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which is unobservable to This is a multi-part message in MIME format. --------------A23E8FBF8D393842F4B13C86 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 8bit Hi Steve& All, This is essentially what I said in a less roundabout way. For ease of detection in the lab it clearly helps to have a single light source and the means to manipulate path length readily. And by doing so one can demonstrate destructive interference. And by random this may happen to some degree in nature but it can not be expected to have any effect on the frequency of spectral lines. YT, DW On 5/24/2020 2:30 PM, Stephen Shaw wrote: > Hi Dave: The key is ‘from one (a single) source’, and what that is. > Light is emitted from a finite luminous body like a light bulb or a > star independently from different points on the body, with the waves > originating with all different phases and polarizations* and with a > range of frequencies/wavelengths (physical scientists generally > specify frequency F, while biologists often use wavelength L as a > descriptor, simply related through the speed of light, c = F * L). > Even if you make an approximate point source like a pinhole > illuminated by the sun, the waves are still ‘incoherent' and you won’t > observe interference or selective dimming. You have to isolate two > similar beams with two slits (or use a beam splitter) and then you can > observe interference between beams in patterns projected on a screen, > where dark is destructive interference and light is constructive. At > the edges of the dark and light bands there will be grey zones or > bands where the intensity is reduced — you currently focus on ‘dimming’. > Even if you select a single hydrogen line to observe, because light > waves are emitted from the star with the whole range of phases from > all points on its surface (and which points are also at different > distances from the observer), you won’t see any obvious ‘dimming’ > interference effects as an observer at this end. To see dimming by > interference, you have to carefully arrange the optics to get waves > in-phase that you can then manipulate, and prefereably use a coherent > source, a laser, that comes ready made and almost ideal for this. And > dimming does not translate into a wavelength change, your apparent > desired alternative endpoint — a red-shift. > Steve > *actually not quite true for most tungsten light bulbs — the output is > somewhat plane polarized. > > On May 24, 2020, at 9:32 AM, David Webster <dwebster@glinx.com > <mailto:dwebster@glinx.com>> wrote > > Hi Patrick & All, > When all else fails consult the manual. So I dug out a good > Physics book and refreshed the screen (Duncan & Starling, 1948). >> >> Your first two lines are misleading, in that when beams of >> monochromatic light of equal intensity and exactly out of phase are >> mixed the result is darkness, as you go on to explain explain in your >> second paragraph (You can get....). >> >> This demonstrates that light from one source, under suitable >> circumstances, can interact with light from other sources in spite of >> the absence of a medium. And if beams of equal intensity result in >> darkness then beams of unequal intensity would result in dimming. >> >> If I understand this correctly, the spectrum signature of some >> element, e.g. H2, will have a number of lines. And, in the absence of >> a Doppler effect, the lines of greater frequency may experience >> greater opportunity to be dimmed, as a result of interference, but no >> opportunity for shift in the red direction. >> >> YT, DW, Kentville >> >> >> On 5/21/2020 3:58 PM, Patrick Kelly wrote: >>> Interference won't work either. Unlike water waves, which travel in >>> a medium, which can physically interact, light waves do not travel >>> through a medium at all, so they pass by and through each other with >>> no effect. >>> >>> (In the last 1800s, Michaelson and Morley devised an experiment to >>> look for the "aether" though which it was though that light >>> propogated. Their experiment proved there is no such thing. >>> >>> https://en.wikipedia.org/wiki/Michelson%E2%80%93Morley_experiment) >>> >>> You can get waves to interfere with each other if they come from a >>> single source and pass though a narrow slit, and then a double slit, >>> but the constructive and destructive only occurs in a limited area, >>> and affects their amplitude, not their wavelength. Plus, the size of >>> the slip would only affect waves of a certain wavelength. You can >>> prove this to yourself at a beach. Take a whole bunch of stick, and >>> line them up in a row parallel to the shore. Space them about 3 or 4 >>> wavelength apart. The waves will just ignore them. If you keep >>> filling it to get the gaps close to the size of the wavelength you >>> will then see some interference and if you take lots of sticks and >>> make the gaps a lot smaller than the wavelength, you will see that >>> the waves will now reflect off the barrier. (That is why radio >>> telescopes can be made with, what looks like chain link fencing >>> material. The wavelength of radio waves is sol long compared to the >>> gaps that they just see it as a smooth surface. >>> >>> The other problem is that at the large scale the structure of the >>> matter in the universe is "frothy" like soap bubbles with large >>> voids with almost no galaxies, and galaxies found in sheets, >>> filaments and lumped together in cluster and supercluster where >>> these come together. So any process that depends on light >>> interacting with matter, would have to produce identical effects on >>> electromagnetic radiation of all wavelengths, coming through all >>> manner of distributions of matter AND give results that are exactly >>> the same as those of an expanding universe which is predicted by >>> relativity, a theory which has passed (perfectly) every test we have >>> been able to devise for it as the technology to do so