Absolute zero is the theoretical temperature at which entropy is at minimum. It is a physical limit to the lowest possible temperature. When a system reached absolute zero, pressure, volume and internal pressure also become zero. At this temperature, the energy of the matter involved is at the minimum, though it is not correct to say that energy is also zero.

Laws of quantum mechanics points out that even at absolute zero, atoms will still possess energy called the quantum mechanical zero-point energy. Atomic motion also won’t cease at absolute zero. Thus, it is not correct to say the energy is zero at absolute zero. Energy is just at minimum.

By international convention, absolute zero is defined to be at 0 K. This converts to -273.15°C or -459.67°F. In industrial jargon, absolute zero is at 0 R (Rankine). The third law of thermodynamics states that this temperature is not achievable, as it would contradict all other established physical laws if absolute zero is achievable. However, scientists were able to cool down matter up to a few nano kelvins, or a billionth of a Kelvin. At this temperature, matter begins to show quantum effects like super fluidity and superconductivity. The Bose-Einstein Condensate (BEC), the fifth state of matter, is achievable at temperatures very near absolute zero.