A light Interference doubt

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  • #26
sophiecentaur
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How about little bullets that wave a little bit, snake-like, and can split in two and interfere with itself? Kind of like some of these electrons here:



As far as I know, we can make very narrow beams of light, and it appears the thickness does not variate, so they must have some defined 'cross section' radius, or width and height, which is defined by the peaks of photon amplitude, right? And they also have defined some length since we can emit individual photons with a gap between them, right? So something that has certain cross section radius kind of does look like a bullet, or an arrow, depending on how long they are. Do you know how long photons are?
You cannot make a beam of light that never spreads out, I'm afraid. Lasers do pretty well but even laser beams have a width which increases by a predictable amount once they've gone far enough. Moreover, a laser only works because there are many photons - to define a direction of emission. Just one photon has equal probability of 'going in any direction' from an atom (Being detected anywhere around the atom, is a more correct way of saying it because, until it's detected, it could be anywhere).

1. How much did you want them to wave - anything related to the wavelength, perhaps? (careful with your reply to this as it would be difficult to generate a beam of 1MHz Radio waves, only 1mm width).

2. What do you mean by "peak of photon amplitude"? All photons of one frequency have the same energy. If they split, then one photon would have to be sub divided - not just into two (for two slits) but into thousands for a diffraction grating.

3. Do your answers to 1 and 2 extend to photons of LF radio signals with a wavelength of over a km and individual energies which are 10^-10 of the energy of a photon of light? If they don't then you have to think again.

4. Would the (split) bullets also be travelling (and wiggling) through the amplifiers and feeders, too, in a multi-element transmitting antenna?

I realise that, from the perspective of experiments with light, 'little bullets' fit , emotionally and comfortingly, with what we see - or think we see. But the same model absolutely has to fit all cases of EM waves if it can be considered as a candidate for 'the truth'. (And photons are very different from electrons, in many ways)
 
  • #27
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You cannot make a beam of light that never spreads out, I'm afraid. Lasers do pretty well but even laser beams have a width which increases by a predictable amount once they've gone far enough. Moreover, a laser only works because there are many photons - to define a direction of emission. Just one photon has equal probability of 'going in any direction' from an atom (Being detected anywhere around the atom, is a more correct way of saying it because, until it's detected, it could be anywhere).
I think photo-sensors can be made with fine enough resolution and good enough sensitivity. So given we can emit individual photons at specific time intervals we could see how many photons impact the same pixel, what pixels they impact, how many of them they impact, and at what time. Perhaps not for each one of them, but surely we could see they don't fly everywhere.

I'm pretty sure that, if not all of them, then at least large majority of them would end up at exactly that same pixel we aimed for. Wouldn't they? And if so, that would confirm just one photon doesn't really have equal probability to go in any direction. Now, depending on how fine the resolution is I guess we would also be able to see some radius of photons cross-section. Not sure if we would be able to say anything about length though.


1. How much did you want them to wave - anything related to the wavelength, perhaps? (careful with your reply to this as it would be difficult to generate a beam of 1MHz Radio waves, only 1mm width).
Is it even plausible? Could it be interpreted like that, I mean does it change anything about equations? Could it explain optics for example? I guess they would wave just like we draw them, as electromagnetic waves, kind of literally.

180px-Polarisation_%28Linear%29.svg.png
180px-Polarisation_%28Circular%29.svg.png
180px-Polarisation_%28Elliptical%29.svg.png



2. What do you mean by "peak of photon amplitude"? All photons of one frequency have the same energy. If they split, then one photon would have to be sub divided - not just into two (for two slits) but into thousands for a diffraction grating.
If you look at those images above, amplitude peaks would describe a helix with certain radius, defining the cross section, or width and height, of our little photon bullet.


3. Do your answers to 1 and 2 extend to photons of LF radio signals with a wavelength of over a km and individual energies which are 10^-10 of the energy of a photon of light? If they don't then you have to think again.
If they don't then there is nothing to talk about. I don't know, could it work like that?


4. Would the (split) bullets also be travelling (and wiggling) through the amplifiers and feeders, too, in a multi-element transmitting antenna?
They must, but if they don't it means we should not be interpreting things too literally.


