This is an informational post, not part of debate.
Metrologists are like hi-fi nuts. the urge to measure physical constants very accurately is akin to the urge to play vinyl records properly.
Brian Kibble works at National Physical Laboratory Teddington, Middlesex. He gets today's heros of metrology award. In mid-1970s he invented the "moving-coil balance" a kind of force gauge. It has become famous--the other metrologists have gradually over several decades grasped its importance. NIST in Maryland has built a Kibble force gauge that is two stories tall. The crafty Swiss have one. There is one in New Zealand. Kibble's own, in Teddington, is quite possibly twice as accurate as the NIST although not quite so big and expensive. There is a "balance du watt francaise" project at the Bureau National de Metrologie in Paris under M. Lecollinet.

The watt balance or "moving coil balance" (as Kibble originally called it) allows one to measure forces using only electrical standards (volts and amps) and speed measurement.

Here is an article from the journal Science:

http://ep.llnl.gov/msds/Chem120/Kilogram.html

The author interviewed Kibble. It is about the effort
to get rid of the metal kilo standard and why people want to do that.

Here are some parts of an article from the journal
Physics Today (March 2001):
http://www.physicstoday.org/pt/vol-54/iss-3/p29.html
http://www.physicstoday.org/pt/vol-54/iss-3/captions/p29cap3.html
http://www.physicstoday.org/pt/vol-54/iss-3/captions/p29box3.html

There are some pictures, including one of Ed Williams who is in charge of the watt balance in Maryland.

Here are some miscellaneous Swiss watt balance URL:
http://www-optics.unine.ch/research/metrology/Watt_balance/Watt_balance.html

http://www.copernicus.org/URSI/kh_tagung/2001/abstracts/ccc0036.pdf

I only included the Swiss stuff to illustrate how widespread the interest is.

Support your local metrologists. Getting rid of the metal kilogram is kind of revolutionary. It will probably be done by means of Brian Kibble's invention.
The best article I mentioned is the one from Science which is written for general non-tech readers without using formulas and is pretty understandable.

Who are you oh anonymous one who would start this thread?

On this point- "Support your local metrologists. Getting rid of the metal kilogram is kind of revolutionary. It will probably be done by means of Brian Kibble's invention."- I am a very proud man. The man whose ideas will destroy the kilogramme, works in my own precious little county. Although, he will probably destroy the pound as well, won't he?

Bryan it was nice of you to read that.
It really is just informational.
No harm will come to the kilogram or to
the pound from this work at NPL Teddington
or anywhere else. It is merely redefinition.

They have been having trouble with the metal
kilogram artifact (called "Le grand K") in
Paris. Because of tarnishing and such the weight
does not stay the same. Same with the copies
like the one in Maryland. This is describe in
the general-reader Science article I mentioned.

In one sense it would be a great coup to be
be able to redefine the kilogram mass using
nothing but electricity--and then put the old
metal block in the Musee Tech as a curiosity or
historical memento. In another sense it is nothing
to worry about because what do we care what these
science gnomes do?

But I am thrilled. New work in a what is
becoming a hot field and these people with their
freshly built machines cannot publish a single paper
without a reference to Kibble's 1975 paper. He (if
not English in general) can be proud of this.

KvK born Schroda bei Posen 1943 discovery c.1979 nobel 1985 ampere standard 1990

Srodka near Poznan is now in Poland about halfway between Berlin and Warsaw. Since 1985 Klaus von Klitzing has been the director of the MPI-Stuttgart which does solid state physics research.

By discovering the quantum Hall effect KvK made possible the extremely accurate current gauge which since 1990 has been the basis of the ampere standard. This von Klitzing quantum Hall gauge measures current by a producing a voltage which is exactly proportional to the the current flowing through the device.

Voltage can, in turn, be very accurately measured by another quantum device (Josephson effect.)

