"Elio Fabri" ha scritto:
....
> A quale teorema alludi?
> Ha a che fare con la necessita' per un campo vettoriale di avere punti
> critici su una superficie omeomorfa a una sfera?
Si'.
Puff Puff! (ho appena trasportato il MTW Gravitation :-)
Cito letteralmente dal libro (p. 978):
"this theorem is the "topological fixed-point theorem" [e.g.,
Lifshitz (1949)]"...
"there is no way to lay down on the surface of a two-sphere a
continuous vector field, the magnitude of which is non-zero and
everywhere the same ("no way to comb smooth the hair on the
surface of a billiard ball").
Likewise, there is no way to lay down on the surface of a two-sphere
a continuous non-zero transverse-traceless 2 x 2 matrix field
that differs from one point to another at most by a rotation.
Topology thus excludes the possibility of any spherically symmetric
source of gravitational radiation whatsoever."
A proposito di stile, ricordo anche la celeberrima frase, sempre
su MTW: "a black hole has no hair".
Ciao
--
Giorgio Bibbiani
Received on Sat Aug 13 2005 - 08:56:29 CEST