Talk:Absolute zero

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[edit] Early discussions

The article mentions that the "ground state" energy is not zero. I assume that it is refering to the Zero Point Energy (ZPE), which arises in the "particle in a box" problem and elsewhere. While it is true that the ZPE is non-zero, is it considered kinetic energy or some other form of energy? (MS)

It is kinetic energy. You can solve for the velocity of the particle, and the answer is non-zero. (GJ)

On a related note, at temperatures near absolute zero, atoms move very slowly. At absolute zero are the atoms completely stationary or is there some zero point vibrational frequency? (MS)

For a particle in a crystal at low temperatures, simple harmonic motion is a better approximation. Again, there is non-zero velocity and kinetic energy in the ground state, except when the particle is instantaneously motionless at the extremes of the SMH. It was about 20 years ago that i knew a little quantum mechanics, so i can't quote formulae any more. Try an undergraduate quantum mechanics text book (sold mine long ago :-() (GJ)

Finally, at least for the case of temperature defined in terms of the heat engine (Lord Kelvin's definition of temperature), where temperature is related to the efficiency of a reversible heat engine:

 efficiency = 1 - TH/TC

it is impossible to obtain a temperature below 0 K. If such a temperature were possible, it would be possible to develop a thermodynamic cycle that exhausted heat at that temperature. The result would be an engine with efficiency >100%, which violates the first law of thermodynamics. (MS)

I think you mean 2nd law. I'm not sure if Kelvin's definition is one of the ones that allow negative temperature. Even if it does, the above reasoning might be faulty. At negative temperatures a lot of other things go negative or just plain weird. I called for real thermodynamicists here because my physics is now only half remembered and i am confused about some of these things. (GJ)

Efficiency >100% means that you get out more energy than you put in. This violates the 1st law (yes, it also violates the 2nd law). In addition efficiency = 100% violates the 2nd law, except for the special case of reversible processes. Since in practice it is pretty much impossible to implement a reversible process, the 2nd law implies it is impossible to even reach absolute zero.(MS)

Also, even for population inversion, isn't the ground state still defined as the lower energy of the two states?

--Matt Stoker

Sometimes, sometimes not. In most practical lasers there are three or four relevant quantum states and the population inversion involves only two of them, not the ground state, and for a four level system not the highest. The negative temperature figure comes about only if you include only the atoms (or whatevers) in the two "inverted" states of the population inversion.

It is also possible to build a two level laser system, with the ground state being the low energy state in population inversion, but for various practical reasons these are a lot less fun.

The definition of temperature usually used for such systems is, derivative of entropy with respect to energy (perhaps multiplied by a constant for the system of units you are using). Adding energy to a system with population inversion actually decreases the entropy, and subtracting energy increases the entropy, hence negative temperature.

BTW for such systems, there are two good approximations to absolute zero. One is with all atoms in the low energy state. The other is with all in the high energy state (perfect population inversion).(GJ)

I did a little reading from: <a href="http://www.google.com/search?q=cache:FJjlpW9h4es:math.ucr.edu/home/baez/physics/neg_temperature.html+absolute+zero&hl=en">Physics FAQ</a>

One important distinction is that the negative temperature, so defined, is for only one mode (eg. the nuclear spin mode). Thus, the entire system (i.e. all modes) still has a positive temperature. This is why such a negative temperature is possible without violating the 1st & 2nd laws of thermodynamics. It would not be possible to exhaust heat to only the negative temperature mode (other modes would still play a role), so TC would still be >0 and efficiency < 100%. (MS)

All those "billionths of a degree absolute" record holders are using this kind of definition of temperature, and they are applying to a specialised system such as "only the atomic nuclei in the material, and only for their temperature calculated with energy states in the magnetic resonance system i am running". Geronimo Jones

Actually, no, the "billionths of a degree above absolute zero" record holders are defining temperature in terms of the velocity of the atoms (translational mode). Since the cooled particles are gaseous atoms, they have no rotational or vibrational modes. For this case nuclear modes should be negligible. They probably are neglecting electronic modes, since they have no way to measure them. This could be an issue, since they are using the momentum transfer associated with photon absorption to slow the moving atoms, which would result in electronic excitation. However, I am fairly certain the lifetimes of the excited electrons are short enough that on average the electronic energy is quickly redistributed to the translational mode via photon emission. In fact, I am pretty sure it is this energy transfer due to photon emission that limits the minimum possible temperature that is obtained (20nK). (I recently attended a lecture on this by William D. Phillips, who received the 1997 Nobel Prize in Physics for this work. He spent quite some time discussing this energy transfer, since the original theoretical calculations indicated a larger energy for the electronic transition than was actually the case and when the experiment resulted in a lower temperature than was theoretically possible they had to go back and revise the theory).

