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I'm so bad at (physical) science I had to see if "simple" Wikipedia had an entry for this because I couldn't follow it at all and.. it does! :-) https://simple.

I'm so bad at (physical) science I had to see if "simple" Wikipedia had an entry for this because I couldn't follow it at all and.. it does! :-) https://simple.wikipedia.org/wiki/Negative_temperature https://simple.wikipedia.org/wiki/Negative_temperature

Cthulhu_ 5y ago
Thanks for the link; I glazed over when the article said "Confined point vortices are a system with bounded phase space as their canonical momenta are not independent degrees of freedom from their canonical position coordinates." It's like I understand the individual words like phase, canonical and coordinates, but the combination is... an entirely different field of study.
- lekevicius 5y ago
  Huh, I stopped trying to understand at that sentence. Maybe Wikipedia could start linking to "simple" articles for these topics? Or at least include some more links to more basic concepts. That sentence is a fortress even for a curious person.
  - petercooper 5y ago
    I do think Wikipedia should make the link to the "simple" branch more obvious on standard English Wikipedia. Currently they treat it merely as an obscure alternative language, but it could really help a lot of people if it were more prominently linked on each article that has a simple variant.
- crdrost 5y ago
  Haha, no yeah, that's a very jargony sentence indeed. Phase space is jargon for the set of all allowed configurations of a system. In the simplest case, an ideal gas of n spherical atoms, each atom is specified by 3 independent numbers for position and 3 for momentum, so you need 6 n numbers total to specify the whole configuration... That is the phase space. This phase space is only partly bounded, it is bounded in position (V^n where V is the volume each particle can occupy) but not in momentum (the temperature can always go higher). Because each of these numbers can vary independently from each other, they are called “independent degrees of freedom.” Now, point vortices are an abstract mathematical limit of physical vortices as they get really small. Generally we take these mathematical limits because it's much easier to work with and we are lazy. The article is saying that Onsager chose to explain his theory with point vortices because you can't give them arbitrarily high momentums, in fact their positions have to be tied up with where they are going, so that they are not independent anymore like they were with the gas. So Onsager knew that if he chose this system then the boundary on volume (well, area, the vortices live in 2D) would become a boundary on momentum space and then you couldn't dump infinite energy into the system. And this is important because it means that when you add more energy, the number of allowed configurations with that energy eventually shrinks. This is the negativity of negative temperature, increase something and something else decreases. The thing that is decreasing, a volume in phase space, is also called the entropy. Increase energy, and entropy decreases... most normal systems work the opposite way, entropy increases. As systems share things to maximize total entropy, this overcharged vortex system is going to share energy with any normal system at any temperature, because that normal system will increase its entropy with energy coming into it, and the overcharged vortex system will gain entropy when it loses energy. So it is hotter than any other thing in the world. (I am erasing the jargon word “canonical” from this explanation... It just refers to a particular procedure we use to define momentum coordinates based on your position coordinates. When you are not dealing with a point particle with defined mass in a flat space, you have to make these sorts of choices.)
1970-01-01 5y ago
Thank you. The key is the last sentence: Only very small things discussed in quantum mechanics can reach this state.
- wyager 5y ago
  This is not really true - lots of macroscopic objects have negative temperatures, like lasers in their pumped state.
technobabbler 5y ago
Thanks for the link! PS If you ever see something like that on regular Wikipedia, please add the {{Jargon}} tag to it. In theory, at some point, some editor might come and make it better.
jessriedel 5y ago
Keep in mind that the "simple" in "simple English wikipedia" (SEW) does not refer to the simplicity of the explanation/exposition, only to the simplicity of the language; it is intended for readers less proficient in English. >Use Basic English words and shorter sentences. This allows people to understand complex terms or phrases. > Write good pages. The best encyclopedia pages have useful, well-written information. > Use the pages to learn and teach. These pages can help people learn English. You can also use them to make a new Wikipedia to help other people. > Simple does not mean short. Writing in Simple English means that simple words are used. It does not mean readers want basic information. Articles do not have to be short to be simple; expand articles, add details, but use basic vocabulary. https://simple.wikipedia.org/wiki/Main_Page https://simple.wikipedia.org/wiki/Main_Page It's true you might find a explanation on SEW that you find simpler or easier than on the regular English Wikipedia page, and this might (or might not) be because the constraint of using simple English forces it. However, there is no reason this explanation could not also be put in the regular English Wikipedia page. So you should be bold and consider improving the regular English Wikipedia if you find it inaccessible to the intended audience.
- petercooper 5y ago
  does not refer to the simplicity of the explanation/exposition, only to the simplicity of the language Sure, but the use of simple language commonly seems to play out in easier to follow explanations of things on Simple Wikipedia. So you should be bold and consider improving the regular English Wikipedia if you find it inaccessible to the intended audience. I appreciate your confidence, but I find the topic almost unintelligible. I dare say a science educator or the like would make a more reliable job of it. Plus, I'm not sure articles should be dumbed down, because for topics I do understand, I would find it annoying if Wikipedia entries were boiled down into layman's terms.
  - stavros 5y ago
    But it's not Simple Wikipedia. It's Wikipedia in Simple English. I do agree the two correlate, though, even though I think you could use simple language to describe complex topics without losing information.

