5 ms·

-40K are impossible AFAIK

by lostmsu 3y ago

a2800276 3y ago
That's why they say it's -40 degrees. :P
Lester_Square 3y ago
Kelvin is not measured in degrees however, so is excluded by implication
- flangola7 3y ago
  It's not? What is it measured in then?
  - bmicraft 3y ago
    K, not °K
  - unwind 3y ago
    It is simply measured in Kelvin. Kelvin is the standard unit for temperature, 0 Kelvin is the absolute zero point. Each step is the same size as a degree Celsius, but there are no "degrees". Edit: remove assertion that the scale does not go into negative, because physics.
    - deelly 3y ago
      As a non-native reader, I`m not sure that I understand. Could you explain why 100 Kelvin, but 100 degrees Celsius and 100 degrees Fahrenheit? Is there some special meaning in a word "degrees" there?
      - forbiddenlake 3y ago
        Earlier comment - https://news.ycombinator.com/item?id=36584908 https://news.ycombinator.com/item?id=36584908
- arrowsmith 3y ago
  Wait, so it's just "five Kelvin", not "five degrees Kelvin"? TIL. Now that I think about, what's the etymological reason we use "degrees" to talk about temperature? We don't measure force in "degrees Newton" or electric current in "degrees Ampère". Why do we do it for Celsius and Fahrenheit?
  - Y_Y 3y ago
    Five kelvins. Just like five metres, no capital letters or funny symbols. The reason you can do it for Celsius or Fahrenheit is that those are scales but not units. The energy in two bodies (with constant heat capacity) at 100° is not the same as in a single body at 200°, but if you use kelvins then it works out.
  - ben_w 3y ago
    > We don't measure force in "degrees Newton" Not for force, no, but: https://en.wikipedia.org/wiki/Newton_scale https://en.wikipedia.org/wiki/Newton_scale
  - evanb 3y ago
    I don’t know but freezing and boiling of water are separated by 180 degrees F.
onion2k 3y ago
You can go below absolute zero, but things get weird. https://www.sciencedaily.com/releases/2013/01/130104143516.htm https://www.sciencedaily.com/releases/2013/01/130104143516.h...
- cinntaile 3y ago
  That seems to be taking a theoretical approach. I don't think there are any experiments that have proven it is possible?
  - xen0 3y ago
    Population inversion is a thing; many lasers exhibit this behaviour. But we tend not to talk about the 'temperature' of electron energy levels. If we did, then they would have negative temperature.
  - Y_Y 3y ago
    Negative temperature is a perfectly normal and well-studied phenomenon with lots of common examples. Temperature is defined as the rate of change of entropy wrt internal energy, usually more energy means more entropy, but it's not a given. https://en.wikipedia.org/wiki/Negative_temperature https://en.wikipedia.org/wiki/Negative_temperature
    - deleted 3y ago
      [deleted]
    - aziaziazi 3y ago
      > A system with a truly negative temperature on the Kelvin scale is hotter than any system with a positive temperature. If a negative-temperature system and a positive-temperature system come in contact, heat will flow from the negative- to the positive-temperature system Wait what?!! That feeds my daily “oh oooh” moment.
      - Y_Y 3y ago
        Energy flow wants to maximize entropy. Usually things flow from hot to cold because a cold thing will "make better use" of the energy to create entropy (i.e. permit microstates). Something with negative temperature will increase entropy by losing energy, and the positive temperature thing will increase entropy by gaining it, so it's (thermodynamically) a no-brainer.

-40K are impossible AFAIK

a2800276 3y ago

That's why they say it's -40 degrees. :P

Lester_Square 3y ago

Kelvin is not measured in degrees however, so is excluded by implication

flangola7 3y ago
It's not? What is it measured in then?
- bmicraft 3y ago
  K, not °K
- unwind 3y ago
  It is simply measured in Kelvin. Kelvin is the standard unit for temperature, 0 Kelvin is the absolute zero point. Each step is the same size as a degree Celsius, but there are no "degrees". Edit: remove assertion that the scale does not go into negative, because physics.
  - deelly 3y ago
    As a non-native reader, I`m not sure that I understand. Could you explain why 100 Kelvin, but 100 degrees Celsius and 100 degrees Fahrenheit? Is there some special meaning in a word "degrees" there?
    - forbiddenlake 3y ago
      Earlier comment - https://news.ycombinator.com/item?id=36584908 https://news.ycombinator.com/item?id=36584908
arrowsmith 3y ago
Wait, so it's just "five Kelvin", not "five degrees Kelvin"? TIL. Now that I think about, what's the etymological reason we use "degrees" to talk about temperature? We don't measure force in "degrees Newton" or electric current in "degrees Ampère". Why do we do it for Celsius and Fahrenheit?
- Y_Y 3y ago
  Five kelvins. Just like five metres, no capital letters or funny symbols. The reason you can do it for Celsius or Fahrenheit is that those are scales but not units. The energy in two bodies (with constant heat capacity) at 100° is not the same as in a single body at 200°, but if you use kelvins then it works out.
- ben_w 3y ago
  > We don't measure force in "degrees Newton" Not for force, no, but: https://en.wikipedia.org/wiki/Newton_scale https://en.wikipedia.org/wiki/Newton_scale
- evanb 3y ago
  I don’t know but freezing and boiling of water are separated by 180 degrees F.

onion2k 3y ago

You can go below absolute zero, but things get weird. https://www.sciencedaily.com/releases/2013/01/130104143516.htm https://www.sciencedaily.com/releases/2013/01/130104143516.h...

cinntaile 3y ago
That seems to be taking a theoretical approach. I don't think there are any experiments that have proven it is possible?
- xen0 3y ago
  Population inversion is a thing; many lasers exhibit this behaviour. But we tend not to talk about the 'temperature' of electron energy levels. If we did, then they would have negative temperature.
- Y_Y 3y ago
  Negative temperature is a perfectly normal and well-studied phenomenon with lots of common examples. Temperature is defined as the rate of change of entropy wrt internal energy, usually more energy means more entropy, but it's not a given. https://en.wikipedia.org/wiki/Negative_temperature https://en.wikipedia.org/wiki/Negative_temperature
  - deleted 3y ago
    [deleted]
  - aziaziazi 3y ago
    > A system with a truly negative temperature on the Kelvin scale is hotter than any system with a positive temperature. If a negative-temperature system and a positive-temperature system come in contact, heat will flow from the negative- to the positive-temperature system Wait what?!! That feeds my daily “oh oooh” moment.
    - Y_Y 3y ago
      Energy flow wants to maximize entropy. Usually things flow from hot to cold because a cold thing will "make better use" of the energy to create entropy (i.e. permit microstates). Something with negative temperature will increase entropy by losing energy, and the positive temperature thing will increase entropy by gaining it, so it's (thermodynamically) a no-brainer.