The application of this particular low temperature work is for atomic clocks, the accuracy of which are improved by using very slow moving atoms. Check the NIST website for details. --Matt Stoker

How can they have a gas at a few billionths of kelivns? Doesn't helium, the hardest element to condense, liquify at 4K? I could understand if they could stretch the condensation point down to 1 K or .1 K by playing with the volume, but even just down to a μK is a difference of 6 orders of magnitude. Especially with a gravitational field pulling the atoms toward the bottom of the tank, I couldn't see them getting anywhere near absolute zero without letting the gas condense.

Also interesting to note is that there are rotational modes available to single atoms. The problem is that the amount of energy necessary to access them is enormous compared to the energy involved in temperature. because of the quantization of angular momentum.--BlackGriffen

Check the NIST website [1] to be sure, but I believe the reason it is considered a gas and not a solid is that the sample consists of a very small number of atoms (on the order of ten or less) under high vacuum. In order for condensation to occur the atoms must collide and stick together. Under the experimental conditions collisions are fairly rare, so condensation takes a long time. In other words condensation is kinetically limited. Under some conditions, the scientists were able to observe formation of a Bose-Einstein condensate, so some form of condensation does occur. -- Matt Stoker

It seems to me the definition given needs to point out that absolute zero is a theoretical temperature. It has never been ( & cannot be) attained. Article says

Absolute zero is the lowest temperature that can be obtained in any macroscopic system

--JimWae 23:15, 2004 Dec 2 (UTC)

"Ideal gas has no volume and exerts no pressure?" Why it has no volume and can't exerts no pressure?

Because that's what the equations of an ideal gas says happens at 0 K. Ideal gases don't exist. 0 K?
All known gases will liquefy before attaining a temperature of 0 K.

Is this really true? I was under the impression that helium needed some heavy pressure to liquefy at all - even at 0K. \Mikez 16:10, 14 Feb 2005 (UTC)

at atmospheric pressures found at sea level, helium liquefies at 4k, but it has some unusual properties, and it is very difficult to attain that temperature with helium.

Ah, ok. I was thinking of solidifying :) That's another story. Thanks anyway :) \Mikez 17:58, 14 Mar 2005 (UTC)

Huh?A system with a negative temperature is [...] hotter than infinite temperature? This reads like nonsense. Can anyone improve/explain this? --DLeonard 15:44, 2005 Jun 19 (UTC)

a negative temperature cannot be a positive temperature 8-\

"All known gases will liquefy before attaining a temperature of 0 K. Is this really true? I was under the impression that helium needed some heavy pressure to liquefy at all - even at 0K. \Mikez 16:10, 14 Feb 2005 (UTC)"

helium liquifies at -269 degrees celcius*. But to become a solid, helium needed a pressure change. at normal pressure though, helium cannot become a solid. (MCC) =)

  • In case you did not know this, helium becomes a [[superfluid]]; all of its molecules move in the same direction, making it EXTREMELY smooth-flowing; it can even climb up the sides of containers.

two requests. One is for a graph showing the extrapolation to absolute zero, the other is for some details (perhaps in another article) on how they get to absolute zero. Vicarious 23:43, 17 August 2005 (UTC)

I have added a reference to cryocoolers under "Cryogenics". Graph is a good idea. I will add it to my to-do list. Cutler 08:00, August 18, 2005 (UTC)

[edit] Edited intro

"It is an infinite number of orders of magnitude below any attainable temperature. It is by definition unachievable (after all, T appears in the denominator of many equations of thermodynamics), ..."

I can only speculate as to what an infinite number of orders of magnitude means. That absolute zero is practically unachievable is the third law of thermodynamics and not inherent in the definition. Cutler 17:41, 17 January 2006 (UTC)

There's a pretty good reason why it will be nearly or fully impossible to reach Absolute Zero: Since the uncertainty principle states that an electron's position cannot be plotted at a given moment, then at any

[edit] Theory

I started thinking about 100 Kelvin, if it exists; and I was wondering... When you start a particle vibrating, raising its temperature, its position in space decreases in size. If you could create such high temperatures that the particles poition in space is a singularity, its temperature zould be infinite, no? But if its position is a singularity, would it have the room to vibrate, to produce heat?

