In physics, exotic matter is matter that somehow deviates from normal matter and has "exotic" properties. A broader definition of exotic matter is any kind of non-baryonic matter—that is not made of baryons, the subatomic particles (such as protons and neutrons) of which ordinary matter is composed. Exotic mass has been considered a colloquial term for matters such as dark matter, negative mass, or complex mass.
There are several proposed types of exotic matter:
- Hypothetical particles and states of matter that have "exotic" physical properties that would violate known laws of physics, such as a particle having a negative mass.
- Hypothetical particles and states of matter that have not yet been encountered, but whose properties would be within the realm of mainstream physics if found to exist.
- Several particles whose existence has been experimentally confirmed that are conjectured to be exotic hadrons and within the Standard Model.
- States of matter that are not commonly encountered, such as Bose–Einstein condensates, fermionic condensates, quantum spin liquid, string-net liquid, supercritical fluid, color-glass condensate, quark–gluon plasma, Rydberg matter, Rydberg polaron and photonic matter but whose properties are entirely within the realm of mainstream physics.
- Forms of matter that are poorly understood, such as dark matter and mirror matter.
- Ordinary matter placed under high pressure, which may result in dramatic changes in its physical or chemical properties.
- Degenerate matter
- Exotic atoms
Negative mass would possess some strange properties, such as accelerating in the direction opposite of applied force. Despite being inconsistent with the expected behavior of "normal" matter, negative mass is mathematically consistent and introduces no violation of conservation of momentum or energy. It is used in certain speculative theories, such as on the construction of artificial wormholes and the Alcubierre drive. The closest known real representative of such exotic matter is the region of pseudo-negative-pressure density produced by the Casimir effect.
According to mass–energy equivalence, mass is in proportion to energy and the coefficient of proportionality is . Actually, is still equivalent to although the coefficient is another constant such as . In this case, it is unnecessary to introduce a negative energy because the mass can be negative although the energy is positive. That is to say,
Under the circumstances，
where is invariant mass and invariant energy equals . The squared mass is still positive and the particle can be stable.