Evolution of Time Concept in Physics and in Philosophy
Total Page：16
File Type：pdf, Size：1020Kb
Physics International Original Research Paper Evolution of Time Concept in Physics and in Philosophy 1Sivaram, C., 2Kenath Arun and 2Kiren, O.V. 1Indian Institute of Astrophysics, Bangalore-560 034, India 2Department of Physics, Christ Junior College, Bangalore-560 029, India Article history Abstract: What is ‘time’? This is a question that has perplexed many a Received: 07-02-2015 physicist and philosophers alike. The perception of the passage of time Revised: 25-03-2015 appears ingrained in all biological systems where growth, evolution and Accepted: 25-03-2015 decay of objects, etc. are measurable indicators of the passage of time. Here we look at various physical models of time, from Newtonian to Corresponding Author: Kenath Arun relativistic. We also explore the idea of perception of time including the Department of Physics, Christ Junior possibility of travel into the past and future. Time in the quantum world College, Bangalore-560 029, India (as measured by differences in energy transitions of various levels) and Email: [email protected] classical world (as energy transformations) are also discussed. Keywords: Newtonian Time, Relativistic Time, Steady State Universe, Multiverse, Tachyon, Closed Time-like Curves, Arrow of Time Introduction up development of accurate pendulum clocks improving on earlier devises like sundials, water clocks and The perception of the passage of time, either periodic hourglass sand clocks etc.). or continuous, appears ingrained in all living (biological) The sexadecimal measure, introduced by the systems. The diurnal cycle and the annual passage of Babylonians applied both to measurements of angles seasons create visible changes in ambient parameters and time, the hour being sixty minutes and a minute influencing the behaviour of organized systems which being sixty seconds. This is purely historical and any perceive and respond to these changes. Growth, other number for subdividing would have been evolution and decay of objects, organisms or systems acceptable. Navigators at sea (during the great ocean provide measurable indicators, of the passage of time. The advent and advance of humans, capable of voyages of the early European colonial power) needed meticulous observations of entities around them along to know their position on the globe and the passage of with capacity for abstract thought enables quantitative time more accurately. Measurements of latitude and measurement and recording of the passage of time. longitude were begun. The definition of the metre in Even early humans were aware of the regularity of terms of the meridian passing through Paris led to the panoply of celestial objects discerning subtle motions more precise measurements. It was realized that local time was determined by longitude (as the earth of the moon and planets enabling at a later stage the rotates) and the Greenwich meridian was adopted as accurate prediction of phenomena like eclipses. The the longitude with respect to which times at all other Mayans deduced the orbital periodicity of Venus with an places are measured (this of course led to GMT). accuracy only improved in the twentieth century. Japan would be several hours ahead of GMT, while Calendars to record events evolved early with meticulous Hawaii would be several hours behind. book-keeping (in the temporal sense) of religious There is an amusing anecdote involving the festivals, harvests, sowing of crops or even flooding of International Date Line (IDL) which involves the rivers. The year (associated with the earth’s orbital addition and subtraction of a whole day depending on period) was divided into twelve months (the lunar orbit) which direction one crosses it. This has to do with the and months into weeks and days (for the diurnal earth global circumnavigation of the Magellan expedition rotation). Calendars as chronological indicators were (1519-1522). The captain Magellan was killed while crucial for culture, religion and all day to day activities. battling the Pacific islanders, but much of the remainder The need to measure time over the passage of a day led of the crew now led by Juan Sebastián Elcano, managed to the invention of clocks (Galileo’s observation that the to reach the starting point (Lisbon) of their voyage. period of a pendulum depends only on its length speeded Being strict Catholics, the crew were expected to keep © 2015 Sivaram, C., Kenath Arun and Kiren, O.V. This open access article is distributed under a Creative Commons Attribution (CC-BY) 3.0 license. Sivaram, C. et al . / Physics International 2015, 6 (2): 68.77 DOI: 10.3844/pisp.2015.68.77 track of all festivities like Lent, Easter, etc. and for this fraction of a centimetre. So also bouncing radar signals purpose had to maintain a log book. On their successful from the