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Offline Gile na Gile

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I've often been confused when thinking about electromagnetic radiation. We have the oscillating electric and magnetic "fields" and we have the notion of light being transmitted in "packets" called photons. We also have the notion of light being both particle and wave.

Where is the photon in the electro-magnetic field? Let us suppose the line of force in the electric field is travelling horizontally, while the line of force in the magnetic field is travelling vertically. Both lines of force are interweaving and intersecting one another as they move along (at the speed of light)creating as they do so the electromagnetic field. Excuse my ignorance but are the photons dotted along these lines of force. Are these lines of force comprised entirely of photons? When I say the "line of force" I mean of course the troughs and peaks of the electric and magnetic waves.

Are the photons the "particle" element of light while the electromagnetic field is the wave?
« Last Edit: 17/12/2009 20:44:01 by Gile na Gile »


 

Offline Vern

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« Reply #1 on: 17/12/2009 21:26:46 »
I don't see how we could consider one force to be the particle and the other to be the wave. I suspect that we can consider the particle to simply be the points of maxima in the amplitude of the fields. The fields drive the points of maxima through space, interaction only happens very close to the points of maxima.

Then I can go on with speculation to produce all the forces in a self consistent hypothesis. But that would need to be in a different forum.


 

Offline Gile na Gile

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« Reply #2 on: 17/12/2009 22:38:32 »
Ok Vern, thanks for the reply.

Let me put it another way. If we regard the point of maxima as particle is this then the photon. All I wish to know is what part of the em field is occupied by the photon/s. I mean the photon is infinitely smaller than the amplitude of the wave so  it is contained within the em -field, so where is it's location within that field. I don't mean it's precise location obviously but isn't the photon for all intents and purposes behaving like a point particle within the area circumscribed by the field.

Also, the way I see it at the moment - and I'm open to correction of course - is that the waves in the em field are composed of particles or a particle and thus you have in a typical wave cross section two particles/photons interweaving and intersecting. It being the manoeuvres of their interactions which create the field in the first place.
 

Offline Soul Surfer

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« Reply #3 on: 17/12/2009 22:59:07 »
The wave and the particle are two ways of looking at the same object.  all fundamental particles even those with mass have wavelike and particle like properies.  It makes no sense to locate the particle at any point in the wave a quantum is a quantum and that is that.  The best way of thinking about it is as a wave packet with a probability function associated with it.  ie it is most probable that if you measured precisely where the particle aspect was it would be in the middle of the peak of the wave but it could in fact be anywhere in the entire universe.
 

Offline Gile na Gile

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« Reply #4 on: 17/12/2009 23:52:07 »
Soul Surfer,

Thanks for an excellent response on the other thread - which I am still attempting to digest.

With regards to what you have said here my understanding of wave/particle duality is that it is the inadequacy of our measuring apparatuses which create the confusion. Were we to somehow have access to a device that could 'freeze' the behaviour of the em field in time would we not be presented with two particles (and no waves) - one whose path draws the troughs and peaks of the magnetic line and the other the troughs and peaks of the electric line. If they were frozen in time however there would be no wave, only two particles. It is only because they are moving at such high speeds and interweaving that a wave effect is created. There may also be an entire train of particles each following the path of another - I really don't know - but I guess it stands to reason if the wave function is proceeding from a constant light source then we are dealing with a constant train of particles.

The question I wished to ask though concerned the photon. Do we regard the photon as one of these two particles? (Let's make it simple and think of the em field as having just two of them) I can see clearly how probability functions are used for practical purposes but my query is really more to do with an understanding for it's own sake, y'know the philosophy of the thing. I am also puzzled by what you mean by saying it - the particle aspect - could be anywhere in the universe (whilst highly improbable). How could this be? Surely the particles are bound to one another within very circumscribed limits - as is evidenced by the amplitude of the wavelengths.

Also, the photon is a part of the atom that has been dislodged from it's shell is it not. Where is it coming from? Is it being emitted by the electron or is it coming from within the atom?
« Last Edit: 17/12/2009 23:56:21 by Gile na Gile »
 

Offline Soul Surfer

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« Reply #5 on: 18/12/2009 00:15:48 »
YOU ARE WRONG  The wave particle duality is a fundamental property of our quantum universe and has to be accepted for what it is.

Let me go back to my simple concept of the hydrogen atom  the single electron has lots of potential metastable orbits (all the potential higher level orbits) and one stable one in the vicinity of the proton. The one with the lowest energy.

