Taking a Fresh Look at the Physics of Radiometers.
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From: NoEinstein on 4 Jun 2010 14:38 On Jun 3, 5:09 pm, "Tim BandTech.com" <tttppp...(a)yahoo.com> wrote: > Dear Tim: You have the right sort of analytical mind! I've made a new post about my proposed Gravity Swing experiment. That should answer most of your questions. If you have access to funding, that experiment would be well suited to your intellect. NoEinstein > > On Jun 2, 6:09 pm, Timo Nieminen <t...(a)physics.uq.edu.au> wrote: > > > On Jun 3, 12:46 am, "Tim BandTech.com" <tttppp...(a)yahoo.com> wrote: > > > I'm sorry but the effect in a perfect vacuum has not been clearly > > > demonstrated. As you've accepted the flaws of Nichols work then the > > > question of whether the radiation pressure is observable in vacuum > > > still exists. The experiments that you've exposed in your paper must > > > not be the modern experiments that you speak of. > > > Perfect vacuum, no. Very good vacuums, yes, especially with atom > > trapping. I've seen classical experiments done in vacuum (can't recall > > how good), where absorbing particles were blasted by short pulses of > > light, to measure their radiation pressure cross-sections. > > > The bulk of the modern experiments aren't experiments on radiation > > momentum; they just use it in the experiment. But the experiment by > > Calos Lenz Cesar's group (http://apl.aip.org/applab/v87/i22/p221109_s1 > > as cited above) is an excellent modern experiment. > > There are a number of weak points in the post that I am responding to, > but I want to focus on one for now. I'd like to come back to some of > the others later, but here is one crux that still is unanswered. The > link > http://www.mcallister.com/vacuum2.html#params > exposes that modern vacuum apparatus is capable of 10E-11 torrs(mm of > mercury). > One experiment exposing the Nichols or Crooks radiometers operating > cleanly at this gas pressure would be quite a piece of evidence. > Nichols got down to .02 torrs, and had an anomaly between .05 and .02. > > As you identified, there is a confluence between radiation absorption > as temperature and a figure of radiation pressure. Specific dependence > upon atmospheric effects is already understood. The word 'radiometer' > is intended as a device to measure the amount of radiation. We would > like a 'radiation pressure meter' which will not generate any > behaviors due to thermal absorption from the 'radiation energy' which > I believe you will agree is encompassed in > e = hv > as a sum of photon energies. Because the 'radiation energy' is so > substantial at 1300 W/m/m for sunlight then eliminating the effect of > this large energy which could easily power quite some motive work is a > substantial problem for the verification of the claimed pittance that > is 'radiation pressure'. I see no work so far that proves the > existence of radiation pressure since all of the experiments that I > have seen do rely upon some gas effects. The only claimed exception > that I've read so far is Nichols, and his logic is falsifiable. None > of the experiments you've studied consider a solid dielectric placed > in a vacuum of 10E-11 torrs, which would be a fine experiment with a > Nichols torsion fiber style experiment. > > Here is a link I just came accross very similar to your own work > though more concerned with semiconductors: > http://www.colin-baxter.com/academic/research/downloads/prl063802.pdf > I do not have access to pay for links like the aip.org link you site > about optical tweezers. > Here is another link in support of the challenge to radiation > pressure's validity: > "It is therefore much more likely that in a given case the apparent > 'radiation pressure' is caused either by thermal surface effects or > electrons which are released from the surface by the radiation." > -http://www.physicsmyths.org.uk/#radpress > This would really be something if Nichols anomaly was repeatable and > turned out to be a mild photoelectric effect. > It was after all an inversion. A freed electron would exit the > silvered side; not the insulated glass side. The photovoltaic cell is > the rectifier that converts AC light to DC. You've ignored the > instantaneous momentum argument I made haven't you? This AC/DC > problem, well, now I'm going too far again. One thing at a time, eh? > > - Tim > > > > > > > > > > > If the reflector is moving, there will be a Doppler shift, and energy in > > > > > > will be different from energy out. If the reflector is stationary, then > > > > > > you could have, e.g., 1300W in and 1300W out. But no work would be done. > > > > > > Very good. We have agreement, particularly at the low velocities that > > > > > these instruments work at. As far as we can tell there is no reliance > > > > > upon red shifting of light, which could provide some work. > > > > > The force doesn't depend on redshift. But it doesn't take any > > > > expenditure of energy to produce a force - just ask a fridge magnet or > > > > a paperweight. Having the force do work does very much depend on > > > > redshift, since the reflector has to move for the radiation pressure > > > > to do work on it. > > > > Awww, come on.... The claim is that the force is doing work, and the > > > existence of any redshift in doing that work has been completely > > > ignored in any of these theories or experiments. > > > This is just wrong. It's true that a lot of the theory doesn't take > > any redshift into account, but that's because they're calculating the > > force on a stationary object, when there's no redshift. (more below) > > > > Without doing some > > > work there will be no indication as of a vane which rotates on a > > > tensioned fiber. We know we're at extremely low velocity in this > > > experiment, so any redshift observed would be a highly impressive > > > mechanism. > > > At very low speeds, you don't need to deal with redshift to find > > forces in classical experiments. The force exists at v=0 (when there > > is no redshift and no work), and for small v, the force is almost > > exactly the same. The difference between the v=0 force and the small > > but non-zero v force is much, much, smaller than can be detected in > > most experiments. > > > It does matter in atom trapping and cooling, and is essential for the > > proper functioning. > > > > I don't mean to get too ornery, but you are sweeping over these points > > > as if there is no fundamental problem. > > > In this case, there isn't any fundamental problem. The known theory > > gives a very good quantitative match for the observed results. > > > > we will