Absolute temperatures, efficiency>100%, definitions, limits

[Skakos]

What is normal to most people in winter has so far been impossible in physics: a minus temperature. On the Celsius scale minus temperatures are only surprising in summer. On the absolute temperature scale, which is used by physicists and is also called the Kelvin scale, it is not possible to go below zero. Physicists at the Ludwig-Maximilians University Munich and the Max Planck Institute of Quantum Optics in Garching have now created an atomic gas in the laboratory that nonetheless has negative Kelvin values ("http://dx.doi.org/doi:10.1126/science.1227831").

These negative absolute temperatures have several apparently absurd consequences: although the atoms in the gas attract each other and give rise to a negative pressure, the gas does not collapse – a behaviour that is also postulated for dark energy in cosmology. What is more, atoms in this “negative temperature” are more hot than any set of atoms in infinite positive temperatures! Ans this does end here: supposedly impossible heat engines such as a combustion engine with a thermodynamic efficiency of over 100% can also be realised with the help of negative absolute temperatures. (huffingtonpost.com/2013/01/04/absolute- ... 04666.html) (phys.org/news/2013-01-atoms-negative-ab ... ttest.html)

Science has always been setting "limits". Limits to temperatures, limits to numbers (remember the case of imaginary numbers), limits to efficiency, limits to the Universe, limits to the speed of light... And people who thought otherwise were considered insane and ridiculed. How many times were people's carreers desctroyed because they thought that a thermal machine with efficiency > 100% could be built? "Discoveries" like these remind us of a simple truth: that we are the ones who set the limits. These limits are in our mind. And it is up to us to overcome them...

[Teh]

How embarrassing! Probably best to at least consult wikipedia before you post about things you haven't a clue about:

wiki/Negative_temperature

[Naughtorious]

I'm going to produce a new type of cereal: Skank O's. It will be dirty, a waste of time and it will make a lot of people become INFURIATED by its zero substance.

[Cronos988]

Science has always been setting "limits".

Defining a scale is not stating that there is a limit. Furthermore, stating that there is a limit is not the same as setting a limit. The one is a statement about what is, the other is a statement about what ought to be.

[Skakos]

How embarrassing! Probably best to at least consult wikipedia before you post about things you haven't a clue about:

wiki/Negative_temperature

Could you at least write a line or two of what you mean? In the wiki you posted it states rather clearly in the beginning: "still warmer than absolute zero".

Haven't you read it before posting?

Have you been taught in school, high school or any university that we can create a machine with thermodynamic efficiency of over 100% as the articles I posted say?

Please. Elaborate.

-- Updated January 27th, 2013, 12:50 pm to add the following --

(Nested quote removed.)


Defining a scale is not stating that there is a limit. Furthermore, stating that there is a limit is not the same as setting a limit. The one is a statement about what is, the other is a statement about what ought to be.

We so far said that one cannot build a machine with a thermodynamic efficiency of over 100%. This is a LIMIT. A limit set by our theories, which are based on our axioms.

[MazerRackhem]

You have to be very careful about what you mean with each of your terms. 1st the negative temperature you describe is achieved via a very special quantum state in which the system actually loses entropy (disorder) as additional energy is added to the system. This is because there are more particles in higher quantum states then there are in lower states. However, this does not under any circumstances imply that the Kinetic Energy of the system (which is what is generally referred to when discussing Temperature) is negative. In fact the systems with Negative Kelvin temperatures actually have so much energy it flows from them to the positive Kelvin systems, so the Negative Temperature systems are physically hotter than the positive ones. The system is considered to be at a negative Temperature on the Kelvin scale (due to quantum states) while still possessing a positive quantity of Kinetic (and therefore available) energy. The Kelvin scale is set up to measure the point at which quantum particles have reached there lowest state as Zero, however in certain very odd circumstances this measure can yield a negative value do to the situation I described above.

The laws of thermodynamics however remain firmly in place and a Carnot Engine still can not perform above (or even at) 100% efficiency. You talk about engine's performing at greater that 100% efficiency and this too is possible. Refrigeration engines (Air Conditioners, Food Fridges, etc.) preform at much greater that 100% efficiency from a thermodynamics perspective. This is actually a consequence, not a violation of Carnot's laws. Since supplying HEAT is inefficient it takes less energy to cool something (remove heat) than to supply it. Thus a refrigerator can cool a space at much greater than 100% efficiency, but to reheat the same space to the previous temperature will involve an engine far below 100% efficiency as measure against the perfect Carnot engine.

