Where does interference occur in light waves?

In summary, the conversation discusses the concept of interference in light, which occurs when two light waves interact with each other. This can happen when two photons are close together and their electric and magnetic fields interact, creating a pattern of constructive and destructive interference. However, it is important to note that light should be thought of as waves, not photons. The conversation also delves into the question of where exactly the interference occurs, with different theories and explanations being offered. Ultimately, it is understood that the interference occurs in a single point, but it is difficult to pinpoint exactly where due to the complex nature of light waves.
  • #1
jaumzaum
434
33
I'm really confused about the way the light can suffer interference. I'll try to explain the way I think all this occurs and the question I have if this explanation was correct. I would like you guys to correct me if anything I say is wrong and to try to explain me the final question.

Light is a set of photons that oscilates creating an eletric and a magnetic field around them. When 2 photons are too close their eletric/magnetic fields can interact generating the interference. But this would need the 2 photons to be really close, doesn't? And this interference would occur only while the 2 photons were together. Like in the picture.

http://img13.imageshack.us/img13/5903/20573870.png [Broken]

Now look at the picture

http://img89.imageshack.us/img89/1899/skhgfshgdfgsdg.png [Broken]

Consider all light rays to be almost perpendicular to the surface. So the difference of luminous path would be 2d and, like all interference book says:

If 2d = (2n+1)/2 λ - constructive interference
If 2d = n λ - destructive interference

This is due to the phase inversion in B.

OK, BUT WHERE THE HELL DOES THE INTERFERENCE OCCURS?
B isn't in the same place than D, so the interference can't occur ON the surface. Does it occur in the human eye? How? Because I don't thinks the 2 rays will actually hits each other exactly IN the human eye.
 
Last edited by a moderator:
Science news on Phys.org
  • #2
When thinking about interference of light, do not think about photons. Think about waves.
Light waves interfere with each other in the same manner as other types of waves. Go fill your bathtub and experiment with disturbing the smooth surface with different objects in different locations. Look at the interference patterns that occur.
Rays BE and DF are out of phase, so their amplitudes subtract. One is "pulling" while the the other is "pushing". Like two water waves encountering each other but one pushing water up while the other pushing the water down.
 
Last edited:
  • #3
the_emi_guy said:
When thinking about interference of light, do not think about photons. Think about waves.
Light waves interfere with each other in the same manner as other types of waves. Go fill your bathtub and experiment with disturbing the smooth surface with different objects in different locations. Look at the interference patterns that occur.
Rays BE and DF are out of phase, so their amplitudes subtract. One is "pulling" while the the other is "pushing". Like two water waves encountering each other but one pushing water up while the other pushing the water down.

I understand this push and pull interference. But the waves should be close (in other words, superposing) each other to interact, right? BE and DF aren't superposing each other. How can they interact? How can theey interfere?
 
  • #4
jaumzaum said:
BE and DF aren't superposing each other. How can they interact? How can theey interfere?

What makes you so sure these are not superposing? There are at least three ways to answer your question. I do not know which is best for your level of understanding, so I will try all three of them.

1) In the kind of drawing you show, you see straight light rays. If light were really only located on a small spatial scale, it would suffer badly from diffraction and spread quickly. That is why books typically tell that they assume plane waves for the kind of image you show. That means you have lots of such parallel beams next to each other. Therefore, there is also a parallel beam to A-B which ends at D and overlaps perfectly with the CD-Beam.

2) The lateral extent of any wave cannot be made arbitrarily small. The lower bound is roughly the wavelength of the light involved. In the picture you have shown, yon need a total path difference of lambda or 0.5 lambda for constructive or destructive interference. As most of the difference in path is covered by the vertical thickness of the thin film, the horizontal offset is significantly smaller than that and therefore typically much smaller than a wavelength. As the lateral extent of the wave is typically larger than the wavelength of the light, the two beams will indeed overlap pretty well.

3) The do-it-yourself-approach. Read up on the Huygens-Fresnel principle, which states that every point of the light wave serves as a source of a spherical wave, grab a pair of compasses and draw the whole interference scenario yourself. This will not help you at the moment, but is very instructive in the long run.
 