first need something working in vacuum > > > which observes the supposed radiation pressure. > > > Basically, the atom-trapping experiments are as close to "perfect > > vacuum" experiments as will likely be available. > > > > From the theoretical > > > side there is a reliance upon a third of the energy density for this > > > pressure that we still have not arrived at, though you've gotten very > > > close in Maxwell's treatise. > > > No, there isn't any such reliance; as I already said, there are many > > pathways (Lorentz force, Noether's theorem, thermodynamics, the simple > > derivation in my other post). (The 1/3 turns up for omnidirectional > > radiation, like blackbody radiation. For a directed beam or a plane > > wave, p = P/c.) > > > > Here is the strongest link that I have > > > found in support of challenging the existing theory: > > > http://www.neumann-alpha.org/lightpressure.pdf > > > This site is a bit out there, but then, so too was Nichols. Any who > > > will rest on top of his work, and that is how science is done, are on > > > a shaky ladder. > > > Will look when I have time. > > > -- > > Timo- Hide quoted text - > > - Show quoted text -- Hide quoted text - > > - Show quoted text -
From: NoEinstein on 4 Jun 2010 14:44 On Jun 3, 6:09 pm, spudnik <Space...(a)hotmail.com> wrote: > Dear Spudnik: Please leave the name of the person to whom you are replying at the top. Or just say: "Dear Timo, or etc." And try to shorten your replies. "Truth in science is INVERSELY proportional to the amount of words needed to explain things! NoEinstein > > how can there be "pressure" from a massless wave?... I know, > "photonics" is a huge field, but you don't have to use equations > with momentum to describe lightwaves; the photoelectrical effect > is electronic. how do photons interact with atoms, > excepting electromagnetically via electron orbitals? > > thusNso: > current Sci ... no, it's in Nude Scientist, issue-before-last cover- > article, almost like it's New Science, covering the main three > orbital variations of Milankovitch. now, it is just not true that > humans cannot (or aren't) affecting the climate; > the tiny differences of insolation form the orbitals probably > are not "forcing" anything, just tweaking them. > > any real theory of glaciation has to account for "glass house gasses" > as the primary forcers, and how the biota & tectonic systems interact > with that. > > > There is not a single article anywhere describing what the Earth's > > orbit is doing as it moves along its annual circumference so this is > >http://daphne.palomar.edu/jthorngren/tutorial.ht > > Commentariolis > > thusNso: > yes, but special relativity assumes general relativity > in the "twin paradox," because acceleration is required > to get the home-leaving twin, relativistical (I mean, Duh .-) > > > Special Relativity considers that relativistic effects such as time > > dilation and length contraction are perspective effects that occur > > when an observer observes an object moving relative to himself. > > thusNso: > anyway, Einstien's **** is not really dysprovable, if > it is merely a matter of odd interpretations (viz, *photon* > means "particle" ipso facto "herr Albert thought, So.") > > thusNso: > always the "doubling" of CO2 is used as an outcome in the GCMs, > when it is clear that there would be change of the whole phase > of the weather, before that was reached (if you are familiar > with studies of the Quaternary Period, Shackleton et al e.g.). > > Dear Editor; > The staff report on plastic bags, given when SM considered a ban, > before, refused to list the actual fraction of a penny, paid for them > by bulk users like grocers & farmers at markets. A rational EIR'd > show that, at a fraction of a gram of "fossilized fuel (TM)" per bag, > a) > they require far less energy & materiel than a paper bag, and b) > that recycling them is impractical & unsanitary, > beyond reusing the clean ones for carrying & garbage. (Alas, > the fundy Greenies say that the bags are not biodegradeable, > but everyday observation shows, they just don't last so long.) > > As I stated at that meeting, perhaps coastal communities *should* ban > them -- except at farmers' markets -- because they are such efficient > examples of "tensional integrity," that they can clog stormdrains by > catching all sorts of leaves, twigs & paper. But, a statewide ban is > just too much of an environmental & economic burden. > > --Stop BP's and Waxman's capNtrade arbitrageur rip-off!http://wlym.com
From: NoEinstein on 4 Jun 2010 14:49 On Jun 4, 7:59 am, "Tim BandTech.com" <tttppp...(a)yahoo.com> wrote: > Dear Tim (and Timo): Photons are massless ENERGY. Such don't impart a kick to the mirror when such arrive, nor do they impart a "thrust" (force), 1/2 phase later, when they are re emitted. My proposed Gravity Swing experiment (Please search and find.) should prove those points, conclusively. NoEinstein > > On Jun 3, 5:59 pm, Timo Nieminen <t...(a)physics.uq.edu.au> wrote: > > > On Jun 4, 7:09 am, "Tim BandTech.com" <tttppp...(a)yahoo.com> wrote: > > > > As you identified, there is a confluence between radiation absorption > > > as temperature and a figure of radiation pressure. > > > Not quite. For a _given experiment_, the radiation pressure and the > > temperature increase are proportional. This is because the absorbed > > power, and hence the temperature increase, and the radiation pressure > > are both proportional to the radiation power. > > > Across experiments, this isn't so. As already said, R. V. Jones, and > > pretty much all optical tweezers experiments. That the forces in > > optical tweezers on weakly depend on the absorption (over orders of > > magnitude of change in the absorption and heating) while strongly > > depending on the refractive index amply demonstrates that the effect > > is not thermal. > > > What shows the weak dependence on absorption? Trapping the same object > > at different wavelengths, with different absorption at the different > > wavelengths, and looking at the effect on the forces; this has been > > done to look at thermal damage to the trapped object, especially > > living trapped objects. Trapping at 1064nm in water vs heavy water, > > which have very different absorption, gives very different temperature > > rises. We've trapped objects that absorb about 10x as much as water, > > and therefore get significantly hotter (we can see the effects of > > convection at high power), and objects that absorb significantly less > > than the surrounding water. The temperature makes little difference. > > > > Specific dependence > > > upon atmospheric effects is