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Ampere Could Be Redefined After Experiments Track Single Electrons Crossing Chip

timothy posted about 7 months ago | from the micro-management dept.

Science 299

ananyo writes "Physicists have tracked electrons crossing a semiconductor chip one at a time — an experiment that should at last enable a rational definition of the ampere, the unit of electrical current. At present, an ampere is defined as the amount of charge flowing per second through two infinitely long wires one meter apart, such that the wires attract each other with a force of 2×10^-7 newtons per meter of length. That definition, adopted in 1948 and based on a thought experiment that can at best be approximated in the laboratory, is clumsy — almost as much of an embarrassment as the definition of the kilogram, which relies on the fluctuating mass of a 125-year-old platinum-and-iridium cylinder stored at the International Bureau of Weights and Measures in Paris. The new approach, described in a paper posted onto the arXiv server on 19 December, would redefine the amp on the basis of e, a physical constant representing the charge of an electron."

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fluctuating weight of KG? (1)

noh8rz10 (2716597) | about 7 months ago | (#45953513)

why would the weight of the platinum/iridium slug fluctuate? I could imagine the size fluctuating, but not the weight.

Re:fluctuating weight of KG? (5, Informative)

Chris Mattern (191822) | about 7 months ago | (#45953583)

why would the weight of the platinum/iridium slug fluctuate?

Because a few atoms of the slug can sublimate into the surrounding atmosphere, even at room temperature. And because a few atoms of the surrounding atmosphere can adhere to the slug. And yes, at the precision we're talking about here, it makes a difference.

Re: fluctuating weight of KG? (0)

Anonymous Coward | about 7 months ago | (#45953591)

Because anytime someone touches it, the air moves around it, or anytime the atoms vibrate atoms will fall off.

Re:fluctuating weight of KG? (1)

forrestt (267374) | about 7 months ago | (#45953619)

I can only imagine it fluctuating as a result of corrosion. For example, if it were iron the act of rusting would alter the weight.

Re:fluctuating weight of KG? (0)

Anonymous Coward | about 7 months ago | (#45954129)

Fucking genius! If only it were iron it would be corroding, but it's platinum and irridium. Corrosion is not a big factor. Forgetting to dust it would alter the mass more.

Re:fluctuating weight of KG? (2, Insightful)

Minwee (522556) | about 7 months ago | (#45954281)

Fucking genius! If only it were iron it would be corroding, but it's platinum and irridium. Corrosion is not a big factor. Forgetting to dust it would alter the mass more.

Actually, remembering to dust it is what causes its mass to change [wired.com] . The problem of how to properly clean the things has been going on for years.

Gravity is not constant... (2, Informative)

fullmetal55 (698310) | about 7 months ago | (#45953627)

It's hard to consistantly and accurately measure weight when the force of gravity constantly changes, add to the fact that there may be radioactive decay of trace elements, oxidation of metals, Dust/erosion, sublimation of trace components), it's easy to understand how using a physical object to consistantly measure a weight, would fluxuate. when your "constants" are actually "variables" it's really hard to nail down constants...

Re:Gravity is not constant... (2)

IDtheTarget (1055608) | about 7 months ago | (#45953847)

The kilogram [wikipedia.org] is a measure of mass [wikipedia.org] , not weight [wikipedia.org] .

Re:Gravity is not constant... (2)

oodaloop (1229816) | about 7 months ago | (#45954131)

No shit. And measuring the mass of the slug in question involves weighing it. Or do you have another method involved for determining the mass of an object used as the constant for measuring mass?

Re:Gravity is not constant... (2, Informative)

Phreakiture (547094) | about 7 months ago | (#45954255)

Or do you have another method involved for determining the mass of an object used as the constant for measuring mass?

Placing two masses on a balance is the usual method . . . . and it is gravity-independent. Gravity is necessary, of course, but it only needs to be constant across the two platters of the balance.

Re:Gravity is not constant... (3)

LordLimecat (1103839) | about 7 months ago | (#45954297)

Except now all you have is a ratio of two masses, rather than an absolute quantity. What exactly would you balance the kilogram reference against?

Re:Gravity is not constant... (4, Funny)

djdanlib (732853) | about 7 months ago | (#45954437)

A duck.

Re:Gravity is not constant... (1)

Phreakiture (547094) | about 7 months ago | (#45954449)

So if it weighs the same as a duck . . .

