# What is Absolute Zero

The lowest temperature – at least theoretically – is -273.15 degrees Celsius (-459.67 degrees Fahrenheit), or o degrees Kelvin. The latter is the SI unit of temperature named after Lord Kelvin, who devised his scale based on the laws of thermodynamics in 1848. At this point no more heat can be removed from a system as it has reached a stage of absolute cold.

The more heat an object has, the more its atoms move around and vice versa. As the temperature approaches absolute zero, atoms move very slowly and, in theory, at o degrees Kelvin there should be no movement, although according to experimental evidence there is some minimal vibrational motion.

The lowest temperature achieved by man was in a Massachusetts Institute of Technology (MIT) lab in 2003, where a cloud of sodium atoms was cooled to 0.45 nanokelvin, or less than half one-billionth of a degree Kelvin above absolute zero. The reason why it’s so difficult to achieve this temperature is because it requires an exponential amount of energy to continually lower the temperature to extreme cold – to the point that it needs an infinite amount of energy to reach absolute zero. Nevertheless, scientists are continually striving to find more efficient ways of achieving super-low temperatures because the strange effect they have on molecules can be extremely useful.

## Superconductivity

One of the main benefits of lowering the temperature of an object is that, with less atomic vibration being caused, there’s less electrical resistance. Why is this significant? All electrical systems experience a degree of energy loss to resistance – that’s why copper wiring is commonly used to transfer energy from the power station to our homes. It offers less resistance than other materials and is relatively cheap (gold is a more effective conductor, but far more expensive). Generally, resistance is in reverse proportion to efficiency, so the less resistance, the greater the efficiency of the system to the point that 100 per cent of the energy put in is available at the other end if there is zero resistance. Practical superconductivity is obviously of use within the energy industry for these reasons, however its properties have applications in dozens of other fields too, including medicine, transport and astronomy.

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Absolute Zero May Not Be Coldest Temperature

Have physicists ventured below absolute zero?