The measurement of time

Abstract

To measure correlations between events, whose unstoppable scroll is defined Time, it is necessary to use events that recur regularly and adopt them as units of measure that are homogeneous and congruent. The periodic natural event that has always been used as main unit of measure is the day, the succession of two consecutive periods of light and dark, which has harmonized life. The ratio between the duration of light and dark varies continuosly, but with a periodicity called year, unfortunately not an integral multiple of the day, about 365,25 days. Other temporal units, commonly used, but not dependent on Earth's rotation (the day) and revolution (the year) periods, are the week and the month: the first related to the particular movements on the celestial sphere of the seven Solar system boodies visible to the naked eye from Earth, the second to the appearance of the twelve constellations of the Zodiac. These temporal units of measurement form the Calendar: the one adopted in most of our Planet derives from the Julian calendar established by Julius Caesar in 46 BC and modified with a papal bull by Pope Gregorio XIII in the Council of Trent in 1582. Until Galileo Galilei, observing the isochronicity of the oscillations of a lamp in the Cathedral of Pisa, developped the pendulum harmonic motion giving rise to the construction of the pendulum clocks, the timing measurements exploited the different height of the Sun above the horizon resulting in the direction and lenght of the shadows in sundials and elongation of the light bezel at noon along the meridian line. The electricity and atomic theory advent have allowed the construction of clocks which can measure time intervals up to a billionth of the day, in contrast, translating analithically the principle of conservation of mass and energy and applying it to the expansion process of the our Universe, in the case of elliptical solution, it would have a periodic phenomenon that would allow very large measurements of Time.