I realise that, from the perspective of experiments with light, 'little bullets' fit , emotionally and comfortingly, with what we see - or think we see. But the same model absolutely has to fit all cases of EM waves if it can be considered as a candidate for 'the truth'.
Yes, and they should also pass through double slit. But you know what? There are actually two parts to this bullet, like this:

340px-Light-wave.svg.png

http://en.wikipedia.org/wiki/Photon


So I guess it's really a double helix, of sorts, but sinusoidal wave for sure, as it should be. And then I suppose with double-slit experiment magnetic field splits from electric field, for some uncertain reason at some uncertain point, just to later come back together on the other side with slightly different trajectory. Is this kind of what almost everyone thinks? Both wave and particle, so it's "particle-wave", literally.
 
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  • #28
sophiecentaur
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This is all far too speculative. You are only considering the double slit experiment in your model In fact, EM waves do not ever come from infinitely narrow sources and it is very rare that there are only two at a time. If you don't know about diffraction, in general then you can hardly postulate a model that will predict it.
I suggest that you read more about this rather than making up a set of 'possible' explanations that are not actually possible.
You don't seem to have taken on board the fact that the longer the wavelength (i.e. 'bigger' in your terms) the less energy there is in each photon. The fact is that 'size' is not a meaningful property of the photon and it is a waste of time trying to imbue it with an extent - be it large or small.
 
  • #29
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This is all far too speculative.
Emitting individual photons at specific time interval and detecting them with high-resolution high-sensitivity photo-sensor is not speculation. It was your questions that asked of me to explain what even QM doesn't try to explain, and I wasn't speculating, just being literal.


You are only considering the double slit experiment in your model In fact, EM waves do not ever come from infinitely narrow sources and it is very rare that there are only two at a time. If you don't know about diffraction, in general then you can hardly postulate a model that will predict it.
We started to talk about photon size. Photons can be focused and that's good enough for the experiment to aim them at very narrow and specific area where they are detected on high-resolution sensor. Do you think that kind of experiment tells us nothing about photon size, about its cross-section radius?

You don't seem to have taken on board the fact that the longer the wavelength (i.e. 'bigger' in your terms) the less energy there is in each photon. The fact is that 'size' is not a meaningful property of the photon and it is a waste of time trying to imbue it with an extent - be it large or small.
If we can emit photons, most if which, if not all of them, end up around a single pixel we aim for, does that not us tell us something about photon size?
 
  • #30
Cthugha
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I think photo-sensors can be made with fine enough resolution and good enough sensitivity. So given we can emit individual photons at specific time intervals we could see how many photons impact the same pixel, what pixels they impact, how many of them they impact, and at what time. Perhaps not for each one of them, but surely we could see they don't fly everywhere.
Having high spatial resolution and single photon sensitivity at the same time is a major pain, but in principle possibly, for example by using a spad array or something. Creating single photons is also complicated, but possible. Creating single photons at a specific time interval is VERY complicated and you will get pretty rich if you can do that in a reliable manner in a non-lab surrounding. But at least you can do that with some mediocre fidelity.

I'm pretty sure that, if not all of them, then at least large majority of them would end up at exactly that same pixel we aimed for. Wouldn't they? And if so, that would confirm just one photon doesn't really have equal probability to go in any direction. Now, depending on how fine the resolution is I guess we would also be able to see some radius of photons cross-section. Not sure if we would be able to say anything about length though.
I can assure you that they do not. Diffraction is always there, whether you have an intense beam or single photons. If you integrate over a large number of photons, the total diffraction pattern will be the same for intense beams or single photons under otherwise identical circumstances.

And then I suppose with double-slit experiment magnetic field splits from electric field, for some uncertain reason at some uncertain point, just to later come back together on the other side with slightly different trajectory.
Sorry, but that does not make any sense. Do you have any reference for this?

MarkoniF said:
We started to talk about photon size. Photons can be focused and that's good enough for the experiment to aim them at very narrow and specific area where they are detected on high-resolution sensor. Do you think that kind of experiment tells us nothing about photon size, about its cross-section radius?
No, one should not interpret this as a photon size. The Mandel/Wolf, the bible of quantum optics devotes a whole subchapter to this topic. In a nushell, you run into severe problems trying to use this interpretation for polychromatic lightfields. For example, when you do the math, you will find out that the probability density to detect a photon peaks at a position which does not coincide with the maximum of the energy density. If you wanted to attribute something like a size to photons, the coherence length is a better measure than the diameter it can be focused on. Still, the coherence length should not be interpreted as a photon size. You still run into problems doing that.

