Absolute zero is the lowest temperature theoretically possible. At absolute zero atoms have the minimum amount of vibration (i.e., motion) possible. Although this state cannot be achieved physically, the temperature has been extrapolated from experimental data beginning with observations correlating decreasing pressure and temperature in gases. This temperature is -459.69°F, or 0K on the Kelvin scale (-273.16°C, 0°R on the Rakine scale).
Heat is actually the motion of atoms. The hotter something seems to be, the faster its atoms are moving, vibrating back and forth. If the vibrations become frenzied enough, phase transitions can occur, such as when boiling water changes to steam. Conversely, when vibrations slow, cooling takes place, as when water freezes to ice. Just as the velocity of objects can approach but never reach the speed of light, however, neither can atoms be absolutely motionless. At this minimum vibratory motion, no work can be done by the atoms on their surrounding environment. Accordingly, atoms at this minimum vibratory level have zero heat and the temperature measuring this heat is at a minimum on whatever scale is used.
The Heisenberg Uncertainty Principle bars absolute zero from being attained. This inviolable law of quantummechanics states that either the momentum or the position of particles can be known, but never both simultaneously. Once one of these values is established, it becomes impossible to establish the other. Any atom at absolute zero would violate this immutable law, as both its momentum and its position would be known.
Even in the vacuum of deep space, temperatures measure approximately 3K due to background radiation left over from the big bang. Scientists can do better in the laboratory, but even there absolute zero is an unobtainable goal. Scientists can use various methods to slow the motion of atoms and thus cool them to temperatures very near absolute zero. For example, in 1995, Eric Cornell led a group of researchers at the Joint Institute of Laboratory Astrophysics in Boulder, Colorado, in creating a Bose-Einstein condensate, a previously theoretical state of matter existing at a few billionths of a degree above absolute zero. In February, 1999, a group at Harvard University, utilizing a Bose-Einstein condensate and laser cooling techniques, achieved a temperature of 50 billionths of a degree above absolute zero and, in the process, slowed the speed of light from its speed in a vacuum (186,000 miles per second) to an astonishingly low 38 MPH (61.15 km/h).
Although absolute zero remains out of reach, scientists continue to look for new ways to reduce the temperature of atoms. Continuing research into Bose-Einstein condensates as well as other esoteric low-temperature states of matter such as Fermi degenerate gases promises to lead to fresh discoveries whose applications will be as important for industry as for science. The booming field of superconductivity, for example, began with experiments conducted at temperatures near absolute zero, where certain materials acquired the ability to carry an electric charge with no loss of energy.
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