The Debate on Light: Particle or Wave?

[terrabyte]

the ones hitting the left side of the slit scatter to the right and have to travel through the flow of the main stream. the ones on the right scatter to the left and similarly have to travel through the stream.

the ones that hit the left and scatter MORE to the left are very faint <very small number of TRUE edge particles that can shoot that angle without hitting another material atom.

what happens when the slit is made extremely narrow is that noise that drowns out the particles from left to right and right to left is reduced enough to where we can view the scattering effects easily.

i really do need to find the text i read... it had diagrams and stuff

 

[terrabyte]

this page gets into it a little as far as photon-atom interactions

Link to crack pot site deleted


gonna have to hunt down more stuff later, must... sleep

I suggest careful reading of ZapperZ's posts, much more reliable then random web searchs.

Integral

 

[ZapperZ]

this page gets into it a little as far as photon-atom interactions

Removed link
Integral
gonna have to hunt down more stuff later, must... sleep

Yikes! You should learn to read established physics journals and texts, and not someone's personal website. I hate to think that you based your physics knowledge on something like this! If you really want to screw up your understanding of physics, then go to Crank Dot Net. You'll find enough "ideas" to even contradict what you read on that site. So then you will be left with the delima of which quack to believe in.

Secondly, it appears that when I said that even if the scattering off the edge of slit model is correct, you would only get something resembling a gaussian distribution of intensities behind the slit, this seems to have not made any impression on you. Keep in mind what a "gaussian distribution" looks like, and what an actual diffraction pattern looks like. You'll notice why those two are not compatible.

Thirdly, and this is the most imporant error in your whole model, is that you seem to not know that the scattering probabilty between two photons are unbelievably small. In the visible range, it is almost non-existent. Instead, we have a SUPERPOSTION of light - they passed though each other "unharmed". Thus, your argument that a large slit will cause more of the "scattered" photons to get washed out doesn't hold water. And we haven't talked about the validity of photons "scattering" off an opaque material that make up a slit.

Zz.

 

[jatin9_99]

light has both the nature of wave and particle, as according to de broglie he showed his work as folllowing

Einstein said e=mc^2 so this is particle nature

and max Planck said h=wc where w is wavelenght and c speed of light
=> c=h/w
and e=mc^2
=> e=m(h/w)^2
this proves that light have wave nature too

 

[ZapperZ]

light has both the nature of wave and particle, as according to de broglie he showed his work as folllowing

Einstein said e=mc^2 so this is particle nature

and max Planck said h=wc where w is wavelenght and c speed of light
=> c=h/w
and e=mc^2
=> e=m(h/w)^2
this proves that light have wave nature too

Ok, now see what I mean? It is as if all the things that have been discussed here on this string didn't exist!

And before someone tells me not to pop a blood vessel or something over this, let me just say that I'm not "distressed". I'm just disappointed that I wasted all that effort for nothing. Even after spending more than 10 years on the 'net participating in discussion forums such as this, it still doesn't lessen the disappointment whenever something like this occurs.

Zz.

 

[dodo]

May I add a layman's question to the thread?

19th century postulated an 'ether', as the medium on which light waves would propagate. The current story they tell you at school is that EM waves "carry their own media", being composed of, I seem to recall, two orthogonally-polarized components, one being the "E" and the other the "M". If this goes back to Maxwell, I suppose it might not be quite the "current" story. Then, which is?

And... in which way can this be related to gravity? In a sense, the "media" of gravity is the space itself, which is distorted by the presence of masses. Can (or cannot) be the same for light? Imagine light as a ripple in space - in which way could this account for the "alternate" particle explanation for light?

I apologize in advance for the complete sci-fi tone of the question - in the hope that the act of explaining to a layman can in itself be a source of enlightened amusement.

 

[russ_watters]

Dodo, quite a number of experiments have been done in an effort to find a medium on which light propagates. None have been successful and the laws of physics work just fine without one. It appears that there isn't one (the Electric and Magnetic fields are not the same as the classical ether).

 

[terrabyte]

lol why delete my link.

i just pulled the first one i found that explained photon-atom interactions. i did not "base" my entire physics knowledge on "crackpot's website"

you people are way too touchy.

not going to even bother taking this any further. <wave>

 

[Integral]

lol why delete my link.

i just pulled the first one i found that explained photon-atom interactions. i did not "base" my entire physics knowledge on "crackpot's website"

you people are way too touchy.

not going to even bother taking this any further. <wave>

Why delete your link? Because it did not contain valid physics. This thread has been answered quite throughly by someone who knows what they are talking about. The fact that you were unable to identify the link as nonsense says that you either did not have sufficient knowledge of Physics to tell, or are a crackpot pushing bad information. I do not know, and I do not care, which. I just do not want crackpot links in the middle of a good thread. Please be more careful in the future. If you do not know, ask questions, do not post random links from the web.

