Shape of Light: Uncovering the Mystery

[physixlover]

Does light have a definite shape? (this may be stupid question but from many days this question is hanging in my brain

Thanks

 

[Anti-Meson]

Light doesn't have a shape in the same sense a tennisball has shape (sphere).

Light is neither wave nor particle but both. Confusing eh?

 

[physixlover]

Light doesn't have a shape in the same sense a tennisball has shape (sphere).

Light is neither wave nor particle but both. Confusing eh?

yes confused,it's not a partice nor a wave,but how is this possible

 

[Anti-Meson]

Truth be told, we don't exactly know what light is. It both demonstrates particle properties (see photoelectric effect) and wave properties (see diffraction), though it is neither one of them singularly and yet both simultaneously.

 

[pgardn]

yes confused,it's not a partice nor a wave,but how is this possible

Because we as humans have metaphorical ways of thinking about how objects behave imo. We have a model of how a particle and a wave behave and light behaves as both to us experimentally. I don't see a problem with this as we made these models up to begin with because they work.

It just helps us to understand and predict how light behaves a little better. So its a decent model. We make up the concepts to help us understand nature. If the models start falling short in certain situations, we change them to fit the new situations.

 

[Dale]

Truth be told, we don't exactly know what light is. It both demonstrates particle properties (see photoelectric effect) and wave properties (see diffraction), though it is neither one of them singularly and yet both simultaneously.

I tend to disagree with this type of statement. We have a very accurate theory called QED that completely describes the behavior of light. AFAIK there is no indication that QED fails to accurately predict any aspect of light's behavior. In other words it is both accurate and complete.

As far as I am concerned, that means that we do know what light is. There is a philosophical sense in which we cannot know what anything is, but from a scientific standpoint I think that solipsism-type argument is completely pointless. The problem is not that we don't know what light is, it is just that we have a lot of linguistic baggage.

 

[Anti-Meson]

I tend to disagree with this type of statement. We have a very accurate theory called QED that completely describes the behavior of light. AFAIK there is no indication that QED fails to accurately predict any aspect of light's behavior. In other words it is both accurate and complete.

As far as I am concerned, that means that we do know what light is. There is a philosophical sense in which we cannot know what anything is, but from a scientific standpoint I think that solipsism-type argument is completely pointless. The problem is not that we don't know what light is, it is just that we have a lot of linguistic baggage.

The only problem with QED is that is treats light as a particle.

 

[Dale]

So, why is that a problem as long as it accurately predicts the behavior?

 

[Anti-Meson]

So, why is that a problem as long as it accurately predicts the behavior?

There is nothing wrong with QED, it does as you say, accurately predicts the behaviour. Is just that we can also think of light in the classical sense, as a wave. Let me make this clear, there is no problem that light can be described as a wave or a particle. The problem is classifying it singularly as one or the other, when it is both or neither.

 

[Dale]

The description in QED is completely unified. There is no dichotomy between wave and particle in QED and all of the behaviors are predicted in a single framework.

 

[Anti-Meson]

The description in QED is completely unified. There is no dichotomy between wave and particle in QED and all of the behaviors are predicted in a single framework.

I am not arguing about the validity of QED, its probably the success story of the 20th century in physics. The problem is that we classify light as particles and waves when we know it cannot be just a wave nor just a particle, it is either both simultaneously. Or it is neither and something we have yet to discover.

 

[pgardn]

I tend to disagree with this type of statement. We have a very accurate theory called QED that completely describes the behavior of light. AFAIK there is no indication that QED fails to accurately predict any aspect of light's behavior. In other words it is both accurate and complete.

As far as I am concerned, that means that we do know what light is. There is a philosophical sense in which we cannot know what anything is, but from a scientific standpoint I think that solipsism-type argument is completely pointless. The problem is not that we don't know what light is, it is just that we have a lot of linguistic baggage.

I think that closely questioning the way we think helps us immensely when modeling falls short. It forces us to break new ground in math or to take a very diff. view when our metaphorical world based on senses (largely sight as humans) fails us as an accurate descriptor.

I would agree that the argument you gave is pointless. For us predicting is a type of knowing.

 

[Dale]

I am not arguing about the validity of QED, its probably the success story of the 20th century in physics. The problem is that we classify light as particles and waves when we know it cannot be just a wave nor just a particle, it is either both simultaneously. Or it is neither and something we have yet to discover.

I think you are missing my whole point. There is a lot of linguistic baggage associated with the English words "particle" and "wave", neither of which in common-usage adequately expresses what light is. This is not the case with the math of QED which accurately and completely characterizes light in one single unified way with no disparity.

