Time in Physics

Time is a form of physical and mental processes, the condition of possibility of change [1] . One of the basic concepts of philosophy of physics, a conditional comparative measure of the motion of matter, as well as one of the coordinates of space-time, along which the world lines of physical bodies are stretched.

In philosophy, this is an irreversible flow (flowing only in one direction - from the past, through the present to the future) [2] , within which all the processes that exist in being that are facts take place. Nevertheless, there are theories with symmetric time, for example, the Wheeler-Feynman theory.

In the quantitative (metrological) sense, the concept of time has three aspects:

• coordinates of the event on the time axis. In practice, this is the current time: the calendar, defined by the calendar rules, and the time of day, determined by any numbering system (scale) of time (examples: local time, universal coordinated time);
• relative time, the time interval between two events;
• subjective parameter when comparing several different-frequency processes.

Time properties

First of all, time is characterized by its one-pointedness (see Arrow of Time). Also, time is determined in a certain frame of reference, which can be either uneven (the process of the Earth rotating around the Sun or a human pulse), or even . The uniform reference frame is chosen “by definition”, earlier, for example, it was associated with the movement of the Solar System bodies (ephemeris time), and now atomic time is locally considered, and the second standard is 9,192,631,770 periods of radiation corresponding to the transition between two hyperfine levels of the ground state of the cesium-133 atom in the absence of a perturbation by external fields. It should be noted that this definition is not arbitrary, but associated with the most accurate periodic processes available to mankind at this stage in the development of experimental physics [3] .

Time orientation

Most modern scholars believe that the distinction between the past and the future is fundamental . According to the modern level of development of science, information is transferred from the past to the future, but not vice versa. The second law of thermodynamics also indicates that the entropy does not decrease in the future for an isolated system.

However, some scientists think a little differently. Stephen Hawking in his book "A Brief History of Time" disputes the claim that for physical laws there is a difference between the direction "forward" and "back" in time. Hawking argues that the transfer of information is possible only in the same direction in time, in which the total entropy of the Universe increases. Thus, the Second Law of Thermodynamics is trivial, since entropy grows with time, because we measure time in the direction in which entropy grows [4] .

The uniqueness of the past is considered very plausible. Opinions of scientists regarding the presence or absence of various "alternative" options for the future are different [5] .

There is also a cosmological direction of time, where the beginning of time is the Big Bang, and the passage of time depends on the expansion of the Universe.

Time dependence

Since the states of our entire world depend on time, the state of any system may also depend on time, as it usually happens. However, in some exceptional cases, the dependence of any quantity on time may turn out to be negligible, so that with high accuracy this characteristic can be considered independent of time. If such quantities describe the dynamics of a system, then they are called conserved quantities , or integrals of motion . For example, in classical mechanics, the total energy, the total momentum and the total angular momentum of an isolated system are integrals of motion.

Different physical phenomena can be divided into three groups:

• stationary - phenomena, the main characteristics of which do not change with time. The phase portrait of a stationary phenomenon is described by a fixed point;
• non - stationary - phenomena for which time dependence is fundamentally important. The phase portrait of a nonstationary phenomenon is described by a point moving along a certain trajectory. They, in turn, are divided into:
  • periodic - if there is a clear periodicity in the phenomenon (phase portrait is a closed curve);
  • quasi - periodic - if they are not strictly periodic, but on a small scale they look like periodic ones (the phase portrait is an almost closed curve);
  • chaotic — aperiodic phenomena (phase portrait — an unclosed curve that sweeps a certain area more or less evenly, an attractor);
• quasistationary - phenomena that, strictly speaking, non-stationary, but the characteristic scale of their evolution is much larger than those times that are of interest in the problem.

Time concepts

At present, there is no universally accepted theory explaining and describing such a concept as Time. Many theories are being advanced (they may also be part of more general theories and philosophies) trying to substantiate and describe this phenomenon.

Concepts adopted in science

Classical physics

In classical physics, time is a continuous quantity, an a priori characteristic of the world, not defined by anything. As a basis for measurement, a certain, usually periodic, sequence of events is used, which is recognized as the benchmark of a certain period of time. This principle is based on the work hours.

