Re: wave and light
From: Andr? Michaud (srp_at_microtec.net)
Date: 09/18/04
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Date: 18 Sep 2004 12:48:10 -0700
zigoteau@yahoo.com (zigoteau) wrote in message news:<a836cacf.0409180432.109af886@posting.google.com>...
> srp@microtec.net (Andr? Michaud) wrote in message news:<562f286c.0409170908.11410809@posting.google.com>...
>
> Hi, André,
>
> > Your post got me to thinking of the hypothetical physical structure
> > of a maxwell pure EM wave "if it really could exist".
>
> Of course EM waves exist. Light is an EM wave.
To my knowledge, since Wien and Planck, we know that this is no so.
Even if plane wave treatment gives precise results at the macro level
this can't mean that light is not quantized at the fundamental level.
Light has been proven ad noseam to be physically quantized and no
argument for or against can change anything about it.
> > Maxwell's original theory (before the idea of photons was conceived
> > of) has traditionally been dealt with strictly from the mathematical
> > point of view offered by plane wave treatment, which resulted, obviously,
> > in the space geometry that mandatorily must underlie it to perpetually
> > remain obscured.
>
> Obviously?
Not obvious to all, obviously :-]
> > Space being three-dimensional, it seems to me that treatment by plane
> > wave analogy can only be a mathematical approximation that easily
> > obscures the fact that physically, an actual electromagnetic wave,
> > if they could exist as Maxwell defined them) could only be in spherical
> > expansion in vacuum from its point of origin, assuming unbounded
> > isotropic expansion in deep space; Maxwell's equations describing
> > the electromagnetic interaction only once the wave already is in full
> > swing and has begun to propagate.
>
> This all seems OK, eve if the way you express it suggests you don't
> know how to analyze it.
Thank you for your appreciation. You mean of course that I don't
analyze it in sync with orthodoxy. I agree. I am totally unorthodox.
> > Consequently, if electromagnetic waves such as Maxwell imagined really
> > existed, the geometry of their propagation would of necessity be much
> > more similar to the spherical expansion of sound waves in the air than
> > to the propagation of waves on a plane liquid surface, but it then
> > becomes somewhat difficult to accept the idea that the intensity of
> > the initial energy of the wave could be maintained at all points of
> > the wave front.
>
> Well of course, real light beams usually become weaker with distance,
> although using a lens you can get the intensity to increase for a bit.
Real "light beams" become "weaker" with distance only because of
angular spread of the photon stream. Don't forget that each individual
photon is emitted by a different quantum jump of an electron moving
to a lower orbital in as many atoms, not even considering repetitions
on the same atoms or quantum jumps to lower states in nuclei.
The lens increases the intensity only by causing photons in the
spread out "beam" to travel closer together.
> > Obviously, he found no way to mathematize the wave at its source,
> > most probably due to the insurmountable problem caused by the assumed
> > infinite energy that is associated with all such a punctual electromagnetic
> > event in his theory.
>
> Maxwell lived a long time ago, and various aspects of the analysis
> have become easier with new methods.
Not for this particular problem, to my knowledge.
> > That's where photons came into the picture to solve the problem of
> > maintaining the energy at all points of the so-called wavefront.
>
> No. Your statement here suggests that you don't know any quantum field
> theory.
I know about QFT. Although mathematically useful, I disagree that it
represents fundamental physical reality. Just like Maxwell's theory,
although useful and precise at the macro level, can't account for
quantization.
> Maxwell's equations are still the basis for modern quantum optics.
Of course. Why not!
> > Plane wave treatment does that, as for physical counterpart,
> > only photons come to mind, and not continuous spherically
> > expanding wave.
>
> Mathematically-perfect plane waves cannot be implemented. However
> it is possible to implement beams of light whose behavior can be
> understood in terms of the ideal mathematic objects. It is possible
> to do even better and treat a real light beam as if it were the sum
> of an infinite number of ideal plane waves.
Sure. At the macro level, the method is clean.