You say that light cannot be "just a wave nor just a particle", but that is not correct. It is a particle, but in the full sense of the QED usage of the word "particle". In QED particles have a single unified framework which shows diffraction, interference, reflection, and all of the other traditional "wave" aspects of light's behavior as well as scattering, quantization and all of the other traditional "particle" aspects of light's behavior. This single unified concept is called a "particle", but just like you can understand the difference between "banking to the right" and "banking with CitiBank" you should be able to understand the differences between a "classical particle" and a "quantum particle".

Light is a particle which behaves as described by QED.

 

[Anti-Meson]

I think you are missing my whole point. There is a lot of linguistic baggage associated with the English words "particle" and "wave", neither of which in common-usage adequately expresses what light is. This is not the case with the math of QED which accurately and completely characterizes light in one single unified way with no disparity.

You say that light cannot be "just a wave nor just a particle", but that is not correct. It is a particle, but in the full sense of the QED usage of the word "particle". In QED particles have a single unified framework which shows diffraction, interference, reflection, and all of the other traditional "wave" aspects of light's behavior as well as scattering, quantization and all of the other traditional "particle" aspects of light's behavior. This single unified concept is called a "particle", but just like you can understand the difference between "banking to the right" and "banking with CitiBank" you should be able to understand the differences between a "classical particle" and a "quantum particle".

Light is a particle which behaves as described by QED.

Aye, I am not disagreeing with you. But I think you are missing my point, light is a phenomenon which cannot only be described as a particle as described by QED but also as a wave in classical physics. Both areas of physics can explain what the other one can't so it is fruitless to say the QED is the definitive theory on light. Here is my argument: The fact that we have this disparity in classifying light means we are unable to singularly point at one theory and say that is the correct one. We simply don't know. Due to this disparity, I ask you a question to which I invite your answer, what is light?

 

[russ_watters]

Aye, I am not disagreeing with you. But I think you are missing my point, light is a phenomenon which cannot only be described as a particle as described by QED but also as a wave in classical physics. Both areas of physics can explain what the other one can't so it is fruitless to say the QED is the definitive theory on light.

That isn't correct. QED is a comprehensive theory of light. It doesn't have the limitation you are saying it has. There is no aspect that it can't explain while the wave theory can.

DaleSpam is right - the way I see it is this entire issue is based on the English language not having a one word description for what light is (other than saying it is just light). It's not a wave and not a particle - it is light!

Here is my argument: The fact that we have this disparity in classifying light means we are unable to singularly point at one theory and say that is the correct one. We simply don't know.

Again, the wave theory is wrong, the particle theory is wrong, QED is right. [fixed spelling mistake]

Due to this disparity, I ask you a question to which I invite your answer, what is light?

Light is light.

 

[Anti-Meson]

DaleSpam is right - the way I see it is this entire issue is based on the English language not having a one word description for what light is (other than saying it is just light).

It's not a wave and not a particle - it is light! Again, the wave theory is wrong, the particle theory is wrong, QED is light. Light is light.

First you say light is light, then you say QED is light, then light is light again. Which is it to be? I have posed a purely philosophical question to which you have provided a lousy answer. C'mon guys you can do better than this.

 

[russ_watters]

Spelling mistake fixed. That should have been "QED is right"...

I have posed a purely philosophical question to which you have provided a lousy answer.

I'm not really concerned with the philosophy here, which I consider to be just argumentative and pointless. What I am concerned with is your assertion that QED can't describe all of light's behavior. This assertion is just plain factually wrong.

 

[KingNothing]

No, light does not have a definite shape. Normal object maintain their shape because of different atoms bonding together in some way and 'holding on'. Light particles do not have any such bonds with each other.

 

[sas3]

I came across this http://blogs.discovermagazine.com/cosmicvariance/files/uploads/gallery_photon.jpg" once when looking for the answer to that same question I thought there was an article with it but I do not see it now

 

[physixlover]

your all discussion made me to know about Quantum Electrodynamics it's amazing

thanks a lot

 

[Dale]

light is a phenomenon which cannot only be described as a particle as described by QED but also as a wave in classical physics. Both areas of physics can explain what the other one can't so it is fruitless to say the QED is the definitive theory on light.

This is wrong. QED does not have any such limitation. If you disagree then please specifically identify which aspect of light's behavior classical physics can describe that QED cannot.

