4 ms·

Your guess? So to clarify, you're sure that the headline is misleading, or you're guessing that it is? Could someone explain in terms we non-physicists can unde

Your guess? So to clarify, you're sure that the headline is misleading, or you're guessing that it is? Could someone explain in terms we non-physicists can understand? I'm willing to bet most people (myself included) don't understand the equations you posted. Still, it's the top comment because every top comment on Hacker News is "that headline is misleading."

Xcelerate 14y ago
I was trying to write my post so that it comes across in a way that doesn't require stat. mech to understand (you just need to know how derivatives work). You don't have to understand how the equations are derived to understand what the result means. To explain what I mean by states, consider a 3-bit string. How many states are there? 2^3 = 8 states. Similarly, if you have a collection of particles, there's only a finite number of "arrangements" (for lack of a better word) that these particles can be in. The more possible arrangements, the higher the entropy. I added another post on why I think the headline is misleading. Basically, if the article's intent is to explain the subject to non-physicists, they're just going to confuse people by using that word "temperature". Instead, it's better to say what you normally think of as temperature (hot and cold) has a more precise, mathematical definition that doesn't really correspond to intuitive notions of hot and cold any more. > Still, it's the top comment because every top comment on Hacker News is "that headline is misleading." And for good reason. That's why the article gets so much attention and discussion. If it had been submitted as "Unique quantum gas has decreasing entropy for increasing energy" it would have no replies.
- boboblong 14y ago
  But isn't that just as fascinating (as long as you know what it means)? I just finished my first college-level physics course a few weeks ago and I'm already fuzzy on the thermodynamics stuff, but the entropy of this gas shouldn't decrease with increasing energy, should it?
gus_massa 14y ago
A little late, but I hope this clarifies why the headline is misleading. The natural interpretation of "Quantum gas goes below absolute zero" is that someone had a super-freezer that cooled a gas so much that it is passed the 0K and it's so cold that it has negative temperature. The real thing is that it is so hot that the temperature "goes beyond" infinity and is negative. A better headline would have been "Quantum gas goes negative absolute temperature". Usually "bellow zero" and "negative" mean the same thing. The problem with "absolute" temperature is that the natural order of the real numbers is not the same as the hot-cold order. (It's a topological problem :).) (It's explained in more detail in other comments.)

Xcelerate 14y ago

I was trying to write my post so that it comes across in a way that doesn't require stat. mech to understand (you just need to know how derivatives work). You don't have to understand how the equations are derived to understand what the result means. To explain what I mean by states, consider a 3-bit string. How many states are there? 2^3 = 8 states. Similarly, if you have a collection of particles, there's only a finite number of "arrangements" (for lack of a better word) that these particles can be in. The more possible arrangements, the higher the entropy. I added another post on why I think the headline is misleading. Basically, if the article's intent is to explain the subject to non-physicists, they're just going to confuse people by using that word "temperature". Instead, it's better to say what you normally think of as temperature (hot and cold) has a more precise, mathematical definition that doesn't really correspond to intuitive notions of hot and cold any more. > Still, it's the top comment because every top comment on Hacker News is "that headline is misleading." And for good reason. That's why the article gets so much attention and discussion. If it had been submitted as "Unique quantum gas has decreasing entropy for increasing energy" it would have no replies.

boboblong 14y ago
But isn't that just as fascinating (as long as you know what it means)? I just finished my first college-level physics course a few weeks ago and I'm already fuzzy on the thermodynamics stuff, but the entropy of this gas shouldn't decrease with increasing energy, should it?

gus_massa 14y ago

A little late, but I hope this clarifies why the headline is misleading. The natural interpretation of "Quantum gas goes below absolute zero" is that someone had a super-freezer that cooled a gas so much that it is passed the 0K and it's so cold that it has negative temperature. The real thing is that it is so hot that the temperature "goes beyond" infinity and is negative. A better headline would have been "Quantum gas goes negative absolute temperature". Usually "bellow zero" and "negative" mean the same thing. The problem with "absolute" temperature is that the natural order of the real numbers is not the same as the hot-cold order. (It's a topological problem :).) (It's explained in more detail in other comments.)