Not so absolute now, are you?
January 4, 2013 9:57 AM Subscribe
Quantum gas goes below absolute zero. "It may sound less likely than hell freezing over, but physicists have created an atomic gas with a sub-absolute-zero temperature for the first time. Their technique opens the door to generating negative-Kelvin materials and new quantum devices, and it could even help to solve a cosmological mystery."
For instance, Rosch and his colleagues have calculated that whereas clouds of atoms would normally be pulled downwards by gravity, if part of the cloud is at a negative absolute temperature, some atoms will move upwards, apparently defying gravity.
IMMA GET ME MY HOVERBOARD
posted by mightygodking at 10:02 AM on January 4, 2013 [13 favorites]
IMMA GET ME MY HOVERBOARD
posted by mightygodking at 10:02 AM on January 4, 2013 [13 favorites]
What this universe really needs is a decent bug tracking system.
posted by theodolite at 10:02 AM on January 4, 2013 [44 favorites]
posted by theodolite at 10:02 AM on January 4, 2013 [44 favorites]
Dr. Bishop was trying to make ice cream and then this happened.
posted by The Whelk at 10:02 AM on January 4, 2013 [12 favorites]
posted by The Whelk at 10:02 AM on January 4, 2013 [12 favorites]
"Why don't you just make 0 Kelvin lower and make 0 be the lowest temperature and make that a little lower?"
"These go to negative Kelvin."
posted by 2bucksplus at 10:03 AM on January 4, 2013 [128 favorites]
"These go to negative Kelvin."
posted by 2bucksplus at 10:03 AM on January 4, 2013 [128 favorites]
This really sounds like one of those "Oh, that's weird" kind of discoveries that eventually winds up spinning off a new branch of physics.
posted by boo_radley at 10:04 AM on January 4, 2013
posted by boo_radley at 10:04 AM on January 4, 2013
/r/science clarifies what's going on with "negative temperature" (which is actually not colder than absolute zero).
posted by a snickering nuthatch at 10:05 AM on January 4, 2013 [11 favorites]
posted by a snickering nuthatch at 10:05 AM on January 4, 2013 [11 favorites]
It doesn't go below absolute zero. Negative temperature just means that adding more energy to the system cools it down and vice versa.
posted by empath at 10:06 AM on January 4, 2013
posted by empath at 10:06 AM on January 4, 2013
Negative temperature just means that adding more energy to the system cools it down and vice versa.
That's negative heat capacity, not negative temperature (although their "negative temperature" system might also have that feature). The sun, for example, has a negative heat capacity but positive temperature
posted by kiltedtaco at 10:08 AM on January 4, 2013 [2 favorites]
That's negative heat capacity, not negative temperature (although their "negative temperature" system might also have that feature). The sun, for example, has a negative heat capacity but positive temperature
posted by kiltedtaco at 10:08 AM on January 4, 2013 [2 favorites]
Another peculiarity of the sub-absolute-zero gas is that it mimics 'dark energy', the mysterious force that pushes the Universe to expand at an ever-faster rate against the inward pull of gravity. Schneider notes that the attractive atoms in the gas produced by the team also want to collapse inwards, but do not because the negative absolute temperature stabilises them. “It’s interesting that this weird feature pops up in the Universe and also in the lab,” he says. “This may be something that cosmologists should look at more closely.”That is interesting.
posted by stbalbach at 10:08 AM on January 4, 2013 [11 favorites]
Man, there are so many Douglas Adams quotes that I could apply to this article and I don't know where to start.
posted by ardgedee at 10:11 AM on January 4, 2013 [2 favorites]
posted by ardgedee at 10:11 AM on January 4, 2013 [2 favorites]
This phys.org article does a good job of explaining it.
posted by vacapinta at 10:11 AM on January 4, 2013 [4 favorites]
posted by vacapinta at 10:11 AM on January 4, 2013 [4 favorites]
"These go to negative Kelvin."
I hated favoriting that because at that moment the favorite count had gone to eleven. But it wouldn't have lasted.
posted by George_Spiggott at 10:13 AM on January 4, 2013 [12 favorites]
I hated favoriting that because at that moment the favorite count had gone to eleven. But it wouldn't have lasted.
posted by George_Spiggott at 10:13 AM on January 4, 2013 [12 favorites]
The universe is so strange and complex and fascinating. Thanks to all in this thread who posted links to resources for making sense of this.
posted by clockzero at 10:13 AM on January 4, 2013
posted by clockzero at 10:13 AM on January 4, 2013
I observed negative temperature over two decades ago when I was dating two women in college and ran into one while out with the other. The event also lead to quantum entanglement; though it wasn't the hoped for superposition that might of let me solve complex problems that have vexed man for thousands of years.
