This is about whether it can actually exist (i.e. is obtainable) in the real universe we are in, not whether it could exist in some other universe that follows most of the same laws. Resolves YES if it's proven that we can create it, or perhaps that it exists as a leftover from the big bang. Resolves NO once we have a theory of everything that says it can't exist. If it can technically be created but decays on the order of a Planck time, I'll also count that as a NO.

Possible clarification from creator (AI generated): Either negative gravitational mass or negative inertial mass would be sufficient for a YES resolution.