Time in classical physics exists by itself, separately from space and any material objects in the world. Time as a stream of duration equally determines the course of all processes in the world. All processes in the world, regardless of their complexity, have no influence on the passage of time. Therefore, the time in classical physics is called absolute. I. Newton: “Absolute, true mathematical time by itself and by its very essence, without any relation to anything external, flows evenly, and is otherwise called duration ... All movements can accelerate or slow down, while the absolute time cannot change [6] The absoluteness of time is mathematically expressed in the invariance of the equations of Newtonian mechanics relative to Galilean transformations. All moments of time in the past, present and future are equal among themselves, time is uniform. The flow of time everywhere and everywhere in the world is the same and cannot change. Each real number can be assigned to a point in time, and, conversely, a real number can be assigned to each point in time. Thus, time forms a continuum. Similarly, by arithmetization (comparing each point to a number) of points of Euclidean space, it is possible to conduct arithmetization of all points of time from the present unlimited back to the past and unlimited forward to the future. To measure time, only one number is needed, that is, time is one-dimensional. The time intervals can be associated with parallel vectors that can be added and subtracted as straight segments. [7] [8] The most important consequence of the homogeneity of time is the energy conservation law (Noether’s theorem) [9] [10] . The equations of Newtonian mechanics and Maxwell's electrodynamics do not change their form when the sign of time changes to the opposite. They are symmetric with respect to time reversal (T-symmetry). Time in classical mechanics and electrodynamics is reversible. The mathematical expression of the reversibility of time in classical mechanics is that time enters the formulas of classical mechanics through the operator [eleven]

Thermodynamics

In thermodynamics, time is irreversible due to the existence of the law of increasing entropy of a closed system. The entropy of a closed system can only increase with time or remain constant [12] .

The quantum physics

The same is the role of time in quantum mechanics: despite the quantization of almost all quantities, time remains an external, unquantized parameter. Introduction of the time operator prohibited by the fundamentals of quantum mechanics. [13] In quantum mechanics, time is irreversible, due to the interaction in the process of measuring a quantum-mechanical object with a classical measuring device. The measurement process in quantum mechanics is asymmetric in time. In relation to the past, it gives probabilistic information about the state of the object. In relation to the future, he himself creates a new state. [14] The mathematical expression of the irreversibility of time in quantum mechanics is that time enters the Schrödinger and Dirac equations by the operator or its equivalent - energy [11] . In quantum mechanics, there is an uncertainty relation for time and energy: the law of energy conservation in a closed system can be verified by two measurements, with a time interval between them in , only accurate to the magnitude of order . [15]

Relativistic physics

In relativistic physics (Special Theory of Relativity, Special Relativity) two main postulates are postulated:

1. The speed of light in a vacuum is the same in all coordinate systems moving rectilinearly and uniformly relative to each other.
2. The laws of nature are the same in all coordinate systems moving in a straight line and uniformly relative to each other.

These postulates lead to the conclusion that events that are simultaneous in one frame of reference can be non-simultaneous in another frame of reference moving relative to the first. Thus, the course of time depends on the movement of the reference system. Mathematically, this dependence is expressed through the Lorentz transformation. [16] Space and time lose their independence and act as separate sides of a single space-time continuum (Minkowski space). Instead of absolute time and distance in three-dimensional space, preserved during Galileo’s transformations, the concept of an invariant interval appears, which remains under Lorentz’s transformations. [17] The cause-effect order of events in all reference systems does not change [18] . In a moving frame of reference, the passage of time from the point of view of a fixed frame of reference slows down (relativistic time dilation): . Here - time interval in a fixed frame of reference, - time interval in the moving reference frame, - the speed of movement of the moving frame of reference, - the speed of light in vacuum [19] .

Experience shows that in particle physics time is reversible in all processes, except for the decay of neutral mesons and some other heavy particles (violation of CP-invariance) [20] .