In short, although Negative Kelvin temperatures can be created in the lab they do not allow the extraction of any energy for mechanical purposes in violation with the LoT since the Kinetic Energy is always positive (in fact systems with Negative K temps actually are hotter than those with positive K temps since the heat flows from Negative to Positive system). Such seeming inconsistencies are nothing new to physics and do not undermine its laws. For another instance it is a relativity straightforward thing to model an electromagnetic wave so that the group velocity of the wave exceeds the speed of light. This does not violate relativity however since no mass or information is carried by the group velocity waveform. Such concepts are fun to play with but we can't let them muddle our understanding of the way the world truly works.

[Skakos]

I see what you mean although I am not sure things are so "clear". Science is sometimes over-using defintions and this does add up to the confusion. Up to a point we knew that energy can only be "positive" but now we know that there is a kind of exotic form of energy which is "negative". The same applies with the temperatures. And even though a refrigerator can cool a place with efficiency more than 100%, the article for the "negative temperatures" advertised the "new found >100% efficiency". Who is to blame here? Is it something the article writers did on purpose? Or not?

I am saying that in a place (call me Science) where everything is based on defintions, it is really scary to be so adherent to the validity of some "truths" (which are actually defintions) and then when it is to our interest simply claim "Ok, this can change. Why not?" with disarming innocence...

[MazerRackhem]

Up to a point we knew that energy can only be "positive" but now we know that there is a kind of exotic form of energy which is "negative". The same applies with the temperatures. And even though a refrigerator can cool a place with efficiency more than 100%, the article for the "negative temperatures" advertised the "new found >100% efficiency". Who is to blame here? Is it something the article writers did on purpose? Or not?

Although Mathematicians have played around with the concepts of negative mass and negative energy for many decades I am unaware of any physical experiments which suggest such exotic quantities exist (I have already explained above how negative temperatures are not actually negative in the classical sense). To my knowledge what you are describing is much like the mythical Tachion particle which travels faster than light. Science fiction writers and mathematicians have worked out its properties with alarming accuracy, however no experiment has ever suggested the existence of such a particle. Furthermore, although it was initially found not to disobey any laws of relativity, recent experiments and theoretical work suggest that such a particle cannot exist in reality.

Or when you speak of Negative Energy are you referring perhaps to the continued expansion of the universe and the concept of either 'dark' energy or of an unknown impelling force which drives expansion? Astrophysicists and cosmologists have played around with these concepts to great effect, however neither of these represents a true negative energy. Perhaps you could link some of these articles you refer to. I personally am unaware of any kind of negative energy as you describe it.

[Keen]

The limits in science just translate the observations made during experiments. If someone finds an object with negative temperature, then the laws of thermodynamics should be revised and a new theory, that would explain better the observed phenomena, should be invented, but as long as they are compatible with what is observed, we can consider them as true.

[Skakos]

(Nested quote removed.)


Although Mathematicians have played around with the concepts of negative mass and negative energy for many decades I am unaware of any physical experiments which suggest such exotic quantities exist (I have already explained above how negative temperatures are not actually negative in the classical sense). To my knowledge what you are describing is much like the mythical Tachion particle which travels faster than light. Science fiction writers and mathematicians have worked out its properties with alarming accuracy, however no experiment has ever suggested the existence of such a particle. Furthermore, although it was initially found not to disobey any laws of relativity, recent experiments and theoretical work suggest that such a particle cannot exist in reality.

Or when you speak of Negative Energy are you referring perhaps to the continued expansion of the universe and the concept of either 'dark' energy or of an unknown impelling force which drives expansion? Astrophysicists and cosmologists have played around with these concepts to great effect, however neither of these represents a true negative energy. Perhaps you could link some of these articles you refer to. I personally am unaware of any kind of negative energy as you describe it.

I have opened a dedicated thread for the speed of light at onlinephilosophyclub.com/forums/viewtop ... amp;t=8657.

As far as negative energy is concerned, this is the energy of negative mass. Surely I got too far claiming that "we know of negative energy". It is much of a hypothetical thing now. But negative absolute temperatures were also hypothetical and even impossible... As did many other things (see imaginary numbers for example)

I read (from a "forbidden site"): "In general relativity, negative mass is generalized to refer to any region of space in which for some observers the mass density is measured to be negative. This can occur due to negative mass, or could be a region of space in which the stress component of the Einstein stress-energy tensor is larger in magnitude than the mass density. All of these are violations of one or another variant of the positive energy condition of Einstein's general theory of relativity; however, the positive energy condition is not a required condition for the mathematical consistency of the theory"...

Maybe its all a matter of definition.