### 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 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
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

Bob Novak
Sr. Process Engineer
Carpenter Technology Corporation

```

Current Queue | Current Queue for Physics | Physics archives