Photons are typically treated as point particles which renders the concept of photon size obsolete. The underlying fields have some characteristic length scales like the mentioned coherence length.
 
  • #31
Khashishi
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How do you aim for a specific pixel? If the pixel is smaller than a wavelength, forgetaboutit. If it's larger than a pixel, you might be able to aim for it by using an aperture, but you lose a lot of photons hitting the aperture.
 
  • #32
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How do you aim for a specific pixel? If the pixel is smaller than a wavelength, forgetaboutit.
I don't know, depends on how fine resolution photo-sensor can be made. Do you know?


If it's larger than a pixel, you might be able to aim for it by using an aperture, but you lose a lot of photons hitting the aperture.
Losing photons due to aperture size is what we want, I think. This helps us to aim, as well as produce individual photons with some gap or time interval between them.
 
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  • #33
Cthugha
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Losing photons due to aperture size is what we want, I think. This helps us to aim, as well as produce individual photons with some gap or time interval between them.
To get single photons, you want to reduce the variance of your photon number distribution. That means you want to reduce the noise. Using an aperture reduces the amplitude or the mean of the photon number distribution, but the relative variance will stay the same and not be reduced. One cannot create single photons simply by reducing intensity.
 
  • #34
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Having high spatial resolution and single photon sensitivity at the same time is a major pain, but in principle possibly, for example by using a spad array or something. Creating single photons is also complicated, but possible. Creating single photons at a specific time interval is VERY complicated and you will get pretty rich if you can do that in a reliable manner in a non-lab surrounding. But at least you can do that with some mediocre fidelity.
I did read few weeks ago about some type of laser emitting individual photons at the rate of super-high time resolution.


I can assure you that they do not. Diffraction is always there, whether you have an intense beam or single photons. If you integrate over a large number of photons, the total diffraction pattern will be the same for intense beams or single photons under otherwise identical circumstances.
Having individual photons, what is the diffraction? Increase or whatever change in their individual amplitudes? Some probability cloud of possible trajectories as a sum of many of them, or what?


No, one should not interpret this as a photon size. The Mandel/Wolf, the bible of quantum optics devotes a whole subchapter to this topic. In a nushell, you run into severe problems trying to use this interpretation for polychromatic lightfields. For example, when you do the math, you will find out that the probability density to detect a photon peaks at a position which does not coincide with the maximum of the energy density. If you wanted to attribute something like a size to photons, the coherence length is a better measure than the diameter it can be focused on. Still, the coherence length should not be interpreted as a photon size. You still run into problems doing that.

Photons are typically treated as point particles which renders the concept of photon size obsolete. The underlying fields have some characteristic length scales like the mentioned coherence length.
Can we not say with certainty what is the distance between two amplitude peeks of a single photon by knowing its wavelength? Is that distance not real, and would it not describe "thickness" of individual photons?
 
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  • #35
Cthugha
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I did read few weeks ago about some type of laser emitting individual photons at the rate of super-high time resolution.
I read something somewhere is not really a good reference. Do you by chance have a link to the real reference? That makes it much easier to check whether that was just "second-hand" pseudoscientific journalism for the masses or a crude simplification of much more complex matter. Lasers typically emit coherent light which is about as far away from single photon emission as you can get.

Having individual photons, what is diffraction? Increase in their individual amplitude? Or some probability cloud of possible trajectories as a sum of many of them?
You do not have trajectories in standard quantum optics. You have probability amplitudes for certain events - typically detections. So if you repeatedly prepare single photon states with well defined momentum (which is already complicated) and a small "beam" diameter, you will find that the probability amplitudes for detection events away from the center of the beam and at larger distances from the initial beam diameter will increase with the distance traveled by the single photons.


Can we not say with certainty what is the distance between two amplitude peeks of a single photon by knowing its wavelength? Is that distance not real, and would it not describe "thickness" of individual photons?
If you are in the lucky situation of having a monochromatic single photon (which would be infinitely long in time by the way), you have at least a certain wavelength. However, typical photons are polychromatic. In any way the probability amplitude for detection events is typically nonzero over some area which is not at all related to the wavelength. Depending on the coherence properties of the emitter, the area in which detections are possible can range from micrometers to meters, maybe even kilometers. The wavelength is real, but can by no means be interpreted as a size or even thickness. You can have different light fields with the same wavelength, but very different detection probability distributions.
 
