The Kilogram is Shrinking!

I doubt there's any threat posed to the kilogram by this because it's tied into other relationships that make that metal bar somewhat redundant these days. A litre of water is 1000cc (cubic centimetres) and with each cc of water weighing 1 gram, the litre weighs in at 1 kilogram (with controlled purity, temperature etc of course).

Originally posted by Long Lance
50µg is very little and i'd like to know what kind of reference they are using. gravity for one isn't really constant and i don't know of any direct mass measurement.

Well, you're right if they're using gravity to measure it.

Given that things weigh slightly less at the equator, and the talk about a pole shift, maybe the equator is coming their way...

I believe the real reason the US doesn't switch to metric is because our government is owned by corporations. Ye olde English system of stone age measures favors merchants because it keeps consumers in a state of confusion. Why else would they sell electric power by the watt, electric heat by the BTU, electric air conditioning by the ton of ice per day and electric motors by the horsepower?

When is the last time a 2x4 was actually 2" x 4"? I measured them in a 100 year old house once; they were 1⅞ x 3¾. Today's 2x4s are more like 1½ x 3⅝, and they get thinner when they dry out. The original rationale was that you get 18 2x4s from a 12x12, allowing for the thickness of the saw blade. Have saw blades gotten thicker?

Getting back to the topic: There is an obvious flaw in the modern defintion of "kilogram". The mass of that International Prototype Kilogram (IKP) is now the official SI definition of "kilogram". Therefore, any reduction in the number of atoms in the IKP makes all other objects in the universe more massive. If 50μg of atoms evaporate from the IKP, that does not change the mass of the IKP; it is still a kilogram by definition. Instead, the mass of Earth, the sun, and the universe is increased by one part in 20 million. If the mass of Earth was 5.9736×10^24 kg, and the kilogram lost 50μg of its atoms, that means Planet Earth is now 3 x 10^17 kg more massive than before.

So how did they determine that the IKP has lost mass? What are they comparing it to? Are they falling back on the previous definition? Is the density of water at 4°C the "real" standard? If so, how is the purity of water defined? Must it be pure light water, or must it have a certain percentage of deuterium oxide?

I'd like to propose a new standard, based on E = mc². We can measure energy to a high precision, and the units of time and distance are defined in terms of photons emitted by specific natural processes. If we define the kilogram as the mass equivalent of its energy, we get 1kg * c² = 8.9875517873681764000 x 10^16 joule. While it may not be practicable to measure mass in this way routinely, it would serve as an unchangeable standard which could be measured periodically by the people who monitor standards.

did you mean 10 ^ -17 ? 'cause 3 x 10^17 kg is one big ass number for 50 microgram to be adding to earths mass

after a week or so of reading this I have realised the definition of kilogram refers more to mass than weight, and no gravity is not included in its equation. there are other SI units that do that.

it begs the question, what changed? I also fail to see what converting the formula into planck lengths will do.

ed: there is...one explaination I can think of. mass gets heavier when you travel at speed, even in a plane as proved by adding einstins genious and an atomic clock, so...earth is moving at a different relative speed to ? than before =)

reply to post by madscientistintraining


3 x 10^+17 kg is correct. If the object which is DEFINED as 1 kg loses 1/20,000,000 of its atoms, the mass of Planet Earth (in kilograms) increases by 1/20,000,000. 1/20,000,000 of the mass of Earth is about 3 x 10^+17 kg. It just goes to show how stupid it is to define the kilogram as the mass of a perishable object. We might as well go back to the days when the foot was defined as the length of the king's foot.

What changed??? I think the most likely explanation is that some atoms evaporated or rubbed off of the IKP. We're talking about the equivalent of a fingerprint. This is not a relativistic mass increase, because that requires relative speed between the IKP and person measuring it.

A more relevant question is, "What are they comparing it to?"

I think we are all missing the point.

Scientists have predicted that has lost weight, they obviously know why it would lose weight, they are just not telling us in the article. It is predicted because as the defacto kilogram there is no other more exact kilo to compare it to.

The boffins are meeting to discuss a better way to define the kilogram that will not change over time.

@ Phractal Phil, very impressed with the old calculations, I am pretty impressed with myself for being able to understand it lol

Originally posted by dniMnepO
reply to post by thoughtsfull

 

Mechanics in Britain is awfully hard to understand and also when somthing is built useing the Metperial method sized nuts and bolts you need a completely new set of tools, they just wanted to be different??
On topic about the bars weight loss could be due to a few bumps on the way to the scales knocking a few micoscopic particles off it "Over the years". Or possible somthing in the atmosphere is dissolving it? Could there be somthing altering the local gravity?

edit on 26-1-2011 by dniMnepO because: (no reason given)

Gravity varies from place to place, especially over volcanic zones. I kind of wonder if something is changing under paris.

reply to post by mydarkpassenger


Actually, some idiot used emergy paper to clean it, and the methods used to compare it to other standards do not involve gravity. They think it may have also had some dissolve hydrogen which has evaporated.

