Absolute zero is 0 degrees Kelvin or -460 degrees Fahrenheit and where molecular motion stops. It’s one end of the spectrum for measuring heat. So what’s on the high end? What is the ‘hottest’ measurable temperature on the opposite end of the spectrum from Absolute Zero?
The answer is the ‘Planck Temperature‘ or 10^32 degrees Kelvin, or at least in theory that’s the answer.
Scientists believe that the universe experienced the Planck temperature approximately 10^-43 of a second after the Big Bang, and the universe has been cooling off ever since.
As molecules speed up they increase in temperature. As that temp reaches 10^10 Kelvin, the electrons in that matter are now approaching the speed of light and they are increasing in size so that their temperature can continue to increase.
At 10^32 K, each particle is becoming its own black hole and at this point our understanding of space and time collapse and the temperature likely isn’t observable so this is why scientists call Planck’s Temperature the theoretical highest temperature possible.