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Absolute zero is the lowest possible temperature where all atomic motion ceases. To reach true absolute zero, all internal components of an atom must stop, which is impossible due to quantum mechanics. Temperatures close to absolute zero have been reached using laser cooling and magnetic evaporative cooling, forming Bose-Einstein condensates.
The lowest possible temperature, or absolute zero as it is called, is -459.67°F (-273.15°C). It’s also called 0 kelvin, a scale with increments equivalent to degrees Celsius, but using absolute zero rather than the freezing point of water as a starting point. This is the point where all atomic motion ceases.
The above definition may be incomplete, however, as an atom is itself an entity with a complex internal structure. To reach the lowest possible temperature, or true absolute zero, not only must the atomic motion stop, but all the internal components of the atom must also stop. The electrons should stop orbiting their respective atomic nuclei, the neutrons and protons in the nuclei should stop dragging each other by their internal forces, the quarks and any underlying substructures should cease all activity. Due to the effects of quantum mechanics, this is impossible. Therefore, a more precise definition applies to collections of matter from which no further thermal energy can be extracted, i.e. another collection of atoms brought into contact with the sample will always transfer energy to it, never the other way around.
Like the efficiency of a system, the speed of a particle, or the maximum possible temperature, absolute zero is actually a theoretical quantity that can only be approached, but probably never reached.
Temperatures close to absolute zero have been reached with the techniques of laser cooling and magnetic evaporative cooling. In laser cooling, fast-moving atoms are propelled by photons until they slow down to 1/10,000th of a degree kelvin. In magnetic evaporative cooling, the remaining atoms are held loosely in place by a magnetic field, and the more energetic atoms eventually escape, leaving the slower remnants behind. Using these techniques, temperatures of up to 250 picokelvins (pK) have been achieved. Matter this cold can behave in bizarre ways, forming structures called Bose-Einstein condensates, which demonstrate a property called superfluidity, or the flow of atoms without viscosity.
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