  • #36
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I read something somewhere is not really a good reference. Do you by chance have a link to the real reference? That makes it much easier to check whether that was just "second-hand" pseudoscientific journalism for the masses or a crude simplification of much more complex matter. Lasers typically emit coherent light which is about as far away from single photon emission as you can get.
I meant it is precise like laser, in a sense they could aim or focus those photons to narrow area on the sensor. I couldn't find that link. Found a lot of stuff about quantum dot LEDs. And also this interesting link, about sensor though, rather than photon emitter:

http://phys.org/news173957578.html
- "camera capable of filming individual photons one million times a second... a pixel that is 50 microns-by-50 microns, with a lot of functionality in it... high-precision lenses work amazingly well to lead the photons onto the photosensitive areas that are just 10 microns in size."


You do not have trajectories in standard quantum optics.
If we can detect individual photons then we know exactly what trajectory each photon went through. Light travels in straight lines, doesn't it?


You have probability amplitudes for certain events - typically detections. So if you repeatedly prepare single photon states with well defined momentum (which is already complicated) and a small "beam" diameter, you will find that the probability amplitudes for detection events away from the center of the beam and at larger distances from the initial beam diameter will increase with the distance traveled by the single photons.
I guess it depends on how well can we focus.


If you are in the lucky situation of having a monochromatic single photon (which would be infinitely long in time by the way), you have at least a certain wavelength. However, typical photons are polychromatic. In any way the probability amplitude for detection events is typically nonzero over some area which is not at all related to the wavelength. Depending on the coherence properties of the emitter, the area in which detections are possible can range from micrometers to meters, maybe even kilometers. The wavelength is real, but can by no means be interpreted as a size or even thickness. You can have different light fields with the same wavelength, but very different detection probability distributions.
Not wavelength, amplitude. Do individual photons have amplitude? Does that amplitude represent some actual distance?
 
  • #37
Cthugha
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I meant it is precise like laser, in a sense they could aim or focus those photons to narrow area on the sensor.
With the right filtering you can focus any light to a narrow area. laser light is not that special in that respect.

I couldn't find that link. Found a lot of stuff about quantum dot LEDs.
Yes, you can get single photon sources by placing single quantum dots in microcavities. They are not really efficient, especially at room temperature, but you get single photons out.

And also this interesting link, about sensor though, rather than photon emitter:

http://phys.org/news173957578.html
- "camera capable of filming individual photons one million times a second... a pixel that is 50 microns-by-50 microns, with a lot of functionality in it... high-precision lenses work amazingly well to lead the photons onto the photosensitive areas that are just 10 microns in size."
Yes, this is a SPAD array. So what about it? 10 microns is still rather large, by the way.

If we can detect individual photons then we know exactly what trajectory each photon went through. Light travels in straight lines, doesn't it?
In fact, you cannot say anything about what happens between emission and detection. For the double slit experiment to work with single photons, it must be uncertain which slit a certain photon has taken. So if one could say light travels strictly in straight lines, there would be no interference in double slit experiments. Yet, there is interference.


I guess it depends on how well can we focus.
We were talking about diffraction. What does focusing have to do with that?


Not wavelength, amplitude. Do individual photons have amplitude? Does that amplitude represent some actual distance?
I do not get your question. Even for a classical em field the amplitude is given in newton per coulomb or equivalently volts per meter. This is not a mechanical displacement amplitude related to distance via Hooke's law or something like that. You can associate single photons with probability amplitudes and you can often also find a description in terms of underlying fields.
 
  • #38
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Yes, this is a SPAD array. So what about it? 10 microns is still rather large, by the way.
I guess whether that's large or small would depend on photons amplitude. In any case the question is if we made pixels small enough whether a single photon could ever impact more than one pixel at once?


