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The proper time interval between two events on a world line is the change in proper time, which is independent of coordinates, and is a Lorentz scalar. [1] The interval is the quantity of interest, since proper time itself is fixed only up to an arbitrary additive constant, namely the setting of the clock at some event along the world line.
A fuller explanation of the concept of coordinate time arises from its relations with proper time and with clock synchronization. Synchronization, along with the related concept of simultaneity, has to receive careful definition in the framework of general relativity theory, because many of the assumptions inherent in classical mechanics and classical accounts of space and time had to be removed.
A definition of a terrestrial time standard was adopted by the International Astronomical Union (IAU) in 1976 at its XVI General Assembly and later named Terrestrial Dynamical Time (TDT). It was the counterpart to Barycentric Dynamical Time (TDB), which was a time standard for Solar system ephemerides, to be based on a dynamical time scale ...
A clock that is stationary with respect to the observer has a world line that is vertical, and the elapsed time measured by the observer is the same as the proper time. For a clock traveling at 0.3 c , the elapsed time measured by the observer is 5.24 meters ( 1.75 × 10 −8 s ), while for a clock traveling at 0.7 c , the elapsed time measured ...
Standard time zones of the world. The number at the bottom of each zone specifies the number of hours to add to UTC to convert it to the local time. As international commerce increased, the need for an international standard of time measurement emerged. Several authors proposed a "universal" or "cosmic" time (see Time zone § Worldwide time zones).
The concept of proper reference frame was later reintroduced and further developed in connection with Fermi–Walker transport in the textbooks by Christian Møller (1952) [7] or Synge (1960). [8] An overview of proper time transformations and alternatives was given by Romain (1963), [9] who cited the contributions
This is an accepted version of this page This is the latest accepted revision, reviewed on 10 January 2025. Primary time standard "UTC" redirects here. For the time zone between UTC−1 and UTC+1, see UTC+00:00. For other uses, see UTC (disambiguation). It has been suggested that UTC offset be merged into this article. (Discuss) Proposed since December 2024. Current time zones Coordinated ...
It is therefore not influenced by the gravitational time dilation caused by the Sun and the rest of the system. TCB is the time coordinate for the Barycentric Celestial Reference System (BCRS). TCB was defined in 1991 by the International Astronomical Union, in Recommendation III of the XXIst General Assembly. [1]