The general theory of relativity (GTR), based on the principle of equivalence of the forces of gravity and inertia, generalized the concept of four-dimensional Minkowski space-time in the case of non-inertial reference systems and fields. [21] . The metric properties of the space-time at each point under the influence of the field of aggression become different. The influence of the gravitational field on the properties of four-dimensional space-time is described by the metric tensor. Near massive bodies (at points with a large absolute value of the gravitational potential), the passage of time always slows down compared to the passage of time away from them (at points with a smaller absolute value of the gravitational potential). The relative time delay for two points of a weak constant gravitational field is equal to the difference of gravitational potentials divided by the square of the speed of light (Gravitational redshift). [22] On the horizon of a black hole event, from the point of view of the reference system associated with a remote observer, the passage of time completely stops [23] .

Quantum field theory

The most common relationship between the properties of space, time and matter in quantum field theory is formulated as a CPT theorem. She argues that the equations of quantum field theory do not change with the simultaneous application of three transformations: charge conjugation C - replacing all the particles with the corresponding antiparticles; spatial inversion P - replacing the signs of all spatial coordinates with opposite ones; time reversal T - replace the sign of time on the opposite.

By virtue of the CPT theorem, if a process occurs in nature, then a CPT-conjugate process can occur with the same probability, that is, a process in which particles are replaced by corresponding antiparticles (C-transformation), the projections of their spins change sign (P- transformation), and the initial and final states of the process are reversed (T-transformation). [24]

When using the method of Feynman diagrams, antiparticles are considered as particles propagating backwards in time. [25]

Synergy

Synergetic, during the resolution of the paradox of the arrow of time (why do reversible processes lead to irreversible phenomena?) Based on the study of processes in non-equilibrium statistical mechanics using the theory of chaos based on Poincare and Kolmogorov, advanced the concept of non-reducible to individual trajectories (classical mechanics) or wave functions (quantum mechanics) of a probabilistic description of chaotic classical or quantum systems by applying nonunitary transformations with complex eigenvalues and. [26] [27] This formulation of the equations of dynamics includes the violation of symmetry in time and irreversibility already at the level of the equations of motion. I. Prigogine: “time acquires its true meaning, associated with irreversibility or even with the“ history ”of the process, and is not just a geometric parameter characterizing movement” [28] .

Some theories operate on the so-called. “Instant”, chronon [29] - the smallest, elementary and unbreakable “quantum of time” (corresponding to the notion of “Planck time” and approximately 5.3 · 10 −44 s).

Psychology

In psychology, time is a subjective sensation and depends on the state of the observer. There are linear and circular (cyclic) time.

Philosophical concepts

One of the first philosophers who began to reflect on the nature of time was Plato. Time (Greek χρόνος) he characterizes in his treatise Timaeus as a “moving likeness of eternity”. It is a characteristic of the imperfect dynamic world, where there is no good, but only the desire to possess it. Time, thus, reveals a moment of incompleteness and inferiority ( there is never time ). Eternity (Greek αἰών), by contrast, is a characteristic of the static world of the gods. Aristotle developed this understanding of time by defining it as a “measure of movement.” This interpretation was enshrined in his "Physics", and it laid the foundation of the natural science understanding of time.

At the beginning of the Middle Ages, Augustine developed the concept of subjective time, where it becomes a psychic phenomenon of changing perceptions (soul stretch — lat. Distentio animi ) [30] . Augustine distinguishes between three parts of time: present, past and future. The past is given in memory, and the future is in expectation (including in fear or in hope). Augustine notes such an aspect of time as irreversibility, since it is filled with accomplished events ( time is passing ). In addition to the human soul, time reveals itself in human history, where it is linear.

In the future, both interpretations of time develop in parallel. The natural science understanding of time deepens Isaac Newton, introducing the concept of “absolute time”, which flows quite evenly and has no beginning or end. Gottfried Leibniz follows Augustine, seeing in time a method of contemplating objects inside the monad. Leibniz is followed by Immanuel Kant, who owns the definition of time as “an a priori form of contemplation of phenomena” [31] . However, both the natural science and the subjective concept of time reveal something in common, namely, the moment of change of states, because if nothing changes, then time does not reveal itself. A. Bergson in this connection denies the “separate” existence of time and objects, asserting the reality of “duration.” Время является одной из форм проявления длительности в нашем представлении. Познание времени доступно лишь интуиции. А. Бергсон: «Ведь наша длительность не является сменяющими друг друга моментами: тогда постоянно существовало бы только настоящее, не было бы ни продолжения прошлого в настоящем, ни эволюции, ни конкретной длительности. Длительность — это непрерывное развитие прошлого, вбирающего в себя будущее и разбухающего по мере движения вперед.» [32]

Схожие представления развиваются в столь различных философских направлениях, как Диалектический материализм (время как форма существования материи) и вфеноменологии. Время уже отождествляется с бытием (например, в работе Хайдеггера «Бытие и время», 1927) и его противоположностью уже становится не вечность, но небытие. Онтологизация времени приводит к его осознанию как экзистенциального феномена.

