Time is fundamental concept of both, physics and the common sense, for the quantitative description of sequence of events, classifying them in terms "previously" (past), "simultaneously" (present) and "after" (in future). Time is one of coordinates of the Minkovsky's space of signature "1+3"; three coordinates are referred to "space", and one (usually, either the zeroth one, or the fourth one) is called "time". This term has also other meanings.
Scientific sense
All the observable events are classified as "past", "present" and "future". Time appears as transition of events from future to present and from present to past. In the most of paradigms used by the human civilization, the the future event may become present and them past, but the present event cannot become future and the past can become neither future nor present.
Any device, measuring time, can be called "clock". Historically, various ways to design clocks are known.
Most of variation of the clocks design refers to the representation of data rather than to the physical principles used to make the frequency standard. The principles are usually either the mechanical oscillations, like in the the obsolete "rolex" (that became a symbol of unwanted junk messages), or low-loss vibration of a crystal in computers. Sometimes also the dropping of water, or more often, sand is used (so-called sand-clock). After realization of quantum clock (atomic clock), the measurement of time is the most precise among other kinds of measurements; all the standards of physical units are based on the standard of frequency and therefore refer to time.
The measurement of time is based on the homogeneity of our Universe: the translational invariance holds with more than a dozen of decimal digits, and the most of human devices work pretty far from the limits related with the approximate character of the translational invariance. Due to translational invariance, the phenomena in past, present and future happen in a similar way; in particular, the periodic processes exist. Any periodic process can be used as a basic element of a clock. The clock usually consists of some realization of the periodic process and the system of counting of periods. These may be rotation of the Earth around the Sun with fixation of each roundtrip in a calendar, or rotation of the Earth around its axis, or various pendulums, oscillators, including quantum beats of the specially prepared systems (usually molecules or atoms).
In the classical physics, the three coordinates of any object are supposed to be functions of the fourth (or zeroth) coordinate. This fourth (or zeroth) coordinate is time. In the more general cases, the meaning of time changes. It is no more a unique parameter that characterizes the movement in terms of trajectory. In the Special Theory of Relativity, the time is not universal, but depends on the frame of reference, although there exist unambiguous relation between times measured in different frames of references. In non-relativistic quantum mechanics, the time cannot be used to determine the movement of bodies in terms of their trajectories (spatial coordinates versus time), although the time coordinate remains a universal parameter; all the evolution is described as dependence of the state of the system on this parameter. In the more general theories, neither classical trajectories, nor universal time exist, but the Quantum Field Theory allows (at least in principle) to trace the evolution of a system in any frame of reference.
In even more general case, the space cannot be considered a flat; and the conventional "space" and "time" appear only in the asymptotical limit. Such a "most general" theory has an internal defect: in order to create the asymptotically-classic space and time (with classical spatial coordinates and classical time), the frame of reference should be related to some massive body; over-vice, the quantum fluctuations set the limit to the precision of the measurement. On the other hand, such a massive body disturbs the metrics (and even the topology) of the space-time, and there is no linear equations that would allow the measurement in the common sense.
The abilities of the measurement devices of the 21st century are still very far from this limit; in some sense, yet there is no need to consider it. In the similar sense, there is no need to assume the existence of the "biggest natural number" building-up the mathematics in XX or XXI centuries (although the existence of such a number follows from the materialistic dialectics by Marx and Lenin). Nevertheless, the
science, as defined in TORI, is ready to consider the existence of some Mizugadro's number as soon as any evidence of such a need appears. The same refers to the
violation of the law of conservation of momentum, or that the Second Law of thermodynamics (perpetual motion), or violation of the principle of Causality (time machine). However, while such an evidence is not presented, any governmental supports of development of technology based on such a hypothesis should be considered as a fraud.
Common sense
The term "time" may have many different meanings.
One may say "I have no time for this", meaning existence of other activities that have highest rank in his/her scale of priority. "Have no time" may refer also that some activity is supposed to be finished before some moment at the time scale, occupies too long time interval. If a girl did not have an orgasm during a coitus, she may say "I did not cam this time", also referring to the specific interval on the time coordinate. (In such a case, her partner is supposed to revise his attitude to women.) Also, time may refer to some set of paradigms accepted during certain epoch of development of civilization. (for example, "The time of cannibals already past away.")
