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From: NoEinstein on 12 Jun 2010 20:36
On Jun 12, 12:39 am, Timo Nieminen <t...(a)physics.uq.edu.au> wrote:
>
Dear Timo: Momentum is: The increase or decrease in the impact force
of a mass due to the mass's velocity, measured in increments of the
standard velocity of 32.174 feet per sec. The correct formula for
momentum is: F = v / 32.174 (m). Please explain what you
'suppose'... "(total) momentum", "momentum density", "momentum flux",
and "momentum flux density" mean?? — NoEinstein —
>
> On Jun 12, 11:24 am, "Sue..." <suzysewns...(a)yahoo.com.au> wrote:
>
> > On Jun 11, 4:17 pm, Timo Nieminen <t...(a)physics.uq.edu.au> wrote:
>
> > > For a beam of light, the radiation force is the change in the momentum
> > > flux when the beam is reflected, refracted, or absorbed. For a photon,
> > > the impulse imparted to a reflector, refractor, or absorber, is the
> > > change in the photon momentum when it is reflected, refracted, or
> > > absorbed.
>
> > The notion certainly didn't come from the sci-fi
> > shelves. It may  be instructive to examine the
> > differences in two concise statements.
>
> > <<Since the force on a dielectric object is given
> > by the change in momentum of light induced due to
> > refraction of the light by the object, the total
> > force on the object is the difference between the
> > momentum flux entering the object and that leaving
> > the object. The total force on an object due to
> > refraction of light is therefore >> eq3,p2
> > "Optical Tweezers: Measuring Piconewton Forces"http://www.biophysics.org/Portals/1/PDFs/Education/williams.pdf
>
> In an ideal world, one clearly distinguishes between "(total)
> momentum", "momentum density", "momentum flux", and "momentum flux
> density". In practice, we are sometimes too lazy. This aside, it all
> just comes done to conservation of momentum, or, if you prefer to
> express it longhand, Newton's 3 laws of motion.
>
> > I get  the impression the method is an approximation
> > using kinetic theory to speed up calculations where
> > molecular dynamics (many bodies) is more accurate,
> > but too intense computationally for a laboratory
> > tool. Just one more reason I hesitate to scale
> > it up to larger objects.
>
> Matter, ultimately, isn't a continuum characterisable by a simple
> epsilon, mu, and sigma (or mu and complex epsilon). "Atomic theory",
> in the old sense of the word, kinetic theory, the existence of
> discrete atoms (well, they were assumed to be a-tomic, literally) is
> the first of our non-classical, quantum, theories. Classical theories
> assuming continuous matter are just an approximation. Where the
> approximation is sufficiently good so as to be exact past the point
> where we stop bothering to write down digits, it's a pretty safe
> approximation to make.
>
> Same for the EM field. If we're interested in the time-averaged force,
> whether the time-average over 1 optical cycle, or merely an average
> over a time orders of magnitude shorter than the time-scale on which
> the measurements we're comparing with, classical EM theory is a very
> convenient approximate method for dealing with, e.g., 10^20 photons
> per second.
>
> Worry instead about failure as we scale down, not up!
>
> > Can one learn about the Rayleigh regime and the
> > Mie regime anywhere near books about the Mao regime?
> > (Spudnik wanted me to ask because he is too shy)
>
> Despite Mao's rhetoric on Western physics, he didn't have anything
> against the core concepts in particle physics. Quite friendly to them,
> even, since positive and negative charge merely demonstrates that the
> validity of materialist dialectics extends to the physics world. He
> knew of, read, and had published in Chinese, work by Sakata Shiyouchi.
> Apart from his "Talk on Sakata's article", he mentioned Sakata's work
> elsewhere. Perhaps the would-be philosopher of dialectic materialism
> who wants something from Rayleigh and Mie might find it in E vs H, TE
> vs TM. Considering the latter, and the consequent affront that a third
> polarisation would be to the core principles of dialectic materialism,
> we find a sound socialist affirmation of div(E) = 0 = div(H). Plasma,
> therefore, is deeply reactionary, as well as potentially quite
> reactive.
>
> http://www.starpathvisions.com/enchanted.html- Hide quoted text -
>
> - Show quoted text -

From: Sam Wormley on 12 Jun 2010 21:28
On 6/12/10 7:46 PM, NoEinstein wrote:
> Dear Sam: The time (CLOCK) slowing is caused by ether pressure. The
> real time rate never varies!

