I’ve just looked this one up, apparently matter undergoes a phase transition at 0K in quantum theory as it becomes governed by quantum fluctuations.
Ignoring quantum for a minute, theoretically speaking, you can’t cool a block down to Zero. This is part of the Third Law of Thermodynamics. This applies to a block with enough particles that it can be treated as a statistical system. You could in theory stop all motion of a single particle. However, at that point it’s kind of silly to say that it’s at Absolute Zero, since thermodynamic temperature itself is a statistical property, not very good at dealing with single particles. We don’t really think of a single atom as having a temperature.
However, that’s in classical theory. As has been noted, quantum physics makes it even more difficult, in that you can’t even stop all motion of a single particle. There’s something called zero-point energy, which oddly enough is not zero. It’s the least energy that a particle can have, but it’s still positive. Even if all the particles in your block were at their zero-point energy, the block would still be a few femtoKelvin above Absolute Zero.
The lowest temperature, IIRC, is absolute minus twelve. 
Hey Whack-a-Mole,
This is something that puzzles me. I understand that temperature is an indicator of molecular motion. How can you describe the temperature of a vacuum when, by definition, it doesn’t even possess any molecules?
Here’s Cecil’s stab at it.
-Apoptosis
Are you askig me to answer? Cecil put it better than I could have. You are correct that a vaccuum has no temperature but as Cecil notes whatever you place in space will not cool below 3[sup]o[/sup] K due to background radiation and the odd particle flitting about. I’m reasonably certain this temperature is cooling however and will continue to do so forever eventually resulting in the heat death of the Universe.
Hmm…I guess the Universe someday will be composed of nothing but Bose-Einstein Condensates. Humans will of couse be LONG gone before then.
You know when you are close to that temperature:
Lawyers have their hands in their own pockets.
And for those sticklers for accuracy, absolute zero is:
-273.15 Celsius and
-459.67 Fahrenheit
My X is much more frigid than absolute zero. Maybe scientists should check into her to see how she breaks the rules of thermodynamics and quantum mechanics… she does what she pleases.
I forgot to add that while speaking of the temperature of deep space might be technically wrong and a little loose with the concept in some ways you can still think of it that way. When you place a glass of water on your desk it eventually comes into equilibrium temperature-wise with the ambient temperature in the room. Place an object in deep space and its eventual equilibrium temperature with the space around it will be about 3[sup]o[/sup] K. Since all of that is a hassle to explain everythime you want to talk about the idea you usually just hear it as space being around 3[sup]o[/sup] K in temperature.
That explains those love handles! What you thought was fat was actually just a Bose-Einstein Condensate smear!
Ok,
So if absolute zero is the same as zero movement, and scientists have gotten a particle to within a billionth of a degree of absolute zero, how do the scientists acount for the rotational movement of our solar system and it’s affect on the particle?
Or is absolute zero now being defined as zero movement relative to all of the other particles around it?
Very interesting thread. And related I want to ask if there is no upper limit to temperature? The OP mention 10 000 million degrees (which would almost be the same in F and C, no? Or at least and infinite number of degrees F is the same temperature as an infinite number of degress C?)
This was asked just yesterday in a recent thread Is there a maximum temperature? Cecil also covered it here.
To summarise (if you don’t want to read those threads) is that the highest temperature possible is called the Planck Temperature and is around 10[sup]32[/sup] degrees Kelvin. Compare that to the interior of our sun which is around 15*10[sup]6[/sup] (or 15 million degrees). The hottest stars will push up into 10[sup]9[/sup] degrees (or billion degrees) but I suspect hotter temperatures occur in supernova explosions and maybe some other special cases. However, 10[sup]32[/sup] degrees Kelvin is WAY up there and presumably only reached instants after the Big Bang.
Apparently the limiting factor here is that at 10[sup]32[/sup] degrees Kelvin an individual particle has enough energy to form its own, mini-black hole. Remember that mass and energy are interchangeable. Even though the particle doesn’t haev much mass (normally) at that energy it effectively does and will collapse on itself. I don’t know if a singularity inside a black hole could be said to have a temperature but at a guess I would think it is infinite. Of course getting close enough to one to stick a thermometer into it would make you a part of the singularity and you wouldn’t be able to tell anyone anyway.
Originally posted by The Gaspode
Very interesting thread. And related I want to ask if there is no upper limit to temperature? The OP mention 10 000 million degrees (which would almost be the same in F and C, no? Or at least and infinite number of degrees F is the same temperature as an infinite number of degress C?)
Interestingly enough…we can create this temperature when we explode an H-bomb.
I can’t even conceive of 10,000,000,000 degrees Farenheit.
After that what’s a few million degrees? Wow! It really cooled down today! It’s only 9,000,000,000 degrees! Better grab a sweater:)
Planck this, Planck that; geez, that guy Planck must be doing cartloads of money with the royalties. 
Hey, quick, what sound do two Quarks when they crash into each other?
“Planck!!!” of course.
runs away in shame
“I used to walk to school in temperatures below absolute zero, 'course that was on a warm day.”
/Grandpa
I’ve seen heat death refer to the cooling down of the universe, but the first use of heat death was when it was thought that the universe was static. Heat death referred to when max entropy was reached and all energy was in the form of heat and unusable. Cold death more accurately describes what we now expect.
‘Heat death’ describes when an isolated system reaches it’s maximum entropy, it can be applied to any (isolated) thermodynamic system.
A new coldest temperature has been recorded just today.
the researchers cooled a sodium gas to only a half-billionth of a degree
bRRRRRRR!!!
IANAPhysicist, but because black holes have a finite entropy, and radiate like a black box of temperature (6 x 10^-8)/M kelvin (where M is the mass in units of the sun’s mass), I believe they can be viewed as having a finite temperature, albeit a very cold one. Although I don’t believe what is happening in a black hole is entirely understood (pending a proper theory of quantum gravity).
http://math.ucr.edu/home/baez/physics/Relativity/BlackHoles/hawking.html