<P> 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 × 10 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 (10 K) that no current or foreseeable experiment can reach it . </P> <P> Quantum physics formally assumes infinitely positive or negative temperatures in descriptions of spin systems 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 . 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 . </P>

What is the highest possible temperature in celsius