Clock rates are perspective dependent. Two different observers can
measure different clock rates. This happens all the time and shoots
your theory to the rubbish heap.
From: Sam Wormley on 12 Jun 2010 21:30
On 6/12/10 7:36 PM, NoEinstein wrote:
> Dear Timo: Momentum is: The increase or decrease in the impact force

Nope. Momentum is conserved in closed systems. Momentum can be
changed by force. See Newton's second law: F = dp/dt



From: Sue... on 13 Jun 2010 06:11
On Jun 12, 4:46 pm, Timo Nieminen <t...(a)physics.uq.edu.au> wrote:
> On Jun 12, 9:04 pm, "Sue..." <suzysewns...(a)yahoo.com.au> wrote:
>
>
>
> > In this less than ideal world there is still some
> > expectation that displacements will at least have
> > the correct signs. The "push" of a pressure
> > won't become the "pull" of a suction just by
> > small changes in and experiment's size or changes
> > in a dominate mode. The scale of your tweezing
> > example is specifically where the effects of
> > London forces would cause such an inversion of
> > force.
>
http://en.wikipedia.org/wiki/Lennard-Jones_potential
>

> A force between what and what?

The simple case is between the emitter and the
~reactant~. That is implicit where the term traversed-volume
was used. But multiple ~reactants~ are possible as you
describe below.

> Take a sphere in a uniform medium. If
> the medium pushes on the sphere more or less ("pull" if you want, with
> the usual cautions on "pull", vacuum "sucking" etc), what does this do
> to the motion of the sphere? (OK, a medium with a temperature gradient
> isn't uniform, see below.)

Good idea. Let's put aside the effect Wikipedia describes
as Radiation-pressure with the traversed volume
Boltzmanmm constant etc.

For induction couplings the media and the reactant(s)
are modeled (actually simulated) together. Here
is one (of several) long-range methods that has been
~firm-wared~ :

http://www.research.ibm.com/grape/grape_ewald.htm

But it is surely too slow to keep up with a tweezers
operator.

>
> Where sphere meets sphere, or sphere meets cell, or sphere meets
> substrate, this is a different story. These things stick, and vdW/
> London forces are among those at work. These don't scale with trapping
> beam power;

Indeed, more illumination just gives induced dipoles
more power to do what they were already doing.

> enough power can unstick the stuck.

I could be wrong but position relative to the
beam-waist might be more important than power.

> It's a known practical
> issue, sometimes useful, sometimes really bad, sometimes avoidable. (L-
> J isn't the same, and isn't relevant here beyond a not-needed-for-the-
> current-purposes explanation of why real matter isn't as compressible
> as an ideal gas.)

"why real matter isn't as compressible as an ideal gas"?

Tim freely admits he is an incurable thread hijacker
but are you sure that is one of his vicims? Atom
lasers might inform us too but focus (figuratively
speaking) seems to be what is lacking.

>
> (Salt (i.e., NaCl) crystals are _really_ sticky!)
>
> > And the mode alters the displacement as well:
>
> Yes, it does. In the way expected from the usual theory of photon
> momentum/radiation pressure.
>
> > Optical tweezers based on Laguerre-Gaussian
> > beams have the unique capability of trapping
> > particles that are optically reflective and
> > absorptive.
>
> This isn't true. If one is fussy and demands 3D trapping, then LG
> beams generally don't give you 3D trapping of reflective or absorbing
> particles; in the typical experiment, the particles are trapped in 2D,
> and pushed against a surface. If this is sufficiently trapped to be
> called "trapping", then this isn't unique, since you can do the same
> with a Gaussian beam. Low-index particles are another story (even if
> still a 2D story), but that isn't the wiki-claim.

Hmmm... Now you've got me thinking I should try to
get a few more years of service from the tweezers
that came with my toiletry kit.