 

[terrabyte]

Are you saying photon-atom interaction is wrong?

i could have swore that was common physics. Energy kicks electrons into higher but unstable orbits, atom randomly kicks back down to lower orbit and emits a photon in a uncertain direction.

the rest of the page was pure gibberish of course, but that's not why i linked it.

anyways, i said i was gone <wave again>

 

[JohnDubYa]

light has both the nature of wave and particle, as according to de broglie he showed his work as folllowing

And what physical property does this "matter wave" represent? If you draw a picture of this wave, what physical properties do the horizontal and vertical axes correspond?

 

[dodo]

Found this in Google's cache - guess it points to what I was looking for. Thank you all!

http://216.239.59.104/search?q=cache:SWDu2I0gBTMJ:arxiv.org/abs/gr-qc/9701034

 

[Tsunami]

I think I know what you are getting at here. Unfortunately, as you can see from the previous post, it can easily be misinterpreted or misrepresented. The biggest obstacle in this issue is trying to convey the meaning of the mathematics. QFT (and QED) makes NO provision for classical fields. Therefore, classical fields (and thus, "waves") essentially do not exist and are meaningless in QFT.

Then what are we left with? I hate to say we have a "particle field", because that again can be misinterpreted (refer to my discussion what classical particle is and why this is NOT what a photon is). Can I get away with saying a "quantum field" without grossly misrepresenting the mathematics? Maybe. If we stick by that, then I would not want to leave the impression that photons can flip back and forth between two apparently different perpective.

Zz.

(Know that this comment comes from a student who only has introductory knowledge of QM: )

Maybe a nice way to explain the wave/particle behaviour of light, is that light behaves more like a particle when its energy increases? For instance, it's pretty useful to talk about microwaves as if they were particles. However, X-rays almost always behave like particle streams.
One could say that it's less probable that light with low energy behaves as particles than that light with high energy behaves like particles.. I think.

 

[dextercioby]

(Know that this comment comes from a student who only has introductory knowledge of QM: )

Maybe a nice way to explain the wave/particle behaviour of light, is that light behaves more like a particle when its energy increases? For instance, it's pretty useful to talk about microwaves as if they were particles. However, X-rays almost always behave like particle streams.
One could say that it's less probable that light with low energy behaves as particles than that light with high energy behaves like particles.. I think.

Nope,it's incorrect.Light is either all wave (macroscopical/classical description,or all particle (microscopical/quantum description).There's no overlapping...And quantum/photonic description can account for macroscopical phenomena as well,it's just that the photons need to form a statistical ensemble (plus coherence,...).

Daniel.

 

[Tom Something]

could someone describe how diffraction can be explained by the photons rather than waves?

 

[misogynisticfeminist]

Particle. No experiment has ever been performed on a photon that demonstrated wave properties to my knowledge.

no no no. What about thomas young's experiment?

Photons are interpreted in terms of its wavefunction, the photon field in which photons are the quanta.

 

[ZapperZ]

could someone describe how diffraction can be explained by the photons rather than waves?

You may want to read this thread:

https://www.physicsforums.com/showthread.php?t=68917

In addition, my journal entry on the misconception of the Heisenberg Uncertainty Principle illustrates this using the diffraction from a single slit due to photons. So you may wish to read that also.

Zz.

 

[Tsunami]

Nope,it's incorrect.Light is either all wave (macroscopical/classical description,or all particle (microscopical/quantum description).There's no overlapping...And quantum/photonic description can account for macroscopical phenomena as well,it's just that the photons need to form a statistical ensemble (plus coherence,...).

Daniel.

Bah... now you got me confused again...

so both the wave and particle description are part of the same universal description of light (dixit ZapperZ) yet at the same time light is either all wave, or all particle...?

Something tells me that the case is :

either
1) I'm not going to understand any of this until I see a more expansive course about QFT.
or
2) Virtually nobody completely understands this and this is why the interpretations of you and ZapperZ (at least seem to) logically contradict.

