Absolute hot
Absolute hot is a concept of temperature that postulates the existence of a highest attainable temperature of matter. The concept has been popularized by the television series Nova. In this presentation, absolute hot is assumed to be the high end of a temperature scale starting at absolute zero, which is the temperature at which entropy is minimal and classical thermal energy is zero.
Contemporary models of physical cosmology postulate that the highest possible temperature is the Planck temperature, which has the value 1.416785(71)×1032 kelvins, or 142 quintillion kelvins (142 nonillion on the short scale). Above about 1032K, particle energies become so large that gravitational forces between them would become as strong as other fundamental forces according to current theories. There is no existing scientific theory for the behavior of matter at these energies. A quantum theory of gravity would be required. The models of the origin of the universe based on the Big Bang theory assume that the universe passed through this temperature about 10−42 seconds after the Big Bang as a result of enormous entropy expansion.
Another theory of absolute hot is based on the Hagedorn temperature, where the thermal energies of the particles exceed the mass-energy of a hadron particle-antiparticle pair. Instead of temperature rising, at the Hagedorn temperature more and heavier particles are produced by pair production, thus preventing effective further heating, given that only hadrons are produced. However, further heating is possible (with pressure) if the matter undergoes a phase change into a quark–gluon plasma. Therefore, this temperature is more akin to a boiling point rather than an insurmountable barrier. For hadrons, the Hagedorn temperature is 2 × 1012 K, which has been reached and exceeded in LHC and RHIC experiments. However, in string theory, a separate Hagedorn temperature can be defined, where strings similarly provide the extra degrees of freedom. However, it is so high (1030 K) that no current or foreseeable experiment can reach it.
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