Нерешённые проблемы физики времени

• Почему вообще течёт время? [33]
• Почему время всегда течёт в одном направлении? [34]
• Существуют ли кванты времени? [35]
• Почему время одномерно? [36]
• В некоторых решениях уравнений Эйнштейна присутствуют замкнутые времениподобные линии. Вероятно, это свидетельствует о неполноте геометрического описания времени в общей теории относительности и необходимости дополнения общей теории относительности топологическими аксиомами, задающими свойства времени как порядкового отношения. [37]

Отсчёт времени

Как в классической, так и в релятивистской физике для отсчёта времени используется временна́я координата пространства-времени (в релятивистском случае — также и пространственные координаты), причём (традиционно) принято использовать знак «+» для будущего, а знак «-» — для прошлого. Однако смысл временно́й координаты в классическом и релятивистском случае различен (см. Ось времени).

Отсчёт времени в астрономии и навигации

Время в астрономии и навигации связано с суточным вращением земного шара; для отсчёта используются несколько родов времени.

• Местное истинное солнечное время ( local apparent solar time ) — полдень определяется по прохождению Солнца через местный меридиан (наивысшая точка в суточном движении). Используется, в основном, в задачах навигации и астрономии. Это то время, которое показывают солнечные часы.
• Местное среднее солнечное время ( local mean solar time ) — в течение года Солнце движется слегка неравномерно (разница ±15 мин), поэтому вводят условное равномерно текущее время, совпадающее с солнечным в среднем. Это время своё собственное для каждой географической долготы.
• Всемирное время (Гринвичское, GMT) — это среднее солнечное время на начальном меридиане (проходит около Гринвича). Уточнённое всемирное время отсчитывается при помощи атомных часов и называется UTC (англ. Universal Time Coordinated , Всемирное координированное время). Это время принято одинаковым для всего земного шара. Используется в астрономии, навигации, космонавтике и т. п.
• Поясное время — из-за того, что неудобно в каждом населённом пункте иметь собственное время, земной шар размечен на 24 часовых пояса, в пределах которых время считается одним и тем же, а с переходом в соседний часовой пояс меняется ровно на 1 час.
• The decree time is the procedure for calculating time "standard time plus one hour." In 1930, by the decree of the government throughout the USSR, the time was transferred 1 hour ahead, so Moscow, formally being in the second time zone, had a time different from Greenwich by +3 hours. For many years, the decree time was the main civil time in the USSR and Russia.
• Summer time ( daylight saving time, summer time ) is a seasonal transfer of arrows, in the spring 1 hour ahead, in the autumn 1 hour ago (canceled in Russia since summer 2011, in the autumn the arrows were not translated).
• Star time is marked by the upper climax of the vernal equinox. Used in astronomy and navigation.

Time units

Main article: Time units

In geology

• Eon (ancient Greek αἰών "century, epoch" ) - in geology, a time interval of geological history during which the eonotem was formed; combines several eras.
• An era is a section of a geochronological scale, a sub-interval of an eon, for example: Cenozoic (Cenozoic era). Most geological eras are divided into smaller units, called geological periods .
• Epoch - a unit of geochronological scale, part of the geological period, is divided into geological ages. In stratigraphy, it corresponds to the geological department, that is, the geological epoch is the period in the paleontological and geological history of the Earth, during which a layer of rocks forming the corresponding geological department was deposited or formed.
• Период — это участок геохронологической шкалы, подынтервал геологической эры.
• Век — стратиграфическое подразделение, единица общей стратиграфической шкалы, подчинённая геологическому отделу. Подразделяется на стратиграфические зоны. Объединяет толщу горных пород, образовавшуюся в течение одного геологического века и отвечающего определённому этапу геологического развития Земли. Характеризуется типичными для него и только ему свойственными родами, подродами и группами видов.
• Stratigraphy (from Lat. Stratum - flooring, layer, etc.-Greek. Γράφω • - writing, drawing, drawing) - science, section of geology, on determining the relative geological age of sedimentary rocks, the division of strata of rocks and the correlation of various geological formations. One of the main sources of data for stratigraphy is paleontological definitions. In archeology, stratigraphy refers to the mutual disposition of the cultural layers relative to each other and the natural rocks that overlap them. Establishing this location is critical for dating finds ( stratigraphic dating method , planigraphy).