In fact, you cannot say anything about what happens between emission and detection. For the double slit experiment to work with single photons, it must be uncertain which slit a certain photon has taken. So if one could say light travels strictly in straight lines, there would be no interference in double slit experiments. Yet, there is interference.
And if we don't have any slits, wouldn't the path of each photon be along the shortest distance from the aperture opening to the pixel where it was detected? Maybe the path wouldn't be a straight line, maybe it would be a helical or sinusoidal line, but on average it surely wouldn't deviate too far from the shortest distance line.


We were talking about diffraction. What does focusing have to do with that?
I'm not sure, shouldn't focusing be opposing diffraction?


I do not get your question. Even for a classical em field the amplitude is given in newton per coulomb or equivalently volts per meter. This is not a mechanical displacement amplitude related to distance via Hooke's law or something like that. You can associate single photons with probability amplitudes and you can often also find a description in terms of underlying fields.
I expected photon amplitude would be actual, or what you call "mechanical", displacement, or at least correspond to some actual distance in terms of whatever measurable effects, like the wavelength does.
 
  • #39
sophiecentaur
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You guys are are talking in circles when you are considering the 'size' of a photon because it is a non-concept. If any statement that you make doesn't apply to Long Wave EM then it is not valid. It's the acid test and should bring you down to the ground from flights of fancy.
What has pixel size specifically got to do with things? A detector of any size in wavelengths can detect an em wave - some are just easier to implement than others.
You are trying to be far too concrete in your description of a photon. The best I have read here is to associate the extent of a photon with coherence length but isn't even that just trying to force the idea to fit when it doesn't need to? If you come across a photon, from a random direction in space and you don't know what generated it, how can you assign it a 'coherence length'? If it was produced in a distant laser, will it have a different probability density function when going through two slits from a photon that was generated by a local atom having been randomly ionised? I though that photons were supposed to have just the one parameter - their energy. Is there a whole classification system for photons?
 
  • #40
sophiecentaur
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Photons are a bit like 'holes' in semiconductors. You can treat them both as particles in the context of specific problems because that's how they happen to present themselves at the time. They exhibit momentum, for instance and they can be said to move around. But no one would seriously think that they could take a hole out of a piece of semiconductor and keep it in a box. its nature would change as soon as you grabbed it - it would become a simple +ion. Likewise, a photon only has relevance as a particle in certain contexts and its particular nature is not the same as that of a proton, for instance - which stays like a particle in more situations.
People wouldn't disagree with that view that holes are only a way of looking at how electrons move about in a semiconductor (largely, I think, because they do not feel that 'familiar' with them) but there is something about the (over?)confidence that people have with their personal ideas about light that they can't let go of the idea that a simple valid model for a photon actually exists.
All the Greats in QM acknowledge that it just isn't that simple and that if you think you understand it you don't. So why not just accept that any home brewed picture one might come up with is very very likely not be sufficient?
 
  • #41
sophiecentaur
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I guess whether that's large or small would depend on photons amplitude.

. . . . .


I expected photon amplitude would be actual, or what you call "mechanical", displacement, or at least correspond to some actual distance in terms of whatever measurable effects, like the wavelength does.
If a photon is to be as defined in QM and has energy that is dependent upon the frequency of EM it's associated then please tell me what you mean by "photon amplitude". Can you quote me anywhere reputable that you have read this expression?
 
  • #42
Cthugha
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You guys are are talking in circles when you are considering the 'size' of a photon because it is a non-concept.
Well, I said like five times now that there is no meaningful concept of photon size and at least once that they are treated as point particles...

MarkoniF said:
And if we don't have any slits, wouldn't the path of each photon be along the shortest distance from the aperture opening to the pixel where it was detected? Maybe the path wouldn't be a straight line, maybe it would be a helical or sinusoidal line, but on average it surely wouldn't deviate too far from the shortest distance line.
As stated before, you cannot say anything about what happens between emission and detection for a single photon. You can define something like an average trajectory for an ensemble of identically prepared states (Science 332, pp. 1170-1173 (2011)), but that does not have any implication for single photons. You are having a way too classical concept of what photons are. Thinking about them as tiny balls flying through space is about as far away from a sensible description as you can get.

MarkoniF said:
I'm not sure, shouldn't focusing be opposing diffraction?
Not really. Of course you can focus light somewhere, but behind the focus point, it will of course spread again. Even if you place a series of lenses, repeatedly focusing your light beam, it will broaden with distance.
 
