# Temperature less than absolute zero possible

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#### derekmcd

##### Guest
Need to fix your link... you've got "We" stuck in there at the end. <div class="Discussion_UserSignature"> <div> </div><br /><div><span style="color:#0000ff" class="Apple-style-span">"If something's hard to do, then it's not worth doing." - Homer Simpson</span></div> </div>

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#### lsbd

##### Guest
according to the definition of absolute zero...is that even theoretically possible?

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#### derekmcd

##### Guest
I would say no. There is a difference between Negative Temp and below Absolute Zero. I think it is more of a mathematical concept rather than something that can be observed in reality. The Laws of Thermodynamics don't allow for it. Similar to C... you can get close, but never quite reach it. <div class="Discussion_UserSignature"> <div> </div><br /><div><span style="color:#0000ff" class="Apple-style-span">"If something's hard to do, then it's not worth doing." - Homer Simpson</span></div> </div>

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#### harmonicaman

##### Guest
I would guess that the center of a black hole can be mathematically modelled to be at absolute zero; but it will never be possible to measure this because the very act of measuring it would raise the temperature...

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#### derekmcd

##### Guest
Are not atoms in an absolute zero state still in their original form? In that they have not broken down to fundemental particles? There is just no movement, thus no heat. Maybe a singularity could be defined as both infinitely hot and absolute zero, thus undefinable. <div class="Discussion_UserSignature"> <div> </div><br /><div><span style="color:#0000ff" class="Apple-style-span">"If something's hard to do, then it's not worth doing." - Homer Simpson</span></div> </div>

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#### alokmohan

##### Guest
Temperatue is kinetic energy of molecules.In a closed system it may perhaps be controlled.

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#### 3488

##### Guest
I would have thought no. As far as I understand it, Absolute Zero is when ALL molecular motion ceases, thus infrared & microwave radiation stops, all gases freeze into ice including Hydrogen & Helium (strange concept, Hydrogen ice).<br /><br />So no, I think minus 273.16 Celsius is as cold as it can ever get. <div class="Discussion_UserSignature"> <p><font color="#000080">"I suddenly noticed an anomaly to the left of Io, just off the rim of that world. It was extremely large with respect to the overall size of Io and crescent shaped. It seemed unbelievable that something that big had not been visible before".</font> <em><strong><font color="#000000">Linda Morabito </font></strong><font color="#800000">on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.</font></em></p><p><font size="1" color="#000080">http://www.launchphotography.com/</font><br /><br /><font size="1" color="#000080">http://anthmartian.googlepages.com/thisislandearth</font></p><p><font size="1" color="#000080">http://web.me.com/meridianijournal</font></p> </div>

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#### enigma10

##### Guest
The next interesting thought is does matter cease to be defined as such , if all motion/energy is stopped? If absolute zero was reached within an atom and all motion stopped, what force would keep it in its predefined state? <div class="Discussion_UserSignature"> <em>"<font color="#333399">An organism at war with itself is a doomed organism." - Carl Sagan</font></em> </div>

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#### vogon13

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All motion can't stop.<br /><br />Heisenberg won't allow it.<br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

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#### doubletruncation

##### Guest
As described pretty well at the end of the wikipedia article, (you can also see Kittel & Kroemer or some other thermodynamics textbook), negative temperatures are possible (temperatures really running from -infinity to +infinity can be possible). The point is that the thermodynamic definition of temperature is that<br />1/T = d(entropy)/d(internal energy) (where d's are partial derivatives taken with the number of particles in the system held constant). Where the entropy is the logarithm of the number of states accessible to the system. If you include the Boltzmann constant correctly then the temperature is temperature on the Kelvin scale. For most systems the entropy increases as the internal energy is increased (you increase the energy of the system, then there are more states available to the system), so usually temperature is positive. However, you can think of systems in which the entropy decreases as you increase the internal energy, these would have a negative temperature (negative on the kelvin scale). You can show that these systems must have a finite upper limit to their energy (so an ordinary gas of atoms, or a harmonic oscillator - which are all the things that we usually have intuition for when it comes to temperature - can't have negative temperature). Some systems like a collection of lasing atoms, for example, actually have a negative temperature. <br /><br />Keep in mind though, that a system with negative temperature (less than "absolute zero") doesn't have negative energy. The point is that the definition of temperature was chosen to describe how energy will flow between different systems when they are allowed to exchange their energy. Energy will flow (if it can) from the hotter system (greater temperature) to the cooler system (lower temperature) so that entropy increases. So a measure of temperature isn't necessarily a measure of the energy in the system. For some systems temperature and energy are directly related, so for a harmonic <div class="Discussion_UserSignature"> </div>