 

[marlon]

so both the wave and particle description are part of the same universal description of light (dixit ZapperZ) yet at the same time light is either all wave, or all particle...?

Zapper is correct. The duality exists only because of our 'classical minds' ; we want to think in terms of either particles or waves. There is no problem with that but we do need to keep the correct perspective on things here. First of all 'particles' in this case does not mean little objects with finite boundaries. It means little finite pieces of energy (this is the actual quantization , right ?)

Secondly, and this is what dextercioby meant, in QM we have experiments that are better explained with the wave-like notion (eg the double slit experiment) and we have those experiments that are better described with the particle-like notion (eg photo-electric effect). However in the end both descriptions are just ONE SINGLE way of describing the physical properties of light...that is all.

Another common misconception is the fact that the photo-electric effect proved the existence of photons. That is not true because this photo-electric effect can be described in terms of the wavelike-notion of the incident EM-radiation too. It is only the atoms of the target electrode that are treated with QM. However, the particle-like notion of light is suggested by this experiment. If you want to read more, check out my journal and find the article on creating an entangeled photon-state in an undergrad lab

marlon

EDIT : well, here's the article : Create entangled photons yourself in an undergrad laboratory :
http://marcus.whitman.edu/~beckmk/QM/grangier/Thorn_ajp.pdf

 

[ZapperZ]

Bah... now you got me confused again...

so both the wave and particle description are part of the same universal description of light (dixit ZapperZ) yet at the same time light is either all wave, or all particle...?

Something tells me that the case is :

either
1) I'm not going to understand any of this until I see a more expansive course about QFT.
or
2) Virtually nobody completely understands this and this is why the interpretations of you and ZapperZ (at least seem to) logically contradict.

Without even going into QFT, let's make sure we make something very clear here:

All of the properties of light can be described by QM, and even so-called wavelike properties can be obtained using the photon description.

Now, contrary to popular beliefs, especially among students, physics instructors are not heartless masochists who will force the students to use the photon description when the classical wave picture is easier and more direct to be used. That is why the classical wave theory are still used when we describe diffraction and interference effects, especially in classical optics classes. It doesn't mean, however, a unified QM description doesn't exist for such things. It is just more involved and requires a bit more of a sophistication in knowledge to do it. The classical wave picture is simply a "short cut" to getting what we want to get.

Zz.

 

[marlon]

Just to add what Zapper has said, QFT does not 'explain' the duality more or better as QM. You know, everytime somebody drops the term QFT, my heart goes...You know why ? Well, because lot's of people like the use the posh-sounding epitheton QFT but i always feel the urge to ask : do you know what it means. I mean, if i were a professor teaching QFT, my first chapter in my course would explain why we need the quantum-part, why we need the fields part and why we need the relativistic part. Every principle of QM is copied, to some extent, by QFT since QFT really is the unification of both QM and special relativity. Beware, i said SPECIAL relativity and not GENERAL relativity...

marlon

 

[Thomas2]

You read wrong. What I said was...

"Having said that, the most common explanation for the "wave-particle duality" is that light behaves as waves in experiments such as the double slit, and behaves as particles when we do things like the photoelectric effect."

The photoelectric effect can well be explained in terms of the wave picture if the wave-atom interaction is properly being considered. In contrast, the particle theory of light is completely inconsistent and would in fact not enable photoionization at all because (due to its small mass) the photon could not transfer enough energy to the photoelectron.
A further proof for the incorrectness of the particle model for light is the experimental fact that photoelectrons are not primarily released in the direction of propagation of light (as one should expect it for particles) but perpendicular to this in the direction of the electric field vector .

See my webpage http://www.physicsmyths.org.uk/photons.htm for more details (I can't copy the page here because it contains a number of formulae).

 

[marlon]

In contrast, the particle theory of light is completely inconsistent and would in fact not enable photoionization at all because (due to its small mass) the photon could not transfer enough energy to the photoelectron.

Well, i don't want to be impolite but do you really mean this ? Anyhow, you are totally wrong...I suggest you actually check the history of the photo-electric effect-explanation and just to be sure, also double check what is meant by the words : "particle theory of light"...Why do you even bring the 'small mass' of photons...That small mass is ZERO

marlon

 

[Thomas2]

...Why do you even bring the 'small mass' of photons...That small mass is ZERO

Well ,that would be even worse, because then it could not transfer any energy at all. But I think you mix up mass with 'rest mass' here. Only the latter is zero in the relativistic theory of the photon, but since the photon does not rest in any reference frame it has a finite mass (or at least it is supposed to have).

