Slashdot Mirror
Kilogram Gets a New Definition (bbc.com)
Scientists have changed the way the kilogram is defined. Currently, it is defined by the weight of a platinum-based ingot called "Le Grand K" which is locked away in a safe in Paris. On Friday, researchers meeting in Versailles voted to get rid of it in favour of defining a kilogram in terms of an electric current. From a report: The decision was made at the General Conference on Weights and Measures. But some scientists, such as Perdi Williams at the National Physical Laboratory in the UK, have expressed mixed feelings about the change. "I haven't been on this project for too long but I feel a weird attachment to the kilogram," she said. "I think it is such an exciting thing and this is a really big moment. So I'm a little bit sad about [the change]. But it is an important step forward and so the new system is going to work a lot better. It is also a really exciting time, and I can't wait for it to happen."
Le Grand K has been at the forefront of the international system of measuring weights since 1889. Several close replicas were made and distributed around the globe. But the master kilogram and its copies were seen to change -- ever so slightly -- as they deteriorated. In a world where accurate measurement is now critical in many areas, such as in drug development, nanotechnology and precision engineering -- those responsible for maintaining the international system had no option but to move beyond Le Grand K to a more robust definition.
Le Grand K has been at the forefront of the international system of measuring weights since 1889. Several close replicas were made and distributed around the globe. But the master kilogram and its copies were seen to change -- ever so slightly -- as they deteriorated. In a world where accurate measurement is now critical in many areas, such as in drug development, nanotechnology and precision engineering -- those responsible for maintaining the international system had no option but to move beyond Le Grand K to a more robust definition.
This is good, and very important. But exciting?
No need to feel left out. The definition of the pound is also updated by this:
The international pound has been defined as exactly 0.45359237 kg.
The strength of the earth's gravitational field varies. If you are using a Kibble balance to calibrate your weights, how do you compensate for that? Your kilogram mass will vary from location to location.
Google: earth gravitational field
https://earthobservatory.nasa....
How many times do you need a very precise absolute measurement in drug development or nanotech ?
https://xkcd.com/2073/
Wrong, the pound was defined as that in 1959. nothing changed here
I know it's pedantic to have this discussion outside of a classroom environment, but Kilogram is a unit of mass and not a unit of weight. I suppose it was the electroshock therapy administered in science courses that makes it sound like fingernails on chalkboard to me when someone gets it incorrect in a publication.
I'm amazed at your constant ability to out-think all of our scientists. Your value is wasted as a Slashdot troll. If only they'd have seen you for your genius we'd have cured cancer by now.
Do they have a guaranteed efficiency vs electric input? Or does this not somehow apply?
Doesn't each kibble scale require calibration whenever the altitude changes? What do they use as a reference for calibration since it appears even the Kg reference is not stable?
- Yep I got plenty of dumb questions.
The current pound is based on the kilogram, so we all suffer the same flaw haha.
The reasons changed like this have been talked about for a long time but only just now changed, is researchers spent a long quantifying exactly what the accuracy of the new method is and how it changed with time.
A lot of people wanted mass to be defined as a fixed number of atoms. Efforts to make test masses from scratch showed that the variation was larger than the le grand K approach, so that didn't get used.
Even though the Kibble balance requires a measurement of local gravity, the accuracy and drift with time have been shown to be an order of magnitude smaller than the prototype based approach. So from an accuracy perspective, yes, it has been quantitatively demonstrated to be better. The only complaint is how expensive it is, so likely only the larger national standard institutes will be able to maintain one.
So no, just because no measurement is perfect does not mean all measurements are equally bad. The reason the BIPM and CGPM take their time is to actually measure these things, to be sure new definitions are more repeatable.
Basically what they did was they defined Planck's constant to be a fixed value pretty close the the calculated number previously used. So instead of calculating Planck's constant from an arbitrarily defined kilogram they define the kilogram (and a few other constants) from an arbitrarily defined Planck's constant. This takes the error bars away from Planck's constant and the other fundamental measurements fall out naturally as a result to precisely defined and fixed numbers.
