The specific type of exotic matter would be imaginary matter, that is matter with imaginary mass (a complex number) - tachyons. Negative matter, which is also e

The specific type of exotic matter would be imaginary matter, that is matter with imaginary mass (a complex number) - tachyons. Negative matter, which is also exotic but has a negative real mass, behaves normally under gravity so long as the two bodies are sufficiently different in absolute mass.