>
> > If Newton's first and second laws can replace intensive
> > molecular dynamics to make a tool easier to
> > use, that's fine with me. But I don't see
> > the basis for sweeping statements that apply
> > with any great generality.
>
> There are two kinds of approximations we can make here. First, we can
> use convenient approximate theories, such as continuum models of
> matter, classical electrodynamics, simple semi-classical models of
> atoms for atom trapping. Using conservation of momentum _isn't_ an
> approximation of this type; as far as we know, it is correct at all
> scales.


> If the usual classical (i.e., continuum) approximations work
> for tweezers, they should be fine for larger scales, too.

Well, If you are blasting sticky things loose with power
that may not be very different from considering 1 or 2
trips through the media. (wiki's version of radiation pressure)

> Be careful
> when going down to trap nanoparticles, quantum dots, molecules, and
> atoms.

Yes, that's Mie, Rayleigh and London effects discussed
above.

>
> The second kind of approximation is ignoring effects that are
> (hopefully) not relevant. This is where one can go wrong much more
> easily. What to do? Know what you need to include, know what can be
> safely excluded, and measure or observe what you aren't sure about.
> What else? Be careful, because previous measurements might have been
> made at quite different size scales; you need to know how these things
> scale.
>
> For radiometer forces in particular, how can we do this? Measure
> directly, iirc this has been done by Ashkin, in his pre-tweezers
> (1970-1986) optical force work;

Probably older than this:

http://puhep1.princeton.edu/~mcdonald/examples/optics/ashkin_prl_40_729_78.pdf

> in a gas, so not very relevant to
> trapping in liquid. Vary refractive index or reflectivity while
> keeping absorption and heating the same, or at least not varying in
> the same pattern. Done, e.g., R. V. Jones (forces on things in various
> liquids), lots of tweezers experiments on objects with varying
> refractive index (and therefore varying reflectivity). Even some of
> the optical torque experiments are relevant - the ones with absorbing
> particles (e.g., Friese, Enger, et al., 1996). Vary the absorption and
> keep other stuff the same. Done, e.g., trapping in D2O vs H2O, thermal
> damage to specimens as function of wavelength, slightly absorbing
> particles. Directly measure forces due to thermal gradients in liquids
> (a.k.a. thermophoresis), also done. The lack of temperature dependence
> of the usual tweezers forces, the "scattering" force and the gradient
> force, has been adequately shown.
>
> Not to leave out the really conclusive ones: look at atom trapping,
> where the effects of the background gas is catastrophic to the
> trapping.

Heating of the interstellar media would not seem helpful
for holding a solar-sail in place. That is not a catastrophe
if the intent was propulsion.

Wasn't there a program to change these silly words to
honour people? Cycles became Hertz, Centigrade became
Celsius. Catastrophe probably became Bush or Haward when
you weren't looking. >:-)

>
> Next, does the known physics that is included in the model explain
> what is seen? If so, either all of the important stuff is included, or
> non-included stuffs almost exactly cancel each other out, or non-
> included stuff cancels an error or other problem with the included
> stuff (including, of course, non-existence of the included stuff,
> everything being due to the non-included stuff). Also done.
>
> There was an old optical tweezers pre-print claiming that the forces
> seen in optical tweezers are thermal. (On arxiv? I can't find it
> there.) You might be interested in looking for this. We can discuss
> here, if you wish.

Wiki has the Nichols Radiometer grouped with solar sails. If
the device fits better with tweezers, showing how and why
could be a useful contribution. As you've shown above,
there is a good bit of material that has to be considered
and some is not freely available on the web.
It is more than one hobbyist should take on.

If Tim is interested in review and possible edit of the
relevant wiki pages then I might scrounge a little
time myself. That could be a productive way to better
illuminate the forces in play.

Sue...
From: Tim BandTech.com on 13 Jun 2010 14:40
On Jun 11, 4:17 pm, Timo Nieminen <t...(a)physics.uq.edu.au> wrote:
> On Jun 11, 9:38 pm, "Tim BandTech.com" <tttppp...(a)yahoo.com> wrote:
> > On Jun 10, 10:31 pm, Timo Nieminen <t...(a)physics.uq.edu.au> wrote:
> > > On Thu, 10 Jun 2010, Tim BandTech.com wrote:
> > > Your original argument wasn't coherent, then. As far as I could tell, you
> > > thought it improper that almost all of the energy should go into heating,
> > > not work.
>
> > Jeeze. I pity any onlooker who attempts to decode your own position.
> > Now, via double crossing, I must admit that I do agree with your
> > statement above and that this is exactly what I've been discussing all
> > along.
>
> So, you agree that "improper that almost all of the energy should go
> into heating,
> not work" is a fair summary of your original argument?

