Does time stop at Absolute Zero?

The short answer is not really.

Absolute Zero is an 'asympotic' state which you can only get close to but never reach. In fact there are quantum mechanical phenomena that intervene that probably prevent you from actually reaching it because the physical vacuum itself even at 'Absolute Zero' contains energy that interferes with any physical system in space. Einstein-Bose Condensates are a good example of what happens when you try to cool a small collection of atoms to very cold temperatures. Their wave functions spread out and you end up with an indivisible 'super particle' rather than a collection of even more frigid discrete particles.

among the coldest naturally-occurring things in nature is the cosmic fireball radiation which fills all space in the universe and has a temperature of 2.7 degrees above absolute zero. Above you see in the image of this radiation across the sky, created by NASA's COBE spacecraft, how this very cold light still has faint irregularities in it from the vast collections of matter that it has passed throug to get to us.

Another very cold place in our local universe is called the Boomerang Nebula shown below, whose dark core has a temperature of only 1 degree above absolute zero.

We define time in terms of clocks which are collections of matter that change their states. At Absolute Zero, there would be no thermal energy to keep such collections moving, but that doesn't mean that very large collections of matter would not move. Temperature is only defined for collections of 'small' things such as atoms...or quanta of energy like photons. Planets would still orbit stars and spin on their axis so a physical clock would still exist, and therefore we would still have 'time'.

Return to Dr. Odenwald's FAQ page at the Astronomy Cafe Blog.