  • #5
Cthugha said:
1) In the kind of drawing you show, you see straight light rays. If light were really only located on a small spatial scale, it would suffer badly from diffraction and spread quickly. That is why books typically tell that they assume plane waves for the kind of image you show. That means you have lots of such parallel beams next to each other. Therefore, there is also a parallel beam to A-B which ends at D and overlaps perfectly with the CD-Beam.

Thanks for the answers Cthugha.

The light I've considered in the second image was a light source, not only a light beam (I've draw n a single ray just to make it easier to understand).
I've got your point now. Yes, there are many other rays can interact and "superpose" the AB ray. Part of my question is answered. BUt I still have some doubts.

Look at the following image (third image)

http://img716.imageshack.us/img716/1253/dfgdsfg.png [Broken]

In the second image we had that a ray parallel to AB that passes through D would superpose COMPLETELY DF. But that's because the surface was plane.

At third image we have that as the surface is not plane, the green ray cannot superpose completely the red one. They only intersect at B. The blue ray, eather. That way, the interference occurs only in a single point.

Now let's suppose an absurd thing for a moment (I know it's absurd but it is important for my understanding). If there was only the three beams drawed in the picture (no more light beam). For we to see the interference , should we put the eye exactly in A?
 
Last edited by a moderator:
  • #6
jaumzaum said:
For we to see the interference , should we put the eye exactly in A?

I suppose from a technical point of view, it would be much easier to put a screen there and watch the screen, but in principle yes. The interference will take place only at the positions where beams which are somewhat phase shifted with respect to each other actually have some spatial overlap.
 
  • #7
Thanks Cthugha.

A final and last question.

For we to predict (mesure) where the interference will occur, we have that the light beams (emmited by the light source) have to be in phase immediatelly before the hit the surface. How can this be possible? Is the sun light an example of that? Would the interference occur if the rays were not in phase?

[]'s

João
 
  • #8
If the rays are not in phase initially, that basically just introduces an overall offset. The constructive interference occurs if two different waves are in phase at some point. If you now have an initial phase difference, the additional phase difference you need to achieve for interference by having the two beams take different paths is now not 2d = n λ anymore, but a bit shorter or longer.

For interference patterns to occur, it is more important that two beams have some fixed phase relationship. They need not be in phase, but the phase difference should not change over time. Light from the sun does not have this property as it is composed of many wavelengths and the phase changes randomly (due to the random nature of the light emission process) on a timescale of the order of femtoseconds.
 
  • #9
If we measure the light pattern on a screen, we are viewing the interference at the screen. Any interference that occurs on the way to the screen doesn't matter, since we are not looking at that point. Different light sources don't interact with each other as they travel through space. They just pass through each other.

If you cross the beams of two lasers, the waves will overlap in the crossed region, but two beams will pass out the crossed region as if nothing happened.
 
  • #10
Khashishi said:
If you cross the beams of two lasers, the waves will overlap in the crossed region, but two beams will pass out the crossed region as if nothing happened.

But if we put a screen in the crossed region, we would see interference right?
 
Last edited:
  • #11
Cthugha said:
For interference patterns to occur, it is more important that two beams have some fixed phase relationship. They need not be in phase, but the phase difference should not change over time.

Thanks Cthugha. The light I've mentioned was not composed by 2 beams only, but infinite beams that have a randomly phase difference (like the common-light we see in our houses, that is reflected many times). Would this cause a interference pattern?
 
  • #12
No, if you have infinite beams at random phases, every possible phase difference is realized and therefore also every possible scenario from constructive to destructive interference (and partial interference in between). In summary all of these contributions cancel out and there is no interference at all.
 
  • #13
The picture suggests the 'Newtons Rings ' phenomenon. This is visible with 'ordinary' light sources (the old slide projectors were very susceptible). It's only the first one or two fringes that were visible, though. The point is that all the "infinite beams" will interfere with themselves over a small range of angles, because there is a small degree of coherence. Obviously, with a laser source, the pattern will be much stronger and appear over a wider area of any image.
Light from all over a room will never give you visible fringes but once you start to collimate the beam (in a projector, for instance or just light from one direction), the effect starts to appear. The first thing you tend to see is coloured fringes as RG and B cancel at different angles.
 
