Eric, my understanding of the Crookes radiometer is that it measures light intensity by the rotation of its vane, but the effect is NOT due to photon emission recoil, it is due to the effects of the differential heating of the minute amount of gas present in the bulb. In a hard vacuum, this radiometer would not work - photon emission recoil would be insufficient to make the vanes move. I had one of these as a teen.
As I recall, the radiated photon recoil is proportional to power in the photons emitted, but not wavelength of the photon. For a given power emitted, it takes fewer short wavelength photons but you would get more recoil per photon. Laser emission would seem to be ideal. But the effect is very small. I wish I had some insight in the case of the Shawyer thrust effect. I cannot say that I really even have an informed opinion - that would require far more study than I have done. It is a marvelous mystery and perhaps someday I will participate. For now, I am trying to stay focused on LENR. Bob On Tue, Mar 15, 2016 at 7:21 PM, Eric Walker <eric.wal...@gmail.com> wrote: > On Tue, Mar 15, 2016 at 11:47 AM, Bob Higgins <rj.bob.higg...@gmail.com> > wrote: > > My understanding, and I could be wrong, is that the thrust Shawyer >> calculates and measures from his devices is several orders of magnitude >> higher than what could be obtained from photon radiation recoil - even if >> all of the generated RF were radiated unidirectionally. A small leak of RF >> would provide an undetectable thrust. That's what makes his devices >> interesting. >> > > My intuition is actually in line with this. Obviously there is no > observable thrust with a flashlight, for example. And a powerful spotlight > doesn't budge, even though enough power is being fed into it to drive a > motor. Nonetheless I was curious what the relationship between energy and > radiation pressure is. Here is what Wikipedia says for a blackbody emitter: > > > > P is pressure, epsilon is emissivity, sigma is the Stefan-Boltzmann > constant and T is the temperature. I wonder what the relationship would be > for a non-blackbody emitter emitting photons at a specific frequency. > Although radiation pressure is a small force, apparently it's nonneglible. > Wikipedia says that "had the effects of the sun's radiation pressure on the > spacecraft of the Viking program been ignored, the spacecraft would have > missed Mars orbit by about 15,000 kilometers." We also see it doing real > work in the case of a Crookes radiometer: > > > > I see that the Shawyer device is operating more or less at the level of > measurement uncertainty. There are no unequivocal results at this point by > third parties. Some of the tests even show reverse thrust when positive > thrust was intended. Given this level of uncertainty, it would seem that > little can be ruled out at this point. Even air convection. One imagines > that much more testing is needed. > > Have you formed an opinion on what might conserve momentum in the case of > the EM drive, if something like radiation pressure is ruled out? > > Eric > >
