Absolute zero

[Allen Crisp]

According to a report in today's newspapers, scientists have succeeded in cooling some sodium gas to half a billionth of a degree above absolute zero. The report also says that cooling an object to absolute zero (-273C) is 'impossible under the third law of thermodynamics'. My question is, if you can't get anything to be as cold as absolute zero, how do you know that -273C is ABSOLUTE zero? How do you know you can't reach a lower temperature? Would any responders please pitch their reply at a low level if possible because I'm not of a scientific bent (which is probably fairly obvious).

[sft42]

If my basic grasp of this serves me correct then no matter can exist at absolute zero because it would have no energy at all.......all matter has energy in the particles (gasses have the most, then liquids followed by solids) then energy equating to the space the molecules have to vibrate and move about....to achive -273 would rob all the energy and I think that that is physically impossible.

[j2buttonsw]

Absolute zero (-273 C or 0 K) is a theoretical point derived from extrapolating the linear relationship between pressure and temperature for an ideal gas. See http://www.sun.rhbnc.ac.uk/~uhap057/LTWeb/Zero_Box
1.html

[Gef]

The Third Law of Thermodynamics states that "at absolute zero the entropy of a perfect crystal would be zero".

[bernardo]

In other words, at absolute zero all the molecules stop wobbling. (The hotter something gets, the more the molecules wobble).

[Miss Zippy]

What does the First and Second Law of Thermodynamics say then?

[Gef]

First Law; energy can neither be created nor destroyed. Second Law: the entropy of the universe must always increase. (Got the feeling that Miss Zippy was being a little cheeky here :-)

[Miss Zippy]

Thanks Gef ;-)

[aris]

I really want to know more details about absolute zero, we all heard about it, but there's only a few who know exactly what it is(I'm not included in those) I'd like to know if molecules can actually stop moving, some say it's impossible, as there would be no energy, and there's nothing that could possible exist without it.. so, please ansewer..

ps: sorry if I have spelling or grammar mistakes, I'm from Mexico..

[Hamish]

The reason it is impossible to reach is that the closer you get to it the harder it becomes to cool it further.

It's a bit like the folding paper trick. Try foulding a pice of paper in half. Fold that in half again and so on. You will do very well to get more than seven folds, I think more than eight is impossible.