Absolute Zero
How Low Can You Go?
Launch interactive

How Low Can You Go?

Pioneers in the quest to reach absolute zero relied on a technique known as the "cascade" process. First, they put a gas in a sealed container under high pressure, then cooled the compressed gas by immersing the container in a coolant such as dry ice. For certain gases, this turned the gas into a liquid. In the next step, they released the pressure on the cold liquid, usually through a valve into another container. As it partially evaporated, it grew even colder than the initial coolant. This new gas was then used to cool another, different compressed gas, which, upon partial evaporation, achieved an even lower temperature. By repeating this sequence, scientists approached ever closer to absolute zero. In this interactive, undertake your own three-step cascade and see if you can choose the right combination of gases to liquefy oxygen.—Richard Pommier Swanson

Richard Pommier Swanson is the former Science Content Director for PBS's DragonflyTV. He holds degrees in Education and the History of Science and Technology from the University of Minnesota.

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© | Created January 2008