Scientists Get Below Absolute Zero

[jakeyjake]

I don't believe it. Isn't absoulte zero supposed to be when molecules are not moving at all, and it is impossible to go below that? If they were able to get below absolute zero, then they didn't go below absolute zero, absolute zero was mismeasured.

 

[SifJar]

I don't believe it. Isn't absoulte zero supposed to be when molecules are not moving at all, and it is impossible to go below that? If they were able to get below absolute zero, then they didn't go below absolute zero, absolute zero was mismeasured.

Go back and read my posts explaining what this actually means (hint: it is not colder than absolute zero, despite that perhaps being the most obvious interpretation of the headlines about this story).

 

[Janthran]

>Science post
>CTRL+F "magnets"
>Unsurprised

 

[The Milkman]

Now, my puny 10th grade mind can't quite understand this. Isn't the whole thing with Absolute Zero is that it's a level on which no energy is being fed to matter? Like a complete stillness. How do you go under such a state? Wouldn't this just mean that they made the definition of absolute zero just a few billionths more accurate?

 

[JoostinOnline]

So am I right in thinking that they have "redefined" absolute zero?

 

[FireGrey]

is absolute zero like what freezers have?

 

[FAST6191]

Now, my puny 10th grade mind can't quite understand this. Isn't the whole thing with Absolute Zero is that it's a level on which no energy is being fed to matter? Like a complete stillness. How do you go under such a state? Wouldn't this just mean that they made the definition of absolute zero just a few billionths more accurate?

"Complete stillness", despite being something of a odd idea, would tend only to apply to perfect crystals as the law you are thinking of deals more with entropy. At the risk of grossly misinterpreting the issue and causing others to do the same if you recall the band gap for electrons (you probably encountered it as something to do with light which being taught about photons and quantum wells, later it will probably come if you are taught about semiconductors or it might have been the other way around- I don't know the US education system and what order they do things in). Here despite being very close to absolute zero the electrons* are held at something like the higher state via a clever arrangement of magnets and lasers (though lasers are nothing new when it comes to absolute zero experiments) though the effective entropy is very low, should some more energy near then the state as a whole risks collapsing and causing an entropy loss in the new particle- as entropy tends towards increasing the near particle would have lost entropy. Should you have plugged the relevant numbers into the standard equations you could fool yourself into thinking the temperature of the original particle was lower than absolute zero as it has just sucked energy off something it really should not have.
Going further and seriously risking misinterpretation if you stood on a trampoline, let it level out and straight jumped you would not get as high as if you did the same jump on solid floor. Should the observer not account for the spring and measure the energy you used as well as your mass they might conclude that gravity was stronger on the trampoline.

*temperature is mostly a function of electrons though when getting close to absolute zero it gets a bit odd- recall why you can not just superheat radioactive material to make it not radioactive.

Although I already said something like it- when you get very fast or very small Newtonian mechanics no longer applies (see quantum mechanics), you have probably been told mechanical friction does not vary with surface area- a useful approximation most of the time but not an accurate one when dealing with a lot of plastics, beyond that you might still be operating with the idea that the coefficient of friction is constant (you have the in motion and the from still versions at the very least), - when they teach you science they approximate an awful lot as most of the time it is useful to do so as the approximation works for many things and not many people will be able to take full science. I frequently find myself railing against many of the approximations they choose to make.

 

[back25]

A positive temperature (i.e. Every temperature recorded previously) means most particles have low energy and some have high. As you increase the temperature (becomes more positive), more particles will have higher energy, until infinite temperature where there will be an even distribution. "negative" absolute temperature is beyond that so to speak, at which points most particles have the higher energy. As I mentioned earlier "negative" absolute temperatures are hotter than an infinite positive. It's called negative because it is an inversion of the energy distribution of positive temperatures.

I'm not doubting you but,
To me, it looks like this "negative" absolute you say is more like higher than a low positive temperature and lower than infinite positive.
Unless in the negative state, you somehow have particles with higher energy than the ones you consider "high", and call that negative for some reason.

 

[tatripp]

Okay. I graduate college with a degree in English but even I can remember my high school chemistry class. By definition, absolute zero is the state where there is no heat which also means that there is no movement. There can be nothing colder than absolute zero.
Cold is only the lack of heat. If there is a little heat something will feel cold. If there is no heat then the temperature is absolute zero.

