Ross Edmunds, age 14, of Peterboro, Ontario, Canada, for his question:
How do laboratory experiments reach absolute zero?
There seems to be no limit as to how hot a substance can get. But no solid, liquid or gas can get any colder than absolute zero. This temperature of absolute heatlessness was figured out in theory. But reducing a substance to this colder than cold temperature is very difficult.
A generation of scientists have been trying to reduce a substance to absolute zero but so far the exact degree has not been reached. Several methods have been tried to re¬move the last vestige of warmth from solids, liquids and gases. Each experiment leads the way to a better one. And lately, as researchers get closer, they have been discovering many new facts about substances that become colder than cold. For example, at normal temperatures certain substances are good conductors, others are poor conductors of electricity. At temperatures approaching absolute zero, all substances become good con¬ductors.
The most successful method so far tested can reduce a substance to 'a tiny faction of one degree from the goal. The substance used is copper atoms, or rather the nuclei of copper atoms with their orbiting electrons stripped away. These copper ions are chilled and placed in a strong magnetic field. They become magnetized at a low temperature and then the electromagnet generating the field is switched off. This causes the copper nuclei to become demagnetized.
When the magnetic energy is removed, the copper nuclei lose still more of their re¬maining heat. The best experiments so far have reduced the copper substances to within mil¬lionths of a degree of minus 273.15 degrees Centigrade. This chilling figure is the total heatlessness of absolute zero. On the Fahrenheit scale it equals minus 459.67 degrees. Theoretically, scientists know that any solid, liquid, or gaseous substance loses its last smidgeon of heat at absolute zero. It can get no colder.
Somewhere, perhaps out in the cosmos, there are substances with temperatures of ab¬solute zero and someday researchers in an earth laboratory may chill a substance right down to the coldest possible degree. Heat, of course, is the energy of moving molecules. As a substance cools, it loses this energy and its molecules move more slowly. But even the molecules in a frigid chunk of ice have enough heat energy to shiver and shake. At minus 273.15 degrees Centigrade, there would be no vestige of heat and the molecules in any substance would, in theory, become absolutely motionless.
Scientists figured out the theory of absolute zero by observing the behavior of cooling gases. A gas shrinks or loses volume as it chills, and it does so at a set ratio. When a gas cools from 0 degrees to minus 1 degree Centigrade, it loses one.. in 273 parts of its volume. As it grows hotter its molecules use heat to speed up and the gas expands. But as it chills, the molecules slow down and contract. In theory the last bit of heat and motion depart when the molecules are chilled about 273 Centigrade degrees below the freezing point of water.