It's not so much the stress on 'improper' so much as it is an
observation on the amount of claimed kinetic energy present via the
momentum computation versus the amount recoverable, and most important
that in light the claimed maximum amount of this mechanical work is so
slight. It is this relative discrepancy to the case of the bullet that
you yourself admitted some posts back. I see no point in carrying on
some dispute here. You've contradicted yourself several times here and
I cannot hold a coherent debate when the other side shifts position
per post, then attemtps to degrade the postion which they supported
two posts ago, where I claimed at the end of your paragraph you might
as well have stated 'yes, exactly!' where you opened with 'Not at
all."

>
> Then what complaint do you have against the bullet example? In the
> bullet example, almost all of the energy goes into heating. Surely
> this is just as "improper". If it's OK for most of the KE of a bullet
> to end up heating the target, rather than doing work, why is somehow
> wrong for a photon?

Well, here the same snipe you've used against me could be used, but
you've already admitted that more of the bullets energy will go into
the targets kinetic energy, so here again I just have to point out how
sullied the position you are taking is.

>
> Note well that in both the bullet and photon cases, you get a force if
> the bullet/photon is reflected with no loss of energy. It's simpler to
> consider the reflection case, since you avoid the complications you
> get into below.

No. I've been avoiding the reflected case because we disagree so
thoroughly on it that I don't know where to go with the conversation.
At some points disagreements should merely be clearly specified. I'll
do my own brief synopsis here but I'm not going to get carried away:

For the case of a perfect reflector no work can be done on the
reflector, for otherwise it would have absorbed some energy from the
source, or from the projectile if you wish, whether light or NATO
bullet. This would not be a perfect reflector since it absorbed energy
and so the argument is stained.

>
>
>
> > > We see the same thing in Newtonian mechanics for a light object in
> > > inelastic collision with a heavy object. Qualitatively, the same type of
> > > thing, most of the energy going into heating.
>
> > It is a peculiar thing to discuss an inelastic collision this way.
> > There are more dynamics here and the options as to what happens with
> > the energy are numerous. For instance, if we could design a spring
> > with a ratchet to capture the projectile then we would only heat by
> > the inefficiency of the spring device, rather than by the objects
> > entire kinetic energy. Likewise as I stated before, this capture
> > mechanism could as well generate electricity, and of course this is
> > the quest of many right now; to capture electricity from the sun, and
> > to do it at a better margin than 20%. We cannot grant the heat clause
> > unconditionally, and instead want the mechanism of that heating. It is
> > not so difficult to see electron disturbance; literally microcurrents
> > flowing in short circuit fashion which provide the heating effect.
> > That these charge concerns are so nearby to the Nichols device is a
> > caveat on the operation of that device. That your light traps are so
> > behaved is likewise a caveat. Some would like to free these electrons
> > to take a larger path. Others would like to ignore them for their
> > inconvenient truth.
>
> Yes, we can explain the heating when an EM wave is absorbed in terms
> of electrodynamics. Are you seeking to attribute the observed forces
> to electron ejection? The atom trapping experiments show it isn't so,
> very clearly. Given that the observed forces are predicted by
> conventional theory to within the experimental error (i.e., better
> than 10% in the less accurate experiments, 0.1% in good experiments),
> it doesn't appear to be significant in the macroscopic experiments
> either. Does the magnetic force on a current-carrying wire depend on
> electron ejection? If not, why should the forces due to an EM wave?

