Zero Kelvin is not attainable by a physical system.

Why is absolute zero (0 kelvin or −273.15°C) an impossible goal?

 

Practically, the work needed to remove heat from a gas increases the colder you get, and an infinite amount of work would be needed to cool something to absolute zero. In quantum terms, you can blame Heisenberg’s uncertainty principle, which says the more precisely we know a particle’s speed, the less we know about its position, and vice versa. If you know your atoms are inside your experiment, there must be some uncertainty in their momentum keeping them above absolute zero – unless your experiment is the size of the whole universe.

Let us not quibble about this, let us suppose a crystal very close to absolute zero in a thermally isolated box with. It has its lowest possible entropy.

To break the lattice energy must be supplied. Suppose an equally cold stone detaches itself from the roof (gravity supplying the energy) and falls on the crystal. The system is now broken crystal, fallen stone and the kinetic energy has increased or statistically the number of microstates is orders of magnitude than it was at t=0, i.e. the entropy has been increased.

There is no way the crystal pieces can be connected again without energy being supplied, which will introduce more microstates. To get back to the original entropy of the crystal energy has to be supplied outside the system, to cool it.

So the broken pieces can be back together again in an open system, where one has to count the total and entropy will be increasing.

Zero Kelvin is not attainable by a physical system.

Why is absolute zero (0 kelvin or −273.15°C) an impossible goal?

Practically, the work needed to remove heat from a gas increases the colder you get, and an infinite amount of work would be needed to cool something to absolute zero. In quantum terms, you can blame Heisenberg’s uncertainty principle, which says the more precisely we know a particle’s speed, the less we know about its position, and vice versa. If you know your atoms are inside your experiment, there must be some uncertainty in their momentum keeping them above absolute zero – unless your experiment is the size of the whole universe.

Let us not quibble about this, let us suppose a crystal very close to absolute zero in a thermally isolated box with. It has its lowest possible entropy.

To break the lattice energy must be supplied. Suppose an equally cold stone detaches itself from the roof (gravity supplying the energy) and falls on the crystal. The system is now broken crystal, fallen stone and the kinetic energy has increased or statistically the number of microstates is orders of magnitude than it was at t=0, i.e. the entropy has been increased.

There is no way the crystal pieces can be connected again without energy being supplied, which will introduce more microstates. To get back to the original entropy of the crystal energy has to be supplied outside the system, to cool it.

So the broken pieces can be back together again in an open system, where one has to count the total and entropy will be increasing.