The proportion of voltage to current is h/e^2 and called various things like "quantum Hall resistance" or
"R sub K" for klitzing resistance. David Leadley of Warwick Univ. has the clearest discussion I could find
on line of the quantum Hall effect at:

http://www.warwick.ac.uk/~phsbm/qhe.htm

Von Klitzing worked at Oxford Clarendon Lab 1975-1976 and at Grenoble High Magnetic Field Lab just
prior to publishing his main paper (1980)

For the adopted value of the von Klitzing constant on which the 1990 ampere standard is based see
nist adopted values
http://physics.nist.gov/cgi-bin/cuu/Category?view=html&Adopted+values.x=95&Adopted+values.y=14

The accurate measurement of voltage and current are what Brian Kibble's moving-coil balance requires for its measurement of force and consequently mass. Von Klitzing's contribution is one of the key factors enabling a shift away from dependence on Le Grand K.

"BRIAN DAVID JOSEPHSON b. Jan. 4, 1940, Cardiff...Cardiff High School...Cambridge...Cavendish Lab...British physicist whose discovery of the Josephson effect while a 22-year-old graduate student won him a share of the 1973 Nobel Prize for Physics...
While still an undergraduate, Josephson became interested in superconductivity..." These are exerpts from an on-line encyclopedia article. For more see:

http://search2.eb.com/nobel/micro/306_81.html

On-line resources (by Stephen Godfrey)
URL with diagram of a Josephson junction
http://www.physics.carleton.ca/courses/75.364/mp-2html/node20.html

URL describing and explaining Josephson effect
http://www.physics.carleton.ca/courses/75.364/mp-2html/node22.html

The Josephson effect is the basis of the 1990 volt standard of the BIPM (International Bureau of Weights and Measures). The effect associates to every voltage a particular frequency. Measuring the frequency, which can be done with great accuracy by atomic clock, allows the voltage to be known. A BIPM webpage:

http://www.bipm.fr/enus/5_Scientific/d_electricity/electricity.html

The 1990 volt standard assumes an adopted value for the Josephson constant 2e/h

See the nist adopted values
http://physics.nist.gov/cgi-bin/cuu/Category?view=html&Adopted+values.x=95&Adopted+values.y=14

These three people, Kibble, von Klitzing, Josephson have made recent (1975 and later) major contributions which have changed metrology and make it thinkable to base all measurement on very fundamental things rather than on artifacts.

I believe this thread is now complete unless somebody has another person to suggest.

The aim here is to get brief information on these people posted without getting mixed up in debate. Hope it's been objective and unobjectionable.

Also this kind of information is of very limited interest but the definition of the Forum generously allows for some scientific/technical points and I hope the space here has been acceptably used.

Dear fellow bwma posters.
I am beginning to lose track of who said what in some of the more interesting threads and just now could not find a very clear well-informed statement by Paul Birch. It took me three tries to find it. First looked in MP then in Definition of Units and finally in Anti-BMWA-somethingorother. I hope you will not blame me or object if I make a copy of it here where, because the thread is short and distinctively titled it will be easy to find in future. If I am not mistaken this guy is trinity cambr physics/maths and then radio-astronomy jodrell bank and if you like authority based on knowledge and experience this is it. There is always legitimate range for differences of opinion but as for matters of fact (like about the different systems of units in use) this guy is simply factually correct. Or so it seems to me. So here is one of PB's posts

[[Standards - a few minor points May 17 2002, 9:21 PM

Much of this has probably been said before. But here goes. There has been much discussion about standards for imperial units that aren't based on metric units. It's good fun, but really it's not necessary. Just take the current or proposed SI definitions and multiply the figures by the current legally defined conversion factors. That gives us imperial units defined in terms of basic physics, just like the metric units.
Beyond that, people don't need to know the precise definitions of customary units - the ones we use in daily life. Scientific units are different; it IS necessary for scientists to understand the definitions, though not always to remember the exact numbers.
Natural units, based solely on fundamental constants, have a certain elegance, but it is questionable whether they will ever have much general application. Geometrodynamic units, which suppress the speed of light and the gravitational constant and are thus halfway to being natural units, are highly convenient for analysis in relativity theory; but even there it is easy to slip up, and it is often necessary to reinsert the fundamental constants in order to check one's result for dimensional validity.
By the way, contrary to certain claims on this board, the speed of light in vacuo IS a universal constant; that is the basis of relativistic kinematics, of how length, time, velocity and acceleration are now defined. It is as fixed as twelve inches equals one foot. Accurate measurement of that speed is another matter.
Finally, there is not just one metric system, but many: at my latest count, seven (MKS, MKS electrostatic, cgs electromagnetic, cgs electrostatic, SI, geometrodynamic, natural). Their definitions and standards have many similarities, but also many incompatibilities.