Re:Gravity is not constant... (3, Insightful)

Phreakiture (547094) | about 7 months ago | (#45954499)

Except now all you have is a ratio of two masses, rather than an absolute quantity. What exactly would you balance the kilogram reference against?

You would use it to callibrate another mass as being a kilogram. I know this is kind of a circular problem, but that's really why the fluctuating mass is troubling, because that's supposed to be the stable benchmark, and it has proven not to be so stable.

may i suggest (0)

Anonymous Coward | about 7 months ago | (#45954531)

a banana (for scale)

Re:Gravity is not constant... (1)

Baloroth (2370816) | about 7 months ago | (#45954599)

Except now all you have is a ratio of two masses, rather than an absolute quantity. What exactly would you balance the kilogram reference against?

Unless one of those masses is the reference that you define as the kilogram, in which case you have the "absolute" mass. All masses are defined in terms of some ratio to a fixed reference mass. It's not a terribly good system, but if you have a better one that actually works, the scientists would love to hear about it.

Re:Gravity is not constant... (1)

gardyloo (512791) | about 7 months ago | (#45954293)

1) Measure its acceleration when subjected to a known force.
2) Measure the period of a system where it's part of the inertial loading, and the restoring characteristics are known (or can be decoupled post-experiment).

Re:Gravity is not constant... (1)

quenda (644621) | about 7 months ago | (#45954383)

A simple beam-balance scale can measure mass unaffected by gravity variations. You just need a reference mass.

Re:Gravity is not constant... (1)

oodaloop (1229816) | about 7 months ago | (#45954539)

If you're joking, I think that's hysterical. I'm just not sure you're joking.

Re:Gravity is not constant... (4, Insightful)

Immerman (2627577) | about 7 months ago | (#45954415)

Sure, the same way they "weigh" things in freefall - measuring the radial forces necessary to keep it moving in a fixed circular path at a given speed. You can even vary the speed to get multiple measurements to reduce error. That may be as simple as a scale in a centrifuge, but does not depend on any way on potentially fluctuating gravitational field. It also incidentally directly measures inertial mass, rather than gravitational mass, which *apparently* is always present in precisely proportional amounts, but which we currently have no accepted theoretical reason to believe is a fundamental equivalence.

Re:Gravity is not constant... (1)

Minwee (522556) | about 7 months ago | (#45954443)

No shit. And measuring the mass of the slug in question involves weighing it. Or do you have another method involved for determining the mass of an object used as the constant for measuring mass?

Comparing it to another mass using a balance makes any variation in the force of gravity irrelevant. You could travel to Mercury or Jupiter and still make accurate measures of mass using the same scale. Of course, that brings us right back to needing something to compare your mass _to_, and that something is eventually a cylinder made up of platinum and iridium stored in a vault just outside of Paris.

Re:Gravity is not constant... (0)

oodaloop (1229816) | about 7 months ago | (#45954521)

Um, no. When the force of gravity is different on one from day to the next, then what the balance equals will change. As in, one day the slug balances to 1.000001kg of another weight, and another day it eauals 1.000002kg of another weight. Each day the balance is balanced, but to different weights.

Re:Gravity is not constant... (0)

Em Adespoton (792954) | about 7 months ago | (#45954243)

It's hard to consistantly and accurately measure weight when the force of gravity constantly changes, add to the fact that there may be radioactive decay of trace elements, oxidation of metals, Dust/erosion, sublimation of trace components), it's easy to understand how using a physical object to consistantly measure a weight, would fluxuate. when your "constants" are actually "variables" it's really hard to nail down constants...

Well, you wouldn't want to measure the weight really... you want to measure the mass and then calculate the weight from that. However, objects are in a constant state of decay, as you say. Basing it all on the standard model and building up would probably provide a more consistent result with fewer fluctuations.

Re:Gravity is not constant... (2)

UnknownSoldier (67820) | about 7 months ago | (#45954405)

The parent's point about gravity being variable really needs to be modded up!

To drive the point home ...

http://en.wikipedia.org/wiki/File:Earth-G-force.png [wikipedia.org]

As you get closer to the earth the force of gravity increases as expected however at the Gutenburg discountinuity the force of gravity then goes down to zero at the core.

