Date: Thu, 29 Jul 1999 03:05:51 -0400 (EDT) Subject: Re: City Hunter Status: R david_pacheco@lineone.net (David Pacheco) says: mmcirvin@world.std.com says... > Once I tried to write a completely correct and detailed explanation of why > the sky is blue, which, while it did not completely eliminate jargon, > contained explanations of the jargon I was trying to use, so that people > who were not physics majors could understand the whole thing as long as > they were paying attention. The thing was a horrific failure. It's harder > to understand than the version in Jackson that has all the equations in it. > > I only realized how bad it was recently, when somebody read it and then > threatened by e-mail to do harm to my genitalia. You can read it at > > http://world.std.com/~mmcirvin/bluesky.html > > but, I warn you, you are not going to be able to understand it, because > nobody ever has, except for people who knew why the sky was blue in the > first place. Matt, Matt... when will get down off your high horse in that high tower in which you get high wearing high heels, Mr. High'n'Mighty? Especially considering that you don't get down off a horse, you get down off the peach fuzz in the small of Catherine Zeta-Jones's back. The ability to communicate with the ignorant masses is a skill that has long been ignored in the ivory stone towers of academia. It's an idea whose time has come, since it combines familiarity with the subject at hand with the capacity to "think" like a really dumb person, and speak down to that level without appearing to be too insulting. It's that inability to mix with the common people that made it impossible for Nils Bohr to order a Big Mac without the cashier being at least passingly familiar with LaGrangian equations and Feynmann diagrams. How many times did Nils leave a KFC in tears, frustrated by the pimply-faced adolescent behind the counter and his look of incomprehension as Bohr tried to explain that the concept of "crispy" or "extra-crispy" only collapsed into a single eisenstate AFTER the order had been placed? And that until that time, the chicken existed only as a smear of possibilities on a sheet of greasy wax paper? There are three principal reasons why the sky is *perceived* to be blue, and I will explain each of them in turn. First, I will clarify that I note above that the sky is "perceived" to be blue, because that's a statement equivalent to saying that the horizon is orange: the horizon is a concept, a mental cipher that denotes an idea, not a physical object that can reflect photons within certain wavelengths like a brick or a moyel. When you look at the sky, you're actually looking up into outer space, and to claim that a certain portion of this "outer space" can be defined as "the sky" is misleading to those people who, unlike us, don't understand the underlying issues, of which there are many, and quite diverse from each other. So in the interest of clarity and concise, clear, direct thinking, I will proceed with the above-mentioned explanation as regards the apparent tendency towards the blue end of the spectrum in this "thing" we call "sky". 1- Reason #1: Deep space is dark blue. Many science fiction writers, in their desperation to provide credibility to their wild flights of fancy, refer to the "inky blackness of space." To point out the inadequacies of this description would be a waste of my time (although many readers might find it entertaining), but suffice it to say that the description "inky" implies something liquid, and I would like to see these so called "writers" use some sort of "Space Ink" to write their misleading garbage. They couldn't! Because then their writing would disappear during the day when the sun is overhead! And who wants a book that can only be read at night? Not me, dear reader, and not you either. No, deep space is actually dark blue, not black, While I realize that some may contest this assertion, I merely point out the multitude of times when human eyesight has failed to recognize the difference between the two in local clothing stores, where the light is much better than that found in, say, the middle of a blue hole in space. I myself recently purchased a pair of Underoos which I maintained were black until -- goaded into a frenzy by my fellow scientists -- I burned them and analyzed the gases produced under a mass spectrometer. At that point the telltale amounts of tungsten and traces of molybdenum confirmed that I was wrong, and the article of clothing had in fact been dark blue. So given the propensity of humanity to take a stand on a color and then defend that color until proved wrong, are we to be surprised that mankind has gone through history supporting the thesis probably mumbled by the first caveman? Has everyone just gone along with the idea because Org of Nuntock SAID that the sky was black and he was too big to argue with? It appears so, which casts humanity as a whole in a rather poor light. Now since deep space is dark blue (as we have proved above), it is only natural that as space particles are whizzing around the Universe at speeds that would make a cheetah wonder what the hell we were talking about with our diagrams and blackboards and stuff, that these space particles encounter photons emitted by the electrogravitational field of one of the many suns in our vast Solar System. These photons, being essentially particles of "light", shine on the space particles and make them "lighter". This is why the further away you get from your typical sun, the darker the space around you becomes. This is also why in the summer, when the Earth is *closer* to the sun, the sky seems brighter, bluer, and inversely in the winter, when the space particles reaching the Earth have not traveled as close to the Sun and are therefore darker, the sky also seems darker. But you should remember that this is NOT the sky! This is merely the visible portion of deep space that you are looking at, with space particles that have collided with a varying quantity of photons on their way to your eyeball. So point #1 is made: the "sky" is "blue", or "appears" to "be" "blue", because "space" is "blue" itself, and "this" makes you "think" that you are "looking" at something that is "blue", when in fact you're looking "beyond" it to something "else" that is "blue". 