Xref: utzoo talk.politics.misc:8055 sci.misc:896 Path: utzoo!mnetor!uunet!husc6!bloom-beacon!athena.mit.edu!jfc From: jfc@athena.mit.edu (John F Carr) Newsgroups: talk.politics.misc,sci.misc Subject: Re: The Last Word on Friedman, Sevener, and Cuba Message-ID: <3588@bloom-beacon.MIT.EDU> Date: 9 Mar 88 16:10:11 GMT References: <3405@bloom-beacon.MIT.EDU> <3895@whuts.UUCP> Sender: daemon@bloom-beacon.MIT.EDU Reply-To: jfc@athena.mit.edu (John F Carr) Organization: Massachusetts Institute of Technology Lines: 172 Summary: Not again... Again, I remind those who have no doubt as to Tim Sevener's error to stop here. This has gone on too long. In article <3895@whuts.UUCP> orb@whuts.UUCP (45263-SEVENER,T.J.) writes: : Knowing full well that the Reaganistas will not accept Tim, I ask you again to define "Reaganistas" in terms of groups with which we are familiar. : my explanation of the principle of refraction, : I will herein post quotes from "An Introduction to the : Meaning and Structure of Physics" by Leon N. Cooper. : It is an introductory college physics textbook. And my calculations are based on (besides common sense and scientific reasoning) the CRC Handbook of Chemistry and Physics, an astronomy textbook, and class notes for an astronomy course. : Also knowing full well that Mr. Carr will undoubtedly : attempt to weasel out of his totally inaccurate explanation ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ See below. : of refraction and how it applies to a view of the Sun, : whereas it does not apply scarcely *at all* to the ability ^^^ ^^^^^^^^ ^^^^^^^ Actually, the way I parse this string of negatives Tim has just said my calculations are valid. : to see Cuba from Key West, I will post further proof of : Mr. Carr's lack of understanding of refraction. : TS : 1)the Sun is up in the sky being refracted through an : TS : atmosphere many miles thick. : JFC :This is my point. : JFC :The figure I quoted, .5 degrees, is for the sun on the horizon. : JFC :This means its light passes through the equivalent of about 200 : JFC :miles of sea-level air. Light from Cuba passes through half this : JFC :much air, so will be refracted by half as much (in both cases the : JFC :light travels almost horizontally through the air, so the reasoning : JFC :is valid). : Actually, I was not thinking clearly myself in this passage. : The reason the Sun is refracted whereas day to day objects : (including those seen over the sea) in air are not, is due to : the change in density of the atmosphere at higher altitudes ^^^^^^^^^^^^^^^^^^^ No. See below. The change in density of air is highest at lower altitudes. See the Handbook of Chemistry and Physics. : and the abrupt change to the vacumn of space. ^^^^^^^^^^^^^^^^^^^^^^^^^^^ The earth's atmosphere at low to medium altitudes is well approximated by a decaying exponential. There is NO ABRUPT TRANSITION TO SPACE. Remember Skylab? It was in space. There was air up there. Don't trust me, ask anyone who is involved in any way with space travel. : Cooper's text says this (p. 181): : "Light traveling through a vacumn, or through a uniform medium ^^^^^^^^^^^^^ Here is the key. Air is not uniform. : in a straight line and with finite speed, has what seems to : be an inertial property." : "We now consider the behavior of light as it passes from one : *homogeneous medium* to another, for example as it passes from : -------------------- : air to water." And here is my other point, that light does not pass between media, so this law of refraction does not apply. : Further, (p. 182), Cooper says: : "This constant, known as the index of refraction, is a property : of the two materials and differs for different materials. For : example there is one index of refraction for an air-water surface, : another for an air-glass surface, and a third for a glass-water : surface." This is irrelevant, since there are no discontinuities involved. Also, this is not the correct definition of "index refraction". The index of refraction is measured relative to vacuum, and is defined by (speed of light in material) * (index of refraction) = c. : There is *no such thing* as an "index of refraction" for SeaLevel ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ This is absolutely, totally wrong. No politics involved. I gave the index of refraction for air in my posting (1 + 280x10^-6, approx). : air. There undoubtedly *is* some index of refraction for air at : sealevel density versus air in the upper atmosphere, and of course : there is *certainly* an index of refraction for an air-vacumn : surface. : Which leads back to my original point: No, it doesn't. It does, however, lead to mine: that Tim Sevener has even less understanding of physics than I thought. My reasoning was from first principles (i.e. I drew a diagram comparing path lengths and light travel time for two slightly displaced paths and used the definition of index of refraction [and I am capable of deriving rough values for n by calculating resonances of electrons when excited by light]). Tim quotes an introductory physics text which only gives the result for a special case. More on this at the end. : Michael Friedman could not *possibly* have seen Cuba from Key : West. Mr. Carr, Mr. Swan, and others jumping in to attack : me and defend Mr. Friedman's statement on the grounds that : refraction makes it possible are all wrong. I see. Tim is right and we are all wrong. I can think of a few in my department who will be interested to hear this. Just think of all the astronomers and planetary scientists who will have to redo all their life's work because they corrected for refraction which doesn't exist. On the other hand, there will be no need for the several lectures of 12.117 which teach refraction, saving many man-hours of time. : And I hope this teaches them all a lesson about "seeing : what they want to see" and believing what they want to : believe. : Meanwhile, I have been bombarded with attacks from every : rightwinger on the Net on every statement I have ever made : in this newsgroup, or rather a very small subset of the : statements I have made in this newsgroup. : : I cannot possibly respond to all of them. : : All I can say is: this particular exchange was one which may : demonstrate to others on the net just who has credibility and : who does not. : Remember it in the future... I believe so. I suspect that Tim has discredited yourself with anyone who has any scientific training. Is there anyone in this group who supports Tim's reasoning on the subject (especially the above nonsense)? This question is different from the question, "do you believe Mike Friedman saw Cuba?" : tim sevener whuts!orb : see Tim: have you ever heard of. . . .Calculus? What about limits? One gets the continuous analog of Snell's law by taking the infinite limit of a number of thin layers with a finite difference in index of refraction. The result is that refraction is proportional to the derivative of n wrt distance. A challenge to Tim: derive, from first principles, the laws of refraction in such a way that you can show they do not apply to continuously changing media. If you do that, I will post the derivation by which I got my answer. Start at any level you want (if you don't know quantum physics, etc., to figure out the index of refraction for materials, you can assume an index of refraction for air of 1 + rho * 280 / rho(0) x 10^-6). For a good illustration of this effect, a cover of Scientific American a few years ago had a picture of a laser beam passing through a tank of fluid with a strong density gradient. Can anyone provide a reference? The final proof of refraction by air: look at the air above a road on a hot day. See the ripples? They are caused by differential refraction. John Carr "No one wants to make a terrible choice jfc@Athena.MIT.EDU On the price of being free" --Neil Peart