Please don't make the metric system stop making sense. We already have a nonsensical measuring system, here in the U.S. .
https://www.youtube.com/c/BrendaEM
Any individual Kibble balance will also deteriorate and be out of range of the others. There will also be differences in construction since no system is perfect. You might as well use the current method.
I have a hard time telling if you are a troll or just ignorant. What they did was they redefined Planck's constant to be a fixed number. So instead of measuring Planck's constant from an arbitrarily chosen value for the kilogram they measure the kilogram from an (sort of) arbitrarily chosen Planck's constant.
I thought it was a joke.
Our friend at Veritasium does an excellent job breaking this down:
https://www.youtube.com/watch?...
I tend to rant.
But current definition of current (pun not intended) is defined trough force
This isn't true. Electric current is the flow of a electric charge and isn't composed by force or any other magnitude. The Ampere is one of the few SI units which isn't formed by other units. Force/energy is relevant to understand how a current is created, but it doesn't define its essence.
Custom Solvers 2.0 = Alvaro Carballo Garcia = varocarbas.
No, the pound system is based on the 25 pound weights I use at work to calibrate new scales right before I put the serial number sticker on.
Wrong, the pound was defined as that in 1959. nothing changed here
Since the pound is defined in terms of the kilogram, changing the definition of the kilogram implicitly changes the definition of the pound as well.
Note to ACs: I usually delete AC replies without reading them. If you want to talk to me, log in.
...no system is perfect.
The new method is not purported to be perfect. It does, however, allow people to measure a kilogram with as much accuracy as the current system without shipping reference weights around the world for comparison.
Under the Slashdot Journalistic Standards and Practices accord of 2004, a kilogram is 1e-10 Libraries of Congress.
This makes dimensional analysis a lot easier.
the preceding comment is my own and in no way reflects the opinion of the Joint Chiefs of Staff
Have you read the article you linked?
The ampere is that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed one metre apart in vacuum, would produce between these conductors a force equal to 2×107 newtons per metre of length.
One newton is the force needed to accelerate one kilogram of mass at the rate of one metre per second squared in the direction of the applied force.
And now, kilogram is defined with current. So, could someone explain how this is not recursive definition?
It is not the same thing. The kibble balance can be built to the required accuracy from scratch without using some artifact as a reference. It is not an artifact itself. Itâ(TM)s calibrated against physical phenomena.
Every time this subject comes up you start wittering on about drug dealers. Do you think it makes you sound edgy or something.
P.S. Shouldn't you be in hiding from the caravan? Scary scary brown people who talk funny!
Confucius say, "Find worm in apple - bad. Find half a worm - worse."
Have you read the article you linked?
No. But I don't need it to know what current is.
The ampere is that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed one metre apart in vacuum, would produce between these conductors a force equal to 2×107 newtons per metre of length.
This is pretty much what I explained in my previous post: force (or energy, formed by force) is required to produce an electric current. Or, in other words, an electric current is in a position to generate force/energy. But all this is different to its essence: a flow of electric charges what, from the physics point of view, is considered as an indivisible whole. Pretty much the same than the pair mass and force. A massive object is able to generate force/energy, but it doesn't mean that force is part of its definition.
SI units and Wikipedia are pretty useful on this front, for example, visit the page for force (newton) and see under "SI base units" its components. For Ampere you don't see anything because it is already a base unit, exactly the same than grams or time.
Custom Solvers 2.0 = Alvaro Carballo Garcia = varocarbas.
So did I.
Also bear in mind that physics (and science in general) isn't exactly a perfectly well-planned system which was built one day by carefully thinking about how to do everything perfectly. There are even different fields facing pretty much the same reality from different points of view (e.g., chemistry and physics). Within physics, there are different approaches which, although having a somehow coherent behaviour, can't be precisely used unrestrictedly. For example, electric current (and other electric magnitudes) have their specific treatment, not exactly 100% compatible with mechanical ones. Although the idea force as accelerated mass certainly holds everywhere, the electrical calculations aren't performed in the same way than the mechanical ones. You don't care about f=m*a when dealing with electrical currents, but about concepts like resistance, voltage, etc. which output things like energy which you use to link to other types of calculations like mechanical force.
