Introduction

Now the special relativity theory (SRT) created by Lorentz [1], Poincare [2], Einstein [3] and Minkovsky [4] (translations of articles [1]... [4] are available in [5]), again occupies among the scientific theories a special position - it became the last scientific theory of space and time recognised by the majority of people. Up to quite a recent time the general theory of relativity (GRT) was considered as last scientific space - time theory. But as A. A. Logunov has shown in the book [6], the special theory of relativity is valid not only for inertial reference frames, but also for non-inertial reference frames. Therefore the expansion of the SRT validity field on non-inertial reference frames has returned the status of the last scientific space - time theory to the special theory of relativity. And this means, that the forefront of examinations purposing further development of our most fundamental notions about space and time has already moved from the general theory of relativity to the special theory of relativity.

The basis of the SRT is formed by the so-called Lorentz transformations

x' =(x - V t) (1 - V²/c_o²)^-1/2, y' = y, z' = z , t' = (t - Vx/c_o²) (1 - V²/c_o²)^-1/2, (I.1)

where x', y', z' and x, y, z are spatial coordinates of the same event in two various inertial reference frames - primed and not primed;  t' and t are time coordinates of the same event in two various inertial reference frames; V is the speed of motion of one inertial reference frame with respect to another one; с_o =   299792458    m/s is the speed of light in vacuum, and all symbols in formula (I.1) represent the so-called physical quantities, each of which is defined by a formula

a = m_a e_a , (I.2)

where a is a physical quantity; e_a is a unit of measurements of the physical quantity a; m_a is a dimensionless number showing how many units e_a should be taken in order to obtain the measured physical quantity a.

So, in any space - time theory the basic notions are:

- "physical quantity";

- "coordinates of an event " - position in space of that point, in which the event occurs;

- "time of an event " - time coordinate of an event;

- "reference frame" - a coordinate system and plurality of clocks being at rest in that coordinate system and being synchronised with each other;

- method of synchronisation of clocks being at rest in some reference frame;

- "transformations" of coordinates and time of an event from one frame of reference to another one.

Among all these concepts the most mysterious is the concept " time of an event ".

In article [[3]. Einstein A. Zur Electrodynamik bewegten Korper // Annalen der Physik. - 1905. - B., 17. - s. 891 – 921] for the concept "time of an event " it is possible to find such definition in German:

"Die "Zeit" eines Ereignisses ist die mit dem Ereignis gleichzeitige Angabe einer am Orte des Ereignisses befindlichen, ruhenden Uhr, welche mit einer bestimmen, ruhenden Uhr, und zwar fur alle Zeitbestimmungen mit der namlichen Uhr, synchron lauft".

 In English this definition will have the following wording:

"The "time" of any event is simultaneous with the event indication of a clock, which is at rest in a place of the event and which goes in synchronism with some particular immovable clock, and with the same clock at all determinations of time ".

The development of fundamental scientific theories, to which number the space - time theory belongs also, occurs by overcoming contradictions appearing owing to change of content of concepts under the influence of practical activity of mankind. The successes of this activity in the field of electronics and mass manufacture of electronic digit-showing clocks at the end of the ХХ century have resulted in understanding that the clock indication simultaneous with any event can not be a physical quantity and represents only a group of numerals.

Really, by photographing a clock indication at any moment of time we can fix on a snapshot only a group of numerals, indicated by a clock. In order to determine the time of an event by means of some clock, we at first will need to transform a group of numerals indicated by a clock into dimensionless number, and then mentally multiply this dimensionless number by duration of a unit of measurement of time in this clock. With the best will in the world it is impossible to fix on a photographic snapshot the duration of a time interval, which is a unit of measurements of time in this clock.

Under the "time of an event", which appears in many equations of physics including Lorentz transformations (I.1) and which is designated more often by symbol t, it was understood from time immemorial the time interval between the time zero moment (for example, birth of Jesus Christ) and the event being under consideration, the time interval equal to a product of dimensionless number by duration of a unit of measurements of time, i. e..

t = m_t e_t , t'  = m_t' e_t' , (I.3)

where m_t , m_t' are dimensionless numbers (indications of clocks); e_t , e_t' are units of time measurements.