2- Reason #2: Reflection from the ocean. The Earth is almost completely covered with water: in fact, the latest surveys show that 90% of the world's surface is, in fact, quite wet and slippery in parts. If you take into account that human bodies are 80% water, you must reach the conclusion that if you took a person's lower digestive tract and straightened it out, at some point one of the ends would rest in a body of water of some sort. If you took a person's skin and laid it out end-to-end, you would have enough to cover a small tennis court, which would be quite a lot of surface to cover up with a tarpaulin when it started to rain: that's a lot of water! If you don't cover it up, then the skin absorbs the water until it starts to look like a raisin, and that can really play havoc with the topspin off a well-played backhand, I may assure you. Since the ocean is blue (a fact that you can verify yourself by asking me: go ahead!), it stands to reason that photons that strike the ocean and then rebound into your eyeball are "painted" blue due to the interaction with the ocean, which is how the eye perceives colour. But not all the photons go straight into your eyes! No! that would be painful, and could make you go blind! Some of the photons bounce off the ocean and bounce back up to the ozone layer, in a kind of "greenhouse effect" effect. These photons then travel back down towards the Earth and strike the receptive cones in your eyeball. Since they have been "painted" blue by the ocean, but have lost some of that "blueness" in the bouncing between ocean and ozone (because the colour blue is actually the *slowest* in the colour wavelength, some of it gets left behind on the trip), the sky still looks blue but MUCH LESS so than the ocean. As a corollary, this explains why the "sky" turns "red" as the sun is setting: because the angle of reflection between the photons arriving from the sun and the ocean is increasing, the photons cease to bounce back UP to the ozone, and instead bounce ALONG the ocean surface like skipping stones, and hit your receptive cones directly. Since these photons are arriving almost directly from the hot sun, they "heat up" the receptive cones in your eyes, tinting everything a warm, red colour. This is why it is far more dangerous to look directly at the sun in the late afternoon than it would be to do so at midday: not only do you risk going blind, but your head could be set on fire, and your brain would boil away like haggis. Ah, you say, you have caught me out in a contradiction: if the blue in the sky is partially caused by reflection from the ocean, wouldn't it stand to reason that on cloudy days, the bottom of the clouds would *also* appear to be blue? Ah, I say, good question. It's good because it demonstrates to me how little you have been paying attention to the paragraphs above, which prove conclusively how stupid that question would seem had you been listening in the first place. I will not write it all out for you again because that would encourage your inattentive behaviour, but suffice it to say that clouds and ocean are both composed of water particles, but the cloud water particles are (obviously) packed less densely than the oceans: the blue-painted photons, having no mass, travel freely in the spaces between the water particles in the clouds and shoot back off into outer space, which means they get no chance to bounce back into your eyes. 3- Reason #3: Photons are blue This is a recent discovery in the world of physics, and a hotly contested one it is. The simple proof lies in the well-known "Doppler" effect, in which an object travelling away from the viewer at high speeds will appear to be "red-shifted". In layman's terms, this means that the object appears to be "redder": the same principle is applied when watching spacecraft launches at Kennedy Spaceport. As they fly away, the spacecraft rocket engines appear to "glow" red, when in fact they do not change colour at all: if you could travel as fast as the spacecraft (and someday, dear reader, you may!), the engines would not appear to have changed colour at all! Conversely, when an object is traveling at high speeds TOWARDS the viewer, it will appear to be "blue-shifted". Why this phenomenon, you ask? Well, aren't you just full of questions today, you young whippersnapper! Now sit down and shut up and stop interrupting me. The explanation is as follows: when an object is travelling TOWARDS you, it is compressing all of the photons in its direction of travel, pushing them forward. By the time you see the object, it will have accumulated a vast amount of photons in the opposite of its wake, almost exactly like a speedboat but in reverse and not in water but in something that acts like the opposite of water, with some major differences. These photons will strike you all at once, and since they are blue, the object will appear to be bluer than it really is. Conversely, when an object is travelling AWAY from you, all of the blue photons have been pushed in front of the object and you can't see them. What you CAN see is the result of the intense heat required to move such a massive object at such incredible speeds: the dying, glowing embers of an engine so vast, so powerful, that it strains our imagination to even think of it. But we can try, can't we? NNNNNNNNNNNHHHHHHH!! RRRRRRRRRR!!!! HHHHHHNNNNNN!!! See what I mean? Hard, isn't it! ----- o ----- So there you go, Matt. Wasn't that simple? A brief, to-the-point explanation of why the sky is blue. No equations, no radiation, no "oscillating dipoles" or any of that namby-pamby sciency stuff that's on your web page. Simple. Something everyone can read and understand, even babies with limited comprehension and reduced bowel control, even the seemingly uneducatable masses that we walk past on the metro every day, with their chewing gum, their rock'n'roll and their hydraulic nasal hair clippers. -dp. You're welcome. -- \/David DeLaney dbd@panacea.phys.utk.edu "It's not the pot that grows the flow It's not the clock that slows the hour The definition's plain for anyone to s Love is all it takes to make a family" - R&P. VISUALIZE HAPPYNET VRbeable