already understood. The word 'radiometer' > > > is intended as a device to measure the amount of radiation. We would > > > like a 'radiation pressure meter' which will not generate any > > > behaviors due to thermal absorption from the 'radiation energy' which > > > I believe you will agree is encompassed in > > > e = hv > > > as a sum of photon energies. Because the 'radiation energy' is so > > > substantial at 1300 W/m/m for sunlight then eliminating the effect of > > > this large energy which could easily power quite some motive work is a > > > substantial problem for the verification of the claimed pittance that > > > is 'radiation pressure'. > > > This is why the most reliable experiments use reflection/refraction by > > dielectric surfaces to change the momentum of the light. But one can > > see radiation pressure due to absorption. > > > Some freely-available references for you: > > > Trapping polymer molecules, with a discussion of thermal effects:http://arxiv.org/abs/physics/0702044 > > > Forces and torques due to absorption:http://arxiv.org/abs/physics/0310003 > > and more details:http://arxiv.org/abs/physics/0310022 > > > For comparison, torques not due to absorption:http://arxiv.org/abs/physics/0308113 > > > Note that the same theory works for both cases, absorption and no > > absorption. > > > > I see no work so far that proves the > > > existence of radiation pressure since all of the experiments that I > > > have seen do rely upon some gas effects. The only claimed exception > > > that I've read so far is Nichols, and his logic is falsifiable. None > > > of the experiments you've studied consider a solid dielectric placed > > > in a vacuum of 10E-11 torrs, which would be a fine experiment with a > > > Nichols torsion fiber style experiment. > > > Re: "all of the experiments that I have seen do rely upon some gas > > effects." Most optical tweezers experiments are done in liquid (the > > ones done in air do have significant "gas effects"), Jones's > > experiments were in liquid. The BEC experiments require very good > > vacuums. True, they don't use a solid dielectric, unless you consider > > an atom to be a solid dielectric. What difference does that make? > > Radiation pressure is radiation pressure whether it acts on an atom or > > a group of atoms. > > > > Here is another link in support of the challenge to radiation > > > pressure's validity: > > > "It is therefore much more likely that in a given case the apparent > > > 'radiation pressure' is caused either by thermal surface effects or > > > electrons which are released from the surface by the radiation." > > > -http://www.physicsmyths.org.uk/#radpress > > > That is a _really_ bad webpage! Just consider its claim: "Even if one > > assumes a momentum, a radiation pressure force could only be caused by > > a momentum change dp/dt, but this is not possible because the speed of > > light c has to be constant" (1) Direction of motion matters when it > > comes to momentum, (2) refractive index. > > Yes, and this is very similar to the arguments that I have provided. > The conservation of momentum is a strict principle, one that you have > already cast aside in your argument about changing momenta as media > change in dielectric quality. You already accepted once the farce of > the reflector as a doubling agent of radition pressure effects, and > then go back to supporting it. What do you have to say about > conservation of momentum? > > > > > > > > > > You've ignored the > > > instantaneous momentum argument I made haven't you? This AC/DC > > > problem, well, now I'm going too far again. One thing at a time, eh? > > > Your comment: "I'm pretty sure the radiation pressure argument is > > false. Photons are > > more like AC sources than DC sources. If the pressure is alternating > > then to claim a propulsive acceleration is a misnomer. It would be > > like putting a ping pong ball in front of a speaker, blasting out 100 > > watts and expecting the ping pong ball to accelerate away from the > > speaker."? > > > Acoustic radiation pressure is observed. The ping pong ball _will_ > > accelerate. How does this not address this argument? > > > In the optical experiments, the time-averaged force is what is > > observed. The predicted time-averaged force, which agrees with the > > observations, is the average of the predicted instantaneous force, so > > what reason is there to think that the predicted instantaneous force > > is wrong? > > Well, for one, there is an observation that a black surface is drawn > toward the light rather than being driven away from the light, but I'm > not that strong on this as an argument to hinge upon since the > information is not well presented. > > I can accept that in a plane wave of acoustic pressure that the ping > pong ball will accelerate in an AC fashion, that is to say a > sinusoidal acceleration, yielding no DC acceleration, which is what > the radiation pressure claim is, and thus that it might propel > spacecraft with no need of thrusters, which I am currently in > disbelief of. Even if you were correct about a ping pong ball > accelerating in an acoustic field, it would not be wise to hinge this > discussion on that sideline of thought. You have not provided any > evidence beyond a ping pong ball with a bolt fastened to it sitting in > the magnetic field of a loudspeaker, which I actually provided as you > suggested to youtube this effect. Please provide a more apt link if > you wish. I did not go on to look at every video on youtube and > instead was so displeased with this first one that I plopped it down, > but you do seem to be serious so please do give us a good link. When > the ball is in the proximity of the speaker cone we will have more > dynamics to worry about than in a plane field, so again I say this may > not be a wise point to hinge any discussion of electromagnetic > radiation pressure. > > Within your own analysis of radiation pressure you use cross products > of the E field. We should accept that the E field is sinusoidal, and > so contains instantaneous zeros. These zeros are points in time at > which your effect has gone to zero. This was somewhat the argument > that I was making, which you've somewhat demolished by throwing in the > ping pong ball. > > Really I am trying to discorrupt this thread, as my last post went > toward one simple argument, and by not addressing that argument you > are providing a form of evidence. You have backed off of any radiation > pressure effect in vacuum and instead support it in fluid mediums > only. This is evidence. > > > > > So where lies the problem? > > > What did you think of my simple