We all know about absolute zero, right? You know, the theoretical lowest limit of temperature?
Because of course temperature is really just a measure of the energy of atoms and molecules randomly jiggling around. So absolute zero is when they’ve stopped jiggling and are completely motionless. And since you can’t move slower than stopped, you can’t get lower than absolute zero.
But what about the other direction? Is there a maximum temperature to the universe? An absolute hotness, if you will (and I will)?
Theoretically, yes there is. This mightn’t seem possible, as you’d think the jiggling energy could just keep increasing forever. But as energy increases, it affects the way the fundamental forces of the universe behave.
In particular, there’s an energy at which gravity becomes a purely quantum force. And because gravity is intimately connected with the structure of space-time, the laws of physics as we know them break down and reality itself turns into a sort of quantum foam.
This energy – or the temperature it corresponds to – is known as the Planck temperature, and it’s the theoretical maximum temperature of the universe.
And it’s pretty hot. Roughly about 1.4×1032 Kelvin, or if you prefer, 140 nonillion Kelvin. If you prefer your temperatures in Celsius, it’s still about 1.4×1032 °C (at that level they may as well be the same).
Of course, once we truly understand the quantum nature of gravity, we might find it’s possible to go beyond this temperature. Or it could be that the maximum is at a different level entirely – for more on these possibilities, see the PBS Nova column on Absolute Hot.
And for some more milestones on the temperature scale, click through after the jump.