Custom Solvers 2.0 = Alvaro Carballo Garcia = varocarbas.
The pound is defined as a derivative of the kg, so yes this affects you too.
I understand: newer is always better.
Yeah I know. Defining the Kg to something fixed is right up there with replacing sysv with systemd.
unlike the old method, which was 0.000005%.
Plus and Minus a random change that makes it impossible to know what it was or will be for sure.
Not really, that is only an approximation of the inverse definition. I you want to play that game you should write out 1/0.45359237 (which is exact)
Starts out like: 2.204622621848775807229738013450270338542070273360197835779292319224\ 8582135541653842193156820517064694...
Exactly. All you need to do is build a $10 million balance system and regularly maintain and calibrate it in a clean room and you are fine. I wonder if you guys have even seen a Kibble balance. I guess it keeps the NIST budget going though.
Pretty much the same than the pair mass and force.
I think that the velocity-energy/momentum analogy is more descriptive. You know that having a moving object is associated with energy/momentum, but it doesn't define it essence. Its essence is defined by velocity (certainly started by energy/momentum, but not defined by it) and, together with something else (= mass), it will output energy/momentum.
Custom Solvers 2.0 = Alvaro Carballo Garcia = varocarbas.
A Kibble balance, that will define the kilogram will built using platinum, iridium and other exotic metals. It will be housed in the double walled basement of SI building. This le Grand K(ibble) will be the standard Kibble balance against which all othe Kibble balances will be measured and tested against.
sed -e 's/Chuck Norris/Rajnikant/g' joke > fact
No, just strikes me as kinda funny...and also my usual observation that the US doesn't use the metric system for anything in most citizens' real daily lives.
That no one really uses it here.
Light travels faster than sound. This is why some people appear bright until you hear them speak.........
A pound is a weight, not a mass which is not the same thing. While its definition may be based on the kilogram it must also be based on a value for the gravitational field since it is a force.
The international pound has been defined as exactly 0.45359237 kg.
That's interesting. Since the pound is a weight and the kilogram a mass unless they also fixed the gravitational field in that definition it's open to abuse.
By it's very definition a balance in independent of gravity.
No it is not. Even a standard balance relies on the gravitational field for both sides being equal and, if you get precise enough, this may not be true. However, the watt balance balances the force of gravity with an electromagnetic force. Part of the measurement also requires determining the local gravitational field but this is something that you can measure accurately which is why this is still a far better definition than using a lump of metal outside Paris.
Maintaining the IPK and all the other references that derive from it isn't free. And given how important accurate and repeatable measurements are to the modern world, $10 million is cheap.
In the words of a stand-up comedian (alas I can't remember his name) who used to be a drug dealer: I prefer the term street pharmacutical representative!
I read the source article and nowhere did it say whether the new definition was heavier or lighter than the existing one. Inquiring minds want to know, after all, this stuff is not just exciting, it's really exciting!
No, just strikes me as kinda funny...and also my usual observation that the US doesn't use the metric system for anything in most citizens' real daily lives.
That no one really uses it here.
I know. I was just saying the same thing the other day when I picked up a 2 liter of soda and a bottle of 500mg aspirin at the store. While I was out, my daughter asked me to pick up a new set of headphones with a 3.5mm jack. Since I was at the store I picked up some new LED bulbs to lower my monthly kilowatt usage at home. That reminded me that I needed to order some new 80 and 120mm case fans for my desktop too. I'll probably add 16 more GB of RAM while I'm at it. On the way home some idiot in a 5.0 liter Ford Mustang cut in front of me and got out of his car carrying a baseball bat. Fortunately when he saw my Glock 9mm, he got back in his car and left 2 seconds later. I don't know how he knew I had my wife's 3 carat emerald ring in the car.
but do we have the technology to build something up one atom at a time?
Not accurately enough. There'd be some extra or missing atoms in the final product.
Next he will declare that P = NP and really screw up the world. Though I do like the 1 m = 3 ft part.