Above all, we need to understand that no single system of measurement is best for all uses, and that no government should ever imagine it can determine the efficient or rational usage even for a single economy, let alone the whole world.
It is the moral right - and should always be the legal right - of all individuals to use whichever units they choose; metric or imperial, customary or wildly idiosyncratic. No one has the right to deny them that freedom of choice.]]

Hi Paul this thread is a place we can discuss
the proposed SI redfinitions with little chance of
being disturbed. Brian Kibble and the others will
surely not mind.

In a recent post you wrote:

[[ Problems with SI redefinitions May 26 2002, 6:18 PM

The snag with the photon energy-equivalent definition is that you can't actually "weigh" (measure the mass of) a bundle of photons, whereas you can, for instance, measure the mutual attraction of lumps of metal or the mass of a cubic metre of water. Such an abstract definition therefore has to be supplemented with a secondary standard that is physically reproducible.

The snag with a Boltzmann's constant definition is that its value is only known to around 10 ppm, whereas the triple point of water can be measured to better than 1 ppm.]]

As for Boltzmann's constant, is it possible to measure
the triplepoint or is that taken as basis for definition? But surely one can make sense of the idea--measuring something else like the meltingpoint of gold in relation to the triplepoint of water. It's like: logically speaking it is today impossible to measure the speed of light and yet we can give a meaning to experiments which used to do that. Anyway a paragraph of clarification from you would be good. Your objection or "snag" idea is on the right track. We ought to be able to predict WHEN the measurement of
Boltzmann's will become so accurate that the situation will flipflop and radiation thermometry (now applied over a very wide range) will become the standard. Maybe Taylor or somebody would help us out. It has to do with trends in the accuracies.

BUT I WAS MAINLY INTERESTED in your other comment. You
correctly point out the need to translate that kilogram
definition into operation.

That is described in several Mohr and Taylor papers
and is fascinating. The gist is that today one measures
planck's h very accurately using Kibble's force gauge
and something of known weight. One has something one
KNOWS weighs a newton (I simplify) and one weighs it
and gets Planck's h. Mohr and Taylor say REVERSE this:
adopt an exact value for h and then you can say very
accurately what a newton of force is! And you will be
able to test blocks of metal which are supposed to weigh one or 9.80665 or whatever newtons and say whether or not they actually do. The minute you adopt
an exact conventional value for h, then LE GRAND K is cut
completely out of the picture. The Kibble gauge provides the force standard (and thus the mass standard since acceleration is measurable) by electric means and electric standards are based on h, e and the
atomic clock. The e drops out in their calculation so
the value of h is all you need. The calculation is
shown an on-line Physics Today article as well as the
on-line EJDE article I gave the URL for.
So it is intricate but it just happens that the
photon-frequency definition turns into an operational
definition in a very direct way--through an already
existing force gauge. I wish you could argue with
Barry Taylor about this. It's neat but I can't do it
justice especially in this e-mail-like context.

The Josephson volt gauge and the von Klitzing amp
gauge are absolutely essential to all this because they
base electric units on the atomic clock (Josephson turns volts to frequency according to 2e/h and Klitzing
turns amps to volts according to h/ee) Both are superconducting solid state quantum devices---ie. sort of magic. Do you know about that stuff or would you
like an URL? Should I try to find some URL or maybe
they are already in earlier posts in this thread? I
don't remember exactly what is here.

Metrologists seem anxious to move in this direction
because it will solve several different problems--make several
kinds of measurement more precise and reliable.

People concerned with units really should take a close look at SI metric and know where it is going and who is at the controls. There are certain physicists like Mohr and Taylor who are like pilots taking a ship in or out of harbor because they know the waters--steering the metric ship or flying the metric plane--because accurate measurement is something they understand better than most and the system is changing.

