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| aetherist:
--- Quote from: TimFox on May 15, 2022, 02:50:33 am ---Do you know the meaning of "plane wave" in classical electrodynamics and electromagnetic waves? --- End quote --- 1. Yes, a (cosmic) plane wave is an impossibility, as i explained above in my previous reply. 2. And a (cosmic) non-plane wave is an impossibility. 3. And a (cosmic) wave is an impossibility. 4. However, i am ok with there being a cosmic forced radio wave of sorts, with a forced wave shape, & a forced wavefront of sorts. 5. But the wave in 4 can't be planar, no such thing, natural or forced. 6. But, there can be versions that are nearly planar etc. 7. 1 & 2 & 3 are supposed to be a natural wave, ie waves of the standard rolling E to H to E etc supposed em radiation or somesuch associated with supposed photons. Nope, impossible. https://en.wikipedia.org/wiki/Plane_wave#:~:text=In%20physics%2C%20a%20plane%20wave,a%20fixed%20direction%20in%20space. |
| PlainName:
--- Quote ---Meanwhile back at the ranch we need to ask how we could say see say a doughnut on the moon, if Earth's atmosphere causes so much twinkling, while at the same time there is say a bit of say haze & fog. --- End quote --- Well, let's not try and conflate things too much. First, when the talk is about seeing a doughnut on the moon, that isn't saying we can do that (successfully, anyway). It was said as being the equivalent of what they're doing with the black hole. That is, the angular resolution is equivalent. Doesn't matter if there was a brick wall in the way, the equivalence would be the same. Next, you showed a photo of a doughnut and simulated what it might look like (I think - couldn't quite work out what that was about). When they say you could see a doughnut on the moon I take that NOT to mean you can see the sprinkles and all that stuff. I would seriously expect that they mean it would resolve to a single pixel. If you could see detail like pixels they'd say, instead, you could see a rice grain on the moon. See? Moving on, with optical telescopes the distortion caused by the atmosphere is countered somewhat by using lasers to probe the local distortions and then compensate the capture appropriately. Don't know if the same thing, or similar, can be used for interferometry, but I reckon they would have taken that into account in some way. [Edit: something nags me that this technique isn't used to combat twinkling but something else. Naturally, IANAA.] As to the image we are shown, I would assume that the bright spots we see are probably discrete pixels, and the whole is smoothed for public consumption. Imagine a 3x3 grid where our doughnut lights up the 2,4,6,8 pixels. On the nightly news that's going to look a bit shit, but feed it through a filter and there is your round hole, etc. No idea if that's what's done, but it is hardly cheating if they did. |
| aetherist:
--- Quote from: dunkemhigh on May 15, 2022, 09:40:08 am --- --- Quote ---Meanwhile back at the ranch we need to ask how we could say see say a doughnut on the moon, if Earth's atmosphere causes so much twinkling, while at the same time there is say a bit of say haze & fog. --- End quote --- Well, let's not try and conflate things too much. First, when the talk is about seeing a doughnut on the moon, that isn't saying we can do that (successfully, anyway). It was said as being the equivalent of what they're doing with the black hole. That is, the angular resolution is equivalent. Doesn't matter if there was a brick wall in the way, the equivalence would be the same. Next, you showed a photo of a doughnut and simulated what it might look like (I think - couldn't quite work out what that was about). When they say you could see a doughnut on the moon I take that NOT to mean you can see the sprinkles and all that stuff. I would seriously expect that they mean it would resolve to a single pixel. If you could see detail like pixels they'd say, instead, you could see a rice grain on the moon. See? Moving on, with optical telescopes the distortion caused by the atmosphere is countered somewhat by using lasers to probe the local distortions and then compensate the capture appropriately. Don't know if the same thing, or similar, can be used for interferometry, but I reckon they would have taken that into account in some way. [Edit: something nags me that this technique isn't used to combat twinkling but something else. Naturally, IANAA.] As to the image we are shown, I would assume that the bright spots we see are probably discrete pixels, and the whole is smoothed for public consumption. Imagine a 3x3 grid where our doughnut lights up the 2,4,6,8 pixels. On the nightly news that's going to look a bit shit, but feed it through a filter and there is your round hole, etc. No idea if that's what's done, but it is hardly cheating if they did. --- End quote --- Yes i think i am ok with all of that. Yes the references to a doughnut on the moon is always simply to give an idea of a comparison of the angles of the dangles. A doughnut would show that the usofa had been on the moon. A rice grain would show that the Chinese had been there. My fuzzy pix of doughnuts were a failure. I wanted to show various levels of pixilation, but i don’t know of a program that duz that, so, i tried levels of fuzziness, but i couldn’t even do that properly. I suppose that if one had 100 pix, each with say only 9 large pixels, then praps they could be combined to give a pseudo pix with 900 faux small pixels, & then a NASA computer could create some pseudo edges & pseudo outlines that might or might not be quasi accurate. But my main problem with interferometry is that they assume a perfectly plane wavefront. I have already said that there is no such thing as a wave, photons can't make such a wave (excluding small local manmade effects), ie 2 separate sets of waves, ie at 2 distinct frequencies, ie in the middle of an infinite number of sets of waves at every frequency. I have not already said that a perfect planar wavefront is impossible, ie even before it gets near Earth, & even before it enters the atmosphere. It appears to me that the horizon team require a perfect planar wavefront, to within one wavelength, or to within a small part of one wavelength, praps 0.001 wavelength. And this perfection has to happen at the detector. No, it has to happen at the counter-recorder, ie where the detector signal is finally recorded. Now, here we have a problem. The signal has to go from the detector to the counter-recorder. Via wires probly. Are the wires insulated? What length of wire is needed? What effect duz temperature (of the Cu)(& of the insulation) have on the speed of electricity on the wire? What is the Velocity Factor for electric energy on the wire (which is an antenna) for each of the 2 GHz? Bearing in mind that the VF varies with GHz. How many individual waves are gained or lost along the wire due to temp etc at different times on different days? Is the electric energy on the wires in the Poynting Vector? Or is it in the electons? Have the horizon team watched the Veritasium youtubes? Have the horizon team been following the EEVblog forum? |
| PlainName:
--- Quote ---Now, here we have a problem. The signal has to go from the detector to the counter-recorder. Via wires probly. Are the wires insulated? What length of wire is needed? What effect duz temperature (of the Cu)(& of the insulation) have on the speed of electricity on the wire? --- End quote --- Isn't that why you calibrate stuff? So you can determine that kind of offset and allow for it? |
| TimFox:
Another lecture from a meeting in 2015: https://www.eso.org/sci/meetings/2015/eris2015/L6_Heald_calibration.pdf Those seriously concerned with this interesting engineering problem should consult the references contained therein. |
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