Re:fluctuating weight of KG? (2)

firex726 (1188453) | about 7 months ago | (#45953709)

Wear... Even at a microscopic level the it can still suffer wear as a result of otherwise imperceptible movement and is also why it's designed as it is.
Since one of the most common SI units is based on however much this thing weights it's important that it be left as intact as possible.

http://en.wikipedia.org/wiki/Kilogram#Stability_of_the_international_prototype_kilogram [wikipedia.org]

> K4 was originally delivered with an official mass of 1 kg75 g in 1889, but as of 1989 was officially calibrated at 1 kg106 g and ten years later was 1 kg116 g. Over a period of 110 years, K4 lost 41 g relative to the IPK.

Re:fluctuating weight of KG? (2)

Muad'Dave (255648) | about 7 months ago | (#45954403)

K4 was originally delivered with an official mass of 1 kg75ug in 1889, but as of 1989 was officially calibrated at 1 kg106ug and ten years later was 1 kg116ug. Over a period of 110 years, K4 lost 41ug relative to the IPK.

Your mu's got eaten by slashdot. Those should all be micrograms. Naturally μ doesn't work.

Re:fluctuating weight of KG? (1)

msauve (701917) | about 7 months ago | (#45954563)

s/ g / microgram /

Preview is your friend, /. doesn't support Unicode.

Re:fluctuating weight of KG? (0)

Anonymous Coward | about 7 months ago | (#45953799)

Because to verify, you have to physically use the original slug. Which means that it can get dirtied or (and more importantly) scratched and lose mass.

And when you're dealing with accuracy at the microgram level this cannot be ignored.

Re:fluctuating weight of KG? (1)

gstoddart (321705) | about 7 months ago | (#45953841)

Mostly I think it's dirt and other crud.

Essentially, the reference object isn't free from contamination or interacting with its environment.

We don't have a mechanism which allows us to define it in a more rigorous manner which can be reproduced, so we've got this hunk of of whatever it is sitting on a shelf which is defined as the reference kilogram. (OK, it's not just sitting on a shelf, but close)

Not what you'd call an objective standard. More of an approximation which is official and which the other official approximations are measured against.

Unlike an atomic clock where you can precisely define the unit of time in wavelengths of whatevers, there's no way to define the kilogram in a more specific way.

Re:fluctuating weight of KG? (2, Interesting)

Anonymous Coward | about 7 months ago | (#45953861)

That's part of the problem. Scientists aren't exactly sure. Shortly after it was made, several copies were made in 1889 that were verified to be the exact same mass. Over the years, the mass of the original and its copies have slightly drifted. The copies appear to have grown heavier, while the original has grown lighter. But even that's hard to determine for sure, since we can only be sure of the *difference* of the masses, not their absolute mass, because absolute mass is defined in terms of these kilogram masses in the first place.

It's theorized that air molecules may be attaching to the copies (they are also kept in a vacuum environment, but no vacuum is perfect), but if that's the case, why hasn't it happened to the original? The difference is only 50 ug, but that comes out to be 0.005%, which is huge for scientific applications. All of this means that they need a better quantitative standard for the kilogram.

Fluctuating weight of KG (0)

Anonymous Coward | about 7 months ago | (#45954287)

Weight applies only within a gravity field. Gravity varies over the surface of the earth.
Weight is most often measured within air which varies in density and so the amount of air displaced varies as does the upward force of that displaced air.
Mass however is more constant.

Arbitrariness (1)

Anonymous Coward | about 7 months ago | (#45953555)

Unless we're willing to dump our current units, the new definition will be some arbitrary-seeming number chosen to be consistent with a fairly precise version of what we're already using.

Re:Arbitrariness (1)

Chris Mattern (191822) | about 7 months ago | (#45953663)

Correct. But by tying it to an electron charge, it becomes well-defined and highly accurate, even if it does have to depend on an arbitrary number. That will be an distinct improvement to those depending on extreme precision, even though the average joe with a multimeter in his hand won't see any difference (and won't even need a new multimeter).

Condescend much? (2, Interesting)

Oligonicella (659917) | about 7 months ago | (#45953565)

"almost as much of an embarrassment"

You would have done better with the technologies at hand at the time how?

Re:Condescend much? (1)

kry73n (2742191) | about 7 months ago | (#45953667)

You would have done better with the technologies at hand at the time how?

Can we do better with the technologies at hand right now?