A moment is defined as kg.m^2
The new definition is thus a unitary moment per unit area.
It's a small world and it smells funny; I'd buy another if it wasn't for the money; Take back what I paid (SoM)
https://en.m.wikipedia.org/wik...
It is exactly 0.45359237 kilograms
It's a small world and it smells funny; I'd buy another if it wasn't for the money; Take back what I paid (SoM)
Except that since the pound is defined as a fraction of a kilogram, it too is implicitly a measure of mass, not weight.
Please stand clear of the doors, por favor mantenganse alejado de las puertas
Since this now requires lasers and other ultra-precise devices to provide the reference weight of a kilogram: Who is working on the fully documented bootstrap guide to doing all this from scratch in the case of a cataclysm or apocalypse?
Both the original Iridium(Titanium?) cylinder and the newly updated kilogram standard rely on technology or engineering beyond the common man. And without proper documentation of it, a significant event, like a world war, could in fact leave us in a state where the scientists and manufacturing talent necessary to keep these references possible have been torn down, in which case half of our precision science goes out the window because we have no way to recreate the weight or time standards necessary for precision beyond the laymans level, and even that could deviate over time without the 'constant', neither version of which is reproducible without current knowledge that is not broadly public.
If someone can produce a guide going from the initial technlogies a layman could reproduce and include all later technologies and knowledge required to reproduce the weight, time, and distance references, we would be in a lot better condition, whether sending colonists to remote worlds, or bringing society back to modern technological levels after the next Dark Age.
The second is out of date. Caesium is a horribly outdated method of measuring time. Modern atomic clocks, using strontium quantum gasses, are roughly ten orders of magnitude better.
But because of how the second is defined, you can't use a more accurate clock. The errors in caesium clocks are part of the definition. Remove the error and you're not measuring seconds even if you're measuring more accurately.
It's probably better to use fundamental units as the starting point, or at least something close, rather than arbitrary objects in nature.
Ideally, it shouldn't matter if things get measured more accurately, you won't break anything.
If you can't do that, then the definitions should be aiming at the ten orders more accurate results that can be obtained.
As for constants, they should be justified geometrically, kept simple, or defined in terms of underlying physics.
It's a small world and it smells funny; I'd buy another if it wasn't for the money; Take back what I paid (SoM)
I don't think a five year old would fall for that one.
Besides, what's so special about le grand K? There are dozens of duplicates, all equally valuable platinum.
-- Sometimes you have to turn the lights off in order to see.
The international pound has been defined as exactly 0.45359237 kg.
That's interesting. Since the pound is a weight and the kilogram a mass unless they also fixed the gravitational field in that definition it's open to abuse.
Just to make things even more complicated, the pound is used for both weight and mass.
Please explain the ancient unit of pressure: pounds per square inch then. You cannot measure pressure in kilograms per square metre. This is why the old imperial unit system is utterly ludicrous. It is out of step with basic physics and lacks any coherent or even consistent definition.
PSI uses "pound" as a measure of force, where one pound-force is equal to the force exerted by one pound (mass) under the acceleration of 1g. One pound-force is what is meant when most people speak of "pounds", but in common usage the same is true of the kilogram - most people mean "kilogram-force" when they say "kilogram". The fact remains that "pound" is an SI-derived unit of mass, not weight.
Please stand clear of the doors, por favor mantenganse alejado de las puertas
This. In theory the non-metric unit of mass is supposed to be the "slug" but pound gets overloaded just like kilogram does, to be both mass and force.
I lost you... In the meantime, I found the answer to my first question.
If anyone is still interested, not only kilogram will be redefined. New definition of ampere will not use force as current, but elementary charge. I always wondered why wasn't it always like that.
You lost me? You found the answer? LOL. Haven't you seriously understood what I have explained you various times and with various additional references?!! Seriously and by being as respectful as I can under these conditions: this (physics or properly understanding/learning slightly complex concepts) doesn't seem your calling, better focus on whatever you are doing and let all this for other people. Anyway, I will better write some clarifications about the rest of your post because some people might read it and well... pure ignorance isn't precisely what the world needs.
