Scientists vote on new way to measure a kilogram

[AirPoh]

AV is going to love this.

Friday's vote at the General Conference on Weights and Measures in Versailles -- which is widely expected to be approved -- is set to permanently redefine the kilogram and send the IPK into retirement.
The new definition being proposed is based on the Planck constant -- a constant observed in the natural world, which is inherently stable, according to the NPL.

Full story here -->

 

[steve_bank]

I heard about that in the 90s.

 

[Lion IRC]

Voting? (copycats)
When will they declare the result?

 

[steve_bank]

Voting? (copycats)
When will they declare the result?
View attachment 18835

Only those of us who are faithful believers will be told by the Pope Of Science.

You have to know the Secret Science Handshake.

It is actually important even to you. The kilogram mass primary standard will no longer be a piece of metal in a lab. A primary standard can be constructed anywhere.

When you buy a pound or kilogram of something at a grocery store on what does the accuracy rely and why will it read the same anywhere in the world within instrument error?

Typical ignorant theist anti science rant.

 

[Lion IRC]

I was pointing out the irony of voting on a question that science ought to be able to resolve empirically. Ask yourself, why might one scientist vote x and another vote y ?

Are they using different methods to decide? Don't they all have access to the same data?
Is this politics or science?

 

[bilby]

I was pointing out the irony of voting on a question that science ought to be able to resolve empirically. Ask yourself, why might one scientist vote x and another vote y ?

Are they using different methods to decide? Don't they all have access to the same data?
Is this politics or science?

The definition of the kilogram, like all units of measurement, is completely arbitrary.

It doesn't matter one whit what definition is used - only that everyone agrees to use the exact same definition.

So it is appropriate to vote on which definition to use - it's purely a matter of opinion. How else would you effectively pick an arbitrary value that is to be used by all?

 

[Jokodo]

I was pointing out the irony of voting on a question that science ought to be able to resolve empirically. Ask yourself, why might one scientist vote x and another vote y ?

Are they using different methods to decide? Don't they all have access to the same data?
Is this politics or science?

This is not an empirical question, it is a question purely of convention.

 

[lpetrich]

BIPM - the Bureau International de Poids et Mésures - the International Bureau of Weights of Measures

It officially decided today to endorse some redefinitions of its fundamental units. The vote was unanimous, but I think that it was mostly a formality, publicly something that its members had agreed on informally.

Second: unchanged. Continues to be in terms of the frequency of the unperturbed hyperfine transition of cesium-133.

Meter: unchanged. Continues to be defined in terms of the second by fixing the speed of light in a vacuum.

Kilogram: formerly the mass of a platinum-iridium cylinder in a suburb of Paris, now defined in terms of the meter and the second by fixing Planck's constant.

Electrical units: formerly defined from electromagnetic mechanical effects, now defined by fixing the elementary charge. The magnetic permeability of the vacuum becomes a measured quantity.

Kelvin: formerly from the triple point of water, now defined by fixing Boltzmann's constant.

Mole ( (1 gram) / (1 atomic mass unit or dalton) ): formerly measured. Now fixed.

Candela (luminous intensity, defined from other units): unchanged.

 

[DrZoidberg]

I was pointing out the irony of voting on a question that science ought to be able to resolve empirically. Ask yourself, why might one scientist vote x and another vote y ?

Are they using different methods to decide? Don't they all have access to the same data?
Is this politics or science?

It's both obviously. They're trying to agree on a standard that is 100% arbitrary. What matters is that everybody agrees. Not what specific number it is.

 

[lpetrich]

The fixing of the elementary charge and of Planck's constant were done because of two effects that enable some very precise measurements of voltage and electric current.