The scale of time may be different in different civilizations. The time zones at the Earth are distributed in such a way, that the noon corresponds to the day, and the midnight corresponds to the dark time; however, in the polar regions, the such a definition becomes more convention than physical reality.
In some countries, the authorities like to remonstrate their power, shifting (displacing) the time zones; sometimes, even twice per year. This allows the corruptioners to "wash the money" related with appearance of disappearence of an additional hour in the time scale.
From the scientific point of view, the frequent change of the time zone look idiotic; like the measurement of length in the horizontal direction in miles, while that in the vertical direction in feet; or the use of scale by Kelvin for the temperature while winter but that by Fahrenheit while summer.
Similar suggestions could be the kilogram containing 1000 grams during summer and 1024 grams during winter;
This could be motivated the reduction of density of liquids due to increase of temperature, and also should provide the wide field of frauds for the persons who manages the huge amount of national oil.
(One friend of mine found: let all constants be round; let both ? and e
be equal to 3, and kilogram be 2 lb.)
Some hackers alter the time in their computers in order to hide the traces of their activity.
The historic national time scale in Japan is displaced from the European one for 6.6 centuries; on the Japanese scale, the birth of Jesus Christ corresponds to year 660; and the European year 2011 corresponds to Japanese 2671. In addition, some Japanese banks count the time since the year of birth of the current emperor; the difficulties for users are comparable to those, caused by the often change of the time zone during the epoch of the USSR or the Russian Federation. Fortunately, in the scientific documents, even in Japan, already the European time scale is used; the scientific papers dated by year 2670 do not yet appear.
The astronomers, planning their observations, ignore the governmental decisions about the seasonal displacement of the time zones and use the Greenwich time scale; is smooth compared to that suggested, by some governments.
The ignorance of time as physical quantity is typical for the soviet veterans. For example, the moment of the catastrophe Katyn-2 is known with an uncertainty of order of quarter of hour, and the official Russian representatives do not care that such a precision of measurement of time corresponds to the level of technology of 18 century.
The seasonal alteration of the time zone can be considered as an equivalent of the alteration of the course of the national money, getting the advantage on the speculation on the favorable exchange rate. If the government of some country abuse with such an activity (for example, emits too many bills in order to compensate the massive robbery of the budget), the population is forced to switch for the natural exchange or to use the foreign currency. There is joke about one "new Russian" who returned from the USA:"...But the most wonderful - imagine, their dollars are just the same, as our bucks!".
There are several ways to deal with the governmental efforts to vary the time zones. The criminalists who investigate the reasons that push the officials to alter values of the physical quantity have to trace all the changes. The users, who do not cary about the corruption in government and do not want to spend their time for such a monkey business may either accept such a "national time" as a very rough estimate (with uncertainty of order of a hour), or to use some more stable time scale (for example, the Greenwich time), just as astronomers mentioned above.
Word "Time" can be used also as family name, as well as a name of a Journal. Some newspapers have "time" as part of their name. Perhaps, this should indicate to the readers, that the news appear "in time", id est, soon after the events; or to the modern style of representation, in the style of the epoch, following the paradigms and its taboos, using this meaning of the term "time".
Conclusion
Time is a concept that classifies the events to the sets "past", "present" and "future".
Time as physical quantity appears as parameter in the non-relaticistic theories (Newtonian mechanics, quantum mechanics) and as the coordinate in the Minkowsky's space of signature "1+3". In the General Theory of relativity, sometimes it is still possible to specify one of curvilinear coordinates as time, and let other three be just "space". In the quantum gravity, the term "time" losses its initial meaning and appears only asymptotically. The technology of XX and XXI century is still very far from such a fundamental limit. Usually time can be considered as universal real parameter that determines the relation "before", "simultaneously" or "after" between the events. Some officials alter the time in order to get some temporal benefits (for example, seasonal variation of time zones) or to hide the crime (alteration of time of the
Katyn-2 crash).
In any serious activity, in order to avoid the confusions, one should use some smooth time scale;
such a scale can be established with many decimal digits.