New definition of ampere will not use force as current, but elementary charge
Before answering that, I will clarify something that perhaps isn't too clear for everyone. The current redefinition of the kilogram or of whatever other physical magnitude doesn't affect its essence/theory at all. This is just about updating the used-so-far numerical convention mostly relevant for conversions between different systems (even though, practically speaking, there shouldn't be any noticeable difference). For example, converting kilograms to pounds or knowing the kilogram equivalence of a bag of potatoes. F=m*a will always be like this. Exactly the same than amperes being the unit of electric current and not being defined by force.
What this anonymous, not-accepting-the-limitations-of-his-knowledge, not-willing-to-learn and sharing-pure-ignorance individual is saying makes clearly no sense. The electrical current reality/theory/coordination-with-other-units has always been exactly the same than today (I mean... theories can be changed/updated, but the most basic ideas have remained pretty unaltered since long time ago and most of modifications have consisted in adding new contexts/theories or tuning up some calculations). A different issue which I didn't comment before and which is relevant to clarify the aforementioned nonsense is that there are units below the current/ampere, but its usage depends on the given context/system. As said, for SI and its associated electrical calculations, you usually rely on amperes which is assumed to be a base unit, meaning that it isn't formed by anything else. But this is just a (calculating) convention for that given context/physics-subsystem and it doesn't oppose to the fact that current is formed by charges (whose unit is effectively the coulomb, not considered part of amperes by SI though as a way to keep coherence with other units and because of simply reaching the boundary of its scope, as explained below) or many other aspects at an even lower level (subatomic analysis taken care of by different theories, approaches, units). The idea is that if you perform macro-calculations and you rely on certain context (mechanics or electricity or thermodynamics or any other one) you would use certain units, conventions, systems, not necessarily identical or directly compatible with the ones of different approaches although theoretically coherent with all them. An example is my previous reference to f=m*a, rarely used for electrical calculations, but whose underlying idea (accelerated mass provoking a force) is expected to hold everywhere.
So, electrical current isn't defined by force (not now, not ever), but force might be indirectly defined by electrical current (+ something else). Exactly the same than mass isn't defined by force, but force might be defined by mass (+ something else). Exactly the same than velocity isn't defined by momentum, but momentum might be defined by velocity (+ something else). Another very important idea to bear in mind when dealing with fields helping to understand reality at any level (e.g., any branch of physics or chemistry) is that, although
Custom Solvers 2.0 = Alvaro Carballo Garcia = varocarbas.
It is kind of hard, but I have to recognise that I didn't understand your point properly until after having written my last post. I realise now about my error. I apologise about it. Even though you definitively failed to understand my point, I also failed to understand yours and both errors seem equally bad. I was referring to units/calculations and you were referring to abstract-definition coherence. And you are right, the ampere is being redefined as a way to keep the new system consistent. In any case and to make sure that my point is clear: this has no effect whatsoever in either currents/forces and their respective relationships. They will always be independent entities and, in case of wanting to see any kind of relationship, it would be the definition of force depending on current (or many other things) and not the other way around. Or, in other words, current is assumed to be there, force is assumed to be provoked by something.
The most ironic part is that I found pretty amusing your reference to school physics, but actually I do recall that concept of current being defined as a function of force only at school. This has no logical, calculation sense, just an arbitrary (practical) one. So, I have used/worked on/performed lots of calculations about physics without ever finding that idea again. From a theoretical perspective, it does make sense to define everything from the same basic unit (kilograms) and the easiest way to get to current from mass is logically via force. Never thought about it and yesterday didn't do even a basic research because of being sure about my units/calculations-based understanding.
Anyway, sorry about having been a bit too obtuse. On the bright side, I have thought about/shared quite a few ideas which you or other people might find helpful. And even highlighted a curious irony: until this point, the unit of electric current was theoretical defined as a function of the unit of force, something which theoretically doesn't form part of its constituent elements. I guess that it is a quite descriptive sample of one of the points which I tried to make in one of my other posts: the building of physics/science is very far away from being completely coherent, a reality which is rarely understood by almost anyone regardless their knowledge.
