OT - Kilo prototype mysteriously loses weight

[dp]

You just took a left turn, for no apparent reason, with a quip that has nothing to do with what's being discussed. I am trying to take it on good faith that you understand what master standard is for, and why you wouldn't want to go to Alpha Centauri with one, and why Ebay really doesn't want one.

Sorry - wasn't my intent to offend. Mass and time are related and interdependant, and in today's world they have commercial importance, particularly in power generation and computing. And if a one-way human mission were sent to some far star they definitely would need to have some basic standards with them and I expect a good calibrated known mass standard would be part of that kit.

[littlelocos]

A mass standard cannot be defined in terms of electrical phenomena. The concept of mass falls squarely in the Einsteinian arena. Counting atoms is impractical at best and horrendously difficult to verify, if it can be done at all. Ultimately, the only way to replace a physical mass standard it to define a unit of mass in terms of the total energy content. E=mc^2 is the relation. This requires a complete characterization of the environment including effects such as frame dragging.

Evan,
I would suggest you read the articles I referenced, not just blow off about it. If you would like to argue it with a scientist, I would suggest you contact NIST to discuss. All I can say about it is -- it works very well and does what they say.

Over and out,
Todd.

[aostling]

BTW, 50 micrograms is a lot. That's an easy amount to measure.

Yes, if I calculate correctly, 50 micrograms of platinum has the volume of a cube 0.005" on a side.

The Prototype Kilogram contains 10% iridium. I always thought that osmium was the densest element, but Wikipedia states:

The measured density of iridium is only slightly lower than that of osmium, which is often listed as the most dense element known. However, calculations of density from the space lattice may produce more reliable data for these elements than actual measurements and give a density of 22650 kg/m³ for iridium versus 22610 kg/m³ for osmium. Definitive selection between the two is therefore not possible at this time.

[Evan]

Evan,
I would suggest you read the articles I referenced, not just blow off about it. If you would like to argue it with a scientist, I would suggest you contact NIST to discuss. All I can say about it is -- it works very well and does what they say.

I suggest you read the article. They aren't defining the kilogram in terms of electrical phenomena. They are using a mass artifact to calibrate what amounts to a very accurate scale. The value produced is still traceable back to the artifact made of matter. It changes nothing except that they won't need to constantly refer to the artifact. The definition is still based on the artifact, not some other principle. There isn't any way to define a quantity of matter except by using a quantity of matter as a reference.

From the article you linked:

The NIST watt balance is a two-story-high apparatus designed to redefine mass in terms of fundamental physics and quantum standards. It measures the force required to balance a 1-kilogram mass artifact against the pull of Earth’s gravity, as well as two electrical values (see graphic below). These measurements are used to determine the relationship between mechanical and electrical power, which can be combined with several equations to define the kilogram in terms of basic properties of nature.

That isn't very well worded. What they are doing is calibrating a reproducible method of producing a force equivalent to the mass artifact. Once they do that they can throw away the artifact but it is still the original source of the definition of the unit of mass.

[littlelocos]

Evan,
Cool. Thanks.

Still a difficult concept to understand -- and doubly difficult to explain. The machine is also called a "Watt Balance" which is a little easier for me to comprehend.

When touring the labs with visitors, some of the chatter about "whose kilogram artifact is most accurate" can get rather entertaining, especially when THE kilogram will always reside in Paris. The issue is "What if the French kilogram (a primary standard and the definition of the kg) changes and the US kilogram (a secondary International standard) stays the same?" Sounds frustrating.

Thanks again,
Todd.

[Evan]

The issue is "What if the French kilogram (a primary standard and the definition of the kg) changes and the US kilogram (a secondary International standard) stays the same?" Sounds frustrating.

Similar has happened before. The inch was redefined back in the 50's if I recall correctly to be exactly 25.4 millimeters. Any really accurate inch measuring device made before that isn't correct since that change. Not to worry though, the difference is extremely small.