  • #14
sophiecentaur said:
The picture suggests the 'Newtons Rings ' phenomenon. This is visible with 'ordinary' light sources (the old slide projectors were very susceptible). It's only the first one or two fringes that were visible, though. The point is that all the "infinite beams" will interfere with themselves over a small range of angles, because there is a small degree of coherence. Obviously, with a laser source, the pattern will be much stronger and appear over a wider area of any image.
Light from all over a room will never give you visible fringes but once you start to collimate the beam (in a projector, for instance or just light from one direction), the effect starts to appear. The first thing you tend to see is coloured fringes as RG and B cancel at different angles.

Thanks sophiecentar, but no one has answered my question yet. Would kashishish light cause interference in the crossed region?
 
  • #15
jaumzaum said:
Thanks sophiecentar, but no one has answered my question yet. Would kashishish light cause interference in the crossed region?
What is that? I googled and got nothing relevant except your post. I am not sure what you mean by "crossed region" either. It would be best if you googled thin film interference and Newtons rings for yourself. You will see plenty of diagrams which should help you understand this better. I think you may be making wrong assumptions about which of the light beams you will actually see in your diagram. This could account for your confusion.

I can say that light arriving from all directions that started off as incoherent won't usually produce visible interference patterns. However, if you look at the colours of oil films on puddles, you are seeing an interference effect and light is arriving from all directions (the sky). The interference is very much diluted in this case because of the large amounts of other light. Birds' feathers and butterflies' wings have vivid colours because of interference (not pigments) and, again, the light arrives from all over the place. In the case of so-called interference filters, the films are very thin and the 'fringes' are very wide - consisting of no more than one minimum, which will be a minimum for only one narrow range of wavelengths. The colours you see are 'complementary' colours and not spectral colours (e.g. bright magenta, where yellow has been eliminated)
 
  • #16
sophiecentaur said:
What is that? I googled and got nothing relevant except your post. I am not sure what you mean by "crossed region" either. It would be best if you googled thin film interference and Newtons rings for yourself. You will see plenty of diagrams which should help you understand this better. I think you may be making wrong assumptions about which of the light beams you will actually see in your diagram. This could account for your confusion.

I can say that light arriving from all directions that started off as incoherent won't usually produce visible interference patterns. However, if you look at the colours of oil films on puddles, you are seeing an interference effect and light is arriving from all directions (the sky). The interference is very much diluted in this case because of the large amounts of other light. Birds' feathers and butterflies' wings have vivid colours because of interference (not pigments) and, again, the light arrives from all over the place. In the case of so-called interference filters, the films are very thin and the 'fringes' are very wide - consisting of no more than one minimum, which will be a minimum for only one narrow range of wavelengths. The colours you see are 'complementary' colours and not spectral colours (e.g. bright magenta, where yellow has been eliminated)

Kashishi is the guy up there, sorry

he posted:

If we measure the light pattern on a screen, we are viewing the interference at the screen. Any interference that occurs on the way to the screen doesn't matter, since we are not looking at that point. Different light sources don't interact with each other as they travel through space. They just pass through each other.

If you cross the beams of two lasers, the waves will overlap in the crossed region, but two beams will pass out the crossed region as if nothing happened.

I want to know if you put a screen at the crossed region of the 2 lasers, would you see interference?
 
  • #17
yeah, you will see interference in the crossed region.
 
  • #18
Two different lasers could not interfere because they would not be in phase (coherent). They would measure (near enough) as the same wavelength, perhaps, but that wouldn't be close enough for an interference pattern to be formed. There is a phenomenon called beating when two radio frequency waves of nearly the same frequency are received and this is caused by the phases of the two, drifting steadily in time and producing alternate high and low amplitude resultants. The interference pattern from the two sources is constantly on the move - sweeping across the area- but not forming an identifiable stationary fringe pattern. The same would be happening with two lasers but I don't know of any method of actually plotting the pattern - you certainly wouldn't see it.