The first is the Josephson effect. In superconductivity, current-conduction electrons' motions will become correlated a tiny bit, but nevertheless correlated, and that correlation will have a quantum-mechanical wavefunction that can spread over an indefinitely large size. A thin-enough insulating layer between two superconducting layers will allow the two sides' wavefunctions to interact, and a consequence of a voltage difference across the insulating layer is a back-and-forth current. The frequency of that back-and-forth current can be measured, and it is related to the voltage:

voltage = (h/(2*e)) * frequency

h = Planck's constant, e = elementary charge

The second is the quantum Hall effect. The Hall effect results from an electric current passing through a magnetic field: an electric field perpendicular to both. In the classical limit, that field is proportional to the product of the current and the magnetic field, and the voltage over some distance divided by the total current has units of electrical resistance. In the classical limit, this "Hall resistance" is proportional to the magnetic field, but for small enough systems, one sees quantum effects, effects including the quantization of the Hall resistance. It becomes integer multiples of some number:

Hall-resistance quantum = h/e²


So from the Josephson effect, one can measure voltage very precisely, and from using that and the quantum Hall effect, one can measure electric current very precisely.

What does this have to do with mass? Fixing Planck's constant means that mass is defined in terms of length and time, and one then has to go from electrical measurements to mass measurements. There is a very precise device called a "Watt balance", a device for doing that. It measures how much force a magnet makes on a coil of wire with electric current running through it. The magnet's field is then measured by letting the coil move up and down without a current source. That motion will generate a voltage across it. Combining the measurements gives:

(force) ~ (current) * (magnetic field) ~ (current ) * (voltage) ~ (electrical power)

Thus, the name "Watt balance". Using a Josephson measurement for voltage gives

(voltage) ~ h/e

Using the quantum Hall effect for resistance gives a value for the current, since (resistance) ~ (voltage) / (current). Working it out,

(current) ~ (h/e) / (h/e²) ~ e -- some number of elementary charges per second

Combining them gives (power) = (voltage) * (current) ~ h -- Planck's constant. The elementary charge has dropped out.

So we find (force) ~ h, and that's how one gets mass from Planck's constant.

 

[steve_bank]

I was pointing out the irony of voting on a question that science ought to be able to resolve empirically. Ask yourself, why might one scientist vote x and another vote y ?

Are they using different methods to decide? Don't they all have access to the same data?
Is this politics or science?

Definitions like this are decided by consensus with international representatives. There has been a sequence of chmnges going back to the 19th century.

Another system that influences your life is ISO or the international standards organizing. You can google it. Mostly about technology and now software.

It is mostly sconce but humans are always political.

I expect the French will take a major blow to national pride....

Along with a scale in the grocery store fundamental units define the voltage at your house. Your entire modern life rests on a few fundamental definitions and standards created by scientists.

 

[Tom Sawyer]

So, if my scale is in kilograms, does that mean I lost weight today? If so, I'll celebrate with some ice cream.

 

[Lion IRC]

I was pointing out the irony of voting on a question that science ought to be able to resolve empirically. Ask yourself, why might one scientist vote x and another vote y ?

Are they using different methods to decide? Don't they all have access to the same data?
Is this politics or science?

This is not an empirical question, it is a question purely of convention.

You mean like the definition of bats/birds?
I vote we use the bible definition.

Seriously, aren't those scientists going to use science to answer the question of which way to vote? Do we vote to decide if Pluto is a planet or not?

 

[Tom Sawyer]

I don't think you know what science is.

 

[steve_bank]

I was pointing out the irony of voting on a question that science ought to be able to resolve empirically. Ask yourself, why might one scientist vote x and another vote y ?

Are they using different methods to decide? Don't they all have access to the same data?
Is this politics or science?

This is not an empirical question, it is a question purely of convention.

You mean like the definition of bats/birds?
I vote we use the bible definition.

Seriously, aren't those scientists going to use science to answer the question of which way to vote? Do we vote to decide if Pluto is a planet or not?

Seriously, what else would scientists use other than science, the bible?

 

[lpetrich]

So, if my scale is in kilograms, does that mean I lost weight today? If so, I'll celebrate with some ice cream.

No, it means that you weigh fewer of larger kilograms -- it will exactly cancel out. I don't know which way the redefined kg went relative to the previous standard. It could have gotten smaller instead of larger. In that case, you'd weigh more of smaller kilograms.