Well, electron ejection, if not ruled out, could play a part in the
miniscule forces of the mechanical radiometers. Likewise within the
optical tweezer experiments the claim to observe something with purity
is going to be tainted by these electrical stimuli. Turning off the
lasers for a moment I suppose is going to settle things down a bit,
right? This could be a very interesting figure; how long, having
stabilized a particle, can the beams remain off and still have a
trapped particle when they are turned back on? There I've gotten in
two questions for your two, so we're two for two. You are focused in
here on electron ejection, but you are happy to draw a strong boundary
between it and conduction. Well, now we are going into atomic theory,
and that is fine, but how far in there should we stray? Well, the
thread flow has gone onto some tangents, but the crux that got us here
was the derivation of the photon momentum as an attribute of the
photon's entire energy due to its wavelength or frequency. It seems
that the possibility of capturing all of that energy as mechanical
energy does exist, at least theoretically. This is not my claim so
much as it is my criticism of existing theory. 1300 watts of
mechanical energy per square meter is a very generous figure to work
with, and helps explain how trees and plants can do so well. It is not
necessary to declare the remainder beyond the momentum as waste heat,
yet that is what the existing theory does.

<snip>
> > > We're not attributing the photon momentum to the photon energy.
>
> > > For a moving bullet, does the kinetic energy cause the momentum? Does the
> > > momentum cause the kinetic energy? Do we attribute one to the other?
>
> > > For the photon, consider a spin +1 photon. How much of its energy is "in"
> > > the angular momentum?
>
> > > Be specific: consider a 500nm photon, with hbar angular momentum. We can
> > > write down 3 numbers: its energy, its momentum, and its angular momentum.
> > > How are these 3 related to each other, showing appropriate concern for
> > > angular momentum?
>
> > > How about for a 5Hz photon? Do the same. Does this mean that a 5Hz photon
> > > shouldn't have any momentum?
>
> > From what I've read of the quantum stuff the angular momentum is not
> > so easy to observe. They even go so far as to grant a photon an
> > orbital angular momentum, though the orbital context is not present in
> > freely propagating light. And yet the light as an oscillation is still
> > a coherent concept, and so the rotation momentum that I am considering
> > is more like your NATO bullet spinning.
>
> > As I recall the 5Hz photon will have the same quantum angular momentum
> > than will the 500nm photon, but will have less total energy via e=hf.
>
> Keep it simple,. don't worry about orbital angular momentum. If you
> can't answer the simple question, why make it more complicated.
>
> Don't get sidetracked into pretty pictures of photons, either, or long
> philosophical tracts. Answer the simple question first.
>
> If the momentum and/or angular momentum are attributed to the energy,
> how much of each, in each case, for the 500nm photon and the 5Hz
> photon? Angular momentum hbar, E=hf, p=h/lambda. Write down the
> numbers, and say how much of the energy is "in" the angular momentum
> (or whatever you mean, when you say that having angular momentum means
> that less energy must be "available" for the momentum).

Hmmm... I like nuggets, depending on what nuggets they are.
So let's ditch the concern over quantum spin and just try a classical
angular momentum, which we should still admit is merely a mechanical
analog to an electromagnetic system.
This seems to allow for a coherent model for polarization of light,
but the longitudinal wave takes on a puzzling problem, for it is as if
the photon is blue shifting and red shifting in this longitudinal path
per cycle. Also, to balance an angular momentum we might like to split
our photon into two or more parts such that a balancing effect can be
implemented; otherwise we have one particle travelling in a circle for
no apparent reason. To what degree should I attempt a full model or
just consider the energy equation? I do like the idea of getting a
physical meaning out of the photon's wavelength, for that is how it
came to be, yet modern theory does little with this figure
geometrically.

For now because I do not have a full theory Let's just consider the
photon's energy total
Et,
A net kinetic energy
Ek,
and a rotational energy
Er.
It seems clear that
Et = Ek + Er .
We could introduce some factor such as
Er = r Ek
so that r is a constant. From my understanding, because the amount of
energy present in a photon is so great relative to the amount of
mechanical force claimed this is possible. As to how we would unravel
the math, well, that is another thing. The first problem with the
momentum interpretation is that it relies upon
e = m c c
and we already admit that there is no mass present. The math is
convenient, but is it truthful? Any declaration of a momentum figure
suffers this problem, because there is a kilogram unit in there. At
least we understand that energy can be transformed so that kinetic,
potential, electrical, etc. energies can exist simultaneously. One
problem with rotational momentum is that it will always be defined in
terms of translation within a Euclidean system. Within this analysis I
am not concerned about the reflective situation, because I have
already dismissed the momentum doubling transfer claim. All that I can
do so far is leave the problem open. I have no figure for r above, but
I cannot see why it should not be so. I don't seem to have two nuggets
yet, so maybe you could fill those in.