Custom Solvers 2.0 = Alvaro Carballo Garcia = varocarbas.
Although most of the ideas in this post are correct, it still denotes my misunderstanding of the original intention of the question. I have written a clarification (+ an apology) in another post below.
Custom Solvers 2.0 = Alvaro Carballo Garcia = varocarbas.
After re-reading my posts, I have to further apologise because of my behaviour in general. I didn't understand your point, didn't read your comments properly, didn't care much (not even doing a basic research, reading what I was linking!!), reacted in unnecessarily aggressive ways and wasn't even able to keep the discussion reasonably simple/focused what is particularly important when dealing with so complex issues. This is even more reprehensible by bearing in mind that I was the one spontaneously answering to your question. I am really sorry. The reasons/excuses? Being a bit too tired and some other issues (some nonsensically weird interactions with pretty ignorant and aggressive individuals here lately), but then why posting at all? Actually, my usual reaction when seeing certain behaviours in a website is simply stop using it, at least, temporarily. Completely my fault and sorry again. In any case, I think that I have shared quite a few worthy ideas which hopefully will be useful for someone.
Custom Solvers 2.0 = Alvaro Carballo Garcia = varocarbas.
After all my previous posts which I would delete if I could (unnecessarily confusing), here you have the answer which I should have written since the very first moment. Electric current isn't defined by force. It is either a base unit (no constituents) or a flow of charged particles. For all the intend and purposes, electrical current and its SI unit, Ampere, can be considered at the same level than time or grams (eventually, forming other units but not being formed by anything else other than themselves). A different story is the theoretical definition of the electrical current unit, Ampere in this case.
The SI units are meant to be somehow synchronised with the underlying physical relationships. For example, force equals mass*acceleration and, consequently, N (force unit) equals kg (mass unit) * m/s^2 (acceleration unit). Note that this doesn't happen in other systems of units like Imperial. By putting these ideas together with the basic requirement of setting up a reliable reference system for each unit (1 kg is the basic mass unit, excellent! But how much is this in pounds, potatoes, whatever?), it doesn't seem too difficult to understand that the reference systems (scales, ways to compare them with other units referring to the same magnitudes) of SI units are defined as a function of each other. As far as the basic reference system for SI/metric has traditionally been the kilogram, it does make sense that all the other units were defined as a function of it.
When performing calculations, you can easily do f=m*a or m=f/a or a=f/m and, mathematically/calculation-wise, these three approaches might be considered equally good. If now we look at the physics concepts underlying these formulae, things would be different. For physics (from a microscopical, mechanics, calculations point of view), mass is assumed to be a base unit, an absolute minimum in that context, it only depends on itself. Its value might certainly be determined in quite a few scenarios by relying on calculations like the aforementioned ones. But these indirect ways to determine the mass value in certain scenario can't be confused with these conditions being essentially required to define mass. Force in its simplest form requires, at least, a mass and an acceleration to be defined. Similar ideas are applicable to acceleration. So, from a physics, SI point of view (in this macroscopic context/calculations) mass could only be coherently defined by itself. On the other hand, from a mathematical point of view it could be defined in many different ways (e.g., m=f/a) and, from a system-of-reference/pragmatic point of view, in many other ones (e.g., the current new system where 1 kg isn't the basic reference anymore or any other approach like defining mas as a function of certain volume, force, acceleration, etc.).
If you apply the aforementioned ideas to electric current/amperes (known to be formed by other elements, but assumed to be indivisible in this specific context), you would understand that current doesn't not depend on force. It doesn't happen in its SI/ampere/treated-as-a-whole version or in any other one (e.g., flow of charged particles, coulombs). Rather than mass, you could think of velocity and its relationship with momentum/energy. The energy/momentum definition does depend on a moving object/velocity/acceleration. Analysing a moving object doesn't require caring about the originating energy/momentum, it only depends on its own (space traveled by unit of time). The definition of amperes (not electric current) did actually depend on a unit of force, but only for pragmatic reasons. From the physics point of view, electric current has always and will always continue depending on itself (+ constituent elements which might be considered depending on the given context/branch but none of them being force). Without denying the importance of the changes in the SI systems of reference, they will have no impact on theoretical physics. The will also have no noticeable impact on practical physics as far as the conversion factors will r
Custom Solvers 2.0 = Alvaro Carballo Garcia = varocarbas.
car carrying a baseball bat
Baseball bat? Is that the imperial version of the cricket bat?