Note: you only get interference when you actually measure the vector sum of the waves that are arriving at a location. (For instance, you 'see' the result of the light being scattered from the screen) With nothing in its path, light does not interfere with itself - the waves are totally independent and do not interact. This makes total sense because you can see an object clearly when the Sun is to one side of you. The sunlight is passing across, in front of you, yet you do not see it (except when there is dust or water droplets in the air in front of you and the light gets scattered).
 
  • #19
Khashishi said:
yeah, you will see interference in the crossed region.

Hate to disagree with you but the phase coherence between the two wouldn't be good enough for a pattern. (See above post)
 
  • #20
Khashishi said:
yeah, you will see interference in the crossed region.

I'm afraid it's not that simple, at least experiments proving it are far more complex than just putting a screen at intersection. Also, Paul Dirac claimed the interference of two independent light beams can never occur. In any case here is something interesting about it:

http://prola.aps.org/abstract/PR/v159/i5/p1084_1
- "Interference effects produced by the superposition of the light beams from two independent single-mode lasers have been investigated experimentally. It is found that interference takes place even under conditions in which the light intensities are so low that, with high probability, one photon is absorbed before the next one is emitted by one or the other source."

So if photons are not even "colliding" and if there is no slit where they split and interact with themselves, then what are they interacting with? It sounds as if shining one beam now for a few seconds and then the other 10 minutes later that the pattern would again be there, and not only when you shine the second beam, but also just with the first beam by itself. Unless of course you decided to cheat and not shine the second beam, because then the first beam would know, in advance, and it would not produce the pattern. I'm just kidding, but in reality it's just about as crazy as that, isn't it?
 
  • #21
MarkoniF said:
I'm afraid it's not that simple, at least experiments proving it are far more complex than just putting a screen at intersection. Also, Paul Dirac claimed the interference of two independent light beams can never occur. In any case here is something interesting about it:

http://prola.aps.org/abstract/PR/v159/i5/p1084_1
- "Interference effects produced by the superposition of the light beams from two independent single-mode lasers have been investigated experimentally. It is found that interference takes place even under conditions in which the light intensities are so low that, with high probability, one photon is absorbed before the next one is emitted by one or the other source."

So if photons are not even "colliding" and if there is no slit where they split and interact with themselves, then what are they interacting with? It sounds as if shining one beam now for a few seconds and then the other 10 minutes later that the pattern would again be there, and not only when you shine the second beam, but also just with the first beam by itself. Unless of course you decided to cheat and not shine the second beam, because then the first beam would know, in advance, and it would not produce the pattern. I'm just kidding, but in reality it's just about as crazy as that, isn't it?

It's strange that people always seem to approach this in terms of light. Things can become much easier when you think about the effects at RF. It's identical but you can just treat it classically. The quantum approach is just one way of looking at it but, as in your post, you find yourself talking about photons "colliding" and I see you actually needed to put that in quotes (haha). Laser people have so much more trouble dealing with this sort of thing because of the practicalities of actually producing what a radio engineer would just refer to as "cw". Your notion of shining a laser for a while then turning it off would actually be introducing Modulation, which would be affecting the bandwidth (in RF terms).
You refer to experiments with independent single mode lasers. How were the frequencies maintained accurately enough? I would assume that they were phase locked in some way (like RF sources, synthesised from a common frequency standard) so they wouldn't be totally independent. Of course, there is absolutely no chance of doing experiments with RF sources of such low power that individual photons can be considered because that would be way down in the measuring noise.
 
  • #22
sophiecentaur said:
It's strange that people always seem to approach this in terms of light. Things can become much easier when you think about the effects at RF. It's identical but you can just treat it classically.

I haven't heard of double-slit experiment performed with radio or any other em waves besides visible light. I guess receiver antenna could be connected to TV and with proper setup the display would show stripes corresponding to interference pattern. Are there any experiments like that?


The quantum approach is just one way of looking at it but, as in your post, you find yourself talking about photons "colliding" and I see you actually needed to put that in quotes (haha).

It's because collision usually implies the trajectories of colliding entities are different before and after collision, which it didn't seem would be the case with photons interference, but when thinking about it a bit more it seems it actually is. In either case it doesn't make any sense since in that experiment photons don't even come close to each other. It's as if they leave some kind of trails behind, like a boat wake.


