Thanks, Carleton, for sharing with us this very insightful discussion you've been having with someone.
I'd just like to again point out my VERY big displeasure with BIPM metrology folks for doing what IMHO constitutes clear stupidity (with all due respect). The missivist here brought a yet another serious flaw with the definition of the meter. The fact that it's a fraction! That hit me just a minute ago: Whoa, yes! That's absolutely true! And I thought we've had successfully done away with such messy frameworks. Not that I'm against any and all fractions, BTW, but that to use it for the definition of something so paramount as our meter borders indeed on insanity! By golly, why haven't they continued to treat SI's framework from a fundamentally correct approach. Why can't they use another chemical element with more stable, precise wavelengths whatever? Also, do we REALLy need to continue evolving towards higher and higher degrees of accuracy? Isn't near 9 decimal places already plenty/enough as it is? In any case, this again goes to show that our "friends" at BIPM and CGPM must get more serious about frameworks. The way I see it is that we have a very LOOOONG way to go concerning *fixing* (REALLY fixing) what's fundamentally wrong with the SI system. And again I must *V-E-H-E-M-E-N-T-L-Y* insist that they convoke an extraordinary forum or something to get these wrinkles in SI's framework *out of the way* for once and for all. Ideally, I'd like to see ONLY the conundrum with the second (the hideous 60-60-24 crap thing) left as the last wrinkle in this framework. But things like the definition of the meter, kg, prefixes, special names for ratios, and other... irritants MUST be addressed! I see nothing wrong in doing it. Opponents of the SI system already charge that the SI has been changing too much anyways. However, if we do it and fix these last wrinkles *in one short comprehensive/fundamental way* we would go a very long way towards finally convincing EVERYONE that we do indeed have a near perfect flawless system, *finally*! Comments anyone, please? (Thanks) Marcus On Sat, 6 Apr 2002 14:35:40 CarletonM wrote: >I got into an off-list discussion with an engineer friend of mine about how >certain fundamental units are defined. I'm not an engineer at all, but >thought some on the list might find this dialogue interesting. > >In a previous message he commented on how the meter's length was "changing" >as its definition did. I responded: > >> Carleton: > >> > Length stayed the same, only how it was calculated got more and more >> precise. >> > >Friend: > >> Well, yes, but... one could have constructed a Platinum-Iridium >> bar whose length corresponded to the average of the lengths of the feet >> of 16 randomly selected individuals. Or the distance from some Monarch's >> nose to the tip of his outstretced hand. My point was not the standard, >> but the arbitrary way it was chosen. _NOT_ that I'm saying feet or >> noses are _less_ arbitrary, just that they are no more. In each >> case a "secondary standard" (e.g. those metal bars) is needed to >> convey the representation beyond the Royal Court. In contrast, >> a system based on things like absolute zero, wavelength of primary >> hydrogen emission, etc, can be _described_ without reference to >> purely local phenomena, and hence duplicated at a distance (think, >> a _l_o_n_g_ distance, like to some extraterrestial civilization >> or our "descendants" 10 million years from now). No need for anybody >> to travel to the holy bar. Now, the newer standards tend to be of this >> form, but they also tend to be pretty arbitrary multiples, because they >> _really_ are descriptions of the form "All our measurements are based on >> this holy bar, which _happens_ by chance to be 299792458 times as >> long as the distance traveled by light in a Vacuum during a time >> which is related to our planet's orbit but _happens_ by chance >> to be (insert constant here, no time to look it up) times the duration >> of one cycle of the primary component of the Cesium spectrum." >> Any reasonably competetent alien equivalent of a high-school physics >> student could figure out from that description how long a meter and >> second are, but would be left wondering why we chose such awkward >> numbers. They aren't powers of any small integer, let alone sane numbers >> like 2, pi, or e. In fact, I wonder about the regression expressed >> below, as "Ma Be" also did, and was not answered: >> >> > Ma Be quoted me in USMA 19107: >> > >> > >>The advantage of these definitions of the second and the metre is that >> they >> > >>do not depend on the preservation of physical prototypes. They can be >> > >>replicated by any well equipped standardizing laboratory anywhere in >> the >> > >>world. >> > >> > And added: >> > >> > >Perhaps so, but what was wrong with the previous one, that didn't need >> the >> > >second for its definition? We're told that this was largely to increase >> > >accuracy to 8 decimal places or something to that effect. Now, does >> this >> > >mean we may not have another similar alternative? Just wondering... >> >> ... >> >> > In 1957 the CIPM declared the metre to be equal to 1 650 763.73 >> wavelengths >> > in vacuo of the radiation corresponding to the transition between the >> level >> > 2p10 and 5d5 of the krypton 86 atom. This definition had an estimated >> > precision of =B1 4 nm. >> > >Friend: > >> Note that this does _not_ require the observer to know >> how long a "second" is, while the below does. I suspect that was >> the crux of Ma Be's question, which has been ignored in the answer. >> > >Ma Be: > >> > In 1983 the CGPM decided that "The metre is the length of the path >> > travelled by light in vacuum during a time interval of 1/299 792 458 of a >> > second". >> > >Friend: > >> Of course, folks like me have "informally defined" the meter >> as "wavelength at 300 MHz" for years, for purposes of accuracy along >> the lines that most folks use yardsticks, but then, I _am_ human, >> and make no pretense not to be. If you regularly measure to better >> than one part in 2^^-10 then you get one free sneer. Nonetheless, I >> just had this impish thought that perhaps the change was motivated >> by the fact that 1,650,763.73 "looks messy", exposing the arbitrariness >> of the measure. Although 1/299792458 is a _fraction_, which all good >> Meter-heads claim to have eliminated the need for. OTOH, it's not a >> _continued_decimal_, as crop up so often when one tries to shoe-horn >> real, physical phenomena into arbitrary systems of measure. :-) >> >> Actually, I have a sneaking suspicion that the transition >> above _did_ in fact alter the "defined length" by some minuscule >> amount, but was undertaken because the "Metric for ideological reasons" >> folks realized that the astronomers and physicists, who took the universe >> as it was, had a much better handle on "metrics" (that is, the science >> of measurement) than they did, and by pegging the political unit >> to something with real science behind it, they could avoid looking >> increasingly silly as our capabilities to measure increase. Sort of a >> two-hundred-years-late "Well, that's what I meant to say all along" :-) >> >> You do realize that the folkloric value of 98.6 F for mean >> human body temperature is the result of a false gain in precision >> from a double conversion from Fahrenheit (in which the original >> data were collected) to Celsius (then called Centigrade) and then >> _back_, right? In real life, the temperature of a human body varies >> depending on what part of the body one measures, let alone the >> difference in ambient temperature and among individuals. The >> original 99F (good to 2 sig-figs, matching the error-bounds of >> the data) was converted to 37 C for publication in Europe, then >> erroneously back-converted to 98.6 for "English". MacNab would >> have flunked them. If they had stuck with even approximately correct >> error-bound, they would have made the Celsius number 37.2, which >> would back-convert to 98.96 which even a football star would see >> was 99, to the proper precision. One has to wonder whether the >> folks who settled on 37 were clueless about the precision, or >> deliberately chose the loss of precison to make it "look nicer". >> I know what I believe. >> >> xxxx > > Is your boss reading your email? ....Probably Keep your messages private by using Lycos Mail. Sign up today at http://mail.lycos.com
