The scientist in the video states that they are trying to count how many atoms are in it.  Making the sphere was only half the battle of getting it so precise.  They measured the diameter with a laser.  Ok so now on to why they made this thing..Apparently there are countries who have not used the metric system like the U.S.  Our pound is defined by 0.45359237 kilograms.  So something needed to be done and they are trying to get away from a physical object as a reference point.

Huh?  Well what does a sphere have to do with this?  This particular object is used as a count (or estimate) of atoms in there.  Because it’s pure silicon, there is only one isotope silicon 28.  And silicon works particularly well since we know the amount of space between each atom.

So have we redifined Avogadro’s constant of 12 grams of Carbon 12?  So now a kilogram can be described by a constant?  This scientist is hoping so.