Exotic matter

In physics, exotic matter is matter that somehow deviates from normal matter and has "exotic" properties. A more broad 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 types of exotic matter:

Negative mass would possess some strange properties, such as accelerating in the direction opposite of applied force. For example, an object with negative inertial mass and positive electric charge would accelerate away from objects with negative charge, and towards objects with positive charge, the opposite of the normal rule that like charges repel and opposite charges attract. This behaviour can produce bizarre results: for instance, a gas containing a mixture of positive and negative matter particles will have the positive matter portion increase in temperature without bound. However, the negative matter portion gains negative temperature at the same rate, again balancing out.

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 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 ${\displaystyle m}$ is in proportion to energy ${\displaystyle E}$ and the coefficient of proportionality is ${\displaystyle c^{2}}$. Actually, ${\displaystyle m}$ is still equivalent to ${\displaystyle E}$ although the coefficient is another constant such as ${\displaystyle -c^{2}}$. 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,

...
Wikipedia