About 5, light-years away, this star system is just 1 kelvin above absolute zero. To sneak up on absolute zero, scientists have used vacuums and lasers in elaborate experiments to cool atoms of a gas.
A vacuum can cool a gas without condensing it into a liquid or solid — as would normally happen — but its atoms still move. When an atom absorbs a light particle, or photon, from a laser, it emits another photon. When physicists tune the lasers in just the right way, an atom traveling in one direction absorbs one photon and then emits another in a different direction and at a higher energy. The atom will then slow down, photon by photon. By catching an atom in the crosshairs of multiple lasers, researchers can decrease its momentum from every direction.
This technique, first used in the s, is called laser cooling. By combining lasers and evaporative cooling in new ways, scientists have chilled gases to about 50 trillionths above 0 kelvin.
In , scientists employ it to chill a salt to 0. The experiment suggests a way to see quantum effects, like a single object coexisting in two places at once. Register or Log In. The Magazine Shop. Login Register Stay Curious Subscribe.
The Sciences. Bose-Einstein Condensate BEC , a fifth state of matter, consists of atoms so cold, they condense into a quantum state, acting as one. On the Kelvin scale, 0 Kelvin is the temperature of absolute zero. Absolute zero is the temperature in a system where all particles stop moving ignoring some important quantum mechanics. A degree Kelvin and a degree Celsius are the same unit , as they have the same "spacing" between each degree, but the scales have different zero points see converter below.
Kelvin is usually avoided for everyday use, instead it is always used for temperatures in physics and also often in chemistry , in equations such as the ideal gas law. If a gas had a temperature of Temperature is a measure of the kinetic energy of molecules in a system, and using Kelvin units are essential to explaining this concept clearly. Temperature can be related to energy through a value known as the Boltzmann constant.
By Hazel Muir. The Boomerang Nebula is the coldest natural object known in the universe, seen here by the Hubble Space Telescope. The curious things that happen at low temperatures keep on throwing up surprises. Last week, scientists reported that molecules in an ultra-cold gas can chemically react at distances up to times greater than they can at room temperature. In experiments closer to room temperature, chemical reactions tend to slow down as the temperature decreases.
Practically, the work needed to remove heat from a gas increases the colder you get, and an infinite amount of work would be needed to cool something to absolute zero.
If you know your atoms are inside your experiment, there must be some uncertainty in their momentum keeping them above absolute zero — unless your experiment is the size of the whole universe.
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