Re:Condescend much? (1)

Phreakiture (547094) | about 7 months ago | (#45954369)

Can we do better with the technologies at hand right now?

Um . . . didn't we just do that? Isn't that what the article is about?

Re:Condescend much? (1)

girlintraining (1395911) | about 7 months ago | (#45954051)

You would have done better with the technologies at hand at the time how?

You would have practiced science using methodologies nearly a century out of date when? See that's the thing about science -- it's supposed to change in response to new data. And it usually does, except for some of our basic units of measurement, which remain stubbornly stuck in the past. That's why it's an embarassment. The whooshing sound you heard is the point sailing over your head.

Re:Condescend much? (0)

Anonymous Coward | about 7 months ago | (#45954183)

You would have done better with the technologies at hand at the time how?

You would have practiced science using methodologies nearly a century out of date when? See that's the thing about science -- it's supposed to change in response to new data. And it usually does, except for some of our basic units of measurement, which remain stubbornly stuck in the past. That's why it's an embarassment. The whooshing sound you heard is the point sailing over your head.

Such as using the American Imperial system of measurement?

Re:Condescend much? (2)

blueg3 (192743) | about 7 months ago | (#45954877)

Such as using the American Imperial system of measurement?

Nobody does science using U. S. customary units.

Re:Condescend much? (1)

Anonymous Coward | about 7 months ago | (#45954193)

There is nothing wrong with our units of measurement. They can be anything we want them to be. The point is that we want a unit that can be independently recreated anywhere by anyone and not a magic piece of precious metal that we measure.

Re:Condescend much? (1)

AthanasiusKircher (1333179) | about 7 months ago | (#45954627)

And it usually does, except for some of our basic units of measurement, which remain stubbornly stuck in the past. That's why it's an embarassment. The whooshing sound you heard is the point sailing over your head.

Umm, I'm pretty sure scientists have been working on the kilogram problem for some time. Your use of "stubbornly" implies that there's some sort of resistance to a redefinition. But I don't think there's any evidence that that's the case.

Here's a NYT article [washington.edu] from 2003 detailing the then-current attempts at redefinition. I'm sure there are older things out there detailing the scientific efforts to work on this problem, too... this was literally one of the top three hits in an internet search.

Anyhow, in 2005, the International Committee for Weights and Measures formally recommended [bipm.org] a redefinition. In 2011, the General Conference on Weights and Measures agreed [bipm.org] . If you want to see all the proposed revisions, they are nicely summarized in a Wikipedia article here. [wikipedia.org]

It may be somewhat true that the kilogram redefinition lagged a bit behind other units, mostly because the other units had practical applications where the need for increased precision was rising more rapidly. But given that the attempts to provide a standard measurement system are ongoing, and the proposed redefinitions make use of technology that is still being refined to maintain a high-enough level of accuracy to supersede the old standard, there's no reason to call this an "embarrassment" "stubbornly stuck in the past."

Scientists are actively working on the problem -- and have been for quite some time.

Re:Condescend much? (1)

Baloroth (2370816) | about 7 months ago | (#45954709)

You would have done better with the technologies at hand at the time how?

You would have practiced science using methodologies nearly a century out of date when? See that's the thing about science -- it's supposed to change in response to new data. And it usually does, except for some of our basic units of measurement, which remain stubbornly stuck in the past. That's why it's an embarassment. The whooshing sound you heard is the point sailing over your head.

You have a better idea for a mass unit? The scientific community would absolutely love to hear about it, because every other idea either doesn't work at all, or isn't practically measurable (sure, you could define it as x number of atoms of y substance, but good luck counting out a few trillion atoms with precision every time you want to make an accurate measurement).

Most of the basic units of measurement in science have in fact been redefined when someone came up with a better system. Mass, however, it turns out, is really bloody hard to do better. I wouldn't call it "embarrassing" when the laws of physics prevent you from doing any better.

Definition of a kilogram (4, Funny)

Infiniti2000 (1720222) | about 7 months ago | (#45953579)

A kilogram is straightforwardly defined as 2.20462 pounds. Simple enough.

Re:Definition of a kilogram (0)

forrestt (267374) | about 7 months ago | (#45953707)

A kilogram is NOT defined that way, it is converted from pounds that way. It was originally defined as the weight of one litre of water. It is now defined as being equal to a prototype held at the International Bureau for Weights and Measures.

