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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
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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，
The negative momentum is applied to explain negative refraction, inverse Doppler effect and reverse Cherenkov effect observed in a negative index metamaterial. The radiation pressure in the metamaterial is also negative because the force is defined as . Negative pressure exists in dark energy too. Using these above equations, the energy-momentum relation should be
and range is from zero to infinity
Moreover, the kinetic energy is also negative
In fact, the negative kinetic energy exists in some models to describe dark energy (phantom energy) whose pressure is negative. In this way, the negative mass of exotic matter is now associated with negative momentum, negative pressure, negative kinetic energy and FTL (faster-than-light).
If the rest mass is complex this implies that the denominator is complex because the total energy is observable and thus must be real. Therefore, the quantity under the square root must be negative, which can only happen if v is greater than c. As noted by Gregory Benford et al., special relativity implies that tachyons, if they existed, could be used to communicate backwards in time (see tachyonic antitelephone). Because time travel is considered to be non-physical, tachyons are believed by physicists either not to exist, or else to be incapable of interacting with normal matter.
Materials at high pressure
At high pressure, materials such as sodium chloride (NaCl) in the presence of an excess of either chlorine or sodium were transformed into compounds "forbidden" by classical chemistry, such as Na
3Cl and NaCl
3. Quantum mechanical calculations predict the possibility of other compounds, such as NaCl
2 and Na
2Cl. The materials are thermodynamically stable at high pressures. Such compounds may exist in natural environments that exist at high pressure, such as the deep ocean or inside planetary cores. The materials have potentially useful properties. For instance, Na
3Cl is a two-dimensional metal, made of layers of pure sodium and salt that can conduct electricity. The salt layers act as insulators while the sodium layers act as conductors.
- Antimatter – Material composed of antiparticles of the corresponding particles of ordinary matter
- Dark energy – unknown property in cosmology that causes the expansion of the universe to accelerate.
- Dark matter – Hypothetical form of matter comprising most of the matter in the universe
- Gravitational interaction of antimatter – Theory of gravity on antimatter
- Mirror matter – A hypothetical counterpart to ordinary matter
- Negative energy
- Negative mass ��� Concept in physical models
- Strange matter – Degenerate matter made from strange quarks
- QCD matter – Theorized phases of matter whose degrees of freedom include quarks and gluons
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