Why can't we reach absolute zero?

[Geuis]

I hear in all sorts of experiments that scientists cool materials down to within billionths of a degree of absolute zero. What prevents us, or is there a reason scientists dont, from reaching all the way to absolute zero?

 

[Artman]

Part of the reason is there is no perfect insulator, so there is always some heat being transferred to the substance being cooled.

 

[Chi Meson]

Absolute zero is an approachable limit, like the speed of light. You can always get closer, but you can never get there. IT's called the third law of thermodynamics.

An easy way to consider this one is: in order to cool something down, it must be put into a place that is colder. OTherwise heat won't flow out of the thing. SO: if you theoretically put an object (like a turkey) into a freezer that was at abosolute zero, heat would flow from the turkey into the freezer, and that would make the freezer have some heat and therefore it would not be at absolute zero anymore.

There are fancier ways of cooling things (do a google on "evaporative cooling")but the same law gets in the way no matter which method you choose.

 

[HallsofIvy]

Yet a third point (both the previous responses are true) is "quantum uncertainty". If the particles are known to be with the confines of the experiment then there is enough uncertainty in the momentum to keep the temperature above absolute 0.

 

[quartodeciman]

I believe that third law of thermodynamics and the impossibility of attainment of exactly 0K temperature.

But there is such a thing as NEGATIVE absolute temperature(!)

John Baez: Below Absolute Zero - What Does Negative Temperature Mean? --->
http://math.ucr.edu/home/baez/physics/ParticleAndNuclear/neg_temperature.html

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[Link]

But according to boyles law, volume would be 0 if 0 Kelvin, and that's why its impossible!

 

[Creator]

Originally posted by Geuis
. What prevents us, ... from reaching all the way to absolute zero?

The most fundamental reason for the inability to reach absolute zero temp. is because of something derived from quantum mechanics called 'zero point' energy, (actually Planck 'discovered' it.), meaning energy is there even at the zero point of temperature.

When we talk of absolute zero temperature we usually 'mean' a state where there is no longer any kinetic motion of the molecules, that is, a complete stand still.
Because zero point energy is so ubiquitous (even exists in the vacuum), then all molecules retain a minimum of that amount of energy.

Creator

 

[Link]

but if molecules and electrons stop moving, wouldn't the electrons be dragged into the nucleus of the atom?

 

[Creator]

Who said anything about electrons stopping? Its the molecules (and atomic motion) that slows down kinetically at low temperature. However, they cannot stop completely due to zero point fields.

Creator

 

[KingNothing]

So, which theory is generally more used to prove this: The one Artman/Chi brought up, or the one Creator brought up?

 

[quartodeciman]

Here is something nice:

U. Colorado/Boulder/Physics2000/(uses interactive applets)/Bose-Einstein Condensation explanation--->
http://www.colorado.edu/physics/2000/bec/index.html

check out the site home page for more physics stuff in the same style -> http://www.colorado.edu/physics/2000/index.pl

 

[quartodeciman]

Here is a bit more to expand on the previous:

Analog Science Fiction & Fact Magazine/John Cramer/1995/Bose-Einstein Condensation, a New Form of Matter --->
http://www.npl.washington.edu/AV/altvw77.html

Here is a pretty good historical description of absolute zero temperature --->
http://www.sun.rhbnc.ac.uk/~uhap057/LTWeb/Absolute.html

I would demur on one bit from this explanation.

"we are unable to reach absolute zero itself. It is forbidden by the third law of thermodynamics."

A statement of a law cannot prevent something from happening*. A law is a scientific summary of understanding and its correctness is exactly what is at stake when one asks about reaching absolute zero temperature. Thermodynamics was developed in the nineteenth century essentially to cover nineteenth century physical situations. It is not a foregone conclusion that it remain forever correct in the face of more advanced discoveries. But the author is correct that avoidance of reheating is a formidable practical obstacle to furthur reduction of a tiny absolute temperature.

*remember the joke about the traffic cop that pulled over a car:
cop: "You can't make a U-turn in the middle of that busy street."
uncool driver: "Whadaya mean I can't? I just did!"

 

[Creator]

Originally posted by Decker
So, which theory is generally more used to prove this: The one Artman/Chi brought up, or the one Creator brought up?

Depends on which approach you prefer, thermodynamics or QED.

Here's an interesting report of the first experimental measure of the zero pt. energy of a Bose Condensate showing it to correspond to the uncertainty in the particle momentum (as mentioned by HallsofIvy):

http://www.aip.org/enews/physnews/1999/split/pnu433-1.htm

I believe the first exper. evidence of molecular zero point energy in 'normal' matter was a few years after Planck's derivation of ZPE by a fellow named Mulliken (1924). Planck's discovery was a result of thermodynamic considerations as he was working to derive the correct blackbody distribution formula. Notice this was all actually prior to Heisenberg's derivation of the same using matrix mechanics.

Creator

 

[quartodeciman]

If you stick around with a topic long enough, some news is apt to fly in.

Fermi-Dirac condensation? Potassium atoms instead of Rubidium atoms?

NIST/University of Colorado Scientists Create New Form of Matter: A Fermionic Condensate --->
http://www.colorado.edu/news/releases/2004/21.html

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