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Hello, the coldest natural temperature ever known on Earth was recorded 30 years ago at a Soviet

research base in the Antarctic. At a quarter to three in the morning, the thermometer

registered minus 89.2 degrees Celsius. Beyond our

atmosphere it can be dramatically colder even than this. Astronomers believe

that interstellar space is a temperature of around minus 270 degrees but the

coldest temperatures yet known colder even than space have been created artificially in

the laboratory scientists have been creeping ever

closest to the lowest possible temperature known as

absolute zero. The idea that temperature had a lower limit was first

suggested in the 17th century. The race for ever colder temperatures began 200 years later and has

resulted in some of the strangest most important and useful discoveries of

modern science. But although physicists can get within a

billions of a degree of absolute zero, they'll never quite get there. Why not?

And why does temperature have a minimum? With me to discuss

Absolute Zero are Simon Schaefer, Professor of the History of Science at the University of Cambridge, Stephen Blundell, Professor of Physics at the University of Oxford, and Nicola Wilkin, Lecturer in Theoretical physics at the University of Birmingham.

Simon Schaefer. Let's start with the idea of temperature. What did early scientists

think temperature was and how did they investigate it? Are we going back to the Greeks?

We might want to go back to the Greeks.

They were certainly fascinated by problems of heat and cold.

They lived in a culture in which all energy sources were either human mechanical or thermal,

...