derivation of radiation pressure? What > > do you disagree with in it? > > If this is the expressions with velocity and red shifting then I have > commented in line on that. Summarily the radiation pressure effect > should be apparent at zero velocity and so there is a fault in that > attempt. > > > > > Consider a steady beam of monchromatic light incident on a stationary > > reflector. Each optical cycle has energy E (i.e., the total energy of > > a length of the beam equal to 1 wavelength). The incident power P is > > thus P = Ef, where f is the optical frequency.The output power is the > > same, since the reflected beam is identical, except for the reversed > > direction. Since the reflector is stationary, no work is being done on > > it. > > OK. You've somewhat legitimated my sinusoid argument elsewhere here, > but yes, I am following this construction here. > > > > > Now change to a coordinate system where the reflector is in motion, at > > a speed v away from the source of the incident beam. (For simplicity, > > assume v << c.) The incident beam is now blue-shifted, and the > > frequency of the incident beam in this coordinate system is now f(1+v/ > > c), and the power is P_in = Ef(1+v/c). Similarly, the reflected beam > > now has power P_out = Ef(1-v/c). > > In the frame of the reflector the light will appear redder, since the > reflector is moving away from the source by v, so I disagree with your > blue-shifted claim of the incident beam. > As this light will be reflected and returned toward its source I > believe that an observer in the source frame will observe light that > is red shifted relative to the source off of that receding reflector. > Will the light be doubly red shifted to this observer over an observer > in the reflector's frame? I do fear that we could suffer some > breakdowns here as to whether or not the reflector is perfect, well, > if it does not return all the energy that it received then it is ... > > read more »- Hide quoted text - > > - Show quoted text -- Hide quoted text - > > - Show quoted text -
From: Timo Nieminen on 4 Jun 2010 17:40 On Jun 4, 9:59 pm, "Tim BandTech.com" <tttppp...(a)yahoo.com> wrote: > On Jun 3, 5:59 pm, Timo Nieminen <t...(a)physics.uq.edu.au> wrote: > > > On Jun 4, 7:09 am, "Tim BandTech.com" <tttppp...(a)yahoo.com> wrote: > > > > As you identified, there is a confluence between radiation absorption > > > as temperature and a figure of radiation pressure. > > > Not quite. For a _given experiment_, the radiation pressure and the > > temperature increase are proportional. This is because the absorbed > > power, and hence the temperature increase, and the radiation pressure > > are both proportional to the radiation power. > > > Across experiments, this isn't so. As already said, R. V. Jones, and > > pretty much all optical tweezers experiments. That the forces in > > optical tweezers on weakly depend on the absorption (over orders of > > magnitude of change in the absorption and heating) while strongly > > depending on the refractive index amply demonstrates that the effect > > is not thermal. > > > What shows the weak dependence on absorption? Trapping the same object > > at different wavelengths, with different absorption at the different > > wavelengths, and looking at the effect on the forces; this has been > > done to look at thermal damage to the trapped object, especially > > living trapped objects. Trapping at 1064nm in water vs heavy water, > > which have very different absorption, gives very different temperature > > rises. We've trapped objects that absorb about 10x as much as water, > > and therefore get significantly hotter (we can see the effects of > > convection at high power), and objects that absorb significantly less > > than the surrounding water. The temperature makes little difference. > > > > Specific dependence > > > upon atmospheric effects is already understood. The word 'radiometer' > > > is intended as a device to measure the amount of radiation. We would > > > like a 'radiation pressure meter' which will not generate any > > > behaviors due to thermal absorption from the 'radiation energy' which > > > I believe you will agree is encompassed in > > > e = hv > > > as a sum of photon energies. Because the 'radiation energy' is so > > > substantial at 1300 W/m/m for sunlight then eliminating the effect of > > > this large energy which could easily power quite some motive work is a > > > substantial problem for the verification of the claimed pittance that > > > is 'radiation pressure'. > > > This is why the most reliable experiments use reflection/refraction by > > dielectric surfaces to change the momentum of the light. But one can > > see radiation pressure due to absorption. > > > Some freely-available references for you: > > > Trapping polymer molecules, with a discussion of thermal effects:http://arxiv.org/abs/physics/0702044 > > > Forces and torques due to absorption:http://arxiv.org/abs/physics/0310003 > > and more details:http://arxiv.org/abs/physics/0310022 > > > For comparison, torques not due to absorption:http://arxiv.org/abs/physics/0308113 > > > Note that the same theory works for both cases, absorption and no > > absorption. > > > > I see no work so far that proves the > > > existence of radiation pressure since all of the experiments that I > > > have seen do rely upon some gas effects. The only claimed exception > > > that I've read so far is Nichols, and his logic is falsifiable. None > > > of the experiments you've studied consider a solid dielectric placed > > > in a vacuum of 10E-11 torrs, which would be a fine experiment with a > > > Nichols torsion fiber style experiment. > > > Re: "all of the experiments that I have seen do rely upon some gas > > effects." Most optical tweezers experiments are done in liquid (the > > ones done in air do have significant "gas effects"), Jones's > > experiments were in liquid. The BEC experiments require very good > > vacuums. True, they don't use a solid dielectric, unless you consider > > an atom to be a solid dielectric. What difference does that make? > > Radiation pressure is radiation pressure whether it acts on an atom or > > a group of atoms. > > > > Here is another link in support of the challenge to radiation > > > pressure's validity: > > > "It is therefore much more likely that in a given case the apparent > > > 'radiation pressure' is caused either by thermal surface effects or > > > electrons which are released from the surface by the radiation." > > > -http://www.physicsmyths.org.uk/#radpress > > > That is a _really_ bad webpage! Just consider its claim: "Even if one > > assumes a momentum, a