Ask A Scientist Chemistry Archive

name         Crystal M.
status       student
age          16

Question -   Why cannot absolute zero be attained?
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Crystal,

You may get more detailed answers from other Newton scientists, However,
when reviewing them, consider these ideas. Getting to absolute zero is less
a matter of cooling something to 0 degrees Kelvin (-273 C or -459.6 F) than
it is to designing a way to measure the temperature once you get there.

The atoms of all materials at a temperature above 0 K are in incessant
motion. Heat energy is a manifestation of atomic motion -- the greater the
motion, the greater the heat. At 0 K. atomic motion is stopped -- atoms no
longer vibrate, rotate, or translate (move).

In order to measure temperature, there must be an energy difference between
the thermometer and the environment to be sensed. In other words, the
thermometer either absorbs energy from or releases energy to the test
environment until both the thermometer and the test zone are at the same
temperature. This process is enabled by atomic motions. Absent atomic
motion, there is no energy to be transferred and none to be measured.

If a (room temperature) temperature sensing probe is placed in an
environment that's supposed to be at 0 K, the atoms in the probe surrender
their heat (their vibrational, rotational, and translational energy) to the
test environment thereby warming it above 0 K. There is no easy way to
pre-cool the probe and even if one could, the temperature of the test
environment couldn't be measured because energy must flow from the 0 K
environment to the probe. By definition, at 0 K there is no energy in the
test environment to be surrendered to the probe. When both the test
environment and the sensing probe are at 0 K, the sensor can't report the
temperature.

Put another way, one cannot measure the temperature of a cold place with a
thermometer hot enough to warm up the cold place.

Regards,
ProfHoff 548
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In order to reach absolute zero, all of the heat would need to be removed
from a substance.  It is not possible to remove all the heat, so absolute
zero exists only in theory.

Pat Rowe
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There is a simple and a complicated answer to this question. A consequence
of  the laws of thermodynamics is that it requires an infinite amount of
work to attain absolute zero. And without going into the details, this is a
LAW, a consequence of experimental behavior, and NOT a THEORY, which may or
may not be applicable. Now it is possible to achieve "temperatures"
extremely close to absolute zero milli- even micro- degrees (provided that
the temperature scale is properly established at those temperatures, which
is by no means a trivial problem all by itself). At these temperatures very
close to 0 degrees K. some weird stuff happens -- the speed of light can be
slowed and even stopped, dozens and even hundreds of atoms bond together and
behave as a single macro-molecule (look up Bose-Einstein condensates), of
course some materials become superconductors (that is have zero electrical
resistance), others become superfluids (that is have zero viscosity),
hydrogen can become a metallic conductor at sufficiently high pressures. In
short, the "quantum world" takes over and we have no intuition about that
world. From a practical point of view, it only takes a stray cosmic ray, or
a radioactive decay to keep the temperature above 0 Kelvin, but that is kind
of a cop-out. In other cases the normal thermal distribution of quantum
states can be inverted so that higher energy states are more populated than
lower energy states, which can be interpreted as a negative absolute
temperature, but that too is a bit of a shell game, because they do not
represent equilibrium systems. In all of the descriptions of
atomic/molecular behavior the absolute temperature enters in as 1/T^n where
n>0. This reciprocal dependence always "blows up" as T approaches zero. Just
"achieving absolute zero" even if it were possible would not "do much" that
does not happen at 10^-6 Kelvin -- that is weird enough.

Vince Calder
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