Re:Definition of a kilogram (1, Funny)

forrestt (267374) | about 7 months ago | (#45953733)

I guess I missed the humor tag in your original post.

Re:Definition of a kilogram (5, Funny)

trongey (21550) | about 7 months ago | (#45953949)

I guess I missed the humor tag in your original post.

That's OK. You were publicly correcting someone for the misuse of units of measure.
None of us expected you to have a functional sense of humor.

Re:Definition of a kilogram (0)

Anonymous Coward | about 7 months ago | (#45953793)

Pretty sure he was joking.

Re:Definition of a kilogram (0)

Anonymous Coward | about 7 months ago | (#45953827)

A kilogram is NOT defined that way, it is converted from pounds that way. It was originally defined as the weight of one litre of water. It is now defined as being equal to a prototype held at the International Bureau for Weights and Measures.

Ooohhhh!

So how to do you convert from Dollars, or Euros for that matter?

Re:Definition of a kilogram (0)

Anonymous Coward | about 7 months ago | (#45954005)

Maybe I have been reading too much explain xkcd, but that's a digression for another day.
The Humor in Inifiniti2000 post comes not only for the absurdity of defining a metric measurement on an imperial measurement but also in that it still does nothing to address the real problem of how to find a stable reference for mass. It also confesses mass with weight measurements.

Re:Definition of a kilogram (0)

Anonymous Coward | about 7 months ago | (#45954069)

It is also note worthy that pounds are an american-centric measurement...

actually it's not, (0)

Anonymous Coward | about 7 months ago | (#45953713)

a kilogram is a measure of mass, a pound is a measure of weight...

weight does not equal mass.

Re:actually it's not, (1)

barlevg (2111272) | about 7 months ago | (#45954019)

Actually, the Imperial Pound is legally defined as exactly 0.45359237 kilograms. It is (but possibly has not always been?) a unit of mass. Citation [wikipedia.org] .

Re:actually it's not, (1)

mythosaz (572040) | about 7 months ago | (#45954779)

Pretty sure a Pound is worth about $1.64.

*shrug*

Re:Definition of a kilogram (2)

gman003 (1693318) | about 7 months ago | (#45953781)

And as we all know, the pound is defined as 7000 grains, which are simply defined as the mass of a grain of wheat.

Re:Definition of a kilogram (1)

Vanderhoth (1582661) | about 7 months ago | (#45953849)

How is the pound defined? Thought I'd look it up , but all I can find is Wikipedia [wikipedia.org] that says a pound is defined as "(b) the pound shall be 0.45359237 kilogram exactly".

The definition for a pound of force [wikipedia.org] was even less helpful as it's related to an Avoirdupois pound [wikipedia.org] , which is defined as:

The avoirdupois pound, also known as the wool pound, first came into general use c. 1300. It was initially equal to 6992 troy grains. The pound avoirdupois was divided into 16 ounces. During the reign of Queen Elizabeth, the avoirdupois pound was redefined as 7,000 troy grains. Since then, the grain has often been an integral part of the avoirdupois system. By 1758, two Elizabethan Exchequer standard weights for the avoirdupois pound existed, and when measured in troy grains they were found to be of 7,002 grains and 6,999 grains.

Re:Definition of a kilogram (0)

Anonymous Coward | about 7 months ago | (#45954093)

Pound: a unit of weight in general use equal 0.4536 kg.

Yes, pounds are now officially defined in units of kilograms. +1 funny for you sir.

Re:Definition of a kilogram (1)

girlintraining (1395911) | about 7 months ago | (#45954173)

A kilogram is straightforwardly defined as 2.20462 pounds. Simple enough.

Yeah right! There's over a dozen different definitions for the "pound". You're citing the intuitively named international avoirdupois pound designation. Unfortunately, your own definition is over a century out of date! The Mendenhall Order of 1893 defined it as 2.20462 ... but the following year, someone got their hands on a British kilogram and it was redefined to be 2.20462234.

And where-fore did the previous pound measurement come from, before it was normalized to the kilogram? Why, the weight of 120 Arabic silver dirhams, found in some king's dingy treasury of course! Not to be outdone, the previous definition was based on the average weight of a pile of wheat traded in the town of Troy.

It's all so simple!