radiation pressure force could only be caused by > > a momentum change dp/dt, but this is not possible because the speed of > > light c has to be constant" (1) Direction of motion matters when it > > comes to momentum, (2) refractive index. > > Yes, and this is very similar to the arguments that I have provided. ! I haven't seen you directly arguing such complete nonsense. That web page was saying that the direction of motion doesn't affect momentum, that if an object changes direction and goes, e.g., in the exact opposite direction, there is no change in momentum. Before you claim that the argument given there is very similar to yours, you should understand just how completely defective that argument is. > The conservation of momentum is a strict principle, one that you have > already cast aside in your argument about changing momenta as media > change in dielectric quality ?? Conservation of momentum is why, if the momentum flux of the beam changes, there must be a matching force on the surface, or, if there is a force on the surface of the liquid (as we observe experimentally), then the momentum flux of the beam must change? Why do you say this "casts aside" conservation of momentum? It's directly based on the conservation of momentum. > You already accepted once the farce of > the reflector as a doubling agent of radition pressure effects, and > then go back to supporting it. What do you have to say about > conservation of momentum? You don't think the momentum of an object that reverses direction changes? You don't think that a force (i.e., a change in momentum as per Newton) is needed to change the direction of an object? If one instead, at least provisionally, accepts Newton's laws of motion as correct, if an object with momentum p reverses direction, while maintaining the same speed, the final momentum is -p, for a change in momentum of -2p, with an average force of -2p/t where t is the time over which the force that causes the change in direction is applied. If instead, the object is "absorbed", has a sticky collision, then the change in momentum is -p, only half of the "reflection" change in momentum. What's so mysterious about radiation pressure on a reflector being double? > > > You've ignored the > > > instantaneous momentum argument I made haven't you? This AC/DC > > > problem, well, now I'm going too far again. One thing at a time, eh? > > > Your comment: "I'm pretty sure the radiation pressure argument is > > false. Photons are > > more like AC sources than DC sources. If the pressure is alternating > > then to claim a propulsive acceleration is a misnomer. It would be > > like putting a ping pong ball in front of a speaker, blasting out 100 > > watts and expecting the ping pong ball to accelerate away from the > > speaker."? > > > Acoustic radiation pressure is observed. The ping pong ball _will_ > > accelerate. How does this not address this argument? > > > In the optical experiments, the time-averaged force is what is > > observed. The predicted time-averaged force, which agrees with the > > observations, is the average of the predicted instantaneous force, so > > what reason is there to think that the predicted instantaneous force > > is wrong? > > Well, for one, there is an observation that a black surface is drawn > toward the light rather than being driven away from the light, but I'm > not that strong on this as an argument to hinge upon since the > information is not well presented. This (the classic Crookes radiometer) is _not_ a radiation force experiment. In Crookes, the radiation force is negligible; in a typical instrument, it isn't enough to turn the vanes against friction. The pressure needs to be in the correct range for the device to work - it depends on non-thermal equilibrium low-pressure gas flow. To much gas, and it doesn't work, too little gas, and it doesn't work either. > I can accept that in a plane wave of acoustic pressure that the ping > pong ball will accelerate in an AC fashion, that is to say a > sinusoidal acceleration, yielding no DC acceleration, which is what > the radiation pressure claim is, and thus that it might propel > spacecraft with no need of thrusters, which I am currently in > disbelief of. Even if you were correct about a ping pong ball > accelerating in an acoustic field, it would not be wise to hinge this > discussion on that sideline of thought. You have not provided any > evidence beyond a ping pong ball with a bolt fastened to it sitting in > the magnetic field of a loudspeaker, which I actually provided as you > suggested to youtube this effect. Do a better search (and don't search for ping pong balls, just search for acoustic levitation). For example, search on Google Scholar for acoustic levitation. Since you appear to be arguing (above) in direct contradiction to Newton's laws of motion, and are supporting a web page that certainly does so, will a link here really help? If you don't accept Newton's laws of motion, what of modern science will you accept? That the above- suggested Google Scholar search throws up a screenful of links where acoustic levitation is being put to practical use might convince some, but they're products of modern science. I don't just mean this as rhetoric! You're supporting your argument with a page spouting complete anti-Newtonian nonsense, and rejecting the acoustic radiation pressure just because you didn't like the first youtube video you found (in which, if the force was magnetic due to the bolt, it would attract it towards the speaker magnet). http://www.youtube.com/watch?v=jpvbqdXJ1lM http://www.youtube.com/watch?v=9iQF61Ez000 > When > the ball is in the proximity of the speaker cone we will have more > dynamics to worry about than in a plane field, so again I say this may > not be a wise point to hinge any discussion of electromagnetic > radiation pressure. So what if there are more dymanics? If there is a time-averaged force, there is acoustic radiation pressure. The electromagnetic experiments we do don't use a plane wave. > Within your own analysis of radiation pressure you use cross products > of the E field. We should accept that the E field is sinusoidal, and > so contains instantaneous zeros. These zeros are points in time at > which your effect has gone to zero. Yes, and? For a plane polarised beam, you can think of it as a succession of blobs of energy, 2 per wavelength, moving at the wave speed. It's the blobs of energy that have the momentum (since they have the energy). As the direction of each blob is reversed as the beam is reflected (or each blob is absorbed, if you prefer to consider radiation pressure by absorption), there is