  • #43
sophiecentaur
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Well, I said like five times now that there is no meaningful concept of photon size and at least once that they are treated as point particles...
Yes, I realise you know that but the 'conversation' keeps throwing it up as a concept - along with some actual Pictures!.
But do you have an answer for my point about coherence length and the identical nature of photons? There's something still needs clearing up there, I think.

@MarkoniF
You are hanging on to this classical model and it will get you nowhere. This is all very Zen when you get down to it and you must chuck out many preconceptions, Grashopper.
 
  • #44
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If a photon is to be as defined in QM and has energy that is dependent upon the frequency of EM it's associated then please tell me what you mean by "photon amplitude". Can you quote me anywhere reputable that you have read this expression?
https://en.wikipedia.org/wiki/Photon

340px-Light-wave.svg.png


There are only three things marked on that diagram, wavelength, amplitude of electric field and amplitude of magnetic filed. Waves naturally have amplitudes just like they have a wavelength. How else would you know what is the wavelength if you don't know how far apart are the peaks of the amplitude?
 
  • #45
sophiecentaur
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https://en.wikipedia.org/wiki/Photon

There are only three things marked on that diagram, wavelength, amplitude of electric field and amplitude of magnetic filed. Waves naturally have amplitudes just like they have a wavelength. How else would you know what is the wavelength if you don't know how far apart are the peaks of the amplitude?
Again, you are confusing the classical wave with the photon. That diagram describes a Wave. Is there any mention of photons on it? You seem to be repeating the same thing to yourself, 'explaining it' to PF in your terms, drawing diagrams from inside your head and not accepting any new input about this. Photons and waves are DIFFERENT aspects of the same thing. If it were as straightforward as you seem to think then why would thousands (even more than that) of really clever Scientists have had a problem with it? Your model doesn't actually take you into QM, it just tinkers with the ancient 'corpuscular' theory and tries to make those little corpuscles a bit wiggly.
Everyone goes through this stage of thinking (I am not being patronising) and, once you start asking the sort of questions that you are asking, the ground is continually shifting. You sit there and 'the answer' comes into your head. Later, you realise that it isn't the answer but you modify and re-think. I compare QM with trying to grab the soap in the bath - you touch it with your fingers so you know it's there but it slips away when you put your hand round it. It is a lot easier to say what a photon isn't rather than what it is, which is why you are getting some negative reactions here. You must open your mind beyond where it is at the moment if you want a chance of progressing.
I'm afraid that I can quite confidently say that you have got it wrong, so far. It won't come to you - you have to go to it. :smile:

BTW, from the whole of that wiki article, why did you pick the one diagram that shows the classical description of a wave when photons are dealt with everywhere else?
 
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  • #46
Cthugha
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Yes, I realise you know that but the 'conversation' keeps throwing it up as a concept - along with some actual Pictures!.
Yes, right. I definitely know what you mean.

But do you have an answer for my point about coherence length and the identical nature of photons? There's something still needs clearing up there, I think.
Well, regarding your post about coherence length of some isolated photon encountered somewhere: Coherence length is a somewhat statistical concept. It is a good concept if you have huge intensity or can repeatedly prepare the same state, but if you have neither, it is rather pointless. Also, all photons within a coherence length are indistinguishable, which makes it quite clear that it should not be considered a size. If you have a lump of 16800000 indistinguishable photons, the coherence length of this bunch is obviously not related to a size concept for a single of these particles.

Regarding your other question: There is not really a classification for photons. There are classifications for different states of the light field (a hierarchy of correlation functions, the density matrix, the Wigner function...). These also allow one to identify whether one has a single photon or not, but obviously these only work for states you can prepare repeatedly.
 
  • #47
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As stated before, you cannot say anything about what happens between emission and detection for a single photon. You can define something like an average trajectory for an ensemble of identically prepared states (Science 332, pp. 1170-1173 (2011)), but that does not have any implication for single photons. You are having a way too classical concept of what photons are. Thinking about them as tiny balls flying through space is about as far away from a sensible description as you can get.
Not tiny balls, it's oscillating electromagnetic fields, where their oscillation is defined by their wavelength and amplitudes. That's what Maxwell said and found out the speed of propagation of such oscillating electromagnetic fields would be the speed of light. Coincidence?

