# Absolute zero

## Explanation

Absolute zero is the minimum theoretical temperature at which the entropy of a system reaches its minimum where most of the motion ceases. Or in other words, absolute zero is the lowest scale of temperature (0 K) where the internal energy of any system will be recorded at its minimum. It is impossible for a matter to reach zero energy state due to the quantum fluctuations that can be explained by the Heisenberg’s uncertainty principle. The system would still have zero-point energy. Hence, reaching absolute zero is not possible (Third law of thermodynamics).

### Why can’t we reach absolute zero?

At absolute zero, any system would theoretically have minimum internal energy with the quantum zero-point energy in play, which makes it impossible for such a state to exist. Also, to transfer heat from one system to another, one would need a lower energy system (a heat sink) to transfer to. Such energy states don’t exist, making it impossible for reaching an absolute zero state.

### What is the lowest temperature ever recorded?

As of July 2016, the record for the lowest temperature ever recorded by humans in a laboratory is around 0.45 nK in 2003 at MIT. The lowest naturally recorded temperature on Earth is around 184 K at Antarctica on July 21, 1983.

### How cold is space?

2.7 K, which is the temperature of the cosmic microwave background radiation.

### How zero-point energy affects reaching a zero energy state?

For a system to have zero energy, both its position and momentum will be zero. But uncertainty principle states that if the position of a particle is known accurately, then the momentum of the particle will not be known precisely. So for a system not to violate the uncertainty principle, it always has a minimum amount of energy. This minimum amount of energy is commonly known as the zero-point energy.