The space- time

In physics, space-time is a mathematical representation of space and time as two inseparable notions that influence each other.

This conception of space and time is one of the great upheavals of the early twentieth century in the field of physics, but also for philosophy. It appeared with the special relativity and its geometrical representation that is Minkowski's space; its importance has been reinforced by general relativity
The space-time continuum has four dimensions: three dimensions for space, "x", "y", and "z", and one for time, "t". In order to be able to manipulate them more easily, one arranges so that these four quantities are homogeneous at a distance by multiplying "t" by the constant "c" (celerity of the light in the vacuum).

An event is positioned in time and space by its coordinates "ct", "x", "y", "z", which all depend on the repository. It is very difficult to imagine that time is not the same according to the reference in which it is measured, but it is the case: it is not absolute; the same goes for space: the length of an object can be different depending on the measurement reference.

In the current state of knowledge, only space-time as a unified concept, which is mathematically a Minkowski space in restricted relativity and any curved space in general relativity, is invariant whatever the chosen frame of reference, while its components space and time are aspects that depend on the point of view (referential).

The ratio between the space and time measurements given by the universal constant c makes it possible to describe a distance d in terms of time: d = and with t the time required for light to traverse d. The Sun is about 150 million kilometers, about 8 minutes light from the Earth. By saying "light minutes", we are talking about a measure of time multiplied by c, and we obtain a measure of distance, in this case kilometers. In other words, the factor c is used to convert units of time into units of distance. Kilometers and light minutes are therefore two units of distance measurement.

What unifies space and time in the same equation is that the measurement of time can be transformed into a measure of distance (by multiplying t, expressed in units of time, by c), and thus t can be associated to the other three distance coordinates in an equation where all the measurements are in units of distance. In this sense, we could say that time is space!

However, John Wheeler points out that time and space have great differences of nature, are not completely identifiable, and only partially transform one another in a change of reference.