From Nightbat, quoting Paul Stowe,
quoting "Curious"
:

..our naive research indicates that a
relativistic medium that fits the
experimental evidence leading to the
Standard Model can really only work
properly via a modified Dirac Sea which
is really a concept of dual space-time.
The duality concept in physics is very
important; why not dual space-times?

Dual spacetimes, huh? That would certainly fit with having the Planck
length as the demarkation line, or baseline. Dirac's 'negative energy'
would describe the sub-Planck domain on the 'other side', while our
reality on 'this side' comprizes the 'positive'.
99.99999% of reality (give or take a few decimal
places) resides on the 'other side', with an infinitessimal amount
appearing on 'this side' as the proverbial dust bunny, i.e., the
material universe and its thermodynamics. oc