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#### doubletruncation

##### Guest
I should clarify that the sense of energy flow (from larger temperature to smaller temperature) is true for positive temperature systems. If you were to bring a negative temperature system into contact with a positive temperature system then energy will flow from the negative temperature system to the positive one - the equilibrium will be when both systems have a positive temperature. So, in a sense, negative temperatures are HOTTER than positive temperatures. If you think about why they are negative in the first place: entropy *decreases* as you increase the internal energy, it makes sense. For normal, positive temperature systems, if you increase the energy of a low temperature system its entropy increases more than the amount of entropy that is lost when the hotter system loses the energy - so energy flows from the more positive temperature system to the lower temperature system. But for a negative temperature system the entropy will increase if it loses energy.<br /><br />In the sense of how energy will flow, the cold to hotness scale runs from:<br /><br />+0 K, .... , +1000 K, ..... , + infinity K, - infinity K, .... , -1000 K, -0 K<br /><br />where -0 K is the "hottest" something can be (At -0 K, 1/T = d(entropy)/d(energy) = -infinity, so the system gains infinite entropy by undergoing a slight decrease in energy).<br /><br />If you're interested, this is taken from the appendix of "Thermal Physics" by Kittel & Kroemer. <div class="Discussion_UserSignature"> </div>

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#### Saiph

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so the idea of a negative temperature is a tool...and an odd consequence of the definition, not really a violation of the concept of "absolute zero"?<br /><br />This certainly makes me scratch my head, thermodynamics was never my strong suite. <div class="Discussion_UserSignature"> <p align="center"><font color="#c0c0c0"><br /></font></p><p align="center"><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">----</font></em></font><font color="#666699">SaiphMOD@gmail.com </font><font color="#999999"><em><font size="1">-------------------</font></em></font></p><p><font color="#999999"><em><font size="1">"This is my Timey Wimey Detector.  Goes "bing" when there's stuff.  It also fries eggs at 30 paces, wether you want it to or not actually.  I've learned to stay away from hens: It's not pretty when they blow" -- </font></em></font><font size="1" color="#999999">The Tenth Doctor, "Blink"</font></p> </div>

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#### alokmohan

##### Guest
As seen in the the wikipedia.A matter of higher physics.

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#### doubletruncation

##### Guest
<font color="yellow">so the idea of a negative temperature is a tool...and an odd consequence of the definition, not really a violation of the concept of "absolute zero"?</font><br /><br />Yeah, I think that's right. <div class="Discussion_UserSignature"> </div>

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#### alokmohan

##### Guest
Tool means what?What it is supposed to do?

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#### doubletruncation

##### Guest
Maybe tool is not quite the right word. I would say it really is just a consequence of the definition of temperature. But it really isn't "colder" than absolute zero, it's actually "hotter" than absolute zero (again due to the definition of temperature). <div class="Discussion_UserSignature"> </div>

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#### Saiph

##### Guest
tool, or a way of thinking of things, like the difference between just using forces in a problem, vs using energy conservation. Both are right, they just look at the problem differently to arrive at the same answer (one way is often easier than the other).<br /><br />I guess a better term would be method or approach. <div class="Discussion_UserSignature"> <p align="center"><font color="#c0c0c0"><br /></font></p><p align="center"><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">----</font></em></font><font color="#666699">SaiphMOD@gmail.com </font><font color="#999999"><em><font size="1">-------------------</font></em></font></p><p><font color="#999999"><em><font size="1">"This is my Timey Wimey Detector.  Goes "bing" when there's stuff.  It also fries eggs at 30 paces, wether you want it to or not actually.  I've learned to stay away from hens: It's not pretty when they blow" -- </font></em></font><font size="1" color="#999999">The Tenth Doctor, "Blink"</font></p> </div>

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#### derekmcd

##### Guest
<i><br />All motion can't stop. <br /><br />Heisenberg won't allow it. </i><br /><br /><br />Hence the reason absolute zero can never be reached or at least we could never observe it. <div class="Discussion_UserSignature"> <div> </div><br /><div><span style="color:#0000ff" class="Apple-style-span">"If something's hard to do, then it's not worth doing." - Homer Simpson</span></div> </div>

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#### enigma10

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Perhaps <b>we</b> will never see it, but it is possible. <div class="Discussion_UserSignature"> <em>"<font color="#333399">An organism at war with itself is a doomed organism." - Carl Sagan</font></em> </div>

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#### alokmohan

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Theoritically it may or may not be possible.

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#### enigma10

##### Guest
define how it could not be possible. <div class="Discussion_UserSignature"> <em>"<font color="#333399">An organism at war with itself is a doomed organism." - Carl Sagan</font></em> </div>

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#### doubletruncation

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For a system to be at absolute zero the differential change in entropy caused by a differential change in energy would have to be infinite. It would be a point where the entropy vs. energy curve has a kink. If you think about it, you would have trouble trying to come up with any curve of entropy vs. energy that has a kink over a finite connected region in energy. So your system can't have zero temperature over a finite subset of energy, it can only have zero temperature at exactly a single value of energy (that energy being exactly zero for all real physical systems that I know of). From Heisenberg's uncertainty principle the uncertainty in time (that is the fundamental uncertainty in when the system had a specified value of energy) multiplied by the uncertainty in energy for a system must be greater than planck's constant (times some factor, but let's not worry about exactly what it is). So to know the energy of a system with absolute certainty (i.e. to say that a system has exactly zero energy) would require an infinite uncertainty in when it had that energy. You could never observe the system since if you did the time uncertainty would be finite - therefore there are no observable systems at absolute zero. <div class="Discussion_UserSignature"> </div>

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