The now-replaced primary standard is the International Prototype Kilogram platinum-iridium cylinder, or Le Grand K ("The Big K"). Several nations have copies of it, some 40 cylinders that serve as secondary standards. Every now and then, these secondary ones are brought to Paris and compared with the primary one. They have been observed to vary by something like 10^-8.

The IPK has apparently been increasing in mass, from surface contamination: The Kilogram Has Gained Weight But it's on the order of 10^-8, around the range of relative variations of it and the secondary standards.

I don't know what is going to happen to the IPK. I suspect that it will become a secondary standard, joining the existing ones.

 

[lpetrich]

Of the SI seven base units, the candela seems rather odd to me. The article  Candela has its history. Luminous-intensity standards were first based on lamps constructed in various standard ways.

In 1881, Jules Violle proposed using the blackbody luminosity of platinum at its melting point as a luminosity standard.

In 1948, the standard candle was defined using Violle's proposal.

In 1967, it was clarified to be for one Earth atmosphere of pressure.

In 1979, it was redefined as a certain energy flux of light. Thus defining it in terms of other SI constants.


Blackbody means perfect thermal emitter. A blackbody object must also be a perfect absorber. One can get close to one with a hole. I once saw a picture of a metal pipe that was heated hot enough to glow. It had a hole in it, and the hole glowed brighter than the pipe outside surface.

 

[lpetrich]

Temperature was long defined by physical standards, but with the new redefinition, it is now defined in terms of other SI units.

In 1742, Anders Celsius invented a temperature scale where 100 = freezing point of water and 0 = boiling point of water at sea-level pressure. He was careful about the pressure part, since he had measured how the boiling point of water varies with pressure. The next year, Jean-Pierre Christin independently proposed a scale where 0 = freezing point of water and 100 = boiling point of water. The year after, Carl Linnaeus, botanist and taxonomist, flipped Celsius's scale, making it Christin's.

In 1802, Joseph Louis Gay-Lussac concluded that gases will reach zero size at a temperature that he calculated to be -273 C.

In 1848, William Thomson, Lord Kelvin, proposed a temperature scale starting from "infinite cold" (absolute zero), and with the Celsius system supplying its unit.

In 1948, the triple point of water, where all three phases coexist, was officially defined as having temperature 0.01 C.

In 1954, the triple point of water was officially defined as having temperature 273.16 K (Kelvin), starting from absolute zero. This made 0 C = 273.15 K.

In 2005, this standard was clarified as being for Vienna Standard Mean Ocean Water's isotopic composition.

Today, as I write this, Boltzmann's constant was officially fixed, defining temperature in terms of energy.

 

[Lion IRC]

I don't think you know what science is.

Actually, I'm starting to think YOU don't know what science is.

If there is a more scientifically accurate (empirical) way to determine/define a mass called "The Kilogram" you don't vote on the validity of using that method. It either IS or it is not.

I accept that politicians (or church officials) might want to put it to the vote after a lengthy debate. But surely 100% of scientists looking at the same repeatable, empirical data should laugh out loud if asked - do you think we should decide this by secret ballot.

 

[bilby]

I don't think you know what science is.

Actually, I'm starting to think YOU don't know what science is.

If there is a more scientifically accurate (empirical) way to determine/define a mass called "The Kilogram" you don't vote on the validity of using that method. It either IS or it is not.

I accept that politicians (or church officials) might want to put it to the vote after a lengthy debate. But surely 100% of scientists looking at the same repeatable, empirical data should laugh out loud if asked - do you think we should decide this by secret ballot.

It's entirely arbitrary, you numpty.

All that matters is that everyone agrees on a single (arbitrary) means to determine the (arbitrary) value.

There's nothing empirical about it. It establishes an agreed, definite, and arbitrary standard, to which empirical observations made at different times and places can be related.

The amount of science of which you are deeply ignorant would fill a tome the size of a large family bible.

Not only are you clearly clueless on this topic; you are also clearly clueless about how clueless you are - and so you repeatedly make a total clown of yourself by applying the non-reasoning of your faith to this topic about which you are eminently unqualified to have any opinion at all.