from Hacker News

Negative Temperature

by dave1010uk on 7/8/24, 8:35 PM with 15 comments

• by Anon84 on 7/8/24, 9:10 PM

  Cool. I actually worked on this back in the early days of my PhD (https://arxiv.org/pdf/0705.2385). Never expected to see it on HN

• by Ygg2 on 7/8/24, 10:56 PM

  I always keep remembering Discworld of going one way and becoming the extreme. Rephrased from Moving pictures:

     > Not simply, ordinarily cold. Ordinary cold was merely the absence of movement. It has passed through there a long time ago, had gone straight through commonplace idleness and out the far side. It put more effort into staying still than most things put into movement.

• by mjfl on 7/8/24, 10:17 PM

  Temperature, thermodynamically, is the quantity dQ/dS, which is sort of related to how much the internal energy of the system changes as the system gets bigger, or has more 'stuff' in it, it's like an average energy.

  We experience temperature, however, as the amount of heat coming from an object. Really the experience of temperature should then be something like -dS/dQ which is like how readily the system gives up energy. The more entropy increases when the energy in the system decreases, the more 'hot' it feels.

  Therefore, our 'experience' of temperature is like -1/T = -dS/dQ. The hottest temperatures are negative numbers close to zero.

  Additionally, infinity temperature is simply the crossover point where adding additional heat begins to decrease entropy instead of increasing it. I.e. the places to store the additional heat are running out.

• by derbOac on 7/8/24, 9:08 PM

  I've read and watched different attempts at explaining negative temperature, and the Wikipedia article is actually the one that has made the most sense to me.

  The concept still seems "off" to me intuitively, like an abuse of notation or something, although I understand it logically.

• by skulk on 7/8/24, 9:19 PM

  From the main image caption:

  > SI temperature/coldness conversion scale: Temperatures on the Kelvin scale are shown in blue (Celsius scale in green, Fahrenheit scale in red), coldness values in gigabyte per nanojoule are shown in black

  gigabyte per nanojoule? wat? I understand that this is some measure of entropy but the article never mentions bytes again which is slightly baffling.

• by amelius on 7/8/24, 9:50 PM

  > A system with a truly negative temperature on the Kelvin scale is hotter than any system with a positive temperature.

  How to interpret this sentence?