Absolute hot is a concept of temperature that postulates the existence of a highest attainable temperature of matter. The idea has been popularized by the television series Nova.[1][2] 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 minimized and classical thermal energy is zero.
Current cosmological models posit that the highest possible temperature is the Planck temperature, which has the value 1.416785(71)×1032 kelvin.[3] The Planck temperature is assumed to be the highest temperature in conventional physics because conventional physics breaks down at that temperature. Above ~1032K, particle energies become so large that the gravitational forces between them become as strong as any other force and are identical in the Grand Unified Theory.
Some forms of string theory allow a temperature of 1030K, known as Hagedorn temperature.[2] Instead of temperature rising, at 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.
Quantum physics formally assumes infinitely positive or negative temperatures in descriptions of spin system undergoing population inversion from the ground state to a higher energy state by excitation with electromagnetic radiation. The temperature function in these systems exhibits a singularity, meaning the temperature tends to positive infinity, before discontinuously switching to negative infinity.[4] However, this applies only to specific degrees of freedom in the system, while others would have normal temperature dependency. If equipartitioning were possible, such formalisms ignore the fact that the spin system would be destroyed by the decomposition of ordinary matter before infinite temperature could be reached uniformly in the sample.