Here is my argument: The fact that we have this disparity in classifying light means we are unable to singularly point at one theory and say that is the correct one. We simply don't know. Due to this disparity, I ask you a question to which I invite your answer, what is light?

Your argument is flawed because there is no such disparity, QED is accurate and complete. We can point at QED and say that it is the correct theory because it accurately describes all the observed behaviors of light. I have said it already, but I am glad to repeat my answer to your question: Light is a particle as described by QED.

I think that you have a serious misunderstanding of what QED is. I would recommend this series: http://www.vega.org.uk/video/subseries/8

 

[f95toli]

First you say light is light, then you say QED is light, then light is light again. Which is it to be? I have posed a purely philosophical question to which you have provided a lousy answer. C'mon guys you can do better than this.

QED does not assume that light is a classical particle; a photon in QED is strictly speaking a localized excitation of the vacuum. We usually refer to these excitations as "particles"; but that does not mean that photons are small "balls of light" or anything like that.

And, and has already been pointed out, all "wave-like" phenomena can be described by QED.

 

[madmike159]

The only problem with QED is that is treats light as a particle.

The problem with QED is its described using maths beyond most people. Since we can't see how exactly light behaves we come up with analogies about it which aren’t right.

 

[Dale]

its described using maths beyond most people

The same is true of Newtonian mechanics. That is hardly a failure of a theory, but rather a failure of the education system.

 

[madmike159]

The same is true of Newtonian mechanics. That is hardly a failure of a theory, but rather a failure of the education system.

Yes, but Newtonian mechanics applies to objects we can easily rever dyer.

 

[emc2cracker]

Light is both a particle and a wave is it not? I know we do not understand light completely, and I think light is the key to understanding the beginning of the universe. But I do think we can safely say that light is both particle and wave, maybe not in a perfect sense but maybe that's only because it IS both and by being both it cannot fit into one side or the other perfectly.

I work with wavelengths of light daily, mostly infared. So I am partial to the waveform of light.. I would say light is more wave than particle... but I'm biased I'm a cable tv tech I only work with wavelengths, RF for analog signals, infared for fiber optics.

 

[SimonRoberts]

Hi guys,

Though this thread seems pretty much resolved already, I thought i would pitch in the way i see things to see if its in keeping with the general consensus.

Here goes:

The whole 'wave-particle duality' "problem" is just the unfortunate way in which our understanding of light evolved. First light was 'definitely waves' , then 'definitely particles', until we got ourselves all tangled up, not knowing which or what on Earth it was!

Then with the advent of QED, we saw that in fact it was a '3rd party' descibing 'probability amplitudes' sufficient in its predictions to encompass the predictions of both previous theories. Much in the same way that the orbits of the planets and the falling of an apple were thought to be governed by totally different theories, until the proper underlying framework of gravitational theory was understood.

Does this make for a good explanation?


I strongly recommend that link posted to Feynmann's lecture series. He demonstates his characteristic talent of explaining the seemingly intimidatingly complex in its underlying beautiful simplicity.


,Simon

 

[Tao-Fu]

Light is both a particle and a wave is it not? I know we do not understand light completely, and I think light is the key to understanding the beginning of the universe. But I do think we can safely say that light is both particle and wave, maybe not in a perfect sense but maybe that's only because it IS both and by being both it cannot fit into one side or the other perfectly.

I work with wavelengths of light daily, mostly infared. So I am partial to the waveform of light.. I would say light is more wave than particle... but I'm biased I'm a cable tv tech I only work with wavelengths, RF for analog signals, infared for fiber optics.

You will do yourself a lot of favors if you avoid making statements containing "is" in that way. Fundamentally, we can never really address what anything "is". We can only perceive and communicate these perceptions to each other. We can tabulate observed properties of things but we cannot get at any fundamental "is"ness of them.

I think the whole mess can be avoided by just sidestepping this unanswerable question. I can safely say that under certain conditions light exhibits properties that seem particle-like, and under other conditions it exhibits properties that seem wave-like.

 

[Born2bwire]

Light is both a particle and a wave is it not? I know we do not understand light completely, and I think light is the key to understanding the beginning of the universe. But I do think we can safely say that light is both particle and wave, maybe not in a perfect sense but maybe that's only because it IS both and by being both it cannot fit into one side or the other perfectly.

I work with wavelengths of light daily, mostly infared. So I am partial to the waveform of light.. I would say light is more wave than particle... but I'm biased I'm a cable tv tech I only work with wavelengths, RF for analog signals, infared for fiber optics.