Um... first of all, a single particle does not have a temperature; see the intro to the article Temperature. Second, increasing the energy of a particle does not necessarily decrease its "size", and certainly not for a harmonic oscillator; see for example the figures in the article Quantum harmonic oscillator. You might be thinking of the uncertainty principle, which says something else. Melchoir 22:43, 27 February 2006 (UTC)

[edit] theory & practice

This article seems to lack, in many parts and aspects, a clear NPOV of the differences between the theory and practice.

The theory, the utopia, is essentially separated from the practice, the experiments. The experiments are just trying to prove the theory in practice, and should always be considered but without changing the theory itself. Rather adding rules as they are observed, not trying to add personal conclusions to it.

Quoting an example, from Absolute_zero#Kinetic_theory_and_motion, right on the first paragraph:

But this is contrary to experimental evidence, and it is predicted that helium will never solidify, no matter how much it is cooled or compressed.

It says "it will never solidify", instead of "it would never solidify". I know this looks small, but it's actually pretty bad. I'd change it to the following, but that's not the only problem with this (and many) articles:

Contrary to this, experimental evidence lead to predictions that helium would never solidify, no matter how much it is cooled or compressed.

Experiments happens all the time. There is no such perfect experiment. Today the zero absolute might be considered -273.15K (edit: I mean -273.15C). It wasn't always that number, and it can change again in the future. It resembles just like trying to predict the next digit in Pi without a computer. But this is even worst since there's no mechanism to predict what's the real absolute zero number. It could even not be a static number, since it's practical. Just like trying to say there is a solid and unique number for gravity, or light speed. There are just ways to deduce it through experimentation in a critical mass stage that we might never be able to know for sure what would happen if it goes 0.0001K less, for example.

Maybe absolute zero would be a completely different number in another galaxy, just like gravity and light speed change within different environments.

So, what's the definition for absolute zero? I think we all know what we mean by absolute zero once we understand thermodynamics, but it gets hard to put it in words that wouldn't collide with other physics definitions. I can use two definitions for it:

  • absolute zero is a state of infinite energy within an universe (system wise).
  • If temperature is the movement of molecules and if that movement keeps a balance between the ambient's energy and the body's (heating up one or the other while there is any acceleration, for example), by reaching the absolute zero those molecules would stop moving thus keeping all energy within the body and making no energy exchange with the ambient.

The first one is quite ambiguous, but I consider it to be quite right. Yes, it would imply a coexistence with an "opposite" temperature, but there is no opposite for zero. Adding to that it could be similar to saying it is "infinite entropy of a body" but that can lead to wrong physical conclusions again. And I know the second one must be too childish for physicians, but that's who I am right now.

--caue 10:36, 17 March 2006 (UTC)

Just one more thing: The current definition is also pretty good. I would just remove the word "macroscopic" from it:

Absolute zero is a fundamental lower bound on the temperature of any system.

--caue 10:36, 17 March 2006 (UTC)

Let's see...
  1. There is no problem with saying "it is predicted that X will happen..." since it's still clear that a prediction is being made. Using "would" is grammatically incorrect.
  2. Absolute zero is not -273.15K; it is 0K. If you meant −273.15°C, that's part of the definition of the Celsius scale, and so it cannot "change". Likewise, the numerical speed of light in meters per second is a definition and cannot change.
  3. Where is your "infinite energy" definition coming from?
  4. Actually, there is an opposite temperature to absolute zero; it is −0K, the hottest possible temperature. See negative temperature. This is just one use of negative zero.
Concerning the last two points, yes, physics can be wacky, but not too wacky. Let's not forget that we're bound by WP:NOR too. Melchoir 11:09, 17 March 2006 (UTC)

Cool, thanks for the input Melchior, that was very nice of you. I've enjoyed mostly that WP:NOR thing, and yes, I kinda often violate that rule without noticing. I think most of this comment of mine is basically going against it. I need to stop to think on what I write here before actually doing it sometimes... But I kinda do hope that wikipedia could become more than an encylopedia. While it's true it is a completely new concept, it's still very tightly bound to old paper encyclopedia concepts.

The -273.15K was my mistake. I meant Celsius, and while the definition can't change, both for that and for speed of light, the number can change since it's taken out of observations that could have been misleaded.

My "infinite energy" definition came from my understanding of absolute zero, and infinite and energy. Just as you said, clearly a comment that could have been put aside. When I wrote that, I was truly thinking the article is lacking of NPOV in many parts, and I was trying to explain both my point on the NPOV thing and why I think the article could be reviewed since I feel like it's not a good explanation of what absolute zero is. While I should review all that, I still didn't. And, once again, I could be wrong and be assuming more things than I should, since I'm using just logic and my weak experience while trying to get to empirical definitions without being careful. At least I knew I was going too far, that's why I decided to gather some opinion first, and yours were of great help to me, Melchior.