>
> (There are 2 potential nuggets to be had here, if you bother to do
> it.)
>
> [moved]
>
> > > The ratios or values of energy, momentum, and angular momentum, as
> > > commonly stated for photons, come straight out of classical
> > > electromagnetic theory. Are these ratios or values wrong? Yes or no, no
> > > handwaving, no waffle, just a straight answer.
>
> > As you seek a straight answer I must ask you how crooked is the path
> > of modern theory? Yes, we'd all like a straight answer, yet we do not
> > actually have one yet. This is not to say that we should give up. We
> > seek a straight answer, but I must admit that I do not yet have one.
>
> If you can't say straight-out that it's right or wrong, from what
> information are you arguing?

Well, above I've argued it from the usage of e=mcc to claim a photon
momentum, but I think that particle/wave duality is another stance
that is openly accepted as a self contradiction.

>
> It's simple in a way. We can, directly from Maxwell's equations, by
> finding the induced currents and dielectric polarisation, find the
> force acting on the current and polarisation, via the Lorentz force,
> and find the work done on the current by the field (which is the
> heating).
>
> > beyond this it seems that in the accumulation the overlap of radiation
> > pressure with photon momentum has gotten lost in the shuffle.
>
> No. Or if it did, stop shuffling it. It isn't an overlap, one is the
> rate of change of the other.

Well, I see this description in the link that Sue posted here on Jun
11:
"Radiation pressure is a force per unit area on an object due to
the change in momentum of light."
- http://www.biophysics.org/Portals/1/PDFs/Education/williams.pdf

If the radiation pressure is a constant, then the rate of change of it
will be zero.
This interpretation seems to require a target to generate the
pressure, yet it is claimed to exists independent of the presence of a
target.

No, I do not believe that this interpretation is accurate. I have been
thinking this over and I believe that the best resolution is to accept
that photon momentum exists within the particle interpretation, and
that radiation pressure exists under the wave interpretation. Thus
these two exist in isolation within those branches, and have been
confused due to the confusion of accepting particle/wave duality.

>
> For a beam of light, the radiation force is the change in the momentum
> flux when the beam is reflected, refracted, or absorbed. For a photon,
> the impulse imparted to a reflector, refractor, or absorber, is the
> change in the photon momentum when it is reflected, refracted, or
> absorbed.
>
> If light has momentum, there must be a force when this momentum
> changes. If light can exert a force, it must have momentum. The simple
> versions of the derivation of radiation pressure make use of this
> explictly, which isn't what I would call "getting lost".
>
> This is just Newton's laws of motion, just a statement of the
> conservation of momentum. (It isn't a full application of Newtonian
> mechanics, with Newton's momentum = density * volume * velocity, but
> Newton's laws of motion are fine.)
>
> Newton 2 works for radiation, for waves, for photons. Force is the
> rate of change of momentum, imoulse is the change in momentum. This
> isn't lost. If you prefer to think about photon momentum or wave
> momentum instead of force or radiation pressure, go ahead. But don't
> forget Newton 2!

Well, by my own interpretation that I suggest above, then your
language is a lost cause. Going back to Maxwell's Treatise, I believe
that his radiation pressure was not conditional upon any target.
Still, he uses a kinetic term that is not in use today. I do seek
openings for a new theory, but don't really have one yet. It seems
that we've bottomed out on the rotational momentum claim on a photon
for now, but it wouldn't surprise me if a new theory makes good usage
of rotational principles, just as they exist within electromagnetic
theory.
Your own cross product expressions that you use in your paper are
nearby, but you never did explain the instantaneous zeros. Well, these
rotational systems do not necessarily work over to Newtonian physics
so well. Maxwell's expressions do bother to square the sinusoids. The
photon momentum could be more of an AC effect than it is a DC one.

We have engaged in a mechanical discussion here that is not
necessarily an accurate portrayal. The slightest charge difference
could drive the mechanical radiometers. This is not so much about
electrons ejected inches from the receiving plate, but perhaps microns
from the plate, to return shortly thereafter. This thought makes me
ponder variations on those radiometer experiments which could apply to
your tweezers as well. What is the difference in behavior of metal
particles versus insulating particles?

- Tim
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