well... im thinking that all things
are variable throughout time in the universe. this goes for the nature of atoms, quarks, and subatomic particles.
118 years is a very short time in the universe if it is indeed <4 billion years old, but 50 micrograms is also a very small amount of matter
Ghost of FM said:
Now how the heck did they come up with that combination of materials and size and then call that a kilogram?
good question.. not really sure
it seems they want to define the kilogram by the way of funamental or atomic constants in the future... but are they really as constant as they say?
Atom-counting approaches
One Avogadro approach attempts to define the kilogram as a fixed number of silicon atoms of the same isotope. Silicon is the element of choice because the process of creating ultra-pure monocrystalline silicon is well-known (because of its use in the semiconductor industry). As a practical realization the monocrystaline rod would be cut and polished into a sphere, the weight of which would be measured using three different approaches in development by several different institutes. The sizes of the best spheres would be measured by interferometry. As the crystalline structure of the monocrystal is known, the number of atoms in this one kilogram could be estimated.
The ion accumulation approach involves accumulation of gold atoms and measuring the electrical current required to neutralize them.
Fundamental-constant approaches
In a similar manner that the meter was redefined to fix the speed of light to an exact value of 299,792,458 m/s, there are proposals to redefine the kilogram in such a way to fix other physical constants of nature to exact values.
Planck's constant: The Watt balance uses the current balance that was formerly used to define the ampere to relate the kilogram to a value for Planck's constant, based on the definitions of the volt and the ohm. Using the Watt balance, a possible definition for the kilogram would be: The kilogram is the mass of a body at rest whose equivalent energy corresponds to a frequency of exactly (299,792,458²/66,260,693) × 1041 Hz.
This would have the effect of defining Planck's constant to be h = 6.626 068 96 × 10–34 J s (from the 2006 CODATA value for Planck's constant of 6.626 068 96(33) × 10–34 J•s).
Avogadro constant: The kilogram is the mass of exactly (6.022 1415 × 1023/0.012) unbound carbon-12 atoms at rest and in their ground state.
This would have the effect of defining Avogadro's number to be NA = 6.022 1415 × 1023 elementary entities per mole and, consequently, a simpler and concise definition for the mole (from the 2002 CODATA value for the Avogadro constant of 6.022 1415(10) × 1023 mol-1).
Electron mass: The kilogram is the base unit of mass, equal to 1,097,769,238,499,215,084,016,780,676,223 electron mass units.
This would have the effect of defining the electron mass to be me = 9.109 3826 × 10–31 kg (from the 2002 CODATA value for the electron mass of 9.109 3826(16) × 10–31 kg).
Elementary charge: The kilogram is the mass which would be accelerated at precisely 2 × 10–7 m/s² if subjected to the per-meter force between two straight parallel conductors of infinite length, of negligible circular cross section, placed 1 meter apart in vacuum, through which flow a constant current of 6,241,509,647,120,417,390 elementary charges per second.
Effectively, this would define the kilogram as a derivative of the ampere, rather than present relationship, which defines the ampere as a derivative of the kilogram. This redefinition of the kilogram would result from fixing the elementary charge (e) to be precisely 1.602 176 487 × 10–19 coulomb (from the current 2006 CODATA value of 1.602 176 487(40) × 10–19), which effectively defines the coulomb as being the sum of 6,241,509,647,120,417,390 elementary charges. It would necessarily follow that the ampere then becomes an electrical current of this same quantity of elementary charges per second. The virtue of a practical realization based upon this definition is that unlike the Watt balance and other scale-based methods, all of which require careful characterization of the gravity at any given laboratory, this definition specifies the kilogram in terms of true acceleration of a mass. Unfortunately, it is extremely difficult to develop a practical realization based on the ampere.[18]