In history

• Epoch (Renaissance, Stagnation Epoch)
• Era
• Period
• Century

In the Internet

• Bit - 1/1000 days, that is, approx. 1 min 26 sec The name comes from the English. beat - beat, beat time and beat; Unit of internet time. - should not be confused with beats (from the English. Bit - bi nary digi t .) [ Source not specified 793 days ]

Metrology

Standards

• State primary standard of units of time, frequency and national time scale GET 1-98 - located at VNIIFTRI
• Standard copy of the state standard of frequency and time of VET 1-5 (Located in Irkutsk in the East Siberian branch of VNIIFTRI)
• The secondary standard of the unit of time and frequency VET 1-10-82 - is in SNIIM (Novosibirsk)
• International standards

Current Time Means (Autonomous)

• Calendar (print edition) (day / one-year reading)
• Clock
• Frequency standard

Time Interlay Playback Tools

• Timer;
• Hourglass;
• Metronome;
• Calibrated delay line;
• Time synthesizer [ source not specified 1517 days ]

Means for measuring time intervals

Various calibrated instruments are used to measure time. They have a means for reproducing time intervals - a stable pulse generator (pendulum, quartz or other generator):

• Stopwatch
• Electronic counting frequency meter with interval measurement unit
• Oscilloscope

Centralized methods for determining the current time

• By telephone using the time service;
• In a television or radio program that transmits audio or visual time signals;
• On the receiver of signals of exact time, using special signals transmitted by special radio stations (for example, such as RWM, DCF77);
• By computer using special network services on the Internet and local networks (for example, such as NTP);
• With the help of technical tools to find out the time through GPS ;

Discoveries and inventions

• OK. 1500 years BC er Invented sundial. Egypt; [38]
• OK. 1500 years. Invented pocket (spring) watch. Peter Henlein, Germany; [38]
• 1656 The pendulum clock is invented. Christiaan Huygens, the Netherlands; [38]
• 1686 "Mathematical Principles of Natural Philosophy" published by I. Newton. They formulated the theory of absolute time of Newtonian mechanics.
• 1865 The second law of thermodynamics was opened by R. Clazius. The presence in nature of the fundamental asymmetry in time of all spontaneous processes occurring in it has been established. [12]
• 1905 The basic provisions of the special theory of relativity are formulated. [39]
• 1916 The basic principles of the general theory of relativity are formulated. [40]
• 1918 It was established that the law of energy conservation is a consequence of the homogeneity of time (Noether theorem) [10] .
• 1927 The quantum-mechanical uncertainty principle for energy and time was formulated [41] .
• 1927 Invented water-proof watch case. Rolex Company, Switzerland; [38]
• 1946 A radiocarbon method for determining the age of fossil remains of organic origin in archeology was developed, Willard Frank Libby, USA. Nobel Prize in Chemistry, 1960. [42]
• 1960 An experiment of Pound and Re *** was carried out to measure the effect of the field of the Earth on the passage of time. [43]
• 1964 The phenomenon of violation of CP-invariance and T-invariance during the decay of the K 0 meson was discovered. 1980 Nobel Prize in Physics. [44]
• 1970 The digital wristwatch is invented. John M. Berger, USA; [38]

see also

• 
  Frequency
• Chronology
• The calendar
• Moment of time
• Time Zones
• Time axis
• Space
• ISO 8601

• Time travel
• Time management

• Coordinated Universal Time
• Greenwich Time
• International Atomic Time
• Own time
• Dynamic time
• Ephemeris time
• Satellite navigation time
• Internet time