# Weight, what? The perfect kilogram is nearly in Planck's grasp

One of the standards world's toughest nuts, how to redefine the kilogram in terms of universal constants, is close to being resolved – unless a Russian experiment in 2017 throws a spanner in the works. That's exciting for standards boffins, since it means anyone can have an accurate kilogram without having to trek to Paris for …

1. Well it's been a long weight, but on balance the results should measure up perfectly.

1. That guy sure torques the talk.

2. #### Heavy science

At least it will be a weight off everyone's mind when they have finished

1. #### Re: Heavy science

Bah; trivia. What we really need to know is, exactly how thick is a Planck?

1. #### Re: Heavy science

Also what colour should it be...

2. #### Re: Heavy science

We do know the length of a Planck.

Could we thus call the Planck Interval, the thickness?

They do claim: "there is no reason to believe that exactly one unit of Planck time has any special physical significance"

and

"There is currently no proven physical significance of the Planck length; it is, however, a topic of theoretical research. Since the Planck length is so many orders of magnitude smaller than any current instrument could possibly measure, there is no way of examining it directly."

Possibly nothing smaller can be measured, no matter how good instruments get, unless someone invents an Heisenberg Compensator.

1. #### Re: "...unless someone invents an Heisenberg Compensator."

I'm uncertain whether that is possible.

1. #### Re: "...unless someone invents an Heisenberg Compensator."

"I'm uncertain whether that is possible."

Certainly is! I've got one right here in this box...

2. #### Re: "...unless someone invents an Heisenberg Compensator."

I'm uncertain whether that is possible.

Right not, I agree with you, or to put it another way:

"At the moment, that's my position"

1. #### Re: "...unless someone invents an Heisenberg Compensator."

Are you certain you wouldn't like to put some spin on it?

2. #### Re: Heavy science

Arr, we'll all walk the Planck, and wish it were longer than it be!

3. #### Re: Heavy science

They do claim: "there is no reason to believe that exactly one unit of Planck time has any special physical significance"

Correct. You need two short Plancks for significance.

3. #### Re: Heavy science

A standard plank is 6 x 2 x whatever length so depending on the orientation it could be 2 or 6 or an infinitely variable number.

4. #### Re: Heavy science

Or alternatively it is 0.25 X the thickness of a climate change expert.

2. #### Re: Heavy science

"At least it will be a weight off everyone's mind when they have finished"

Lucky my old physics teacher is unlikely to be reading this ... as otherwise he'd be shouting "Unit! Unit! You nit!" at you while probably dispatching a well aimed piece of chalk in your direction. The kilogram measures mass and not weight!

1. #### Re: Heavy science

So physics teachers all over the world would be suffering mass hysteria at such comments?

2. #### Re: Heavy science

"Lucky my old physics teacher is unlikely to be reading this ... as otherwise he'd be shouting "Unit! Unit! You nit!" at you while probably dispatching a well aimed piece of chalk in your direction. The kilogram measures mass and not weight!"

...yet is presently defined by a weight.

I fancy your old master would thoroughly approve of OP and his chalk would be flying towards gay Paris.

1. #### Re: Heavy science

No the reference kilogramme will weigh a different number of Newtons depending on where you do the measurement, but it will always be 1kg of mass.

2. #### Re: Heavy science

The kilogram(kg) is not a measure of weight. The Newton(N) is.

"...yet is presently defined by a weight."

The weight (object) you refer to has a mass of exactly one kilogram, since it is the reference for that. It will still have that same mass, wherever it happens to be.

On Earth's surface, the weight (force of gravity) of a weight (object) with a mass of 1kg will be approximately 9.81N give-or-take depending where and when you measure it.

3. So - it's about balancing one's spheres on a length of 4 by 2??? Maybe.

4. #### Sorry, but Russia is going to define kilogram in reference to Putin mass

Rumors says that the Russian Academy of Science will soon be asked to redefine all standards in terms of Putin dimensions. Thereby the meter will shrink to ensure Putin is 4.5 metres tall, while the kilogram will be larger to ensure he's light as a butterfly. Time will also be redefines so he's still in his twenties.

1. #### Re: Sorry, but Russia is going to define kilogram in reference to Putin mass

> while the kilogram will be larger to ensure he's light as a butterfly

Ridiculous! The kilogram will be made much smaller so he can bench press 700 kg.

5. #### So what if they disagree - a discussion is a good thing in science

Just don't call it a mass debate.

6. #### What does this mean for the "Olympic Swimming Pool/Double Decker bus" standards?

Does this mean these will be reduced to mathematical equations as well? :-O

1. #### Re: What does this mean for the "Olympic Swimming Pool/Double Decker bus" standards?

"What does this mean for the "Olympic Swimming Pool/"

As the pool is filled with essentially water it could be defined in moles

1. #### Re: What does this mean for the "Olympic Swimming Pool/Double Decker bus" standards?

