Definitions for four-velocity
four-ve·loc·i·ty

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1. four-velocitynoun

   A generalization of velocity in four-dimensional spacetime

WikipediaRate this definition:0.0 / 0 votes

1. Four-velocity

   In physics, in particular in special relativity and general relativity, a four-velocity is a four-vector in four-dimensional spacetime that represents the relativistic counterpart of velocity, which is a three-dimensional vector in space. Physical events correspond to mathematical points in time and space, the set of all of them together forming a mathematical model of physical four-dimensional spacetime. The history of an object traces a curve in spacetime, called its world line. If the object has mass, so that its speed is necessarily less than the speed of light, the world line may be parametrized by the proper time of the object. The four-velocity is the rate of change of four-position with respect to the proper time along the curve. The velocity, in contrast, is the rate of change of the position in (three-dimensional) space of the object, as seen by an observer, with respect to the observer's time. The value of the magnitude of an object's four-velocity, i.e. the quantity obtained by applying the metric tensor g to the four-velocity U, that is ||U||2 = U ⋅ U = gμνUνUμ, is always equal to ±c2, where c is the speed of light. Whether the plus or minus sign applies depends on the choice of metric signature. For an object at rest its four-velocity is parallel to the direction of the time coordinate with U0 = c. A four-velocity is thus the normalized future-directed timelike tangent vector to a world line, and is a contravariant vector. Though it is a vector, addition of two four-velocities does not yield a four-velocity: the space of four-velocities is not itself a vector space.

WikidataRate this definition:0.0 / 0 votes

1. Four-velocity

   In physics, in particular in special relativity and general relativity, the four-velocity of an object is a four-vector that replaces classical velocity. It is chosen in such a way that the velocity of light is a constant as measured in every inertial reference frame. In relativity theory, events are described in time and space, together forming four-dimensional spacetime. The history of an object traces a curve in spacetime, parametrized by a curve parameter, the proper time of the object. This curve is called its world line. The four-velocity is the rate of change of both time and space coordinates with respect to the proper time of the object. The four-velocity is a tangent vector to the world line. For comparison: in classical mechanics events are described by their position at each moment in time. The path of an object is a curve in three-dimensional space, parametrized by the time. The classical velocity is the rate of change of the space coordinates of the object with respect to the time. The classical velocity of an object is a tangent vector to its path. The magnitude of an object's four-velocity is always equal to c. Only its direction can change. For an object at rest its four-velocity points in the direction of the time coordinate.

How to pronounce four-velocity?

1. Alex

   US English

   David

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   Mark

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   Daniel

   British

   Libby

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   Australian

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How to say four-velocity in sign language?

Numerology

1. Chaldean Numerology

   The numerical value of four-velocity in Chaldean Numerology is: 8

2. Pythagorean Numerology

   The numerical value of four-velocity in Pythagorean Numerology is: 9

References

1. ^ Wiktionary
   https://en.wiktionary.org/wiki/Four-Velocity
2. ^ Wikipedia
   https://en.wikipedia.org/wiki/Four-Velocity
3. ^ Wikidata
   https://www.wikidata.org/w/index.php?search=four-velocity