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> formed. As the stars in there galaxies "tu
--_000_489DEF5F65AB44C69E5D52466CB4AF1Ddalca_
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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