Laser people have so much more trouble dealing with this sort of thing because of the practicalities of actually producing what a radio engineer would just refer to as "cw". Your notion of shining a laser for a while then turning it off would actually be introducing Modulation, which would be affecting the bandwidth (in RF terms).

I thought we have technical ability to produce lasers that would emit pretty much identical photons, each one of them. Why is that easier to achieve with radio waves?


You refer to experiments with independent single mode lasers. How were the frequencies maintained accurately enough? I would assume that they were phase locked in some way (like RF sources, synthesised from a common frequency standard) so they wouldn't be totally independent.

I don't have access to that paper. Here is something else instead:
http://www.conspiracyoflight.com/LaserInterference/LaserInterference.html
 
  • #23
MarkoniF said:
Also, Paul Dirac claimed the interference of two independent light beams can never occur.

My favorite comment on that comes from Nobel prize winner Roy Glauber (from "Quantum Optics and Heavy Ion Physics", Nuclear Physics A Volume 774, 7 August 2006, Pages 3–13):

"When you read the first chapter of Dirac's famous textbook in quantum mechanics [8],
however, you are confronted with a very clear statement that rings in everyone's memory.
Dirac is talking about the intensity fringes in the Michelson interferometer, and he says,
Every photon then interferes only with itself. Interference between two different
photons never occurs. Now that simple statement, which has been treated as scripture, is absolute nonsense."

If you take two arbitrary light beams and filter them, so that their properties (spectral width, spatial shape, temporal shape) become comparable, you will also manage to see interference, if the spectral width is narrow enough. A cool demonstration has been given in "Interference of dissimilar photon sources" by Bennett et al., Nature Physics 5, 715 - 717 (2009), where a tunable laser and spontaneous emission from a quantum dot diode were made to interfere.
 
  • #24
Cthugha said:
My favorite comment on that comes from Nobel prize winner Roy Glauber (from "Quantum Optics and Heavy Ion Physics", Nuclear Physics A Volume 774, 7 August 2006, Pages 3–13):

"When you read the first chapter of Dirac's famous textbook in quantum mechanics [8],
however, you are confronted with a very clear statement that rings in everyone's memory.
Dirac is talking about the intensity fringes in the Michelson interferometer, and he says,
Every photon then interferes only with itself. Interference between two different
photons never occurs. Now that simple statement, which has been treated as scripture, is absolute nonsense."

If you take two arbitrary light beams and filter them, so that their properties (spectral width, spatial shape, temporal shape) become comparable, you will also manage to see interference, if the spectral width is narrow enough. A cool demonstration has been given in "Interference of dissimilar photon sources" by Bennett et al., Nature Physics 5, 715 - 717 (2009), where a tunable laser and spontaneous emission from a quantum dot diode were made to interfere.
This is a truly great post and it really justifies the opinion I have held for years. It really brings home the fact that photons really are NOTHING like the little bullets that people want them to be. If photons can only 'interfere with themselves' (and I don't have a problem with that as an idea) it merely indicates that the photon model that everyone starts off with in their heads is total rubbish. Dirac didn't have to be wrong if you think of just what a photon is (could be?).
To address MarkoniF's post which asks if the two slits experiment has ever been carried out with anything but light, it happens every day in a multitude of directional radio and TV transmitting arrays. They are often more complex than just two sources but the nulls and maxima that are produced by your local TV transmitting antenna are absolutely the same as the equivalent optical nulls and maxima.
Dirac says a photon can only interfere with itself. Now this implies that the signals fed to each of a pair of dipoles must contain 'the same' photons. This must even apply when each antenna element is fed via a different amplifier (which does happen!). So the photons - which interfere with themselves are handled by each of the two amplifiers in the system and the probability function that determines the shape of the radiation pattern assumes the same things about the transmitters as it does about the 'slits' in the optical experiment. Well, how about that and what it implies about the nonsense of a little bullet that can go through either or both transmitting amplifiers? These transmitters, in principle, could even have separate oscillators for their drives and merely be phase locked by some drive control mechanism. There is nothing to say that the quantum of energy that is represented by the term 'photon' could not be handled by each transmitter. It's just that the photon cannot be a particle as most of the world sees it.
If that isn't 'the death of the little bullet' then I don't know what is. And such an argument would never have arrived so easily via the path of lasers.
I know this is not particularly revolutionary as there are plenty of people who have a more enlightened view of photons but it is a pretty damned good nail in the coffin which could be appreciated by any receptive mind.
 