 

[ZapperZ]

The photoelectric effect can well be explained in terms of the wave picture if the wave-atom interaction is properly being considered. In contrast, the particle theory of light is completely inconsistent and would in fact not enable photoionization at all because (due to its small mass) the photon could not transfer enough energy to the photoelectron.
See my webpage http://www.physicsmyths.org.uk/photons.htm for more details (I can't copy the page here because it contains a number of formulae).

I disagree. I worked in photoemission spectroscopy for my postdoc, and if you look at the work by Spicer, who almost single-handedly pioneered this technique, you will see why what you said is incorrect.

Furthermore, since when does a photon have a "small mass"? The photon mass is irrelevant in a photoemission process. In fact, if a photon HAS a mass, a bunch of things from photoemission spectroscopy would be wrong, and the band structure we used in the semiconductors in your modern electronics should not work. This is because photoemission spectroscopy is the FIRST such technique that could independently verify the theoretical calculations of band structure of solids. And they all use the photon picture!

And I have said this so many times, I am beginning to bore myself. Look up "multiphoton photoemission". Now explain how the amount of photoelectrons detected as a function of the photon intensity have discrete dependence that just HAPPENS to coincide with the discrete number of photons being absorbed to cause that particular transition. Don't tell me the energy level of the material is discrete since this is a transition from a continuous conduction band into a continuous vacuum band. While the photoelectric alone cannot rule out the wave picture, I haven't seen even a single attempt at reconcilling the multiphoton process with the wave picture.

Zz.

 

[marlon]

Well ,that would be even worse, because then it could not transfer any energy at all. But I think you mix up mass with 'rest mass' here. Only the latter is zero in the relativistic theory of the photon, but since the photon does not rest in any reference frame it has a finite mass (or at least it is supposed to have).

Then let's call it the photon's energy, ok ? Just to be clear. Now, again i ask you to double check the actual proof of the photo-electric effect. This will prove you wrong.

regards
marlon

 

[dextercioby]

Nice debate here,is it still in General Physics ?? Oh,i know Thomas2...Huge misconceptions...The bad part is that he don't seem to be willing to learn anything...

Daniel.

 

[ZapperZ]

Well ,that would be even worse, because then it could not transfer any energy at all. But I think you mix up mass with 'rest mass' here. Only the latter is zero in the relativistic theory of the photon, but since the photon does not rest in any reference frame it has a finite mass (or at least it is supposed to have).

Typically, when someone says something like this, it shows that this person never went through any formal study of SR and QM. They are always surprised that light can have energy and momentum, but NO MASS! Horrors! It shows they haven't seen the complete derivation of the relativistic effects. If that is the case, most of the time, we always have to keep taking several steps backwards each time we introduce an explanation. This can be quite exasperating (at least for me), so I'll let others with more patience on this take over.

Zz [with 2 extra cups of coffee this morning]

Zz.

 

[marlon]

This can be quite exasperating (at least for me), so I'll let others with more patience on this take over.

Thanks but no thanks
I believe the guy with the promotion should do the 'most difficult' tasks

Zz [with 2 extra cups of coffee this morning]

Zz.

Same here...

marlon

 

[Thomas2]

Furthermore, since when does a photon have a "small mass"? The photon mass is irrelevant in a photoemission process. In fact, if a photon HAS a mass, a bunch of things from photoemission spectroscopy would be wrong

Well, this would prove then that light has to be considered as a wave (see also my reply to Marlon above)

And I have said this so many times, I am beginning to bore myself. Look up "multiphoton photoemission". Now explain how the amount of photoelectrons detected as a function of the photon intensity have discrete dependence that just HAPPENS to coincide with the discrete number of photons being absorbed to cause that particular transition. Don't tell me the energy level of the material is discrete since this is a transition from a continuous conduction band into a continuous vacuum band. While the photoelectric alone cannot rule out the wave picture, I haven't seen even a single attempt at reconcilling the multiphoton process with the wave picture.

How should a multiphoton transition work in the particle picture if you can't even make an individual one work? On the other hand, it is no problem with the wave-atom interaction model if the first transition is to a state below the ionization threshold and the lifetime of the level is long enough so that the electron can absorb another wave frequency that ionizes it finally.

Also, as I mentioned above already, the experimental fact that photoelectrons are primarily emitted into the direction of the electric field vector (i.e. perpendicular to the direction of propagation of light) clearly invalidates the particle picture.