"... it could be defined in moles"

So, sort of like my garden then?

2. #### Re: What does this mean for the "Olympic Swimming Pool/Double Decker bus" standards?

"As the pool is filled with essentially water it could be defined in moles"

As opposed to non essentially water??

Why moles? are they aquatic?

And BACON.

Thanks - the one with a map of Friday in the pocket.

NURSE!

1. #### Re: What does this mean for the "Olympic Swimming Pool/Double Decker bus" standards?

moles ARE aquatic, my wife has fished two out of the swimming pool! I was amazed, but they CAN swim.

For those interested, there are several youtube videos of them swimming quite well.

1. #### Re: What does this mean for the "Olympic Swimming Pool/Double Decker bus" standards?

> moles ARE aquatic, my wife has fished two out of the swimming pool! I was amazed,

> but they CAN swim.

The ones I generally see can't. Probably because they are missing major body parts (like the body) with delicate cat-gnasher marks on the remains..

1. #### Re: What does this mean for the "Olympic Swimming Pool/Double Decker bus" standards?

with delicate cat-gnasher marks on the remains.

Excellent! You've just proven we can now determine the mass of a cat by counting how many moles are in them.

1. #### Re: What does this mean for the "Olympic Swimming Pool/Double Decker bus" standards?

"Excellent! You've just proven we can now determine the mass of a cat by counting how many moles are in them."

Furrets Last Theorem depends on modular moles?

2. #### Essentially water

Well some of it is chlorine. And with use, urea is often added.

1. #### Re: Essentially water

"And with use, urea is often added."

So not like a VW then.

2. #### Re: What does this mean for the "Olympic Swimming Pool/Double Decker bus" standards?

No relationship as one measurement is volumetric and the other is mass.

7. This post has been deleted by its author

1. #### Re: Pray all goes well.

But should we make te sign of the cross in the traditional Russian Orthodox way with two fingers or with three fingers as introduced by Patriach Nikon in the 1650's?

1. #### Re: Pray all goes well.

When it comes to matters of religion I generally favour a two-finger sign.

1. #### @Rich 11

Allow me to bless you my son

8. #### But what effect will this have on the Jub?

Will we have to reconvene the Standards Soviet?

http://www.theregister.co.uk/Design/page/reg-standards-converter.html

9. Should the Irish be involved if we want to measure 2 short Planck's?

1. The 70's called - they want their joke book back

1. http://xkcd.com/1072/

1. > http://xkcd.com/1072/

Some people know far too much about xkcd for their own sanity.. (I should know - my nephew is one of them!)

10. #### Sir

It's all very well working out how to measure the mass of an object, but what about how much it weighs?

Are they taking gravitational fluctuations into account when creating these spheres?

11. At the end of the day, what's the point?

1. I think you'll find that with spheres - there isn't one.

1. #### I think you'll find that with spheres - there isn't one.

Its OK, my dog Arrow has one.

(One "attaboy" to anyone who knows the cultural reference.)

1. #### Re: I think you'll find that with spheres - there isn't one.

Hey... You don't have to have a point to have a point!

12. #### Weight a minute!

Someone needs to tell the purveyor of the shonky unbranded 10kg weight plates I bought that were actually 9Kg.

Ah well, they was cheep.

1. #### Re: Weight a minute!

They'll probably be ok when they grow up and go cockadoodledo.

2. #### Re: Weight a minute!

Ah well, they was cheep.

so they were defined in Budgerigars?

3. #### Re: Weight a minute!

Hence the "SALE - 10% OFF!" sign nearby at the shop.

13. #### Kelvin?

I thought the Kelvin was pretty much well defined by the triple point of water?

1. #### Re: Kelvin?

yet the triple point of water is not a measurement (it's a reference point therefore not measured against anything else) and also involves pressure

1. #### Re: Kelvin?

Precisely, it involves pressure, in that the pressure is precisely defined… And since 0K is pretty much defined to be absolute zero, you don't need anything else. What do I miss?

1. #### Re: Kelvin?

It's rather tricky to reach absolute zero in order to calibrate your thermometer.

The unit of a kelvin is based on a degree centigrade which is based on the melting point of a couple of metals (don't remember which) because ice/water/steam is a bit too variable.

1. #### Re: Kelvin?

The unit of a kelvin is based on a degree centigrade which is based on the melting point of a couple of metals (don't remember which) because ice/water/steam is a bit too variable.

Sorry, that's incorrect. The Kelvin is defined as being 0 at absolute zero, and 273.16 at the triple point of water. That's the current official definition, which they are planning to change:

https://en.wikipedia.org/wiki/Kelvin

1. #### Re: Kelvin?

