# The perfect sphere!

A priceless spherical object was created by Australian scientists with its raw material costing around 1 million Euros.

But why!

You might be wondering why would anyone invest such a large amount just to make a sphere! Well this sphere is an attempt to redefine a kilogram i.e SI unit for measuring weight!

To get into detail of why this sphere is created we need to know following facts:

1. A ‘meter’ is defined as the distance travelled by the light in (1/299752458) second

2.A second is dedined as “the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom” (at a temperature of 0 K).

From above examples it can be seen that these units are well defined and won’t change with time.

But then let’s see how a kilogram is defined:

1. Earlier a kilogramme was defined as the mass of a litre of water at 4 degree celcius.

2.Later it was replaced by a pure platinum cylinder and finally a platinum -iridium alloy (which is harder than pure platinum) was used as a standard.

Till now this cylinder which made of platinum-iridium alloy is used as a standard for kilogram.

What is the problem?

1. Kilogram is the only unit of measurement which is defined by a physical object!

2. This is kept at ‘International bureau of units and measurement’ under high security and under temperature control.40 more replicas of this cylinder was sent to different parts of the world as a standard for kilogram.
These sister object were brought together and it was found that their mass had changed. A deviation of around 50 micro gram was found in the weight and it was due to the change in the weight of platinum iridium alloy with time!

Kilogram is a very important unit as many derived units such as Newton ,joules ,watt etc depends on kilogram.Hence this drift in this unit is not acceptable.

How can the sphere solve the problem?

1. The sphere is made of only one isotope i.e Silicon 28

2. Hence it becomes possible to calculate the number of atoms present in the sphere which indirectly gives you the weight! It is similar to a perfect crystal!

3. Diameter of the sphere can be measured by laser. This gives us the volume.Density of atoms of silicon 28 isotope is accurately known .Hence by using Density=(mass)/(Volume) we can calculate atoms in the sphere.

Avagadros number is equal to number of atoms in 12 g of carbon 12.This is how avagadros number is defined.

Now using the sphere we can calculate a fixed value of Avagadros number which will be used to calculate a kilogram!

Interesting Fact!

The sphere mentioned above is so spherical that if this sphere is expanded to the size of earth then the distance between the highest peak and the deepest valley would be just 14meters If you compare this with earth then the distance between highest peak and deepest valley is 19.8 kilometres!

If this sphere is able to bring down the error to 20 micro grams then it might be able to replace existing definition of a kilogram.

Stay tuned for more such updates!Keep reading!

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