 

[SifJar]

So am I right in thinking that they have "redefined" absolute zero?

Nope.

I'm not doubting you but,
To me, it looks like this "negative" absolute you say is more like higher than a low positive temperature and lower than infinite positive.
Unless in the negative state, you somehow have particles with higher energy than the ones you consider "high", and call that negative for some reason.

I could be wrong in my interpretation, but I have read a couple of articles about this on Physics sites quite carefully, and came to the conclusions I have been stating.

For example, this article: http://phys.org/news/2013-01-atoms-negative-absolute-temperature-hottest.html#ajTabs

The title is "Atoms at negative absolute temperature: The hottest systems in the world" (emphasis added).

This diagram is also a useful illustration (to me, at least):

The left image (or the "nearest" image) shows a positive temperature; the particles generally have a low energy, with some very slightly higher (the probability of a given particle having a low energy is high; the probability of a given particle having a high energy is low). The centre image shows an infinite (postive) temperature; there is an equal probability of every different energy level. The final image on the right (or "furthest") shows an absolute negative temperature; most particles have a high energy level, some very slightly lower (the probability of a given particle having a high energy is high; the probability of a given particle having a low energy is low).

As I'm sure you can understand, the negative temperature diagram is the inversion of the positive diagram. (The diagrams are Boltzmann energy distribution diagrams). A typical practice in the case of inversion is to change the sign; positive to negative. Hence the diagram with the red balls is called "negative".

And a quote from that article:

"The inverted Boltzmann distribution is the hallmark of negative absolute temperature; and this is what we have achieved," says Ulrich Schneider. "Yet the gas is not colder than zero Kelvin, but hotter. It is even hotter than at any positive temperature – the temperature scale simply does not end at infinity, but jumps to negative values instead."

I guess if the scale were being defined now, it may be that what is now called infinity would be called zero, and we'd deal with negatives and positives in a more natural manner, with negatives being colder than positives (what we now call "positive" would of course be "negative" in that system, and vice versa). [Of course, the Celsius scale would have be shifted appropriately so that "real life" temperatures e.g. in weather forecasts etc. would still be relatively simple numbers.]

Another quote:

At first sight it may sound strange that a negative absolute temperature is hotter than a positive one. This is, however, simply a consequence of the historic definition of absolute temperature; if it were defined differently, this apparent contradiction would not exist.

Okay. I graduate college with a degree in English but even I can remember my high school chemistry class. By definition, absolute zero is the state where there is no heat which also means that there is no movement. There can be nothing colder than absolute zero.
Cold is only the lack of heat. If there is a little heat something will feel cold. If there is no heat then the temperature is absolute zero.

Correct. But as I've said numerous times in this thread now (sometimes with explanation), negative absolute temperatures are not colder than absolute zero.

 

[back25]

-snip-

First of all, thanks for this post. It was really helpful.
I was completely wrong with my assumption. It is now clear to me why absolute negative exists.
Still, the article could have made it clear that the "absolute zero" used a different scale. They wanna confuse us or what?

edit: I somehow ended confusing even distibution to equal distribution, hence why i said that in my previous post. i know it's stupid, but so am I, and my english skills.

 

[SifJar]

First of all, thanks for this post. It was really helpful.
I was completely wrong with my assumption. It is now clear to me why absolute negative exists.
Still, the article could have made it clear that the "absolute zero" used a different scale. They wanna confuse us or what?

I'm not sure if I'm misunderstanding you or something here, but I'd just like to clarify that there is no different scale. Absolute zero still means what it has always meant. I was just saying that if absolute zero was being defined today, it may be defined differently, to account for absolute negatives and positives. Or maybe not. The current definition does have important meaning (the state of zero internal energy of a system).

But I don't think there is any intention to confuse; it's just inherent of the subject matter i.e. the topic is confusing (particularly without a decent background knowledge of physics, and in your case perhaps, a native grasp of the English language [not that I have seen anything wrong language wise with your posts, just I can understand how that could make it easier to misinterpret things]), so articles about it will be confusing.

 

[back25]

-snip-

You been a big help bro,
I don't wanna be a bother anymore so I'll call it quits here.
This thing can't possibly get into my head.
thanks a lot, really

Edit: nevermind

 

[Wizerzak]

Sorry for the bump but this video just released by sixtysymbols explains this very well:


(Also, the title of this thread is wrong.)