F95toli has stated pretty closely how QED describes light. As has been stated before, when we talk about particles in the QED sense there is a lot of extra baggage that comes with the term that is not used in the classical sense. In QED, we describe light roughly as being a field. The energy of the field is quantized into discrete energy levels. The difference between each energy level is a quanta called a photon. So, as f95toli stated, each photon represents an excitation of the fields above the vacuum state (the vacuum is the absence of all photons). Whenever the fields interact, they do so as a point-like interaction of a photon. So while we are talking about light as a field (and again field here carries a lot more meaning with it then when we talk about a classcal field), the interactions of light is done via the photon particle. This encompasses both the classical wave/particle duality that people try to describe light. When light interacts, it does so with a photon particle. But the field description allows for the classical wave effects, like interference and diffraction, to occur. All of this behavior is described by a single QED theory. There is no differentiation between the wave and particle. In the classical sense, we have the Maxwellian electromagnetics which is purely wave physics. We can augment this by using some pseudo-quantum ideas of the photon like in the photoelectric effect. However, the main problem here is that these are two distinct treatments. QED does not differentiate between what are classically distinct set of properties.

Once again I will defer to referencing two of Art Hobson's papers. These are two sort papers about teaching students the electron matter wave in hopes of clarifying the electron interference pattern. Despite focusing on electrons, the quantum field model for electron wave and light waves are the same.

http://physics.uark.edu/hobson/pubs/07.02.TPT.pdf
http://physics.uark.edu/hobson/pubs/05.03.AJP.pdf

 

[emc2cracker]

You will do yourself a lot of favors if you avoid making statements containing "is" in that way. Fundamentally, we can never really address what anything "is". We can only perceive and communicate these perceptions to each other. We can tabulate observed properties of things but we cannot get at any fundamental "is"ness of them.

I think the whole mess can be avoided by just sidestepping this unanswerable question. I can safely say that under certain conditions light exhibits properties that seem particle-like, and under other conditions it exhibits properties that seem wave-like.

Wow, I can't wait to get all this physics mathematics under my cap. I will use what I learn to attack these problems head on, I think we can answer these kinds of questions and I think we must try. One day mankind will use the word is to describe everything if we survive even another few thousand years. I concede my use of the word may be a little liberal, but at some point we have to claim what we think we know. I'd rather be wrong than to be undecided, so long as I find out I am wrong at some point.

F95toli has stated pretty closely how QED describes light. As has been stated before, when we talk about particles in the QED sense there is a lot of extra baggage that comes with the term that is not used in the classical sense...

...Once again I will defer to referencing two of Art Hobson's papers. These are two sort papers about teaching students the electron matter wave in hopes of clarifying the electron interference pattern. Despite focusing on electrons, the quantum field model for electron wave and light waves are the same.

http://physics.uark.edu/hobson/pubs/07.02.TPT.pdf
http://physics.uark.edu/hobson/pubs/05.03.AJP.pdf

Thank you for the papers and for your detailed description of QED. That was a very very good explanation and I made more sense of that than anything I was able to google on QED. I really do appreciate you taking the time to spell things out for me like that, I hope one day I can return the favor. Maybe if you ever need to know anything about cable television lol :)

If it wasn't for posts like that the people like me that don't have a firm grasp on basic concepts would have a much harder time learning these things. Thanks again I'm printing that up and stowing it in my notes for when it comes up later in my course!

 

[Eric McClean]

Light does not have a shape.

 

[RoughRoad]

Wavefront do have shapes. So doesn't light has a shape?

 

[lightarrow]

...
Once again I will defer to referencing two of Art Hobson's papers. These are two sort papers about teaching students the electron matter wave in hopes of clarifying the electron interference pattern. Despite focusing on electrons, the quantum field model for electron wave and light waves are the same.

http://physics.uark.edu/hobson/pubs/07.02.TPT.pdf

An interesting statement is done in that document:

"Thus, a photon is not really a particle. It is simply a way of talking about the energy increments hf of a spread-out, continuous EM field.

 

[LukeD]

All interactions with photons in QED are at single points, so we can say that as far as QED is concerned, photons are single points. (Though I believe there are theories in which it is larger than a single point and indeed has a shape)

The wave of a photon really isn't the same thing as the photon. We can think of the wave as corresponding to the probabilistic effects of a single photon. However, everything has a wave, even molecules, and the wave of an object can encompass much more space and have a different shape than the object itself.

 

[lightarrow]

All interactions with photons in QED are at single points, so we can say that as far as QED is concerned, photons are single points.

Ok. Now the question is: where is that single point? In the space between source and detector or at detector location?