Doomed to failure, I'm afraid - which is why QM had to be introduced in the first place.
If you are "monitoring" a photon's presence then it no longer can take part in the interference. By eliminating some of the photons that go through the monitored slit, you are, in effect, reducing the number that get through and the classical wave treatment would then say that you will not get total cancellation in the nulls because the amplitudes are not the same. The QM argument would be that you have altered the statistics of the probability of where a photon happens to arrive - again producing an 'impure' interference pattern'.

6:As for the rest of what you write - it is just not a valid set of ideas. For instance, what is a "quantised photon" supposed to be. A photon IS a quantum of energy. All that stuff about whistles and balls is -well - idle ravings (with respect, of course). Spend some time reading what 'people who know' have to say about the topic (I do not refer to my own input, btw) and you have a chance of coming to a useful understanding. Home produced pictures are pretty much guarantee to let you down.

7:The idea of monitoring the presence of electrons is an interesting one - because it can be done. However, in order to monitor it, you have to disturb its path in some way. It will change its energy in some undetermined way. So its wavelength will no longer be exactly the same as its 'alternative self' and it can no longer 'interfere with itself on the way through the two slits at the same time' and its 'wave' collapses into that of a single, uniquely identified, electron going past where it was detected. I defy anyone NOT to have a bit of a problem with that but QM is like that at every twist and turn.

5: See 3. I have not been considering 'purity' of a 'classical' or 'QM' wave &/ particle so far due to the small scales & quantities I had envisaged to be involved! From this statement can I infer that impurity of a 'classical' wave null is taken into account by the QM wavefunction equations!? What is the level of observable 'impurity'?

6: "For instance, what is a "quantised photon" supposed to be. A photon IS a quantum of energy" therefore, a quantised photon = 1 quantum. You are arguing semantics, and ignoring a question.
"Spend some time reading what 'people who know' have to say about the topic (I do not refer to my own input, btw)" Thanks for the insightful suggestion, & I shall henceforth disregard your input :)

7: My analogy did attempt to address this, yet still managed to be met with condescension & ad-hominem remarks. I think you're great.
 
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  • #70
Sorry for the bit of 'ad hominem' but the whistle and ball thing is really pretty preposterous and I don't see how the analogy can seriously relate to QM. If you knew some QM, you would see that. Rather than taking offence, you should do some serious reading. Whilst there are many unsolved questions, you might at least acknowledge that the questions that you pose and have tried answering for yourself have actually been answered and the answers have been subjected to close scrutiny by people much cleverer than me or you. You seem to be missing on some vital aspects of QM.
Your idea of just taking a look at a photon (/particle) without destroying its wave function goes entirely against the whole QM idea. You detect a photon or you don't detect it. If you detect it, you destroy it and if you don't detect it then it is unchanged and ready to be detected somewhere else - possibly the other side of the slits on a screen. Hence, if you detect some of the photons then you are effectively blocking part of one slit. The resulting pattern will be a good interference pattern (narrow bands) plus the (wide) pattern due to the contribution from one slit. This always happens because no two slits are identical and the pattern never has perfect nulls in it.

I should forget about trying to talk of a 'general particle' first and get down to discussing photons. That is difficult enough. The reason why observing a photon upsets the pattern is much easier to discuss than the effect of merely 'perturbing' a massive particle.

Don't knock Semantics, either. A word that is used out of context or with the wrong meaning can be as bad as if you change your symbols on the way through an algebraic argument without telling people. If you had read and understood the accepted QM stuff then you would be using the right terms because you would see that they are important in any argument.
 
<h2>1. What is the double-slit experiment?</h2><p>The double-slit experiment is a classic experiment in physics that demonstrates the wave-particle duality of light. It involves shining a beam of light through two parallel slits and observing the interference pattern that is created on a screen behind the slits.</p><h2>2. Why is the double-slit experiment important?</h2><p>The double-slit experiment is important because it provides evidence for the wave-particle duality of light, which is a fundamental concept in quantum mechanics. It also allows scientists to study the behavior of particles on a quantum level and has led to many important discoveries in the field of physics.</p><h2>3. What is the significance of the interference pattern in the double-slit experiment?</h2><p>The interference pattern in the double-slit experiment is significant because it demonstrates the wave-like behavior of particles. This pattern is created when the waves of light passing through the two slits interfere with each other, resulting in bright and dark bands on the screen. This shows that particles can exhibit wave-like properties, which was a revolutionary discovery in the field of physics.</p><h2>4. Can the double-slit experiment be done with other particles besides light?</h2><p>Yes, the double-slit experiment can be done with other particles such as electrons, protons, and even large molecules. This has been demonstrated through various experiments and has further solidified the concept of wave-particle duality in the field of quantum mechanics.</p><h2>5. How does the double-slit experiment relate to the uncertainty principle?</h2><p>The double-slit experiment is closely related to the uncertainty principle, which states that it is impossible to know both the position and momentum of a particle with absolute certainty. In the double-slit experiment, the interference pattern is affected by the act of observing the particles, which demonstrates the uncertainty in their position. This principle is a fundamental concept in quantum mechanics and has been further explored through experiments like the double-slit experiment.</p>

1. What is the double-slit experiment?

The double-slit experiment is a classic experiment in physics that demonstrates the wave-particle duality of light. It involves shining a beam of light through two parallel slits and observing the interference pattern that is created on a screen behind the slits.

2. Why is the double-slit experiment important?

The double-slit experiment is important because it provides evidence for the wave-particle duality of light, which is a fundamental concept in quantum mechanics. It also allows scientists to study the behavior of particles on a quantum level and has led to many important discoveries in the field of physics.

3. What is the significance of the interference pattern in the double-slit experiment?

The interference pattern in the double-slit experiment is significant because it demonstrates the wave-like behavior of particles. This pattern is created when the waves of light passing through the two slits interfere with each other, resulting in bright and dark bands on the screen. This shows that particles can exhibit wave-like properties, which was a revolutionary discovery in the field of physics.

4. Can the double-slit experiment be done with other particles besides light?

Yes, the double-slit experiment can be done with other particles such as electrons, protons, and even large molecules. This has been demonstrated through various experiments and has further solidified the concept of wave-particle duality in the field of quantum mechanics.

5. How does the double-slit experiment relate to the uncertainty principle?

The double-slit experiment is closely related to the uncertainty principle, which states that it is impossible to know both the position and momentum of a particle with absolute certainty. In the double-slit experiment, the interference pattern is affected by the act of observing the particles, which demonstrates the uncertainty in their position. This principle is a fundamental concept in quantum mechanics and has been further explored through experiments like the double-slit experiment.

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