The concept of absolute zero is well understood, but ‘absolute hot’ is more enigmatic. Heat is a form of energy associated with the motion of the atoms that make up matter. The colder it gets, the less particles move and vibrate, winding down to a virtual standstill at absolute zero, measured at zero Kelvin, or -273 degrees Celsius. At the other end of the scale, conventional physics sets the theoretical maximum temperature at 1.4 x 1032 Kelvin: the Planck temperature, believed to have last occurred a fraction of a second after the Big Bang.
Above this, particles would have so much energy that our current theories could no longer explain their behaviour, meaning that at this time no hotter temperature can be conceived of. But one day a theory of quantum gravitation could allow for even hotter temperatures.