Carleton's friend wrote "absolute zero, wavelength of primary hydrogen emission, etc,"
Thats fantastic, a futuristic system should be based on number 10 and hydrogen as a reference element, since it has these properties 1. hydrogen has mass (Gram) 2. has amount of substance (Mole) 3. can be burned for heat (Temperature) 4. can produce electricity (Ampere) If hydrogen has any radiation, then we can derive the other 3 base units like length, time and luminous intensity. We should put this into time capsule, to be opened in year 2100. Madan --- [EMAIL PROTECTED] wrote: > From: [EMAIL PROTECTED] > Date: Sat, 6 Apr 2002 14:35:40 EST > Subject: [USMA:19297] Re: kWh and time definition > To: "U.S. Metric Association" <[EMAIL PROTECTED]> > Reply-to: [EMAIL PROTECTED] > > 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 > > __________________________________________________ Do You Yahoo!? Yahoo! Tax Center - online filing with TurboTax http://taxes.yahoo.com/
