Physics uses new magic to define the kilogram

Some fifty years ago my Maths and Physics Professors instilled in me the concept of elegance being the hallmark of “rightness” in science. For my Maths Professor, there was nothing more admirable or elegant than being just “necessary and sufficient”. I cannot shake off the gut-feeling that unnecessary complexity of explanation is an indicator of “wrongness”. Modern Physics is no longer characterised by elegance – only by complexities which are not necessarily, necessary. Fifty-seven fundamental particles (why only 57?), magical dark energy and dark matter, even stealth dark energy are all “fudge factors”  to cover the flaws of unsatisfactory theories and which make modern physics grossly inelegant.

A new paper from the National Institute of Standards and Technology:

D. Haddad, F. Seifert, L.S Chao, S. Li, D.B. Newell, J.R. Pratt, C. Williams, and S. Schlamminger. A precise instrument to determine the Planck constant, and the future kilogram. Review of Scientific Instruments, 2016 DOI: 10.1063/1.4953825

There used to be a time when units made common sense. A day was the time from sunrise to sunrise. That one day was a little shorter or longer than the next or that it was a different length in different parts of the world, was of little practical significance. Why the earth rotates around its own axis in its orbit around the sun, even in the most advanced physics theories, remains a mystery and a consequence of fundamental magic. Nowadays, of course, modern physics cannot conceive of using something as elegant and simple as the interval from one sunrise to the next to define time. That interval was too variable, too localised to the earth-sun system to be suitable for the flights of fancy of modern physics and cosmology. The magic involved was just too unsophisticated – too crude, too simple.

So now the unit of time is no longer a day but is a second. The second used to be the 86,400th part of a “standard” day, but now the reference interval is the second, defined as the

duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom, at rest, and approaching the theoretical temperature of absolute zero, including corrections for ambient radiation.

Day-magic is now replaced by a more sophisticated atomic magic. All radiation or vibration requires energy. It follows that the radiation of any atom must eventually cease but physicists are happy enough to invoke the magical acquisition of energy by the reference atom such that its radiation remains magically “constant”.

It is a similar story with the kilogram. Once upon a more common-sensical time, it was the weight (under the force of earth’s gravity) of a mass of one litre of water at 4ºC. Since the litre needed defining and the measurement was of weight rather than mass, physics needed something more sophisticated. So was born the International Prototype Kilogram (IPK).  But that mass of platinum/iridium (90/10) alloy was found to be losing mass (about 50 μg over 120 years) and so a more “independent” and “absolute” measure was needed. Two methods were proposed

One would define the kilogram in terms of the mass of a silicon atom by counting the number of atoms in a 1 kg sphere of ultra-pure silicon-28. (See Silicon Kilogram.) 

The other …..  proposed assigning a fixed value to the Planck constant as the basis for a new definition. Mohr and Taylor reasoned that if a watt balance could use an exactly defined mass to measure the unknown value of h, then the process could be reversed: By setting an exact fixed value of h, the same system could be used to measure an unknown mass.

The idea, which came to be known as the “electric” or “electronic” kilogram, was widely discussed and finally endorsed in principle in 2011 by the international General Conference on Weights and Measures (CGPM), with a few provisions. One of them was that, prior to re-definition, at least one instrument, and preferably more, would have to measure h to a benchmark uncertainty of 2 parts in a hundred million (108). NIST’s most recent measurement has a stated relative standard uncertainty of 3.4 X 108. In addition, the values obtained by the watt balances should be in reasonable agreement with those from scientists using the atom-counting approach to defining the kilogram.

……. The measured values from different groups will have to be in very good agreement in order to set an official fixed value for h.

To get from Planck’s constant to mass is not that simple:

….. the connection between mass …  and a constant deriving from the very earliest days of quantum mechanics may not be immediately obvious. The scientific context for that connection is suggested by a deep underlying relationship between two of the most celebrated formulations in physics.

One is Einstein’s famous E =mc2, where E is energy, m is mass,and c is the speed of light. The other expression, less well known to the general public but fundamental to modern science, is E = hν, the first “quantum” expression in history, stated by Max Planck in 1900. Here E is energy, ν is frequency, and h is what is now known as the Planck constant.

Einstein’s equation reveals that mass can be understood and even quantified in terms of energy. Planck’s equation shows that energy, in turn, can be calculated in terms of the frequency (ν) of some entity such as a photon — or alternatively, with some mathematical substitutions, a significant mass — times an integer multiple of h. The integer aspect is what makes the relationship “quantized.”

Taking the two equations together yields a counterintuitive but hugely valuable insight: Mass – even on the scale of everyday objects – is inherently related to h, which Planck first used to describe the vanishingly small energy content of individual photons emitted by the atoms in hot objects. The value of h is about 0.6 trillionths of a trillionth of a billionth of 1 joule-second. The joule is the SI unit of energy.

As a practical matter, experiments linking mass to h with extraordinary precision became possible in the late 20th century as the result of two separate discoveries which led to two different physical constants related to voltage and resistance respectively.*

*These are the Josephson constant (K= 2e/h) and the von Klitzing constant (R= h/e2). …. Both constants also involve e, the fundamental charge of the electron. Because of the way the watt balance measures electrical power (albeit indirectly), e, cancels out of the equations. That leaves h as the sole quantity of interest.

The new NIST paper describes new measurements of h, with a watt-balance:

 A high-tech version of an old-fashioned balance scale at the National Institute of Standards and Technology (NIST) has just brought scientists a critical step closer toward a new and improved definition of the kilogram. The scale, called the NIST-4 watt balance, has conducted its first measurement of a fundamental physical quantity called Planck’s constant to within 34 parts per billion – demonstrating the scale is accurate enough to assist the international community with the redefinition of the kilogram, an event slated for 2018.

But the Planck constant itself is unexplained and relies on magic.

Classical statistical mechanics requires the existence of h (but does not define its value). Eventually, following upon Planck’s discovery, it was recognized that physical action cannot take on an arbitrary value. Instead, it must be some multiple of a very small quantity, the “quantum of action”, now called the Planck constant. Classical physics cannot explain this fact.

Why Planck’s constant is a constant or has to be a constant is unknown. It’s magic. Why the radiation of a caesium atom would remain constant is also counter-intuitive and just magic. Advances in physics only delve down to deeper layers of magic. Ultimately they all rely on evoking the 4 fundamental magical  forces of the universe. Giving some magic a name and a label does not explain it.

Fifty-seven fundamental particles is just inelegant and unsatisfactory. It is complication for the sake of complication. (Has CERN ever actually discovered anything? Every question it addresses is answered by two more questions – and without ever answering the first. The God of the God particle turned out to be just a deity rather than a God.)

The universe is not that messy. It is just magical.

Far simpler to take a kilogram as being the mass of a litre of water where a litre is twice the amount of beer I can drink in one gulp (when I am parched).


 

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