Classical physics for a negative charge orbiting a positive charge means that the particle will radiate electromagnetic energy until it collapses on to the nucleus.  Quantum physics decrees that the electron CAN ONLY be found in one or other of the metastable orbits or the stable one.  in moving between one metastable orbit with one energy level to another one with a lower energy level it will emit a single quantum of electromagnetic energy of a particular frequency defined precisely by the energy change.

Once it has radiated all the photons it can and reached the most stable lowest energy orbital (the ground state) it cannot radiate any more.  however if you irradiate it with higher energy photons you can lift the electron to a higher energy state and it will have absorbed a photon

Moving the electron between different energy states requires a proton to be emitted or absorbed.

ALL electromagnetic interactions of which we are aware that is absolutely everything you see hear feel and the physical properties of all materials are mediated by the emission and absorption of electromagnetic energy in the form of photons with one exception and that is the gravitational field of the earth.
« Last Edit: 18/12/2009 00:17:39 by Soul Surfer »
 

Offline yor_on

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« Reply #6 on: 18/12/2009 01:16:26 »
"With regards to what you have said here my understanding of wave/particle duality is that it is the inadequacy of our measuring apparatuses which create the confusion."

No, It's not like that. It's like black holes. Black holes are singularities, meaning unapproachable for us, containing infinities. SpaceTime at our macroscopic level is approachable for us as it has limits defining our 'livingspace', but when you go down to the subatomic level the same phenomena as with black holes happens. Once more we meet those infinities, and probability is what defines what will happen.

So it's not our measuring that is at fault, the truth is that HUP (Heisenbergs uncertainty principle) will rule no matter what refinements we make to our instruments. Thats why Feynman used, don't remember the name really, 'possible paths' or 'many paths' as the best description for defining a particles path. And according to that proposition the particle actually do take all possible paths but with different percentage of probability.


It would be nice if you were right there as we then could get rid of those infinities but as it is the best we can do is to count on probability and arbitrarily 'snip of' those answers that only leads us there, to infinities I mean. To get to the best 'limits' of an answer is a never ending project engaging mathematicians physicists etc all over the world.

Einstein for one dedicated a lot of his later life to find proof of that 'God didn't play dice' but without succeeding

-----

I personally like to see QM and Black holes as two 'opposite sides' of a pole containing SpaceTime in the middle, both utmost ends 'fuzzy' like a fog but with us and our macroscopic SpaceTime as a rather clearcut 'reality' with defined 'laws' and a clear succession of time, from a past to a present, to a undefined but still existing future.
« Last Edit: 18/12/2009 01:31:05 by yor_on »
 

Offline acsinuk

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« Reply #7 on: 02/01/2010 11:18:02 »
Hi Gile
"Are photons the particle element of light and EM electromagnetic field is the wave"
EM light can exist without any particles and in fact by definition must be massless if it moves at the speed of light or otherwise it would represent infinite energy.
The massless energy of photons should be measurable in Joules per cubic metre of magnoflux.
Happy New Year
CliveS
 

Offline Geezer

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« Reply #8 on: 02/01/2010 21:36:41 »
Hi Gile
"Are photons the particle element of light and EM electromagnetic field is the wave"
EM light can exist without any particles and in fact by definition must be massless if it moves at the speed of light or otherwise it would represent infinite energy.
The massless energy of photons should be measurable in Joules per cubic metre of magnoflux.
Happy New Year
CliveS

Clive,

At the risk of getting my head bitten off (:D) I will volunteer an opinion.

IMHO it's all waves. No one has ever observed a photon as a particle. When photonic waves interact with matter, they exhibit particle like behaviour, but I suspect that behavior is more a consequence of interaction with the particles in the matter.

The famous double-slit experiment requires the RF energy to interact with matter - i.e., the matter that comprises the slits.

When someone devises an experiment that demonstrates the particle nature of photons that does not allow them to interact with matter in the process, I'll have to change my view.
 

Offline JP

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« Reply #9 on: 02/01/2010 22:48:07 »
Geezer,

I don't think this was your point, but I'd like to clarify it.  There is no question that there are ways light can behave that aren't modeled by classical electromagnetic waves.  Single-photon states are on example, although there are others.  You can still model them with quantum field theory, which involves wavefunctions, however.
 

Offline JP

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« Reply #10 on: 02/01/2010 22:50:32 »
Also, in answer to Clive's question, photons are viewed as massless particles, so they won't have infinite energy.  Also, "magnoflux" isn't a term that's used in physics.  You probably mean electromagnetic energy density, which would be the amount of energy per volume associated with the electromagnetic field.
 