"That's the current official definition, which they are planning to change:"

To judge from the link, they are at roughly the point that they were with kilograms a few decades ago. They've decided what they'd like the definition to be, but don't know how to reproduce it with the required accuracy. You'll excuse me if I don't hold my breath.

2. #### Re: Kelvin?

Wasn't Celsius originally based on 0C being the boiling point of water and 100C being the freezing point.

1. #### Re: Kelvin?

Wasn't Celsius originally based on 0C being the boiling point of water and 100C being the freezing point.

1) No, that's the reverse.

2) The boiling temperature and to a lesser extent the freezing temperature of water depend on the pressure, so that was a little bit imprecise. Celsius are now defined by the triple point of water, which determines both a precise pressure and temperature. The definition is now roughly: "absolute zero is 273.15 °C = 0 K, and at the pressure of the triple point of water, the temperature of the triple point of water is 0.01 °C = 273.16 K". The 0.01 value was chosen because that was the approximate value under the previous definition, and they didn't want to change all existing thermometers.

14. #### In Soviet Russia, Kilogram Defines You!

Alright, alright, I've got my coat..

Bloody hell! I thought I'd heard the last of that bastard at Chemistry O-Level donkeys years ago.

No, I don't like the taste.

If you make smoothies with it instead of bananas it's much nicer

edit: I didn't mean making bananas of course

16. #### Wouldn't it be easier...

To just go back to defining it in terms of water/temperature/volume - seeing as we already have nice clean definitions for temperature and volume? I mean, that's the nice thing about the metric system. The units relate to one another.

1. #### Re: Wouldn't it be easier...

Nice theory, and I did like the linky, but is the water in solid, liquid or gas phase? Which you can't tell unless you define the pressure on the water , which leads you to a density calculation, which leads back to mass units? (haven't done the full thinking so I'm sure someone will be along to correct me shortly. Icon 'cos at least he's doing some thinking)

1. #### Re: Wouldn't it be easier...

You're probably right - I just wanted an excuse to post that image again ;)

2. #### Re: Wouldn't it be easier...

It leads to a circular reference, because you need to specify the pressure of the water, in Pascals, and that unit is derived from the kg.

17. #### Correction

> ...will slide into gentle retirement.

Shouldn't that be "roll into retirement"?

1. #### Re: Correction

> Shouldn't that be "roll into retirement"?

Cognac, Armagnac, Burgundy and Beaune,

This old man came rolling home.

Some fine songs by those gentlemen. Much missed..

If it weren't for the fact that the litre used to be 1.000028 cubic decimetres - that has since been redefined to be exactly 1 - the gram could be defined as the mass of one cubic centimetre of water. Which was its original definition back when the metric system was first invented. Of course, the trouble with that is that water dissolves nearly everything, at least to a small extent, and so maintaining pure water is difficult.

19. #### Another problrem with the standard ...

... is that, being from 19th C. technology, who knows what's in it? I heard it had shrunk by about 50µg since its manufacture (my guess would be loss of about 1ml of H2 but it could be loss of surface greases)

20. #### 1kg

And there was me thinking that the SI measure for 1kg was the ubiquitous bag of Tate & Lyle.

Who knew.

21. #### 6.022 140 82x10^23, plus or minus 180,000,000,000,000,000

Some might say that an error of plus/minus one hundred and eighty million billion atoms is not that accurate.

1. #### Re: 6.022 140 82x10^23, plus or minus 180,000,000,000,000,000

Yes whilst 12 parts per billion is very accurate I'd have thought they needed even more than extremely accurate.

22. #### Not overheard..

Phrases you won't be hearing at NIST/the International Avogadro Coordination project/NPL/NRC:

"Close enough"

"Just a smidge more"

"Eh, it'll do"

"Give it to the work experience kid* to finish off"

"Let's take the average and call it good"

(* but I bet the work experience kid got sent off for "a long weight")

My own take? Just define it as 2.2lb and the job's a good'un.

1. #### Re: Not overheard..

Almost there, just a gnat's more off the end

1. #### Re: Not overheard..

"Close enough for Jazz"

23. #### Balls

Why the piccy of a ball-bearing?

The reference kilo is a cylinder....

1. #### Re: Balls

They wanted to test your reading comprehension and ability to connect pieces of information.

In the article there's a paragraph "One technique is to count the atoms in a sphere of material (Australia's CSIRO has helped contribute to this with its own silicon sphere)."

The picture's label is "CSIRO's silicon sphere".

Since you failed to connect the paragraph to the image, I would call that an E-PIC FAIL.

24. #### Bah!

But gosh, doesn't using a sphere introduce the need for Pi, and a consequent inaccuracy due to rounding errors?

Why not use a diamond shape? That's how the atoms want to arrange the selves anyway.

1. #### Re: Bah!

As I understand it, they've chosen a sphere because they believe corners are susceptible to round-off errors during handling.

1. #### Re: Bah!

A sharp observation, sir.

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