eli5: Why is it temperatures can go up to the trillions but only down to -273?

Question

eli5: Why is it temperatures can go up to the trillions but only down to -273?

In: Physics

Answer 1

Temperature is the measure of the *average kinetic energy* of a system. Kinetic energy can always go up, but it can’t go below zero. (The number -273 is just one we picked so zero lines up with where water freezes.)

In other words, it’s how hard you’re going to be hit by random stuff just bouncing around.

Note that *kinetic energy* is not speed. A heavy thing traveling at 60 mph has more kinetic energy than a light thing traveling at the same speed.

Note also that temperature can never be zero, because of quantum effects.