a force. Between blobs, nothing is happening, so why should there be a force? No energy is changing direction then, so the momentum is changing, so a non-zero force isn't expected, since that would violate conservation of momentum. > This was somewhat the argument > that I was making, which you've somewhat demolished by throwing in the > ping pong ball. > > Really I am trying to discorrupt this thread, as my last post went > toward one simple argument, and by not addressing that argument you > are providing a form of evidence. Sorry, I didn't see what the AC, instantaneous zero thing has to do with it. If you intended the point to be that the time-average of a sinusoidal force is zero, and that therefore radiation pressure can't exist, the example of radiation pressure in action - examples of acoustic radiation pressure, for example - show that the force isn't purely sinusoidal. (Sorry, I don't know a simple direct theoretical argument. If the object scatters any of the incident light/sound, the force isn't purely sinusoidal. The circuit analogy is simple enough. A lossless non-radiating antenna looks like a capacitor to the circuit driving it. P=VI gives exactly sinusoidal power, average power is zero. If there is any Ohmic resistive loss, then it looks like a capacitor + a resistor. Then, P=VI no longer gives zero average ("power factor"). If the antenna radiates energy, then it has non-zero radiation resistance, which looks, to the driving circuit, identical to Ohmic resistance. As far as the circuit is concerned, loss of energy is loss of energy, and the same non-zero time-average of P=VI results with a radiating lossless antenna.) If you mean something else, please explain. > > So where lies the problem? > > > What did you think of my simple derivation of radiation pressure? What > > do you disagree with in it? > > If this is the expressions with velocity and red shifting then I have > commented in line on that. Summarily the radiation pressure effect > should be apparent at zero velocity and so there is a fault in that > attempt. OK, you misunderstood the example. I was not clear enough. Exactly the same physical system is being analysed in two (or more, if you prefer) reference frames. All we do is look at the source and reflector in a frame when both are stationary, and look at the work done on the reflector (based on conservation of energy and redshift/blueshift of the incident and reflected light), and then re-do for a reference frame where the reflector is moving (and the source is moving with velocity indentical to the reflector). It does say something - a lot, even - about force at v=0, but let us first see if you agree with this analysis of work, with this clarification about no relative motion between source and reflector. (Else there isn't any point in discussing the consequences of this analysis, is there?) (Most of your comments deleted for brevity, the relevant one kept.) > > Consider a steady beam of monchromatic light incident on a stationary > > reflector. Each optical cycle has energy E (i.e., the total energy of > > a length of the beam equal to 1 wavelength). The incident power P is > > thus P = Ef, where f is the optical frequency.The output power is the > > same, since the reflected beam is identical, except for the reversed > > direction. Since the reflector is stationary, no work is being done on > > it. > > > Now change to a coordinate system where the reflector is in motion, at > > a speed v away from the source of the incident beam. (For simplicity, > > assume v << c.) The incident beam is now blue-shifted, and the > > frequency of the incident beam in this coordinate system is now f(1+v/ > > c), and the power is P_in = Ef(1+v/c). Similarly, the reflected beam > > now has power P_out = Ef(1-v/c). > > In the frame of the reflector the light will appear redder, since the > reflector is moving away from the source by v, so I disagree with your > blue-shifted claim of the incident beam. We only changed the coordinate system; we didn't introduce any relative motion between the source and the reflector. All we do is choose a new coordinate system with origin moving in the direction from reflector to source. In the frame of the reflector, everything should (must!) remain identical. The question is, what does it look like in _another_ reference frame. > > P_reflector = P_in - P_out = 2Efv/c = 2vP/c. > > > Since P_reflector = F_reflector * v, we have: > > > F_reflector = 2P/c, > > > which is the radiation pressure due to complete reflection at normal > > incidence. > > > And, again, one can predict all of this just from the Lorentz force. > > So, fundamentally, electromagnetic radiation pressure is just what one > > would expect, given that electric motors etc work. If there is no > > radiation pressure due to electromagnetic waves, then the Lorentz > > force is bunk. Thus, some choices: (1) light is not an electromagnetic > > wave (but radiation forces and torques have been done at RF), (2) the > > Lorentz force is bunk, and electric motors work by some other mystery > > mechanism, (3) the forces which have been measured at optical > > frequencies and RF, and which, when thermal effects are made > > observably negligible - that is, their effect is shown to be small - > > agree with prediction based on the Lorentz force or equivalent, are > > really radiation pressure. Seriously, I think (3) is the best- > > supported of these choices. > I really appreciate your effort here Timo, and I do not want to > detract from or inhibit your own thinking. Still, wouldn't you think > that the Nichols radiometer could act as a radiation pressure meter if > it were put in a strong vacuum? Why rely upon fluid media when vacuums > of 10E-11 torr exist? You are quite a dodger on this simplistic > thinking. It might be a nice radiation pressure meter, but we don't need it as a radiation pressure meter. The experiments in fluid media are sufficient, and the many, many atom trapping and cooling experiments are sufficient vacuum experiments (and are done in such ultra-high vacuums). I really don't see a need to do this experiment. I don't know of any non-atomic scale experiments confirming Newton's laws of motion in ultra-high vacuum, and I don't see any need for that to be done either. What will it show? It still isn't a perfect vacuum, so how is a macroscopic experiment done in such vacuum better than one done in an easier to achiever vacuum? Isn't all that is needed a vacuum good enough so that radiometer forces (i.e., the thermal force that drive a Crookes radiometer) are negligibly small? Are the laser-cooling of mirrors experiments good