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started with no metal. Again, observ This is a multi-part message in MIME format. --------------F6ED05AD966772A92D8CE854 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 8bit Hi Patrick & All, Thanks for the further explanation. Light is of course refracted when entering or leaving a medium of different refractive index at an angle but so far as I am aware no energy is lost if the refracting medium is transparent. But many quantitative chemical determinations are based on absorption of light, usually by substances in liquid solution but, given suitable conditions (e.g. Atomic absorption spectroscopy) this may apply also to some suspensions in gas. When absorption is used for quantitative analysis one is interested only in the decrease in intensity at a specific wavelength and filters are normally placed between source and target. But if source light were not filtered would there usually be an abrupt drop in intensity at the absorbed wavelength or a gradual decrease to a minimum ? Does light in any way interact with gradients of electrical potential or magnetic fields ? Or expressed another way modified by them ? I have read that light has no mass but has momentum. Because momentum is usually defined as mass x velocity how can there be momentum at zero mass ? 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 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 centre 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. Science 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 matter) to eventually slow the expansion. That is no longer the > case. The rate of 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 cosmological constant that he later though was > zero) and the universe expands, there are more and more cubic metres > from which the dark energy can act. The eventual result is the heat > death of the universe. > > There are already large prats (the vast majority, actually) of the > universe which is unobservable to us. As the expansion rate continues, > more and more distant objects will disappear. Almost all regular > matter in the universe is in the form of stars or gas and dust. For > the vast majority of stars (including the Sun), at the end of their > life they puff off a bit of their outer atmosphere and end up as a > white dwarf star. They can no longer produce energy and slowly cool > off becoming black dwarves. They are quite small… the mass of the Sun > packed into a ball the size of Earth and kept from collapsing farther > by electron degeneracy pressure. > > For the small number of stars about 2-10 times the mass of the sun, > they end up producing a supernova explosion, throwing some material > back into space with the rest ending up as a neutron star. Again, they > can no longer produce energy and slowly cool off becoming black. They > are even smaller… the mass of the Sun (or a bit more) packed into a > ball the size of Halifax and kept from collapsing farther by neutron > degeneracy pressure. > > The really massive stars end up as black holes as they have so much > leftover mass that neutron degeneracy pressure cannot stop the > collapse. On the low end they produce supernova and end up as a black > hole… on the high end they simply wink out leaving behind a black hole. > > So all stars end up as a dead object that either slowly cools off, or > in the cases of black holes go cold right from the start. You can > always make more stars, but there you run into a problem. You need > gas* and dust** from which to form them. > > About 25% of the galaxies are classed as elliptical. Th