Re:Definition of a kilogram (-1)

Anonymous Coward | about 7 months ago | (#45954329)

i like to pound pussy

Re:Definition of a kilogram (0)

Anonymous Coward | about 7 months ago | (#45954635)

because you are posting on slashdot, i assume you literally mean cats.

2×107 newtons per metre of length? (1)

Anonymous Coward | about 7 months ago | (#45953597)

that's almost 214 newtons per metre of length!

Re: 2×107 newtons per metre of length? (0)

Anonymous Coward | about 7 months ago | (#45953857)

Damit what are these Newtons and Meters you're talking about ?
I'm an American, give me pound force and yards.

Re: 2×107 newtons per metre of length? (0)

Anonymous Coward | about 7 months ago | (#45953877)

Its probably 2e17 or 2 times 10 to the 7th, but slashdot withs its great unicode support may have eaten a piece.

Re: 2×107 newtons per metre of length? (1)

bryanc (142005) | about 7 months ago | (#45954119)

It's 2 × 10–7. (http://en.wikipedia.org/wiki/Ampere)

Re: 2×107 newtons per metre of length? (1)

Waffle Iron (339739) | about 7 months ago | (#45954349)

So in other words, 13?

Re: 2×107 newtons per metre of length? (2)

Overzeetop (214511) | about 7 months ago | (#45954701)

6, if you regularly read Facebook for math tips.

Re: 2×107 newtons per metre of length? (1)

mythosaz (572040) | about 7 months ago | (#45954813)

If it makes you feel any better, I enjoyed your PEMDAS joke :)

yeah because imperial (0)

Anonymous Coward | about 7 months ago | (#45953701)

units are so much better!

Re:yeah because imperial (3, Funny)

Chris Mattern (191822) | about 7 months ago | (#45953749)

I prefer rebel units. If you can't depend on Luke Skywalker for your calibrations, who can you trust?

Re:yeah because imperial (0)

Anonymous Coward | about 7 months ago | (#45953807)

trust the force you must

Re:yeah because imperial (4, Funny)

martinux (1742570) | about 7 months ago | (#45954009)

Force was redefined in the prequels as midichlorians multiplied by anger. Conveniently it's kept the same equation:

f = ma

Re:yeah because imperial (2, Insightful)

mmell (832646) | about 7 months ago | (#45954167)

Well, Imperial units are binary (1/2", 1/4", 1/8" tools, for example). Twelve inches in a foot divides evenly by two, three, four, six. Thirty-six inches in a yard has a lot of factors too. 5,280 feet in a mile seems arbitrary until you start counting the factors. Three hundred sixty degrees in a circle can evenly be divided by 2, 3, 4, 5, 6, 8, 9, 10, 12, 15, 18... - tried that with radians lately? One hundred eighty degrees separate water freezing from water boiling - 180, another composite number with lots of factors. If you're an engineer, there's a lot to be said for Imperial or SAE units - they sure make a lot of the math easier.

On the other hand, Metric is decimal. Last time I checked, everyone had ten fingers. We count base ten. Computers may be great at binary, but most of us do arithmetic for our daily tasks at base ten.

Binary (Imperial) has its place. Decimal (Metric) has its place. And never the two shall meet . . .

Re:yeah because imperial (0)

Anonymous Coward | about 7 months ago | (#45954305)

Last time I checked, everyone had ten fingers.

Well, I've known people born with 9 fingers, and people born with 11. I also knew someone who was born with 12 as he had two thumbs on each hand at birth (they removed the 'extra' ones)

So, for really small values of "everyone", you're mostly almost entirely accurate.

Which is the same problem being discussed here ... mostly almost entirely accurate isn't quite as accurate as they'd like, and they want something more rigorous.

Are we even sure all electrons are the same? (0)

Anonymous Coward | about 7 months ago | (#45953705)

This is a shovel-balancing approach to tweezer level measurements really.

Re:Are we even sure all electrons are the same? (2)

barlevg (2111272) | about 7 months ago | (#45954087)

Charge is quantized. This has been known since Millikan [wikipedia.org] . You can't ever arrive at an electron-and-a-half of charge (though you can, in theory, get a third or two thirds, but not naturally in nature) [wikipedia.org] .

Re:Are we even sure all electrons are the same? (1)

barlevg (2111272) | about 7 months ago | (#45954105)

Crap. I did just type "naturally in nature."

Re:Are we even sure all electrons are the same? (1)

oracleofbargth (16602) | about 7 months ago | (#45954429)

Erk...

