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> formed. As the stars in there galaxies "tu --_000_489DEF5F65AB44C69E5D52466CB4AF1Ddalca_ Content-Type: text/plain; charset="Windows-1252" Content-Transfer-Encoding: quoted-printable Hi Dave: The key is =91from one (a single) source=92, and what that is. = Light is emitted from a finite luminous body like a light bulb or a star in= dependently from different points on the body, with the waves originating w= ith all different phases and polarizations* and with a range of frequencies= /wavelengths (physical scientists generally specify frequency F, while biol= ogists often use wavelength L as a descriptor, simply related through the s= peed of light, c =3D F * L). Even if you make an approximate point source= like a pinhole illuminated by the sun, the waves are still =91incoherent' = and you won=92t observe interference or selective dimming. You have to iso= late 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 e= dges of the dark and light bands there will be grey zones or bands where th= e intensity is reduced =97 you currently focus on =91dimming=92. Even if you select a single hydrogen line to observe, because light waves a= re 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 obse= rver), you won=92t see any obvious =91dimming=92 interference effects as an= observer at this end. To see dimming by interference, you have to careful= ly arrange the optics to get waves in-phase that you can then manipulate, a= nd prefereably use a coherent source, a laser, that comes ready made and al= most ideal for this. And dimming does not translate into a wavelength chan= ge, your apparent desired alternative endpoint =97 a red-shift. Steve *actually not quite true for most tungsten light bulbs =97 the output is so= mewhat plane polarized. On May 24, 2020, at 9:32 AM, David Webster <dwebster@glinx.com<mailto:dwebs= ter@glinx.com>> wrote Hi Patrick & All, When all else fails consult the manual. So I dug out a good Physics boo= k and refreshed the screen (Duncan & Starling, 1948). Your first two lines are misleading, in that when beams of monochromati= c 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 ca= n get....). This demonstrates that light from one source, under suitable circumstan= ces, 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 eff= ect, the lines of greater frequency may experience greater opportunity to b= e 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 mediu= m, which can physically interact, light waves do not travel through a mediu= m 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 exper= iment 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 s= ource and pass though a narrow slit, and then a double slit, but the constr= uctive and destructive only occurs in a limited area, and affects their amp= litude, 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. T= ake 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 wavelengt= h you will then see some interference and if you take lots of sticks and ma= ke 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 s= urface. 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 c= luster and supercluster where these come together. So any process that depe= nds on light interacting with matter, would have to produce identical effec= ts on electromagnetic radiation of all wavelengths, coming through all man= ner of distributions of matter AND give results that are exactly the same a= s 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 has advanced. Humans used to be comfortable with the idea that Earth was at the centre of= everything. Turned out we aren't but then we though we were near the centr= e of the Milky Way. It turned out that we aren't but we though that we were= in the only galaxy. Turned out we aren't, there are billions of them. Scie= nce does not care about what makes humans feel good..... The universe also is highly unlikely to have perpetual renewal. There was a= time when it was though that there was enough matter (including dark matte= r) to eventually slow the expansion. That is no longer the case. The rate o= f expansion appears to be increasing due to dark energy. This is an outward= "pressure" that appears to be a property of space-time (Einstein's cosmolo= gical constant that he later though was zero) and the universe expands, the= re are more and more cubic metres from which the dark energy can act. The e= ventual result is the heat death of the universe. There are already large prats (the vast majority, actually) of the universe= which is unobservable to