Scientists to re-define kilogram
UK: Scientists say they are close to achieving a 200-year-old
goal of creating a universal system of measurements based on stable
quantities, as they progress towards changing how the kilogram is
defined.
The kilogram is the only base unit in the International System of
Units (SI) that is still defined by a physical object a prototype of
platinum-iridium kept in the vaults of the International Bureau of
Measurements (BIPM) in France.
The stability of the kilogram is crucial as it forms the basis from
which many other units are derived.
But measurements made over more than 100 years suggest that the mass
of the international prototype may have changed by about 50 micrograms
the size of a small grain of sand prompting the BIPM to try to develop a
new definition based on a fundamental physical property.
Scientists will gathered at the Royal Society, Britain’s national
academy of science, yesterday to present their progress on redefining
the kilogram according to something called “the Planck constant”, a
fundamental constant of quantum physics.
“International consensus has been achieved, that in the near future
the kilogram shall be redefined, based on a fixed value of the Planck
constant,” Michael Stock, a physicist at the International Bureau of
Weights and Measurements (BIPM), said in a statement.
But the new definition of the kilogram can’t take place until the
results of tests, conducted in laboratories across the world, are in
agreement, he explained. The International System of Units is the
world’s most widely used system of measurements for commerce and
science.
It is made up of seven base units metre, kilogram, second, ampere,
kelvin, candela and mole each of which represents a different physical
quantity. Its origins can be traced back to 18th century France and it
has been recognised internationally as the standard metric system since
the 1960s.
The metre was once defined as the distance between two lines on a
platinum-iridium prototype, but is now defined by the speed of light.
London, Monday, Reuters |