I'll just review all that later on and see if I can give some direction to the article as I first thought or just reconsidering everything I was imagining about this subject.

Oh, one more thing, I never meant "there is no opposite to zero absolute", I just said mathematically (I assume that a zero out of context, or even in physics, is always coming from maths definitions), there is no opposite for plain zero, that is it. But I also never knew there is a definition of opposite absolute zero, which is just obvious to me that it would exist, although it could actually be just two different ways to get to the same point.

And thanks again!

--Caue (T | C) 09:42, Sunday March 26, 2006 (UTC)

[edit] Celsius conversions should be applied.

I reckon that at least with the "low temperature records", a Celsius conversion should be applied, as Kelvin is used by physicists resp., in general, scientists only. A Celsius value (like -272.95 °C) would be far more imaginable for so-called "ordinary people" than the Kelvin value would. -andy 217.91.47.231 12:08, 7 April 2006 (UTC)

As far a general understanding goes, the difference between any temperature here and -270 °C won't affect the general understanding. I can see no benefit whatsoever of listing temperatures such as -273.14999999955 °C. Gene Nygaard 13:03, 7 April 2006 (UTC)

[edit] Sourse inaccuracy

I would just like to point out, that this listed as fourth reference on the page seems to be inacurate to the point of being pseudo-scientific nonsence.

"500 GHz is more than 250 times faster than today's cell phones, which typically operate at approximately 2 GHz."

When giving comparison of the clock speed of the processors in the article, it relates them to operating frequency ranges of cell phones. Obviously no processor in any modern cell phone runs at 2Ghz, but it is their band frequency. I think the segment that references the article and the article itelf should be removed from the page as grossly innacurate and misleading. Tani unit 13:54, 22 June 2006 (UTC)

Tani unit: You gotta forgive the New York Times because the Georgia Tech's press release uses similar language: Silicon-germanium transistor operates 250 times faster than average cell phone. Your opposition to the statement presumes a bit more than is directly stated in the Times article. The NY Times didn't say microprocessor chips; just chips. And this is technically true since there are solid-state devices within a cell phone that oscillate at 2 GHz in order to generate the RF. Having an entire microprocessor running at 250X these speeds and not vaporize into a flash of x-rays is quite an accomplishment. Given that the NY Times' article isn't factually incorrect still means it might be misleading to some, but it can't fairly be characterized as "grossly innacurate [sic]" as you stated. Greg L 22:12, 20 July 2006 (UTC)

[edit] The Boomerang Nebula: Event timing in the heavens

Glossando: Regarding your having converted the Boomerang Nebula paragraph to past-tense form (you justified doing so by stating in your Edit Summary in the History section that “we are viewing the existence of something as it was thousands of years ago”): This is confusing, unnecessary, and unsupportable. Unless an astronomy topic is directed strictly to the origins of the universe (such as the Big Bang or the Cosmic Microwave Background), relatively nearby events are always dated as Earth-receive time. For instance, Supernova 1987A and the 1054 supernova producing the Crab Nebula are events that are dated Earth-receive time. Supernova 1987 is said to have occurred 19 years ago. Any mention of when it "really" occurred is added parenthetically. This sort of distinction properly belongs in articles such as Light year (where it is undoubtedly covered in great detail). You also used past-tense language for the very existence of a heavenly object (the Boomerang Nebula) when you wrote “and existed in the constellation Centaurus” (my emphasis). While you are clearly very bright to have recognized how everything seen in the heavens is actually seen as it occurred at some point in the past, I sure wouldn't have gone out on such a limb as you did trying to emphasis this point; particularly since there is zero evidence that the Boomerang Nebula no longer exists or no longer is still (Boomerang transmission time) the coldest observable object in the heavens. This is about as logical as saying the Crab Nebula “existed” in the sky or that the Voyager spacecraft "used" to exist when they broadcast information (that takes many hours to reach Earth) regarding the edge of the heliosphere that also "used to exist". Greg L 20:47, 26 October 2006 (UTC)

Although I don't think mentioning something that only takes hours to view after it occurred is a good example to give to argue against something we are actually viewing thousands of years after it happened, I think what you are saying is fair enough. It would surely become too cumbersome to find the right past-tense wording every time we are speaking of such a thing that many light years away. I agree that sort of distinction more properly belongs in articles such as in Light year. --Glossando 21:39, 26 October 2006 (UTC)
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