> > > A traveling EM wave consists of coherently arranged
> > > photons, and while it might be empirically impossible
> > > to define a wave front of zero photon energy density,
> > > Old Man knows of no theoretical limitations against
> > > doing so.
> >
> > Since the photon concept (discrete EM events individually moving at c)
> > cannot truly be reconciled with the continuous wave idea (I don't
> > see how, anyway), I can't comment on this.
>
> It sounds as if you have been confused by quantum mechanics. There are
> a lot of people in this situation. I'm not sure if I can totally go
> along with Old Man's statement.
I am not confused by QM. QM is not in the picture at all. I was
talking about the probable physical geometry of Maxwell EM wave if
it could exist at all, not about its mathematical treatment.
> The word 'photon' describes the particle-like aspects of light.
Yes. It describes what light physically is. A bunch of quantized
EM particles individually travelling at c.
> However there is nothing in the quantum field theory of light with the
> individuality suggested by the word.
That's the main reason why I disagree that QFT could really represent
physical reality.
> In modern quantum optics, 'photon' is used almost synonymously
> with 'electromagnetic field'. The particle aspects are apparent when
> the field is observed. A silver halide grain turns to silver,
Chemical dissociation ?
> or an electron-hole pair is created in a block of silicon,
You mean a free moving electron plus a positive ion ?
> and you can say that a photon has been absorbed,
Yes.
> but you would not have been able to predict from the theory which
> grain, or where the e-h pair would materialize.
Why should this be important. I dont think that chemical or
electromagnetic processes care what I think. They just proceed
with or without my consent when circumstances are ripe for them
to proceed.
If I can't name tag the grain or the e + positive ion pair that
absorb a photon on Mars, would it mean that it does not occur
anyway ?
It seems to me that even before mankind appeared, the universe
did pretty well all the same, no ?
Physical reality doesn't seem to care at all whether or not we
can predict it.
> The EM field in any system has modes. You can say "Mode A has 5
> photons in it, and mode B has 6 photons". You can never have a
> fractional number of photons. However you can't say where the
> individual photons in each mode are at any one time, and you certainly
> can't label them and say, "There's the 3rd photon of mode A". If the
> system was definitely in mode A at the beginning of the experiment and
> definitely in mode B at the end, you can say that there's one more
> photon in the system, but you can't say for certain when it arrived,
> because in the middle of the experiment the system is in a
> superposition state.
Sure. But why should it be important that we should know in advance ?
I don't think it is.
> > I can find logic either in continuous EM wave treatement (Maxwell's
> > initial idea) or in discrete EM particles treatment, but I connot
> > reconcile both.
>
> (1) Maxwell's equations are at the basis of quantum optics
> (2) with the added complication of quantization
Yes. Maxwell is the basis of all modern electromagnetic
treatment. With good reason.
> Are you familiar with second quantization notation?
Only superficially. I did not need the approach for my analysis.
> > > Furthermore, it seems that having a wave front of
> > > maximal intensity involves a discontinuity in the field,
>
> > It does only if we try to incorporate the photon idea in
> > wave treatement.
>
> > > whereas a wave front of zero intensity involves, at
> > > most, a discontinuity in the field gradient.
>
> I definitely do not go along with Old Man there. A field discontinuity
> is inconsistent with Maxwell's equations. In quantum optics, the field
> at a point is an operator, which can be attached to a distribution of
> possible values of the classical field. There is no way you can attach
> any operational meaning to the word 'discontinuity'.
>
> On the positive side, quantum optics is a good deal easier to master
> than quantum electrodynamics, the quantum field theory of electrons
> and photons together. If you're serious about learning, I haven't seen
> any textbook good enough to take you from the classical concepts to
> the quantum ones. I think it's essential to have a teacher. I hope you
> can find one.
Thank you for your good encouraging words.
But I am specifically interested in understanding physical reality,
something that I have found to be foreign to the thought processes
of most contemporary physicists.
André Michaud
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