Couldn't decide whether to be pedantic about partial charges, or abuse of the English language...

Congratulations, you have broken my pedantry filter.

Re:Are we even sure all electrons are the same? (1)

barlevg (2111272) | about 7 months ago | (#45954637)

Interesting. I actually wasn't aware of the concept of partial charges [wikipedia.org] before today (I guess they don't teach this kind of stuff to physicists). But, as I read it, this is some sort of shielding effect, and the integer number of charges is still present in the molecule.

Re:Are we even sure all electrons are the same? (0)

Anonymous Coward | about 7 months ago | (#45954723)

Quantum representations aren't usually accurate past a certain point. That's my point.

Re:Are we even sure all electrons are the same? (1)

jeffb (2.718) (1189693) | about 7 months ago | (#45954295)

If not all electrons have the same charge, we have much bigger problems than our standard for measuring current.

As fundamental assumptions in physics go, you can't get much more fundamental than that.

Bah, I say (3, Interesting)

dmatos (232892) | about 7 months ago | (#45953765)

The Ampere was only chosen as an SI fundamental unit because it was easier to measure than a Coulomb. To me, an Ampere will always be 1 Coulomb per second.

And since the electric charge is 1.602E-19 Coulombs, we can just invert that number to find the number of electric charges (ie, electrons) in a Coulomb.

Re:Bah, I say (2)

inode_buddha (576844) | about 7 months ago | (#45953903)

Here's what I don't understand, whats so wrong about defining the Ampere in terms of coulombs per second? Or in terms of anything else for that matter? I guess I fail to see whats so bad about having the Ampere as a derived unit.

Re:Bah, I say (1)

gstoddart (321705) | about 7 months ago | (#45954445)

Here's what I don't understand, whats so wrong about defining the Ampere in terms of coulombs per second?

Really? Because this sounds like it's a pretty darned hand-waving definition to me.

At present, an ampere is defined as the amount of charge flowing per second through two infinitely long wires one meter apart, such that the wires attract each other with a force of 2x10^-7 newtons per meter of length. That definition, adopted in 1948 and based on a thought experiment that can at best be approximated in the laboratory, is clumsy

Where, for instance, are you going to get two infinitely long wires? How are you going to guarantee they're precisely 1m apart? How do you precisely measure 2x10^-7 newtons per meter of length?

If your measure can "at best be approximated in a laboratory", you don't have an objective measure, you have a vague description of what you mean.

Re:Bah, I say (3, Informative)

Chris Mattern (191822) | about 7 months ago | (#45954083)

And since the electric charge is 1.602E-19 Coulombs, we can just invert that number to find the number of electric charges (ie, electrons) in a Coulomb.

Well, yes. But the point here isn't shuffling around the units. The point here is to increase the accuracy at which the elementary charge is known, which would be necessary whether you're defining the Ampere in terms of the charge or the Coulomb in terms in the charge. Currently, we know the elementary charge to ten decimal places. That's not good enough, so that's what this is about--finding out that figure to greater accuracy so it can be used as a universal measurement standard. For comparison, the definition of the second is accurate to 15 decimal places.

Was this discovered by Africans? (-1)

Anonymous Coward | about 7 months ago | (#45953809)

We all know the answer. So can you tell me what Africans have given to the world?

Take your time...

If they've given nothing to the world, why would you want millions of them in your once all white, safe country?

Re:Was this discovered by Africans? (0)

Anonymous Coward | about 7 months ago | (#45954233)

To pick the cotton of course

How an Ampere is defined will NOT change! (3, Insightful)

bobbied (2522392) | about 7 months ago | (#45953881)

The fine article is incorrect. How an Ampere is defined does not change.

What may change is how you can measure current in the lab using other known standards because it's really hard to count electrons. Or perhaps the way a Coulomb is defined may change but the Ampere will not change.

One Ampere will remain defined as One Coulomb per second.

Re:How an Ampere is defined will NOT change! (4, Informative)

barlevg (2111272) | about 7 months ago | (#45954125)

Technically no. As noted above, the Ampere, not the Coulomb, is the fundamental unit. A Coulomb is an Ampere-second.

Re:How an Ampere is defined will NOT change! (4, Informative)

cdrnet (1582149) | about 7 months ago | (#45954269)

This is not entirely correct. Ampere is an SI base unit while Coulomb is a SI derived unit (defined as 1 C = 1 A s) - not the other way round.