Even in this last version, some ideas weren't completely clear. By assuming that it is already clear the difference between physics/magnitudes/force-current (the main, ruling, unmodifiable part) and system-of-units-and-its-improvements (the instrumental, fully-conditioned-by-physics, currently-updated part), it is certainly desirable to keep some coherence. It is possible to divide it into internal (physics/SI with respect to themselves) and external (SI with respect to physics) coherence. As explained in some of my previous posts, I have realised during this discussion that, until this moment, the external coherence wasn't exactly respected at least in the force-current front (SI defining current from force and physics doing it the other way around). And the new SI version is fixing this issue because of making everything depend on what, according to physics, is the real base for everything: atomic-level interactions (logically, only up to certain "depth"). From that, it is certainly possible to build a coherent-with-physics definition of the current/mass/force units.
:)) that your original question was meant to account for (what you thought that was) an issue here. You pointed out that the modification of the ampere definition was the solution which you were looking for, the solution of the circular reference which you thought that the new definition of kg provoked in amperes (via newtons). This redefinition is certainly a pretty sensible consequence of having moved from a macroscopic arbitrary fundamental unit (kg) to the microscopic level (what would have been the point of keeping the old kg-based definitions when the kg isn't the central part anymore?); basically, it is a sensible approach to keep internal coherence within the SI. It is also a way to fix that external incoherence with respect to physics (current shouldn't depend on force).
A different story is the internal coherence of SI. When you set up an inter-connected system of whatever, all the definitions have to make sense with respect to each other. For example and by bringing computer ideas, trying to avoid circular references. There doesn't even need to be truly speaking, unavoidable circular references where the definition of certain item is definitively impossible. For a good enough system, there shouldn't be even apparent, theoretical or conceptual inconsistencies. I understand (since yesterday in my last posts
Despite the previous paragraph and theoretically speaking, it could definitively be possible to include the new definition of kg (and, consequently, newton) together with the previous definition of ampere: amperes would be defined by newtons/metres, defined by kgs as so far (previously defined by itself, now at the particle level). Amperes would be indirectly defined as so far via a magnitude (mass) whose definition has been updated and is now more accurate. I don't see any chicken-egg scenario or logical inconsistency. I do see an external incoherence with physics because of inverting the logical force-depends-on-current-not-the-contrary; and an internal incoherence because of not applying the new basic ideas to the definition of amperes. In any case, I think that all this is tremendously unimportant in comparison with not having clear the main ideas here, namely: differences between physics/SI, magnitudes-&-the-reality-they-model/units-maths, theory-calculations/instrumental-resources.
Custom Solvers 2.0 = Alvaro Carballo Garcia = varocarbas.
I don't see any chicken-egg
I guess that your "kilogram is measured by measuring the current in electromagnet" refers to the way in which the Kibble balance (supposed to be measuring kgs by applying the new definition) works. Firstly, the main idea is relating atomic-level definition (via Planck constant) to kilograms, the measuring methodology/machine is irrelevant from the point of view of the unit. Exactly the same than balances were supposed to be used to compare the previous kilogram version with other objects but the exact way in which they worked was irrelevant for that old definition (any balance weighting in any accurate enough way should be fine).
:)
Secondly and even in case of really caring about the way in which the Kibble balance (or any other approach) works, currents measured in amperes could be used there without any problem. As it should hopefully already be completely clear, one thing is the physics/reality-it-models-via-instruments-like-units and a different story is the internal definition of one of the systems on which it relies. Electric currents and amperes are completely independent on force/mass and that's why they can form part of a formula defining it. The only real utility of the old/new definition of amperes (other than being parts of a system meant to be coherent, reliable, consistent, etc.) are scenarios where you want to compare that unit against ones in other systems. From the internal, SI-based calculations point of view, amperes, kgs, newtons, everything is self-defined. All the units are assumed to mean something, but that exact meaning (what the old/new definition actually does) is irrelevant within the given calculations (1 ampere is/was/will always be 1 ampere; the current definition of ampere is relevant to know the equivalence of amperes with units from other systems, but this would be unit conversion not physics calculations).
