  It is shown that in the presence of virtual wormholes, the vacuum is
unstable, which leads to a series of phase transitions in the early Universe.
Then the standard Kibble scenario predicts the formation of defects such as
domain walls. An unusual feature of virtual wormholes is that they generate
defects with negative energy density. Such defects have macroscopic dimensions
and can support the necks of already real primary wormholes, which gives reason
to consider relic wormholes as realistic astrophysical objects.
