Absolute Zero and the Conquest of Cold  




Topic 6: The Quest for Absolute Zero

In 1703, Guillaume Amontons deduced there was a limit to how cold any object could get, simply because there was a limit to how much heat could be taken out. Amontons didn't know exactly why -- since nobody understood at the time exactly what made heat. Today we know that heat is caused by movement of atoms inside a material. Faster atoms mean hotter matter; slower atoms mean colder matter. The coldest anything can be, therefore, is the point at which all atoms stop moving. That point is known as "absolute zero" and it corresponds to -459.67 F and -273.15 C.

In reality, atoms never stop moving completely, so it is impossible for any object to ever truly be as cold as absolute zero -- but that hasn't stopped scientists from trying to get very close. In the early days of studying refrigeration in the 1800s, researchers discovered that by liquefying gases like hydrogen, helium, and oxygen, they could achieve extremely cold temperatures. By 1908, they had reached 5 degrees above absolute zero.

In the early 1920s Satyendra Nath Bose was researching a new theory that people were just beginning to study, called quantum mechanics. Quantum mechanics stated that light came in little discrete packets that we now call photons. Bose assumed certain rules for deciding when two photons could be considered as either identical or different, but he had trouble getting his ideas published, until he got a little help from a friend – Albert Einstein. With Einstein’s help the ideas finally saw print.

From L-Rr: Emergence of vortex structure in a rotating Bose-Einstein condensate; Decay of a soliton in a Bose-Einstein condensate; Twelve-vortex array in a rotating Bose-Einstein condensate.

Later Einstein applied these same rules to atoms. His math showed that if the atoms were cold enough, something very unusual should happen. Normally atoms move independently of each other, like a crowd of people wandering around on the streets, but Einstein realized that if atoms got cold enough, they would lock up like a marching band in a parade, and begin to move in perfect synch. This group of atoms was named a Bose-Einstein condensate, but in Einstein’s day the temperatures needed to see a condensate were far colder than anyone had ever been able to reach. Now physicists who studied the cold had a new goal -- to get atoms cold enough to create a Bose-Einstein condensate.

It wasn't easy. Simple refrigeration techniques weren't enough. Instead, researchers learned how to slow atoms down using lasers. Remember an atom is "cold" when it's as still as it can be, so if you can hold an atom still you've made it extremely cold. In 1995 three scientists, Carl Wieman, Eric Cornell and Wolfgang Ketterle, all managed to slow down enough atoms and make them cold enough -- at 170‑billionths of a degree above absolute zero -- to create a Bose-Einstein condensate. The condensate behaved as Bose and Einstein predicted: all the atoms joined up into a single superatom and moved as a unit.

From L-R: Cover illustration for Optics & Photonics News, December 2000; Color illustration for Nature, 18 March 1999; Cover illustration for Physics Today, December 1999.

Making Bose-Einstein condensates turned out to be more interesting than simply seeing a new phase of matter for the first time. It has opened up the door to studying the way particles behave in all kinds of situations, including how cold materials have the ability to transmit current so much better than normal metals do. In addition, some researchers have hope that one day, people might be able to use Bose-Einstein condensates to build tiny structures, atom by atom. The possibilities are vast. It took nearly three centuries for scientists to achieve temperatures a hair's-breadth away from absolute zero, but it wasn't the end. The study of absolute zero has just begun. .

Additional Resources

More Topics

  • Topic 1: Measuring the Cold - Thermometers
  • Topic 2: Understanding Heat and Energy
  • Topic 3: States of Matter
  • Topic 4: Refrigeration
  • Topic 5: Cryogenics
  • Topic 6: The Quest for Absolute Zero
  • Topic 7: How Animals Survive the Cold
  • Topic 8: Superconductivity
  • Topic 9: Astronomy
  • Topic 10: Spaceflight
  • Topic 11: Agriculture
  • Topic 12: Cold Medicine
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