  • #25
sophiecentaur said:
It really brings home the fact that photons really are NOTHING like the little bullets that people want them to be.

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:

http://www.brown.edu/Research/electronbubble/videos/firstmovie.html

http://www.brown.edu/Research/electronbubble/videos/firstmovieimages/quantizedvortex.png


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?
 
  • #26
MarkoniF said:
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 traveling (and wiggling) through the amplifiers and feeders, too, in a multi-element transmitting antenna?

I realize 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
sophiecentaur said:
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 traveling (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 realize 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.
 
Last edited:
  • #28
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
sophiecentaur said:
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
MarkoniF said:
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.

MarkoniF said:
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.

MarkoniF said:
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
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
Khashishi said:
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.
 
Last edited:
  • #33
MarkoniF said:
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
Cthugha said:
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?
 
Last edited:
  • #35
MarkoniF said:
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.

MarkoniF said:
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.


MarkoniF said:
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.
 
<h2>1. What is interference in light waves?</h2><p>Interference in light waves is a phenomenon that occurs when two or more light waves meet and interact with each other. This interaction causes the waves to either amplify or cancel each other out, resulting in a change in the overall intensity or wavelength of the light.</p><h2>2. Where does interference occur in light waves?</h2><p>Interference can occur in light waves in any medium, including air, water, and even vacuum. However, it is most commonly observed when light waves pass through transparent materials such as glass or air.</p><h2>3. How does interference affect the color of light?</h2><p>Interference can cause changes in the color of light by altering the wavelength of the light waves. When waves interfere constructively, they can combine to create a longer wavelength, resulting in a shift towards the red end of the visible spectrum. When waves interfere destructively, they can cancel each other out, resulting in a shift towards the blue end of the spectrum.</p><h2>4. What are the two types of interference in light waves?</h2><p>The two types of interference in light waves are constructive interference and destructive interference. Constructive interference occurs when two waves combine to create a larger overall amplitude, while destructive interference occurs when two waves cancel each other out, resulting in a smaller overall amplitude.</p><h2>5. How is interference used in practical applications?</h2><p>Interference is used in many practical applications, such as in the creation of thin film coatings for lenses and mirrors, in holography, and in optical communication systems. It is also used in the study of light and its properties, helping scientists better understand the behavior of waves and the nature of light itself.</p>

1. What is interference in light waves?

Interference in light waves is a phenomenon that occurs when two or more light waves meet and interact with each other. This interaction causes the waves to either amplify or cancel each other out, resulting in a change in the overall intensity or wavelength of the light.

2. Where does interference occur in light waves?

Interference can occur in light waves in any medium, including air, water, and even vacuum. However, it is most commonly observed when light waves pass through transparent materials such as glass or air.

3. How does interference affect the color of light?

Interference can cause changes in the color of light by altering the wavelength of the light waves. When waves interfere constructively, they can combine to create a longer wavelength, resulting in a shift towards the red end of the visible spectrum. When waves interfere destructively, they can cancel each other out, resulting in a shift towards the blue end of the spectrum.

4. What are the two types of interference in light waves?

The two types of interference in light waves are constructive interference and destructive interference. Constructive interference occurs when two waves combine to create a larger overall amplitude, while destructive interference occurs when two waves cancel each other out, resulting in a smaller overall amplitude.

5. How is interference used in practical applications?

Interference is used in many practical applications, such as in the creation of thin film coatings for lenses and mirrors, in holography, and in optical communication systems. It is also used in the study of light and its properties, helping scientists better understand the behavior of waves and the nature of light itself.

Similar threads

Replies
9
Views
1K
Replies
9
Views
2K
Replies
53
Views
7K
  • Special and General Relativity
Replies
18
Views
1K
Replies
1
Views
1K
  • Quantum Physics
Replies
7
Views
965
Replies
9
Views
1K
  • Introductory Physics Homework Help
Replies
5
Views
8K
Back
Top