> These are two different fears. Strange matter would not expand at the
> speed of light, but should only convert other nuclei matter it comes into
> direct physical contact with.
The concern about strange matter is overblown. First, if small
nuggets of strange matter are stable (this is doubted), then they
would have a large Coulomb barrier at their surfaces, estimated
to be around 50 MeV. This would prevent ordinary nuclei from
being absorbed and converted into strange quark matter under usual
conditions.
Second, if we could create these nuggets in accelerators, then they
have certainly been created by cosmic ray collisions in the
atmosphere or on meteorites, and so these nuggets would have been
around from before the Earth's formation. Also, stable strange
matter means that neutron stars are actually strange stars, and so
strange star/strange star collisions (as occur when close binary
systems decay by gravitational radiation, as will occur to the binary
pulsar in about 100 Myr) should eject substantial quantities of
strange debris into interstellar space, which should get swept up in
the formation of stars and planets.
The current bet is that strange matter is not stable at zero
pressure, since it's hard to understand how a strange pulsar could
undergo "glitches" (which are thought to be due, in ordinary pulsars,
to phenomena associated with the degenerate normal matter crust,
which would mostly not exist in a completely strange star.)
Paul