Difference between revisions of "Curvatures of spacetime"
m |
m |
||
| Line 1: | Line 1: | ||
'''Curvatures of spacetime''' is a set of 16 various curvatures that may be specified as components of a curvature tensor that describes the [[curvature of spacetime]] (the same thing as [[curvature of 4-space]]). | '''Curvatures of spacetime''' is a set of 16 various curvatures that may be specified as components of a curvature tensor that describes the [[curvature of spacetime]] (the same thing as [[curvature of 4-space]]). | ||
| − | [[Curvature of spacetime]] is something that describes a fact that some 4-dimensional space is curved | + | [[Curvature of spacetime]] is something that describes a fact that some 4-dimensional space is curved. It can't happen in a stationary universe since its [[spacetime]] has to be flat (or [[Minkowski]], which is another word for the same thing). In particular it may describe also the curvature of the common 3-dimenssional space (given by x,y,z vectors) being a part of this 4-dimensional spacetime (in this case given by t,x,y,z 4-vectors), which is a chance for messing things in astronomy when one says "[[curvature of space]]" but means the "[[curvature of spacetime]]" (that is then called simply [[curvature of 4-space]]) that has to be flat in stationary universe though having its non zero '''curvatures of spacetime''' adding to the flatness of whole [[spacetime]]. |
| − | The 4-space has to be flat since parallel transport of 4-vectors along | + | The 4-space has to be flat in stationary universe since parallel transport of 4-vectors along geodesic lines can't change the angles of those vectors for the reason of conservation of energy and momentum (the 4-vectors have to come back after the parallel transport being directd in the same direction as before the transport (by [[Noether theorem]]). |
That's why it is often important to be aware of various subtleties of names used in physics not to violate suddenly the conservation of energy and/or momentum, since so far the nature does not know how to make energy or momentum from nothing. | That's why it is often important to be aware of various subtleties of names used in physics not to violate suddenly the conservation of energy and/or momentum, since so far the nature does not know how to make energy or momentum from nothing. | ||
[[Category: Physics]] | [[Category: Physics]] | ||
Revision as of 17:17, August 16, 2011
Curvatures of spacetime is a set of 16 various curvatures that may be specified as components of a curvature tensor that describes the curvature of spacetime (the same thing as curvature of 4-space).
Curvature of spacetime is something that describes a fact that some 4-dimensional space is curved. It can't happen in a stationary universe since its spacetime has to be flat (or Minkowski, which is another word for the same thing). In particular it may describe also the curvature of the common 3-dimenssional space (given by x,y,z vectors) being a part of this 4-dimensional spacetime (in this case given by t,x,y,z 4-vectors), which is a chance for messing things in astronomy when one says "curvature of space" but means the "curvature of spacetime" (that is then called simply curvature of 4-space) that has to be flat in stationary universe though having its non zero curvatures of spacetime adding to the flatness of whole spacetime.
The 4-space has to be flat in stationary universe since parallel transport of 4-vectors along geodesic lines can't change the angles of those vectors for the reason of conservation of energy and momentum (the 4-vectors have to come back after the parallel transport being directd in the same direction as before the transport (by Noether theorem).
That's why it is often important to be aware of various subtleties of names used in physics not to violate suddenly the conservation of energy and/or momentum, since so far the nature does not know how to make energy or momentum from nothing.