Units of measurement past, present and future. International system of units

Abstract

Units and quantities in the field of radiation protection have often been a point of intense debate, mainly because of their complex relationship with the human body-related non-measurable protection quantities and the operational dose quantities. The operational dose quantities are defined for measurements but have the same unit, J/kg, and the same special name sievert (Sv) as that of protection quantities. However, this book is not intended to cover these aspects of radiation protection and is dealing with units in all fields of physics. The books starts with an overview on historical units of basic quantities (time, mass, length and volume) in ancient India. It is impressive to see that already in Vedic time, more than 5000 years BC, a time scale existed starting from about 2.6 µs up to years. It may be questioned what was the use of such a small unit of time (2.6 µs, much less than a ms) in ancient India. An answer to this is not presented in the book. The largest time unit ever been defined is surely the time for Brahma. Two Kalpa (equal to 2×4.32 billion solar years) are the day and night of Brahma's era and the lifespan of Brahma resulted in 311 trillion solar years (equal to 100 years of Brahma's life). Obviously one Kalpa corresponds to about the age of the Earth. It would be interesting to know about the religious origin of such time scales in more detail. In general the long history of units for measurements worldwide is a very interesting task, especially if this is combined with information how these units had been realised in ancient times. This, however, would surely be another book and was not the task for the author.