Bench TalkBench Talk for Design Engineers | The Official Blog of Mouser Electronicshttps://hr.mouser.com/blogRedefining the Basic Measurements of Physicshttps://hr.mouser.com/blog/redefining-the-basic-measurements-of-physicsAll,GeneralMon, 22 Jan 2018 16:35:27 GMT<p style="text-align: center;"><img alt="" src="/blog/Portals/11/Golata_Redefining-the-basic-measurements-of-physics-theme.png" style="width: 600px; height: 399px;" title="" /></p>
<p>I’m a writer. So, I must write to be understood. But, there are many obstacles that constantly get in the way (besides my own ineptitude!).</p>
<h2><strong>Vagueness Exists</strong></h2>
<p>I write in American English, and for many of my readers that’s not their native language. Hence, therein lies the obstacle of interpretation. Though I strive to be succinct and clear, it is possible to misunderstand what I have written, because your personal context may orient you differently from the unique perspective that I am writing from. Then, there are the nuts-and-bolts issues of the conventions of human language, which involve discourse, sentence structure, grammar, syntax, semantics, word meanings, and the like that may lead to possible misunderstandings.</p>
<h2><strong>Precision Is Desirable</strong></h2>
<p>But as engineers, you and I also have access to a more precise language—the language of mathematics. It was British philosopher and mathematician Bertrand Russell (1873–1970) who stated, “Ordinary language is totally unsuited for expressing what physics really asserts, since the words of everyday life are not sufficiently abstract. Only mathematics and mathematical logic can say as little as the physicist means to say” (<em>The Scientific Outlook</em>, 1931, 82).</p>
<p>Therefore, we employ the language of mathematics, to express the items, thoughts, measurements, and other such things that we are discussing, with more precision than is conveniently achieved with conventional words. Examples might include:</p>
<p style="margin-left:.5in;">Ohm’s Law: E (volts) = I (amperes) * R (ohms)</p>
<p style="margin-left:.5in;">The speed of light = 2.998 x 10<sup>8</sup>m/s</p>
<p>In mathematics, to be more precise, we state our math with more exact digits. So, the speed of light can now be stated as: </p>
<p>The speed of light = 299,792,458m/s</p>
<p>Still, it is possible to add even more exact digits and be even more precise. It was Russell who observed that “modern science involves itself in an apparent paradox of approximation. Every measurement in science always contains some probable error due to the limits of precision” (<em>The Scientific Outlook</em>, 1931). One may note that Aristotle (384–322 BC) was cognizant of the precision problem. He articulated his thoughts on the topic in <em>Metaphysics</em>, Chapter 10 (<em>Iota</em>), when discussing unity, units of measure, one and many, sameness, and difference. Rocks may be easily counted because they are discrete: one rock, two rocks, three rocks, etc. However, for things that are continuous and/or in motion, the smallest perceptible differences matter. This calls for precision in units and measures in order to generate the best empirical measurements. Russell states that “Vagueness and accuracy are important notions, which it is very necessary to understand. Both are a matter of degree. All thinking is vague to some extent, and complete accuracy is a theoretical ideal not practically obtainable” (Russell, <em>The Analysis of Mind</em>, 1921, 180). Another perceptive thinker in the lineage of physics, noted:</p>
<p style="margin-left:.5in;">The determination of the relationship and mutual dependence of the facts in particular cases must be the first goal of the Physicist; and for this purpose he requires that an exact measurement may be taken in an equally invariable manner anywhere in the world. (German chemist and physicist, Franz Karl Achard (1753–1821) Journal de Physique (1782), 21, 191)</p>
<h2><strong>International System of Units (SI)</strong></h2>
<p>The mathematical language of scientific measurement that engineers agree to employ universally in the area of science and technology is the International System of Units (SI). It has been in place as an agreed upon standard since 1960. It consists of seven base units (<strong>Figure 1</strong>):</p>
<ul>
<li>Ampere (A): Electrical current</li>
<li>Candela (cd): Luminous intensity</li>
<li>Kelvin (K): Thermodynamic temperature</li>
<li>Kilogram (kg): Mass</li>
<li>Meter (m): Length</li>
<li>Mole (mol): Amount of substance</li>
<li>Second (s): Time</li>
</ul>
<p style="text-align: center;"><img alt="" src="/blog/Portals/11/Golata_Redefining-the-basic-measurements-of-physics-f1.png" style="width: 220px; height: 220px;" title="" /></p>
<p style="text-align: center;"><span style="font-size:x-small;"><strong>Figure 1:</strong> The SI base units.</span></p>
<h2><strong>Explicit-Constant</strong></h2>
<p>The definition of the SI base and its derivative units is a topic of ongoing discussion. The ultimate goal is to introduce more precise methods that are mutually agreed upon. In 2018, it is anticipated that four SI base units will undergo a revision, aiming to amend the definitions of these units, so that they are fixed to certain fundamental constants of physics. This revision will enable these SI base units to have an “explicit-constant" definition, whereby “the unit is defined indirectly by specifying explicitly a value for a well-recognized fundamental constant.” (<em>Bureau International des Poids et Mesures</em> (BIPM), an international organization established by the Metre Convention, through which Member States act together on matters related to measurement science and measurement standards).</p>
<p>The four SI base units being looked at for redefinition (and the perceived benefits) and the purpose for each redefinition are as follows:</p>
<h3><strong>Ampere (A): Electrical Current</strong></h3>
<p>The new definition will significantly improve the accuracy of electrical measurements. The impact on electrical measurements will be immediate: the most precise electrical measurements are always made using the Josephson and quantum Hall effects, and fixing the numerical values of h and e in the new units will lead to exactly known values for the Josephson and von Klitzing constants. This will eliminate the current need to use conventional electrical units rather than SI units to express the results of electrical measurements. (BIPM)</p>
<h3><strong>Kelvin (K): Thermodynamic Temperature</strong></h3>
<p>The new definition will significantly improve the accuracy of radiometric temperature measurements. The conversion factor between measured radiance and thermodynamic temperature (the Stefan-Boltzmann constant) will be exact—using the new definitions of the Kelvin and kilogram­—leading to improved temperature metrology as technology improves. (BIPM)</p>
<h3><strong>Kilogram (kg): Mass</strong></h3>
<p>Defining the kilogram in terms of fundamental physical constants will ensure its long-term stability, and hence, its reliability, which is at present in doubt. (BIPM)</p>
<h3><strong>Mole (mol): Amount of Substance</strong></h3>
<p>The revised definition of the mole is simpler than the current definition, and it will help users of the SI to better understand the nature of the quantity "amount of substance" and its unit—the mole. (BIPM)</p>
<h2><strong>The Dignified Work of Accuracy</strong></h2>
<p>It was Baron William Thomson Kelvin (1824–1907), during his Presidential inaugural address at the 41<sup>st</sup> Meeting of the British Association for the Advancement of Science (1871), who said, “Accurate and minute measurement seems to the non-scientific imagination, a less lofty and dignified work than looking for something new. But nearly all the grandest discoveries of science have been but the rewards of accurate measurement and patient long-continued labor in the minute sifting of numerical results.”</p>
<p>As for me, I welcome these changes but will continue to communicate with you in the more personal way that I have been doing so to date—that is (hopefully), through my less than vague power of thoughtful expression, in which I communicate through my fingers (using my keypad) as my words form and physically shape on the page. Lately, that exercise is becoming all too vaguely familiar.</p>
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