A kilogram is still 1,000 grams or 2.2 pounds, just because the unit that represents that standard has shed mass, it does not invalidate the intellectual weight.. I think the American Bureau of Standards has their own weights.

Originally posted by mydarkpassenger
Gravity varies from place to place, especially over volcanic zones. I kind of wonder if something is changing under paris.

As has been said, a Kg is a measure of mass not weight. 1 Kg is the same in space as it is on the earth as it would be on Jupiter. Weight is determined by gravity, but mass remains "constant" (ironic, given the article). Technically, you're supposed to measure weight in Newtons, not Kilograms.

On Earth your mass may be 100Kg and on the Moon it would be exactly the same. As a result, any change in the mass of the bar used is not down to gravity changing, poles shifting, reptilian overlords licking it or because we've aligned to the Glactic equator...

As for this "English" system, I assume you mean Imperial? We use both in the UK, as has been said, because the EU tries to get us to be metric and we like our beer measured in pints and roads measured in miles.

Stones, pounds, farthings, euros, kilometres, miles, . . . . . . . . . what about pi?



Why can't we find a universal, gravitational constant?

The likely cause is radiation from space, Gamma ray. neutrinos, and cosmic rays passing through the metal are knocking atoms apart causing the loss of weight.

Originally posted by phishybongwaters
reply to post by DocEmrick

 

My preferred method of measurement is based on the length of a kings foot. Just saying

anyways, the kilogram has not changed, the mass they used to determine what a kilogram is has changed, a kilogram is still a kilogram. Worst case scenario, get a new 1 kilogram mass of platinum-iridium.

Wuts the big deal?

Apparently the weight of a kilogram is intrinsically tied to that one object. They forgot to factor in the innate radioactive decay.

This is just another step to 2012, lol.

reply to post by DocEmrick


I'm English, not fat and judging by a visit to the states recently I'd say we have a long way to go before we reach the sizes of some of your waddling gastropds.

Various standards under the name English units have applied at different times, in different places and for different things. Prior to the Battle of Hastings in 1066 the Anglo-Saxon system of measurement had been based on the units of the barleycorn and the gyrd (rod), inherited from tribes from Germany. After the Norman conquest, Roman units were reintroduced. The resultant system of English units was a combination of the Anglo-Saxon and Roman systems.

How long has the USA been around, a few years by comparison. Already much dumber and fatter than most other people on the planet. Well done.

Originally posted by debris765nju
...I think the American Bureau of Standards has their own weights.

The American Bureau of Standards has it's own copy of the IKP. The one in France is the IS definition of kilogram; all the others just copies.

Originally posted by beezer
Why can't we find a universal, gravitational constant?

We do have one; it's called "G" in Newton's law of universal gravitation. The trouble is, we have no way to measure it directly with enough accuracy to use it as a definition. One possible way to measure it more accurately, would be as follows:

Put a pair of 1 kg masses (exactly equal to the mass of the IKP) in orbit around one another. Each mass should include a corner reflector which returns a laser beam with the exact same distance as if the beam was reflected off the exact center of the mass, regardless of the direction of the beam. Track the motion of the two masses via laser beam from a distant third satellite, not in orbit with the two reference masses. Determine the exact length of the semimajor axis of the orbiting pair and the exact sidereal orbital period. Plug all that into the 2-body orbit formula and extract the exact value of G. Then, you can set the numerical value of G by definition and measure all other masses, including the IKP, against that standard.

Another natural constant, which is believed to be a fixed ratio of G, is Planck's constant, h. Efforts are under weigh to measure h to the necessary precision so that it can be the new definition from which mass is measured. As I said earlier, E = mc² = hc/λ; so m = h/λc.

Originally posted by ANNED
The likely cause is radiation from space, Gamma ray. neutrinos, and cosmic rays passing through the metal are knocking atoms apart causing the loss of weight.

The least stable isotope in natural Platinum has a half-life of almost a trillion years, and it is only .014% of the total mass. Both natural isotopes of Iridium are stable. So radioactive decay is not to blame. You would have to store the IKP in the core of a nuke reactor to significantly change the mass of its atoms.