As long as they dont change it (1)

viperidaenz (2515578) | about 7 months ago | (#45953969)

And ohms law still works out. ... hang on, that's already a nice easy calculation to define and Ampre. I = E/R

Re:As long as they dont change it (1)

barlevg (2111272) | about 7 months ago | (#45954155)

The Ohm is a derived unit [wikipedia.org] (depends on the Volt and the Ampere). So no, sorry.

what? (0)

Charliemopps (1157495) | about 7 months ago | (#45953987)

Almost as much of an embarrassment as the definition of the kilogram? I'm kind of sick of this complaint... The weight of a kilogram is precise enough for nearly all applications. Those rare applications where its imprecision makes a difference should use a DIFFERENT unit of measurement. Invent a new one, like the mass of a hydrogen atom or something. "This thing here is 458 H masses" There, problem solved. The same with the Amp... it works fine for installing my celing fan. Don't go screwing with it just to satisfy some particle physicists. If Particle physicists don't think the amp is precise enough, USE A DIFFERENT UNIT.

Are they next going to complain that the AU is too imprecise for them to do proper measurements at the atomic level so we should therefore spend millions refining what an AU is? No... because that would be stupid. Measuring things that way thousands of grams with a unit that's precise to within a few hundred atoms is good enough. Stop using measurements designed for Newtonian physics at the atomic level and there's no longer a problem.

Re:what? (1)

skids (119237) | about 7 months ago | (#45954235)

My car does zero to 3.3 european swallow airspeed velococities (unladen) in 9.7 seconds. What does yours do?

Re:what? (1)

leonardluen (211265) | about 7 months ago | (#45954895)

you have nothing to worry about they aren't changing the value that an amp is on your multimeter.

what is happening is that now in extremely high precision experiments they can now measure an Amp down to say 15+ decimal places using the new definition. previously they had no way to calibrate their equipment to that degree of accuracy.

"fluctuating mass" sounds promising (0)

Anonymous Coward | about 7 months ago | (#45954079)

> the fluctuating mass of a 125-year-old platinum-and-iridium cylinder

Why is nobody looking into this?

Once we understand and control that mass fluctuation effect, we have our stardrive.
Make the part we want to keep on board (payload, living space, drive, fuel) go to the lowest possible mass, and make the exhaust flame have the highest possible mass.

Speed of light -- almost attainable.

Work on it, people!

This is why I laugh.... (-1, Flamebait)

Trailer Trash (60756) | about 7 months ago | (#45954133)

when someone tries to school me about how the English system of measurements are arbitrary unlike the metric system.

A modest editorial proposal (4, Funny)

TheloniousToady (3343045) | about 7 months ago | (#45954207)

How about we change "At present, an ampere is defined as" to "Currently, an ampere is defined as"?

Re:A modest editorial proposal (1)

TheloniousToady (3343045) | about 7 months ago | (#45954817)

I guess whoever marked the parent as "Flamebait" didn't get the "Currently" joke. The use of "a modest [editorial] proposal" in the title was a hint, but I guess that wasn't enough. :-)

Re:A modest editorial proposal (2)

EmagGeek (574360) | about 7 months ago | (#45954841)

What idiot moderated this as "Flamebait" when it is clearly "Funny?"

Who the hell is in charge of this place?

Surface contaminants add weight (0)

Anonymous Coward | about 7 months ago | (#45954359)

The material (platinum-iridium alloy) was chosen for its hardness and corrosion resistance, but air pollution deposits a thin film on the surface.

This has long been known, and there is a standard washing procedure which removes most of it, but it turns out there are contaminants that this does not remove. Hydrocarbon contaminants can be removed by a recently developed technique using ultraviolet light and ozone, but mercury appears unremovable. (Without damaging the underlying Pt-Ir metal.)

The accumulation of additional mercury can be prevented in future by storing some gold leaf next to the weights (gold attracts mercury strongly), but the hope is to replace the physical weights with something else.

Charge of an electron? (1)

tomhath (637240) | about 7 months ago | (#45954763)

redefine the amp on the basis of e, a physical constant representing the charge of an electron.

Until some smarty pants physicist comes along and determines that e or the charge of an electron changes depending on [pick something, this is physics after all]

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