Absolute Zero

It’s easy to make heat. Humans have been able to capture or create fire since prehistoric times. Producing cold is a much more difficult task. The universe as a whole has done a very good job of it, as the average temperature of the universe is only a few degrees above absolute zero. And it has done so the way that we do it in our refrigerators: through the expansion of gas.

Michael Faraday, who is far better known for his contributions to the study of electricity, was the first to suggest the possibility of producing colder temperatures by harnessing the expansion of a gas. Faraday had produced some liquid chlorine in a sealed tube, and when he broke the tube (and thereby lowered the pressure), the chlorine instantly transformed into a gas. Faraday noted that if lowering the pressure could transform a liquid into a gas, then perhaps applying pressure to a gas could transform it into a liquid—with a colder temperature. That’s basically what happens in your refrigerator; gas is pressurized and allowed to expand, which cools the surrounding material.

Pressurization enabled scientists to liquefy oxygen, hydrogen and, by the beginning of the 20th century, helium. That brought us to within a few degrees of absolute zero. But heat is also motion, and a technique of slowing down atoms by using lasers has enabled us to come within millionths of a degree of absolute zero, which we now know to be slightly more than –459 degrees Fahrenheit. Absolute zero falls in the same category as the speed of light. Material objects can get ever so close, but they can never reach it. Via James D. Stein’s Cosmic Numbers.

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