Our unit for distance, whole General and Special Relativity, and much of the rest of the physics depends on this electromagnetic oscillation propagating in straight lines. That's also necessary for the speed of light be constant. Just because we have no practical explanation to what happens at the double slit doesn't mean have to abandon the idea photons propagate along straight lines.



Not really. Of course you can focus light somewhere, but behind the focus point, it will of course spread again. Even if you place a series of lenses, repeatedly focusing your light beam, it will broaden with distance.
Then for our experiment we obviously need to place the detector at focus point distance. But it's not really important if we can detect individual photons, so the critical question to answer is if we could make pixels small enough whether a single photon could ever impact more than one pixel.
 
  • #48
Cthugha
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Not tiny balls, it's oscillating electromagnetic fields, where their oscillation is defined by their wavelength and amplitudes. That's what Maxwell said and found out the speed of propagation of such oscillating electromagnetic fields would be the speed of light. Coincidence?
Yes, so? What is your point? Again, please note that the amplitude is in electric field, not distance.

Our unit for distance, whole General and Special Relativity, and much of the rest of the physics depends on this electromagnetic oscillation propagating in straight lines. That's also necessary for the speed of light be constant. Just because we have no practical explanation to what happens at the double slit doesn't mean have to abandon the idea photons propagate along straight lines.
For all of that it is enough that light propagates along straight lines "on average". I do not like it very much, but Feynman's path integral formalism gives a model where photons do not strictly travel along straight lines and nevertheless you get standard results.



Then for our experiment we obviously need to place the detector at focus point distance. But it's not really important if we can detect individual photons, so the critical question to answer is if we could make pixels small enough whether a single photon could ever impact more than one pixel.
I still do not get what you mean by a single photon impacting on more than one pixel. You will never find a single photon detection event taking place on more than one pixel, but if you repeatedly prepare identical single photons, they will end up on very different pixels.
 
  • #49
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Again, you are confusing the classical wave with the photon. That diagram describes a Wave. Is there any mention of photons on it?
Is single photon not oscillation of electric and magnetic field? Does a singe photon not have wavelength? Can a single photon not be polarized? The title of the article is "photon", it also says: -"Einstein showed that, if Planck's law of black-body radiation is accepted, the energy quanta must also carry momentum p=h/λ, making them full-fledged particles." Full-fledged particles, they say.


You seem to be repeating the same thing to yourself, 'explaining it' to PF in your terms, drawing diagrams from inside your head and not accepting any new input about this. Photons and waves are DIFFERENT aspects of the same thing.
How are photons and waves different aspect of the same thing? What is that "thing"? Let me tell you, there is electric and magnetic fields, they are kind of particles since they have momentum, and they oscillate as they propagate, so there it is the wave too. You get exactly what you said, both particles and waves, two aspects of the same thing.


If it were as straightforward as you seem to think then why would thousands (even more than that) of really clever Scientists have had a problem with it? Your model doesn't actually take you into QM, it just tinkers with the ancient 'corpuscular' theory and tries to make those little corpuscles a bit wiggly.
That's not my model, it's what Maxwell came up with. Combined electric and magnetic field and it turned out they would oscillate while propagating at the speed of light. Then Einstein figured out they have momentum, making them "full-fledged particles", to quote Wikipedia.


BTW, from the whole of that wiki article, why did you pick the one diagram that shows the classical description of a wave when photons are dealt with everywhere else?
How about this:

https://en.wikipedia.org/wiki/Polarization_(waves)

180px-Polarisation_%28Linear%29.svg.png
180px-Polarisation_%28Circular%29.svg.png
180px-Polarisation_%28Elliptical%29.svg.png


...and this:
https://en.wikipedia.org/wiki/Circular_polarization

440px-Circular.Polarization.Circularly.Polarized.Light_With.Components_Left.Handed.svg.png



Does that have nothing to do with reality? Just an abstraction, a cartoon?
 
  • #50
56
0
Yes, so? What is your point?
The point is that electromagnetic wave equation describes actual spatial wave where electric and magnetic fields oscillate, that is move "up-down"/"left-right" through actual spatial distance of their amplitudes as they propagate.

Again, please note that the amplitude is in electric field, not distance.
'
What do you mean amplitude is "in electric field"?
 

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