NationMaster - Encyclopedia: Absolute time and space

In physics, the concept of absolute time and absolute space are hypothetical models in which time either runs at the same rate for all the observers in the universe or the rate of time of each observer can be scaled to the "absolute time" by multiplying the rate by a constant. Similarly the notion of absolute space says that space is an inert arena on which other physical phenomena take place. The space affects the other phenomena, but the space itself is not affected by those phenomena. Absolute space underlies the laws of classical physics of Isaac Newton. Newton's absolute space implies that there is one inertial system out of an infinite number that is unique. The first few hydrogen atom electron orbitals shown as cross-sections with color-coded probability density. ... A hypothesis (= assumption in ancient Greek) is a proposed explanation for a phenomenon. ... Classical physics is physics based on principles developed before the rise of quantum theory, usually including the special theory of relativity and general theory of relativity. ... Sir Isaac Newton, FRS (4 January 1643 â€“ 31 March 1727) [OS: 25 December 1642 â€“ 20 March 1727][1] was an English physicist, mathematician, astronomer, alchemist, and natural philosopher, widely regarded as one of the key figures in the history of science. ...

These separate concepts were common in physical theory prior to the advent of special relativity theory, which united the two and showed both to be relativistic. In his theories, the idea of the absolute time and space was superseded by the notion of spacetime in special relativity and especially dynamically curved spacetime in general relativity. The special theory of relativity was proposed in 1905 by Albert Einstein in his article On the Electrodynamics of Moving Bodies. Some three centuries earlier, Galileos principle of relativity had stated that all uniform motion was relative, and that there was no absolute and well-defined state of rest... In physics, spacetime is a mathematical model that combines three-dimensional space and one-dimensional time into a single construct called the space-time continuum, in which time plays the role of the 4th dimension. ... The special theory of relativity was proposed in 1905 by Albert Einstein in his article On the Electrodynamics of Moving Bodies. Some three centuries earlier, Galileos principle of relativity had stated that all uniform motion was relative, and that there was no absolute and well-defined state of rest... General relativity (GR) is the geometrical theory of gravitation published by Albert Einstein in 1915. ...

Absolute simultaneity refers to the hypothetical coincidence of two or more events in different points in space for all observers in the universe. It is shown in the theory of relativity that there may be always observers for whom simultaneity won't correspond to the same moments in time and therefore simultaneity is always relative. The theory of relativity doesn't allow the existence of such time because of non existence of absolute simultaneity. Two-dimensional analogy of space-time distortion described in General Relativity. ... In physics, the term relativity is used in several, related contexts: Galileo first developed the principle of relativity, which is the postulate that the laws of physics are the same for all observers. ... Absolute simultaneity is a hypothetical coincidence of two or more events in different points in space for all observers in the universe. ...

Common moment

Common moment is a hypothetical moment in time that is measured as the same time for two or more events at different points in space by all observers in the universe. It assumes existence of a time that runs at the same rate for all observers in the universe or at least that can be "scaled" to such a common rate, in which this "common moment" can be determined. Such hypothetical time is called absolute time. In cosmology it is usually called "cosmic time". The absolute time is a hypothetical time that either runs at the same rate for all the observers in the universe or the rate of time of each observer can be scaled to the absolute time by multiplying the rate by a constant. ...

According to relativity theory there can't be such time and each observer has its own time running at different rate than the times of at least some other observes in the universe. Therefore, strictly speaking, there are no "common moments" in nature since it is not possible to establish uniquely the simultaneity of two events in two different points in space for some observers. Nature doesn't need "simultaneity" for anything since nature doesn't operate at a distance, but only on contact between interacting agents, so the simultaneity, as not existing in nature, is a human rather than a physical idea, following from imprecise measurements of time. So is the "common moment". Albert Einsteins theory of relativity is a set of two theories in physics: special relativity and general relativity. ...

However the differences between measurements of time may be smaller than the ability to detect them and so we may postulate an "approximate simultaneity" and "approximately common moment" for some practical purposes.

See also