I take issue with the constant reference in the article to "defining the kilogram by properties of nature". They cannot and the reason I stated so is because the property of having mass, inertia, momentum and weight isn't explained by the standard model. It is only explained by the theories of relativity. Until someone develops a unified theory that includes gravity and quantum mechanics we have no knowledge of any first principles of electromagnetic theory that can define the acceleration produced by a quantity of matter. Quantum mechanics has nothing to say about gravity or how much something should weigh.

[Fasttrack]

Well even general relativity falls short. It doesn't account for mass - just the effects of mass on other particles.

The standard model is inherently relativistic, though. I think it would be wise, for the sake of others, to differentiate between special and general relativity. Special relativity is a part of the standard model as a necessity. Also it might be wise to note that the standard model and quantum mechanics are not the same thing, just interelated. The standard model describes matter and three of the four forces while quantum mechanics is primarily concerned with the wave function, uncertainty and quanta.

Incidently, supersymmetry is one likely theory that accounts for mass. It calls for a higgs field and the higgs scalar boson that mediates the field and it acts, in an over-simplified way, like balls rolling over sawdust. Some are hard marbles and they zip right through the patch of sawdust without slowing down while a sticky ball rolls through the sawdust and slows down as it gains mass. Like i said a way over-simplified view, but you all get the idea.

The nice thing about supersymmetry is that, in order for the math to work out, the mass has to be there where as the standard model the masses have to be figured in by hand later or the math explodes leaving you with such things as 0/0 or infinity/infinity etc. Plus it also explains all the other phenomenon that string theory accounts for.

[Yankee1]

Possibility?

How about oxidation due to oxygen molecule collisions. or electron transfers due to close proximity to a Less noble metal and humidity?
Chuck

[Evan]

The standard model describes matter and three of the four forces

I would consider quantum mechanics to be an integral part of the Standard Model today. Funny thing about it is that it describes matter in great detail but cannot explain why it is massive and has gravity.

General Relativity sort of skips around that as well merely explaining that matter curves space in a way that produces the effects of gravitation. It is internally and externally consistent but we are left with the fact that we don't really know why there is gravity or why gravity is unipolar. Or is it?

[Fasttrack]

Right, thats where the higgs scalar boson, theoretically, comes in. I guess i should have more clearly emphasized that the standard model describes matter with quantities such as spin, quantum state, and etc rather than the more conventional "mass".

Since special relativity is as much of an integral part of the standard model as quantum mechanics i just thought it appropriate to differentiate between the two. The standard model is to quantum mechanics what newtons laws are to physics. Not interchangeable in usage, but definantly an integral part as you put it. I was looking for the term "integral" earlier but for some reason i just couldn't come up with it. Oh well, at least i'm not a writer!





p.s. sometimes i wish i could spell; sorry for any glaring errors.

<edit> Evan, you exaclty summarized what interested me in the super-symetric model. I was fascinated at how perfectly it was able to describe why something has mass, which is a really awsome thing to be able to explain, imo. Its like being able to explain what "happy" is!

[guynamedbathgate]

perhaps they didnt realize not to slide the weight back onto the shelf. Always start with the simplest answer first. we will speculate about dark matter later.

[dp]

I would consider quantum mechanics to be an integral part of the Standard Model today. Funny thing about it is that it describes matter in great detail but cannot explain why it is massive and has gravity.

General Relativity sort of skips around that as well merely explaining that matter curves space in a way that produces the effects of gravitation. It is internally and externally consistent but we are left with the fact that we don't really know why there is gravity or why gravity is unipolar. Or is it?

Because we don't know what or why gravity is we don't know what or why time is. But we've managed to find ways to use or waste some of each

[halac]

Saw this article on the Space Daily website concerning the kilo standard.

http://www.spacedaily.com/reports/A_Better_Definition_For_The_Kilogram_Scientists_Propose_A_Precise_Number_Of_Carbon_Atoms_999.html