enough? (I don't know these experiments well, so I don't know how good their vacuums are.) For atomic-scale experiments, the effect of pressure (a collision with another atom!) on an atom is rather catastrophic. Pressure = collision rate = rate at which atoms are lost from the trap. That they're trapped until collision is an excellent high vacuum experiment. What else is needed? There was a recent experiment in which a macroscopic (in the sense that it's many many atoms, so bulk matter, but it was microscopic in size, as in you want a microscope to look at it) object was trapped and tracked between individual collisions in a low- pressure gas, effectively an equivalent experiment, although not in high vacuum (this is to be published in Science, and is still on Science Express, their online prepublication service, at http://www.sciencemag.org/cgi/content/abstract/science.1189403 , not free though, apart from abstract). If I had a spare ultra-high vacuum set-up available, with no serious science going in it, and a student who wanted to (or was wanted to) learn about UHV systems, it would be a good project. Otherwise, it's a big investment in time (and money if you don't have the pumps already, for what gain? It doesn't do any new science, it doesn't produce a practically useful device, so what is the gain? (Don't underestimate the time, effort, and money needed for ultra-high vacuum work!) > I feel very hesitant heading for relativity theory when the > claims are supposedly satisfiable on a lab bench with a laser source > and vane in vacuum, all right there on the bench. Yes, it is > interesting to consider the red shift of the light off of the moving > reflector especially in terms of energy conservation, but it is not > the same problem. As above, it is the same problem (or is meant to be). v<<c, so Galileian relativity is entirely sufficient (I hope that you have no argument with Galileian relativity!). -- Timo
From: NoEinstein on 4 Jun 2010 23:53
On Jun 4, 5:40 pm, Timo Nieminen <t...(a)physics.uq.edu.au> wrote: > Dear Timo: You had said, earlier: "This isn't true. The force on the vanes has been measured in vacuum, and the force is in the opposite direction to the usual Crookes radiometer thermal force. If not for friction, the radiometer in vacuum would rotate "backwards"." Since my New Science has the direction of rotation identical to the Crookes (black squares trailing), your statement seemed to be saying that my New Science is wrongwhich it of course, isn't. The wrongly assumed 'forward' rotation is for the white squares to trail. Friction can STOP or prevent a rotation, but never change its direction. If you are wishing to change the subject to "momentum", you are way over your head. I wrote the book on momentum and KE. PD has fought on those subjects for three years, and has lost (to me). The world doesn't need any more PDs! NoEinstein > > On Jun 4, 9:59 pm, "Tim BandTech.com" <tttppp...(a)yahoo.com> wrote: > > > On Jun 3, 5:59 pm, Timo Nieminen <t...(a)physics.uq.edu.au> wrote: > > > > On Jun 4, 7:09 am, "Tim BandTech.com" <tttppp...(a)yahoo.com> wrote: > > > > > As you identified, there is a confluence between radiation absorption > > > > as temperature and a figure of radiation pressure. > > > > Not quite. For a _given experiment_, the radiation pressure and the > > > temperature increase are proportional. This is because the absorbed > > > power, and hence the temperature increase, and the radiation pressure > > > are both proportional to the radiation power. > > > > Across experiments, this isn't so. As already said, R. V. Jones, and > > > pretty much all optical tweezers experiments. That the forces in > > > optical tweezers on weakly depend on the absorption (over orders of > > > magnitude of change in the absorption and heating) while strongly > > > depending on the refractive index amply demonstrates that the effect > > > is not thermal. > > > > What shows the weak dependence on absorption? Trapping the same object > > > at different wavelengths, with different absorption at the different > > > wavelengths, and looking at the effect on the forces; this has been > > > done to look at thermal damage to the trapped object, especially > > > living trapped objects. Trapping at 1064nm in water vs heavy water, > > > which have very different absorption, gives very different temperature > > > rises. We've trapped objects that absorb about 10x as much as water, > > > and therefore get significantly hotter (we can see the effects of > > > convection at high power), and objects that absorb significantly less > > > than the surrounding water. The temperature makes little difference. > > > > > Specific dependence > > > > upon atmospheric effects is already understood. The word 'radiometer' > > > > is intended as a device to measure the amount of radiation. We would > > > > like a 'radiation pressure meter' which will not generate any > > > > behaviors due to thermal absorption from the 'radiation energy' which > > > > I believe you will agree is encompassed in > > > > e = hv > > > > as a sum of photon energies. Because the 'radiation energy' is so > > > > substantial at 1300 W/m/m for sunlight then eliminating the effect of > > > > this large energy which could easily power quite some motive work is a > > > > substantial problem for the verification of the claimed pittance that > > > > is 'radiation pressure'. > > > > This is why the most reliable experiments use reflection/refraction by > > > dielectric surfaces to change the momentum of the light. But one can > > > see radiation pressure due to absorption. > > > > Some freely-available references for you: > > > > Trapping polymer molecules, with a discussion of thermal effects:http://arxiv.org/abs/physics/0702044 > > > > Forces and torques due to absorption:http://arxiv.org/abs/physics/0310003 > > > and more details:http://arxiv.org/abs/physics/0310022 > > > > For comparison, torques not due to absorption:http://arxiv.org/abs/physics/0308113 > > > > Note that the same theory works for both cases, absorption and no > > > absorption. > > > > > I see no work so far that proves the > > > > existence of radiation pressure since all of the experiments that I > > > > have seen do rely upon some gas effects. The only claimed exception > > > > that I've read so far is Nichols, and his logic is falsifiable. None > > > > of the experiments you've studied consider a solid dielectric placed > > > > in a vacuum of 10E-11 torrs, which would be a fine experiment with a > > > > Nichols torsion fiber style experiment. > > > > Re: "all of the experiments that I have seen do rely upon some gas > > > effects." Most optical tweezers experiments are done in liquid (the > > > ones done in air do have significant "gas effects"), Jones's > > > experiments were in liquid. The BEC experiments require very good > > > vacuums. True, they don't use a solid dielectric, unless you consider > > > an atom to be a solid dielectric. What difference does that make? > > > Radiation pressure is radiation pressure whether it acts on an atom or > > > a group of atoms. > > > > > Here is another link in support of the challenge to radiation > > > > pressure's validity: > > > > "It is therefore much more likely that in a given case the apparent > > > > 'radiation pressure' is caused either by thermal surface effects or > > > > electrons which are released from the surface by the radiation." > > > > -http://www.physicsmyths.org.uk/#radpress > > > > That is a _really_ bad webpage! Just consider its claim: "Even if one > > > assumes a momentum, a radiation pressure force could only be caused by > > > a momentum change dp/dt, but this is not possible because the speed of > > > light c has to be constant" (1) Direction of motion matters when it > > > comes to momentum, (2) refractive index. > > > Yes, and this is very similar to the arguments that I have provided. > > ! I haven't seen you directly arguing such complete nonsense. That web > page was saying that the direction of motion doesn't affect momentum, > that if an object changes direction and goes, e.g., in the exact > opposite direction, there is no change in momentum. Before you claim > that the argument given there is very similar to yours, you should > understand just how completely defective that argument is. > > > The conservation of momentum is a strict principle, one that you have > > already cast aside in your argument about changing momenta as media > > change in dielectric quality > > ?? Conservation of momentum is why, if the momentum flux of the beam > changes, there must be a matching force on the surface, or, if there > is a force on the surface of the liquid (as we observe > experimentally), then the momentum flux of the beam must change? > > Why do you say this "casts aside" conservation of momentum? It's > directly based on the conservation of momentum. > > > You already accepted once the farce of > > the reflector as a doubling agent of radition pressure effects, and > > then go back to supporting it. What do you have to say about > > conservation of momentum? > > You don't think the momentum of an object that reverses direction > changes? You don't think that a force (i.e., a change in momentum as > per Newton) is needed to change the direction of an object? > > If one instead, at least provisionally, accepts Newton's laws of > motion as correct, if an object with momentum p reverses direction, > while maintaining the same speed, the final momentum is -p, for a > change in momentum of -2p, with an average force of -2p/t where t is > the time over which the force that causes the change in direction is > applied. If instead, the object is "absorbed", has a sticky collision, > then the change in momentum is -p, only half of the "reflection" > change in momentum. What's so mysterious about radiation pressure on a > reflector being double? > > > > > > > > > You've ignored the > > > > instantaneous momentum argument I made haven't you? This AC/DC > > > > problem, well, now I'm going too far again. One thing at a time, eh? > > > > Your comment: "I'm pretty sure the radiation pressure argument is > > > false. Photons are > > > more like AC sources than DC sources. If the pressure is alternating > > > then to claim a propulsive acceleration is a misnomer. It would be > > > like putting a ping pong ball in front of a speaker, blasting out 100 > > > watts and expecting the ping pong ball to accelerate away from the > > > speaker."? > > > > Acoustic radiation pressure is observed. The ping pong ball _will_ > > > accelerate. How does this not address this argument? > > > > In the optical experiments, the time-averaged force is what is > > > observed. The predicted time-averaged force, which agrees with the > > > observations, is the average of the predicted instantaneous force, so > > > what reason is there to think that the predicted instantaneous force > > > is wrong? > > > Well, for one, there is an observation that a black surface is drawn > > toward the light rather than being driven away from the light, but I'm > > not that strong on this as an argument to hinge upon since the > > information is not well presented. > > This (the classic Crookes radiometer) is _not_ a radiation force > experiment. In Crookes, the radiation force is negligible; in a > typical instrument, it isn't enough to turn the vanes against > friction. The pressure needs to be in the correct range for the device > to work - it depends on non-thermal equilibrium low-pressure gas flow. > To much gas, and it doesn't work, too little gas, and it doesn't work > either. > > > I can accept that in a plane wave of acoustic pressure that the ping > > pong ball will accelerate in an AC fashion, that is to say a > > sinusoidal acceleration, yielding no DC acceleration, which is what > > the radiation pressure claim is, and thus that it might propel > > spacecraft with no need of thrusters, which I am currently in > > disbelief of. Even if you were correct about a ping pong ball > > accelerating in an acoustic field, it would not be wise to hinge this > > discussion on that sideline of thought. You have not provided any > > evidence beyond a ping pong ball with a bolt fastened to it sitting in > > the magnetic field of a loudspeaker, which I actually provided as you > > suggested to youtube this effect. > > Do a better search (and don't search for ping pong balls, just search > for acoustic levitation). For example, search on Google Scholar for > acoustic levitation. > > Since you appear to be arguing (above) in direct contradiction to > Newton's laws of motion, and are supporting a web page that certainly > does so, will a link here really help? If you don't accept Newton's > laws of motion, what of modern science will you accept? That the above- > suggested Google Scholar search throws up a screenful of links where > acoustic levitation is being put to practical use might convince some, > but they're products of modern science. > > I don't just mean this as rhetoric! You're supporting your argument > with a page spouting complete anti-Newtonian nonsense, and rejecting > the acoustic radiation pressure just because you didn't like the ... > > read more »- Hide quoted text - > > - Show quoted text -- Hide quoted text - > > - Show quoted text - |