Long story short, there wouldn't even be any real problem with keeping the old definition of amperes with the new definition of kilograms. There would certainly be some external/internal inconsistencies and it wouldn't really make too much sense to do that for various reasons. But it wouldn't really be an egg-chicken, circular-reference kind of problem. It might look like this being the case for someone not understanding the situation properly. But this is the problem with not understanding something properly: you might see what isn't really there
Custom Solvers 2.0 = Alvaro Carballo Garcia = varocarbas.
This post with my sincere apology is modded up. It's OK. I have even do things on these lines myself in the past. But then I write a proper answer (+ 2 extensions today) which might be probably ignored. And well... I do think that this is by far much more important than the apology. I guess that finding surprising/highlighting-worthy when someone apologises is unfortunately kind of normal in internet nowadays. Personally, I don't see it as a big deal because I do always apologise and try to correct my mistakes as soon as I am aware of them. I also expect the same from everyone else, even though rarely find it. Anyway, this seems like a good last post before making a pause here. I like Slashdot and will continue reading it regularly. I like most of the community here and their usual concerns (= technical stuff and properly understanding). But here and there, I get a bit tired of tolerating the kind of random stupidity that, unfortunately, is present everywhere and mainly in internet. So, I will better focus on reading/modding for a while.
Custom Solvers 2.0 = Alvaro Carballo Garcia = varocarbas.
I know exactly what they did.
Evidently not.
But apparently you don't, based on your "explanation".
Again, I can't tell if you are trolling or just ignorant. Either way what you said is demonstrably wrong.
I know that and you know that but the people who make, e.g. bathroom scales are perfectly happy to report the force of weight in kilograms.
All we'd have to do is invent some new physics so that we could do it accurately enough.
Unfortunately, I think that I have to make one last clarification. I apologised (twice) because I am rarely in the situation of not properly understanding others (at least, their words within the right context) and did feel bad about it. It is a quite common scenario in internet or here though. Just take look at quite a few of my last posts and at me systematically correcting random misinterpretations (and nobody apologising). As it should already be clear to anyone reading the aforementioned proper answer & extensions, I consider my mistake of not looking up the old SI definition of amperes pretty irrelevant (a bit disrespectful towards that AC though). Basic SI/other system definitions are certainly nice-to-have bits of information, although mostly under very specific conditions (e.g., at school or when writing an article about the given unit). I will never complain about improving my knowledge, but this isn't particularly important for almost any physics/engineering understanding/usage. On the other hand, thinking that electric current does (or did) really depend on force and/or not understanding the difference between physical phenomenon, theoretical definition of a unit and calculations used in a comparison methodology do seem pretty serious misconceptions. The fact of thinking that this new over-clarification, further-summary, still-simpler-and-more-to-the-point post is really required should be understood as the main reason why I will not be posting much here and in general for a while: nobody seems to be able/willing to adequately understand almost anything (+ they rarely apologise).
Custom Solvers 2.0 = Alvaro Carballo Garcia = varocarbas.
These are not, repeat not, the same thing although both called a pound.
That's my point though: using pounds for both mass and force makes imperial units unfit for use because you have no way of knowing what it is that I measured which is entirely the problem that using units is supposed to solve. It also leads to utterly stupid units, for example, you could measure acceleration in pounds per pound even though that looks like a dimensionless unit. Units of pounds-squared has three different possible interpretations etc. It is just nuts.
Indeed since you seem so enamoured with this useless system why not define a pound-length, a pound-time etc. and then you can just use pounds^n to measure everything. Of course, there will be no way for anyone to know exactly what you measured but that's already pretty much the case and at least now you'll only have one unit to remember for everything.