Measurement – The Future

Universal Constants in Nature

With the advancement of science in the last few decades, many universal constants like Plank’s Constant and Speed of light have been discovered. Their value has also been calculated to mind-boggling levels of accuracy.

Scientists have also discovered that these constants are suitable for redefining many of the base units of measurement. This would free the units from dependence on “physical” objects like the meter bar and the kilogram cylinder.

With the development of technology, there was need for more and more extremely accurate measurements in length, mass & time. The international standards were based on the metre rod (in Paris) and the properties of water. These are being found not to be very reliable for the needs of present technology.

With the development of nuclear science, several universal fundamental constants like were discovered like Planck's constant, the elementary charge, the Boltzmann constant and the Avogadro constant. Hence there has been a move to base the basic units of measurement on such fundamental constants.

Time - It was agreed in 1960 that an unchanging frequency of microwave radiation released and absorbed by a cesium atom. which vibrates about 9 billion times a second, would be the basis of all measures of time. In the light of advances in technology and communication, scientists are already looking at other atoms which offer frequencies which are a 100 times better than Cesium!

Length - From 1983 the Meter has been defined in terms of the distance travelled by light in a vacuum in a particular amount of time. (1/ 299792458thof a second)

Weight- From May 2019): The kilogram would be defined in relation to the Planck constant h which is one of the fundamental constants in the universe.

Temperature– From 2019, the kelvin is expected to be defined in relation to the Boltzmann constant which is also one of the fundamental constants in the universe.

The quest for better units of measurement is a constant one. It would continue as science & technology advance and demand more & more accurate measurements.

The redefinition of the kilogram will be part of a planned larger overhaul to make SI units fully dependent on constants of nature. Representatives from 57 countries will vote on the proposed change this month at a conference in Versailles, France, and the new rules are expected to pass. Along with the kilogram, the ampere (the unit of electric current), kelvin (temperature) and mole (amount of a substance) will get new definitions. The four will be based on Planck's constant, the elementary charge, the Boltzmann constant and the Avogadro constant, respectively.

The Importance of Time Measurement

So, for nearly 150 years, the world’s metrologists have agreed on strict definitions for units of measurement through the International Bureau of Weights and Measures, known by its French acronym, BIPM, and based outside Paris.

The bureau regulates the seven base units that govern time, length, mass, electrical current, temperature, the intensity of light and the amount of a substance. Together, these units are the language of science, technology and commerce. Scientists are constantly refining these standards.

Now, with the exception of the mole, all of the standards are subservient to one: time. The meter, for example, is defined as the distance light travels in a vacuum during one-299,792,458th of a second. Likewise, the new definition of the kilogram rests on the second, in a manner too complicated to explain to school students.

Hence the measurement of the duration of a "second" assumes critical importance.