Cthulhu_ 5y ago

Thanks for the link; I glazed over when the article said "Confined point vortices are a system with bounded phase space as their canonical momenta are not independent degrees of freedom from their canonical position coordinates." It's like I understand the individual words like phase, canonical and coordinates, but the combination is... an entirely different field of study.

lekevicius 5y ago
Huh, I stopped trying to understand at that sentence. Maybe Wikipedia could start linking to "simple" articles for these topics? Or at least include some more links to more basic concepts. That sentence is a fortress even for a curious person.
- petercooper 5y ago
  I do think Wikipedia should make the link to the "simple" branch more obvious on standard English Wikipedia. Currently they treat it merely as an obscure alternative language, but it could really help a lot of people if it were more prominently linked on each article that has a simple variant.
crdrost 5y ago
Haha, no yeah, that's a very jargony sentence indeed. Phase space is jargon for the set of all allowed configurations of a system. In the simplest case, an ideal gas of n spherical atoms, each atom is specified by 3 independent numbers for position and 3 for momentum, so you need 6 n numbers total to specify the whole configuration... That is the phase space. This phase space is only partly bounded, it is bounded in position (V^n where V is the volume each particle can occupy) but not in momentum (the temperature can always go higher). Because each of these numbers can vary independently from each other, they are called “independent degrees of freedom.” Now, point vortices are an abstract mathematical limit of physical vortices as they get really small. Generally we take these mathematical limits because it's much easier to work with and we are lazy. The article is saying that Onsager chose to explain his theory with point vortices because you can't give them arbitrarily high momentums, in fact their positions have to be tied up with where they are going, so that they are not independent anymore like they were with the gas. So Onsager knew that if he chose this system then the boundary on volume (well, area, the vortices live in 2D) would become a boundary on momentum space and then you couldn't dump infinite energy into the system. And this is important because it means that when you add more energy, the number of allowed configurations with that energy eventually shrinks. This is the negativity of negative temperature, increase something and something else decreases. The thing that is decreasing, a volume in phase space, is also called the entropy. Increase energy, and entropy decreases... most normal systems work the opposite way, entropy increases. As systems share things to maximize total entropy, this overcharged vortex system is going to share energy with any normal system at any temperature, because that normal system will increase its entropy with energy coming into it, and the overcharged vortex system will gain entropy when it loses energy. So it is hotter than any other thing in the world. (I am erasing the jargon word “canonical” from this explanation... It just refers to a particular procedure we use to define momentum coordinates based on your position coordinates. When you are not dealing with a point particle with defined mass in a flat space, you have to make these sorts of choices.)

1970-01-01 5y ago

Thank you. The key is the last sentence: Only very small things discussed in quantum mechanics can reach this state.

wyager 5y ago
This is not really true - lots of macroscopic objects have negative temperatures, like lasers in their pumped state.

technobabbler 5y ago

Thanks for the link! PS If you ever see something like that on regular Wikipedia, please add the {{Jargon}} tag to it. In theory, at some point, some editor might come and make it better.

jessriedel 5y ago

Keep in mind that the "simple" in "simple English wikipedia" (SEW) does not refer to the simplicity of the explanation/exposition, only to the simplicity of the language; it is intended for readers less proficient in English. >Use Basic English words and shorter sentences. This allows people to understand complex terms or phrases. > Write good pages. The best encyclopedia pages have useful, well-written information. > Use the pages to learn and teach. These pages can help people learn English. You can also use them to make a new Wikipedia to help other people. > Simple does not mean short. Writing in Simple English means that simple words are used. It does not mean readers want basic information. Articles do not have to be short to be simple; expand articles, add details, but use basic vocabulary. https://simple.wikipedia.org/wiki/Main_Page https://simple.wikipedia.org/wiki/Main_Page It's true you might find a explanation on SEW that you find simpler or easier than on the regular English Wikipedia page, and this might (or might not) be because the constraint of using simple English forces it. However, there is no reason this explanation could not also be put in the regular English Wikipedia page. So you should be bold and consider improving the regular English Wikipedia if you find it inaccessible to the intended audience.

petercooper 5y ago
does not refer to the simplicity of the explanation/exposition, only to the simplicity of the language Sure, but the use of simple language commonly seems to play out in easier to follow explanations of things on Simple Wikipedia. So you should be bold and consider improving the regular English Wikipedia if you find it inaccessible to the intended audience. I appreciate your confidence, but I find the topic almost unintelligible. I dare say a science educator or the like would make a more reliable job of it. Plus, I'm not sure articles should be dumbed down, because for topics I do understand, I would find it annoying if Wikipedia entries were boiled down into layman's terms.
- stavros 5y ago
  But it's not Simple Wikipedia. It's Wikipedia in Simple English. I do agree the two correlate, though, even though I think you could use simple language to describe complex topics without losing information.