atmosphere of Venus has enabled the return (the first crew presumably to circumnavigate the determination of the astronomical unit to within less earth) it was observed that they had missed one day, than a kilometre. This accurate monitoring of time not accounted for. For this reason they were intervals has enabled unprecedented accuracy in presumably pulled up by the orthodox clergy. Of measurement of times and distances. The millisecond course it was not their fault. They had no way of pulsar, PSR B1937+21, (Backer et al ., 1982) (rotating knowing that they had crossed the IDL and it was 642 times a second) is slowing down at the rate of one inevitable that they lose a day. Geographical time part in 10 19 , rivalling atomic clocks. sense, based on longitudes had not yet reached the Atto-second laser pulses are now common, while sophistication of the eighteenth or nineteenth centuries. yocto-second pulses (10 −24 s) have been monitored in Local time based on geographical longitude further connection with quark-gluon plasmas. Typical hadronic underwent changes. Countries like the U.S. or Russia, −23 which spanned many degrees of longitude had to interactions are of 10 s duration. That gravity affects introduce time zones (where clocks could show clocks was major offshoot of Einstein’s General theory different times depending on whether you are in the of Relativity (GR). A clock in a strong gravitational field western or eastern part of the country.). When runs slower, so a high altitude clock would run faster. commercial air travel became common, this led to so You gain a pico-second over a lifetime by being in the called jet lags requiring time to adjust to the local time. topmost floor of a skyscraper. Supersonic travel (like the now defunct Concorde) introduced the possibility of going back in time (at Concept of Time and Steady State Universe lease geographical time). You could have lunch in Paris This brings us to the question of a time as a concept and arrive for breakfast in N.Y on the same day. This in physical theories. Early philosophers regarded time has more to do with chronometric book keeping rather as flowing (into the future) like a river. Like in than actually becoming younger. Later on we will see Tennyson’s poem, men may come and men may go, that to really go back into the past one has to travel faster than light (superluminal). With advances in but time goes on forever. Man was conscious of his atomic and nuclear physics even clocks to measure mortality (his limited life on earth) and aspired to be small intervals (like a second) became very precise. immortal. So the concept of afterlife (after death.) was Incidentally one wonders how inhabitants of a planet common to almost all cultures, from Voodoo Africans like Venus (a day being longer than a year, a day of 243 to Egyptians (who buried their kings in fantastically earth days) would measure local time. On Mars it would built pyramids with all paraphernalia) to the nirvana be more reasonable (with a day near to 24 h). Of course of Buddhists and multiple births and deaths in with the precision of atomic clocks, which can measure Hinduism till the soul attains immortality merging slow-down of the Earth’s rotation, these questions are with the infinite. Even early cosmological ideas now academic, even for future colonisers. pictured the universe as without beginning or end. Hermann Hesse’s novel ‘Siddhartha’ for instance is a How Long is a Second? well written account of the ‘river analogy’ flow of time. Fairy tales often ended with the key character The advent of atomic clocks and the more recent being happy forever. Everlasting happiness, nuclear thorium clock has enabled a second to be defined 16 17 prosperity, etc. is what humans always aspired for. to an accuracy of one part in 10 or 10 . The caesium In the steady state cosmology pioneered by British clock has already been in existence for quite some time, astronomers Bondi, Gold and Hoyle the universe has no the second being defined as 9,192,631,770 oscillations of beginning or end. They accounted for the Hubble the Cs hyperfine transition. This has enabled us to 137 expansion by postulating the perfect cosmological verify that the earth does indeed slow down by 1/6 ms principle, which states that no matter where or when an per century, so that starting from 1972, leap seconds observer studies the large scale universe, he would get have been periodically added several times, the last in the same unchanging picture. This implies a constant 2008, so that new year ‘celebrations’ can last one rate of expansion of the universe which in turn would second longer on December 31. This slow down is just what we expect from tidal action of the moon, whose imply a constant density at all times. The rate of distance consequently increases (from the earth) by expansion is given by Equation 1: about three centimetres a year.