MadSci Network: Physics
Query:

Re: Can absolute zero be obtained in a small closed capsul?

Date: Fri Oct 9 20:13:31 1998
Posted By: Bob Novak, Other (pls. specify below), Sr Process Research Engineer, Carpenter Technology
Area of science: Physics
ID: 907123521.Ph
Message:

Absolute zero has never been obtained and may not even be possible.   
Absolute zero is defined as the temperature at which all thermally induced 
motion stops.  As objects (matter) get hotter (acquire more energy) they 
move faster.  All matter that is not at absolute zero is in motion.

All matter that has a temperature greater than absolute zero also radiates 
energy.  At ambient or room temperature, the radiation is mostly in the 
infrared part of the electromagnetic spectrum.  The heat we feel when we 
get close to a hot object comes from our bodies absorbing the infrared 
energy being radiated by the hotter object.  Infrared radiation transfers 
energy from hotter to colder objects. 
 
In terms of heat transfer, the inside of a hollow closed sphere is called 
a blackbody.  Any part of the inside surface of the sphere is radiating 
energy to all the other parts of the surface.  Any hot part of the surface 
will radiate energy to the colder parts of the sphere.  The temperature 
inside the sphere will quickly become the same and the transfer of energy 
from one location to another will stop.  In this condition, when the 
inside surfaces are at the same temperature, there will be no net gain or 
loss of energy inside the sphere.  This is called thermal equilibrium.  
The same thing happens if you place an object inside of the blackbody.  If 
the object is hotter than the sphere, it will radiate energy into the 
sphere until both the sphere and the object are at the same temperature.  
The opposite will occur if the sphere is hotter than the object.  Energy 
will transfer from the hotter object to the colder object until they are 
in thermal equilibrium.

A closed capsule and objects placed inside the capsule will not 
spontaneously cool to absolute zero.  So how do you cool something to 
temperatures approaching absolute zero?  A gas cools when it expands into 
a larger volume.  This is called adiabatic expansion.  Adiabatic expansion 
is used in most refrigerators and air conditioners to provide cooling.  
Using adiabatic expansion to remove energy from the gas and lower its 
temperature can liquefy gasses.  Liquid helium at 269.9 degrees K 
provides the lowest temperature that can be achieved this way.  To get 
even lower temperatures it is necessary to remove more energy than is 
possible using only adiabatic expansion.  It is also necessary to keep the 
object being cooled from coming into contact with the container.  To 
accomplish this, gasses of elements such as sodium or rubidium are 
levitated using magnetic fields to form magnetic bottles.  Very carefully 
tuned laser light then collides with the gas atoms in a way that reduces 
the speed of the gas atom.  Light can act like a wave or a particle.  
Particles of light are called photons.  Photons that collide with the 
atoms of the gas can carry away tiny amounts of energy.   The more 
collisions between the gas and the light, the greater the amount of energy 
removed from the gas atoms.  Less energy equals lower temperature.  By 
manipulating the laser beams and the magnetic fields the rubidium atoms in 
a small chamber at the National Institute of Standards and Technology 
(NIST) were cooled to less than 100 nanokelvin.  That is 0.00000001 
degrees K above absolute zero.  Somewhere near this temperature the 
rubidium atoms that make up the gas stop bouncing off of each other and 
acting independently and start to all move the same way.  The gas becomes 
something called a Bose-Einstein condensate when all of the atoms begin to 
move uniformly.  The atoms in a Bose-Einstein condensate drop into the 
lowest possible energy state and the motion is reduced even further.  The 
temperature of the Bose-Einstein condensate drops to 0.5 nanokelvin or 
less!!!

This is the lowest temperature ever observed.  It is still not absolute 
zero, but there are a lot of zeroes after that decimal point!

The information on the work at NIST was extracted from a paper by Dr. Eric 
Cornell which was published in the Journal of Research of the National 
Institute of Standards and Technology, Volume 101, Number 4, July-August 
1996.  Dr. Cornell attempted to present the information in a manner that 
would be understood by general audiences.  I attempted to simplify it even 
more.  I hope my interpretation is helpful and correct.  The text of the 
original article can be found at: 
http://physics.nist.gov/Pubs/Bec/j4cornel.pdf.  You will need Acrobat 
Reader to view it.  

Bob Novak
Sr. Process Engineer
Carpenter Technology Corporation



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