| Annu. Rev. Astron. Astrophys. 1991. 29:
325-362
Copyright © 1991 by Annual Reviews. All rights
reserved
|
2.2.3. MONOPOLES
The spontaneous breakdown of symmetry in the GUT scenario causes the
initial larger symmetry group of the unified interactions to decompose
into smaller ones, which include the symmetry group of the
electromagnetic theory. A general theorem tells us that whatever the
initial symmetry group, the process of symmetry breaking inevitably
generates physical solutions that describe magnetic monopoles. The
energy of a monopole is about 1016 GeV, corresponding to a mass of
about 1.8 x 10-8 g. Assuming that no more than one monopole
is created
in one horizon-size sphere, the mass density of monopoles at the GUTs
epoch works out to about 1.7 x 1065 gcm-3.This is
diluted by expansion
through a factor of about 4 x 1026 to a present mass density
of 10-15 g
cm-3 - far in excess of the critical density. With a density of this
order, the universe would have contracted to a = 0 in time less than
105 years! Since monopoles are stable objects, they cannot be
destroyed. Thus the problem of excess monopole density seems
insurmountable within the standard model.