Offline Geezer

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« Reply #11 on: 03/01/2010 01:39:57 »
Geezer,

I don't think this was your point, but I'd like to clarify it.  There is no question that there are ways light can behave that aren't modeled by classical electromagnetic waves.  Single-photon states are on example, although there are others.  You can still model them with quantum field theory, which involves wavefunctions, however.

Rats! I knew I was rather pushing the envelope!

Ultimately though, is it true that photons can only be detected by their interaction with matter?
 

Offline JP

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« Reply #12 on: 03/01/2010 02:07:42 »
Quote from: Geezer
Ultimately though, is it true that photons can only be detected by their interaction with matter?

Yes, it is.  They might be detectable by their interaction with gravity or other forms of energy, but all our detectors are ultimately made of matter as far as I know.  So ultimately, even if you had to use a quantum model to describe the light, you could do so with quantum waves up until the point of interaction, which is where you would get a "click" that looks like a particle.

I think a lot of that comes down to how you want to interpret quantum mechanics.  All the interpretations have to agree on the results of measurements, but they disagree on the meaning of the mathematics that precede the measurements.
« Last Edit: 03/01/2010 02:11:29 by jpetruccelli »
 

Offline Geezer

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« Reply #13 on: 03/01/2010 04:11:25 »
JP - Thank you for tolerating half-baked notions.

I love the double-slit experiment, because it seems to be central to the photon model. On the other hand, I hate the duality model (wave/particle) because it seems to leave so many questions unanswered.

I'm sure many great minds have pondered these questions, but is it conceivable that the double-slit experiment is slightly flawed in that the slits actually constitute receiver/transmitters of the transmitted energy?

In other words, as the energy is obliged to conform to the dimensions of the slit, it "terminates" so that it is no longer a photon, then the energy propagates to the other side of the slit and appears as photon.
 

Offline JP

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« Reply #14 on: 03/01/2010 17:34:18 »
I think the only two things you need to grasp in order to understand why classical waves and classical particles don't fully explain light is to look at the two slit experiment and the photoelectric effect.  In the two slit experiment, light from the two slits forms a fringe pattern, and fringes are something you get from waves, not particles.  This shows that light has characteristics of waves.  The photoelectric effect shows that light deposits its energy in tiny packets whose energy only depends on the light's frequency, not on its intensity.  Since classical waves can have a continuous range of energies, the photoelectric effect means that light behaves like particles insofar as you have some "minimal energy packets" of light that can't be subdivided. 

You're absolutely right that working out the details of the two slit experiment for individual photons is a nightmare--the two slit experiment is perfectly well explained by classical waves, however, and at least experimentally it seems to hold for single photons as well.  If you turn down the light source so low that only one photon at a time is expected to pass the slits, you still get an interference pattern.  In order to theoretically describe the experiment in terms of photons, you'd have to do as you said--figure out how they interact with the matter making up the slits, which would be complicated.
 

Offline JP

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« Reply #15 on: 03/01/2010 17:55:53 »
By the way, there is another concept that gets confused a lot in dealing with light.  Rays are not photons.  Rays were used historically since they can provide a good approximation to the behavior of classical light waves in certain cases.  In particular, they can be very accurate when modeling highly incoherent light, such as thermal sources, which were all that was available to early experimentalists.  Thinking of light as little particles traveling along straight lines (rays) allowed physicists like Newton to model a lot of optical effects, including reflection and refraction.  The two slit experiment was important showed that particles/rays weren't the whole story since light has wavelike characteristics as well.  It wasn't until much later (in the early 20th century) that scientists discovered that light seemed to be made up of photons.  These photons have much more complicated behavior than the rays of classical optics, and can lead to optical effects that can't be modeled by classical optics. 
 

Offline Geezer

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« Reply #16 on: 03/01/2010 19:54:13 »
Thanks JP! As always, most informative.
 

Offline acsinuk

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« Reply #17 on: 04/01/2010 11:42:15 »
Also, in answer to Clive's question, photons are viewed as massless particles, so they won't have infinite energy.  Also, "magnoflux" isn't a term that's used in physics.  You probably mean electromagnetic energy density, which would be the amount of energy per volume associated with the electromagnetic field.
Yes, I would confirm "magnoflux" is definitely electromagnetic energy density and should be measured in Joules/cubic metre.  Any other way of defining energy will lead into conceptual errors of imagining that the energy has to have the mass of a particle associated with it?
 

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« Reply #17 on: 04/01/2010 11:42:15 »

 

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