|What is the closest to absolute zero that has
ever been reached?. What would happen to a
substance if it were cooled to absolute zero?
|Question Date: 2002-12-05|
Absolute zero is defined as zero degrees Kelvin.
The closest recorded temperature to absolute zero
that I could find is 0.0001K, for helium gas.
Your question about what would happen to an
object cooled to absolute zero is a great one! All
molecules are constantly in motion (the bonds
between atoms are vibrating and changing shape).
The speed of this motion is dependent on the
temperature of the molecule. As you can probably
guess, motion is faster at higher temperatures.
Changes in molecule motion with temperature are
responsible for phase changes. Water vaporizes at
high temperatures because as the water molecules
move faster they bump into one another more often,
pushing each other away and taking up more and
more space, eventually forming a gas (steam).
Water freezes at low temperatures because as the
water molecules slow down they coalesce, or come
together like pieces in a puzzle to form a
crystal- like matrix. (Why is ice LESS dense than
water, then? If the molecules are moving slower,
they should be closer together, right? Ice is less
dense than water -- it floats.)
Even when water
freezes, the molecules are still vibrating. Only
at absolute zero do molecules stop moving
completely. What sort of phase change would this
cause? According to Einstein, who based his work
on an Indian physicist Satyendra Nath Bose, this
would result in a completely new form of matter.
Albert Einstein speculated that when
molecules stop moving, the atoms would fall
together and merge into one atom. The individual
atoms (oxygen and hydrogen, in the case of water)
would loose their identities and form what
Einstein called a "superatom", or what we now call
a Bose-Einstein Condensate.
Carl E. Wieman at the University of Colorado in
Boulder won the Nobel prise for his work on
The closest to absolute zero anyone has reached is
around 150 nano Kelvin. The group ended up
receiving the 1997 Nobel Prize in Physics for it.
They got the prize because they ended up proving a
theory called Bose-Einstein Condensation which had
been made decades before it was proven.
They achieved the cooling by taking
already cold vapor of atoms, (3K 87Rb atoms) and
slowing them down further with a 3 dimensional
laser setup. If you want more detail your welcome
to look at
this link here
the really good stuff, look up Steven Chu on the
web. He has some good educational equipment hiding
somewhere. A quick explanation of Bose-Einstein
Condensation (or BEC) is that due to quantum
mechanics, there is a limit on how well you can
know the product of a particles momentum and
position at the same time. This theorem is
called the uncertainty principal. So if you know
exactly what the velocity of a particle is, you
can't know its position exactly no matter how good
your equipment is. You do however know a region
that the particle could exist. If you had a
billion particles, each with the same velocity,
each time you looked you would find the particle
in a different place.
So what Einstein
theorized was that if you could slow down an atom
enough, due to quantum mechanics the atom size
would spread out. If you kept slowing the atom
down, it could overlap with other atoms. That is
exactly what happened, the atoms ended up
spreading out enough that the atoms existed as a
single entity, rather than a collection of
PS. An interesting fact:
The navy funded the research. What the grant
proposal promised was the possibility of the most
accurate clock in the world. As far as I know no
one intends to ever build the clock.
The record for the coldest temperature which has
ever been reached depends upon what you kind of
substance you are interested in. The coldest
temperature which a solid object has been cooled
to is about 60 microKelvin, or 60 one-millionths
of a degree above absolute zero. Certain gases
have been cooled to about one nanoKelvin, or about
one one-billionth of a degree above absolute zero.
However, this temperature can't be maintained
indefinitely because the gas slowly solidifies,
and warms up when it does so. In a certain
kind of machine called a "nuclear demagnetization
refrigerator", it is possible to take a piece of
copper and cool only the atomic nuclei to
temperatures of roughly 1/4 of a nanoKelvin. This
is kind of an unusual situation though, where the
nuclei of all the atoms are very cold, but the
electrons of the atoms are much warmer. You can
read some more about nuclear demagnetization
about the very cold gases at
link I don't
know what would happen to a substance if it were
cooled to absolute zero. Certainly very many
changes happen to it on the way to absolute zero.
If you think of water for example, it changes from
steam at high temperatures to liquid water as it
cools. When it gets still colder it becomes ice,
which is a solid. These changes are examples of
phase transitions, in which a substance changes
its properties dramatically as the temperature
changes. Some substances (like the element
dysprosium) become magnetic when they get colder;
others become liquids that flow without any
friction at all (like helium); still others allow
electrical current to flow through them without
any resistance (like aluminum).
changes take place because as the substance gets
colder, the vibrations of the atoms in the
substance become weaker and weaker. At absolute
zero the vibrations nearly stop all together - the
only vibrations left are called the "zero-point
motion", but they can't produce any warmth.
I'm not sure what the current record is, but I
believe it's around a few billionths of a degree
above absolute zero. For reference, the coldest
parts of space appear to be about 3 Kelvin! As you
approach absolute zero, atoms and molecules lose
their energy and slow down. At absolute zero,
atoms and molecules in a system would be in their
lowest possible energy state. However, according
to the Third Law of Thermodynamics, it is not
possible to bring a system down to absolute
However, even though absolute zero
cannot be achieved, dramatic changes in the
physical properties of matter (such as
Bose-Einstein condensation and superconductivity)
can emerge at temperatures near absolute zero.
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