Anyway Mohr and Taylor's proposed redefinition is:

"The kilogram is the mass of a body at rest whose equivalent energy equals the energy of a collection of
photons whose frequencies sum to 135 639 277 x 10^42
hertz."

Like I said in that other thread, I averaged three smart people's guesses about when and got 2009. Taylor's guess was the most conservative or pessimistic (behooves him to act modest.)

Nobody talks about beauty.

Replacing a block of metal by a glittering
cloud of light.

for very practical (even compelling) metrological reasons. the best sort of beauty is necessary
as well.

Anyway, if I was BWMA I would never never never never
let the SI metric people beat me to this. It is a show-stopper.

If their proposal is adopted, as a lot of people
seem to think it will be, then the kilogram block of
metal is to be replaced by pure
energy-- photons--sounds like star trek that sci fi
television serial with Klingons and photon torpedos
and stuff. But no it is just what kids would learn in
school as the basis of the measurement system. Mundane
weighing of bananas connecting somehow with frequency of squiggly electromagnetic boings. Not just one, a whole flock.

I'd have to disagree with your statment that "it just happens that the photon-frequency definition turns into an operational definition in a very direct way". The Physics Today article itself calls it very indirect. The standard wouldn't actually be based on measuring the mass of a collection of photons but upon measuring a force that through the definitions of the electrical units and some fairly hairy physics can be translated into an equivalence to the measurement of Planck's constant that determines the energy of photons; and even then you have to measure the aceleration due to gravity as well to turn the force standard into a mass standard. None of this rules it out as a potential SI definition, but it is a real handicap; it's quite different from redefining the metre in terms of the unit of time and the speed of light, which can be measured or "measured" very directly.

The triple point of water can be quite easily pin-pointed (to a tiny fraction of a degree) so it remains a convenient basis for the scale of temperature, especially one for which accuracy is in practice most important for temperatures near the triple point (say 260K - 320K). A somewhat more indirect scale based on an application of Boltzmann's constant would at present lack a clear and precise tie-in to ordinary use. I don't see any way of predicting when or whether the accuracies are ever likely to swap. Jumps in accuracy are largely unpredictable, because they come from the invention of radically new techniques.

I'd certainly like to see someone invent a good new method for measuring the Gravitational constant to high accuracy - I find it annoying that it's so poorly known. It means that in defining the imperial pound in terms of gravity, I have to accept that the definition will have to be tweaked every time another measurement of G is made, in order to avoid having to adjust the values of all the other more accurately known constants. This is a bit of a cheat but worth it, I think, for the sake of classical tradition and clarity.

Good post. Every point addressed.
I will list the Mohr+Taylor on-line article

http://ejde.math.swt.edu/conf-proc/04/m1/mohr.pdf

because it doesn't seem to be given anywhere in
this thread. I think you have the URL but it's
possible someone else might drop in and want a
source for the proposed kilogram redefinition.

I know what you mean about the uncertainty in G!
Many people must find this bothersome but apparently
no one can figure out what to do about it.
CODATA actually *reduced* the precision (increased
the uncertainty) in its recommended value of G at
the last go-round. I exchanged email with a Russian
who sounded quite angry about it. His extensive measurements of G were in line with earlier estimates
and should have reduced the uncertainty, but CODATA
took account of some new American measurement which
according to him was way off base and unreasonably
increased the uncertainty. Essentially they all still
use the 1798 method devised by the great English
eccentric Henry Cavendish, or so I believe. Funny world.

I find your definition of the Imperial pound based on
G appealing. I think esthetic preference has a role in
the definition of units and your preferences have a
clarity which I like and understand. It is intuitive to
base definition of mass on gravitational attraction
(although it introduces uncertainty into a variety of
measurements as I think you suggest.)

I can't think of anything more that needs saying so
perhaps will let this thread sleep. The big question
in my mind is how will this proposed redefinition (if
put into effect) change the picture. Hard to get a grip on. Could be a liability for SI metric. Introduces more ugly ad hoc numbers. A terrible-looking exact value of h. On the other hand the frequency or energy definition of mass is kind of
jazzy and will certainly intrigue people (and draw
attention to metrology as a field.) It's all almost
too speculative to bother thinking about.