Gone will be the days when physicists would use the old S.I. system of units that we have been using so far, i. e., metre for length; kilogram for mass; second for time; Ampere for electric current; Candela for Luminous intensity and mole for the amount of a substance. Very likely, we might welcome a new system of units in May 2019 that are entirely based on the fundamental constants in nature. Let's take a brief glance on what these new units are going to be :

*Why the new system of units ?*

The base units that we are using as of now have been derived from the fundamental constant quantities of the nature such as speed of light "c", triple point of water -which can be measured accurately and precisely. However, the definition of a kilogram is based on an artefact. The definition of a kilogram is :

" a kilogram is defined as being equal to the *International Prototype of the Kilogram* which is a cylinder of platinum-iridium alloy stored by the International Bureau of Weights and Measures at Saint-Cloud, France."

Now, over the time the weight of this artefact has been found to decrease- even a minor scratch can alter the weight of this prototype by around 30 micrograms. So, is it okay to use an unstable/varying mass as a prototype for an international unit of measurement ? Well, the answer is certainly No!!

**Quantum Metrology:**

Based on the two pioneering quantum effects: the Josephson effect and the quantum Hall effect, a new system of units is proposed to overtake the previously used S. I. system of units which is based on the elementary constants and in which the unit for mass i.e., kilogram will be replaced by Planck's constant "h".

Terry Quinn , *Emeritus Director, International Bureau of Weight and Measures, Paris, France, * in one of his invited talks quoted -*"Key to the new S. I. will be the redefinition of the kilogram in terms of a fixed numerical value for the Planck constant. Such a definition only became possible with the discovery of Quantum Hall effect". *

Here's how the new system of units would look like:

After knowing all this, some of us may freak out thinking that whether our perception of the basic physical quantities and their units is going to change after introduction of this new proposed system of units ? or Will the new definitions change the size of previously defined units?

**The answer to these questions is -NO !**

Commencement of the new system of units shall improve the previously existing S. I. units without changing the size of any units and ensuring a continuity with the present form of measurements.

Sounds Great!!!

Well, I personally feel that new discoveries and amendments in our previously existing believes make us realize the dynamic and revolutionary nature of science. How interesting - the more we delve deep into processes of nature we continue to be more and more amazed at how the universe works!!!

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