Changes

The 4-space has to be flat in a 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 and with the same magnitudes  as before the transport by [[Noether theorem]]. To keep energy and momentum conserved there can't be any permanent changes in components of those vectors between the ''now'' and the ''past'' or the ''future''.

The 4-space has to be flat in a 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 and with the same magnitudes  as before the transport by [[Noether theorem]]. To keep energy and momentum conserved there can't be any permanent changes in components of those vectors between the ''now'' and the ''past'' or the ''future''.

   

   

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 by requring "gravity to happen in the curved spacetime", while it is not required by any physical or geometrical law as [[Einsteinian gravitation]] might be happening just between particles interacting on a quantum level as described in the [[gravitation demystified]].

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 by requiring "gravity to happen in the curved spacetime", while it is not required by any physical or geometrical law as [[Einsteinian gravitation]] might be happening just between particles interacting on a quantum level as described in the [[gravitation demystified]].

[[Category:Physics]]

[[Category:Physics]]