102,854
edits
Changes
From Nordan Symposia
Jump to navigationJump to searchCreated page with 'File:lighterstill.jpg [[Image:Relativity of Simultaneity Animation.gif|right|frame|<center>Events A, B, and C occur in different order depending on the motion of the observer...'
[[File:lighterstill.jpg]] [[Image:Relativity of Simultaneity Animation.gif|right|frame|<center>Events A, B, and C occur in different order depending on the motion of the observer. The white line represents a plane of simultaneity being moved from the past to the future.</center>]]
'''Simultaneity''' is the [[concept]] that simultaneity is not [[absolute]], but dependent on the [[observer]] ([[Frame of reference|reference frame]]). That is, according to the special theory of [[relativity]], it is impossible to say in an absolute sense whether two [[events]] occur at the same [[time]] if those events are separated in [[space]]. Where the event occurs in a single place — for example, in a car crash — all observers whatever their [[velocity]] agree that one car crashed with the other at the same time. But where the events are separated in space, such as one car crashing in [[America]] and another in China, the question of whether such events are simultaneous is [[relative]]; in some reference frames the two accidents happen "at the same time", in others, in a different state of [[motion]], the American crash occurs first, and still others describe the Chinese crash as occurring first.
If we imagine one reference frame assigns precisely the same time to two events that are at different points in space, a reference frame that is moving [[relative]] to the first will generally assign different times to the two [[events]]. This is illustrated in the ladder [[paradox]], a [[thought]] [[experiment]] which uses the example of a ladder moving at high speed through a garage.
A mathematical form of the relativity of simultaneity ("local time") was introduced by [http://en.wikipedia.org/wiki/Hendrik_Lorentz Hendrik Lorentz] in 1892, and physically interpreted (to first order in v/c) as the result of a synchronization using light signals by [http://en.wikipedia.org/wiki/Henri_Poincar%C3%A9 Henri Poincaré] in 1900. However, both Lorentz and Poincaré based their conceptions on the aether as a preferred but undetectable [[frame of reference]], and continued to distinguish between "true time" (in the aether) and "apparent" times for moving observers. It was [[Albert Einstein]] in 1905 who abandoned the ([[classical]]) aether and emphasized the significance of [[relativity]] of simultaneity to our understanding of [[space and time]]. He deduced the failure of [[absolute]] simultaneity from two stated assumptions:
* the principle of [[relativity]]—the equivalence of inertial frames, such that the [[laws]] of [[physics]] apply equally in all inertial coordinate [[systems]];
* the constancy of the [[velocity|speed]] of [[light]] detected in empty [[space]], independent of the relative [[motion]] of its source.[http://en.wikipedia.org/wiki/Relativity_of_simultaneity]
[[Category: Physics]]
'''Simultaneity''' is the [[concept]] that simultaneity is not [[absolute]], but dependent on the [[observer]] ([[Frame of reference|reference frame]]). That is, according to the special theory of [[relativity]], it is impossible to say in an absolute sense whether two [[events]] occur at the same [[time]] if those events are separated in [[space]]. Where the event occurs in a single place — for example, in a car crash — all observers whatever their [[velocity]] agree that one car crashed with the other at the same time. But where the events are separated in space, such as one car crashing in [[America]] and another in China, the question of whether such events are simultaneous is [[relative]]; in some reference frames the two accidents happen "at the same time", in others, in a different state of [[motion]], the American crash occurs first, and still others describe the Chinese crash as occurring first.
If we imagine one reference frame assigns precisely the same time to two events that are at different points in space, a reference frame that is moving [[relative]] to the first will generally assign different times to the two [[events]]. This is illustrated in the ladder [[paradox]], a [[thought]] [[experiment]] which uses the example of a ladder moving at high speed through a garage.
A mathematical form of the relativity of simultaneity ("local time") was introduced by [http://en.wikipedia.org/wiki/Hendrik_Lorentz Hendrik Lorentz] in 1892, and physically interpreted (to first order in v/c) as the result of a synchronization using light signals by [http://en.wikipedia.org/wiki/Henri_Poincar%C3%A9 Henri Poincaré] in 1900. However, both Lorentz and Poincaré based their conceptions on the aether as a preferred but undetectable [[frame of reference]], and continued to distinguish between "true time" (in the aether) and "apparent" times for moving observers. It was [[Albert Einstein]] in 1905 who abandoned the ([[classical]]) aether and emphasized the significance of [[relativity]] of simultaneity to our understanding of [[space and time]]. He deduced the failure of [[absolute]] simultaneity from two stated assumptions:
* the principle of [[relativity]]—the equivalence of inertial frames, such that the [[laws]] of [[physics]] apply equally in all inertial coordinate [[systems]];
* the constancy of the [[velocity|speed]] of [[light]] detected in empty [[space]], independent of the relative [[motion]] of its source.[http://en.wikipedia.org/wiki/Relativity_of_simultaneity]
[[Category: Physics]]