posted by humanfont at 10:16 AM on January 4, 2013 [14 favorites]
posted by humanfont at 10:16 AM on January 4, 2013 [14 favorites]
The difficulty in publishing a popular article on this subject is that at these scales, our macro, experiential notion of the meaning of "temperature" isn't useful.
posted by George_Spiggott at 10:19 AM on January 4, 2013
posted by George_Spiggott at 10:19 AM on January 4, 2013
/r/science clarifies what's going on with "negative temperature"
Without having clicked, I'm going to guess the answer is "journalism".
posted by DU at 10:22 AM on January 4, 2013 [7 favorites]
Without having clicked, I'm going to guess the answer is "journalism".
posted by DU at 10:22 AM on January 4, 2013 [7 favorites]
"Why don't you just make 0 Kelvin lower and make 0 be the lowest temperature and make that a little lower?"
"These go to negative Kelvin."
It's, like, how much more cold could this get? And the answer is none. None more co... what the hell are you guys seeing this?
posted by griphus at 10:27 AM on January 4, 2013 [7 favorites]
"These go to negative Kelvin."
It's, like, how much more cold could this get? And the answer is none. None more co... what the hell are you guys seeing this?
posted by griphus at 10:27 AM on January 4, 2013 [7 favorites]
"These go to negative Kelvin."
I don't usually laugh out loud at work, 2bucksplus. Wish I could favorite you twice!
posted by Pistache at 10:27 AM on January 4, 2013
I don't usually laugh out loud at work, 2bucksplus. Wish I could favorite you twice!
posted by Pistache at 10:27 AM on January 4, 2013
Also supposedly impossible heat engines can be realized with the help of negative absolute temperatures, such as an engine with a thermodynamic efficiency above 100%.
The implications of this are quite interesting, particularly if scale-up is possible. High energy-density batteries? Even at a micro-scale, this could power molecular machinery. One of the fundamental problems of nano-technology is that no-one really knows how to make a dense, lasting energy source on the molecular scale. Could this make high-energy nanomachines possible? What kind of odd environment would such viruses have to live in though?
Also, if this really is an analogue for dark matter, a kind of frozen energy source, all kinds of fantastical science fictiony stuff can be imagined: higher-speed travel with "free" dark matter energy, "space miners" in the dark between the stars, even credible void krakens who live on the stuff---where there's a food source, why not dark, cold, invisible life (inimical to the human mind, bleeding through normal matter....)?
In short, I look forward to cstross' new novels.
posted by bonehead at 10:30 AM on January 4, 2013 [2 favorites]
The implications of this are quite interesting, particularly if scale-up is possible. High energy-density batteries? Even at a micro-scale, this could power molecular machinery. One of the fundamental problems of nano-technology is that no-one really knows how to make a dense, lasting energy source on the molecular scale. Could this make high-energy nanomachines possible? What kind of odd environment would such viruses have to live in though?
Also, if this really is an analogue for dark matter, a kind of frozen energy source, all kinds of fantastical science fictiony stuff can be imagined: higher-speed travel with "free" dark matter energy, "space miners" in the dark between the stars, even credible void krakens who live on the stuff---where there's a food source, why not dark, cold, invisible life (inimical to the human mind, bleeding through normal matter....)?
In short, I look forward to cstross' new novels.
posted by bonehead at 10:30 AM on January 4, 2013 [2 favorites]
..an engine with a thermodynamic efficiency above 100%.
Lisa, I warned you once!
posted by DU at 10:32 AM on January 4, 2013 [17 favorites]
Lisa, I warned you once!
posted by DU at 10:32 AM on January 4, 2013 [17 favorites]
It's not free energy. It takes a lot of energy to cool the gas down to that state.
posted by empath at 10:32 AM on January 4, 2013 [1 favorite]
posted by empath at 10:32 AM on January 4, 2013 [1 favorite]
I'm not at all an expert, but I'll take a shot at explaining "negative temperature" using just high school math.
If you look at the Boltzmann distribution here , you'll notice that for finite positive temperature, then the distribution is decreasing as energy increases. In other words, there are always more particles in lower energy states. If the temperature is negative, then there will be fewer particles in lower energy states (see e.g. The third picture in the phys.org article. I think this is what the researchers have created.
Mathematically, it boils down to exp(-x/T) being increasing for negative T and decreasing for positive T.
posted by ILuvMath at 10:44 AM on January 4, 2013 [2 favorites]
If you look at the Boltzmann distribution here , you'll notice that for finite positive temperature, then the distribution is decreasing as energy increases. In other words, there are always more particles in lower energy states. If the temperature is negative, then there will be fewer particles in lower energy states (see e.g. The third picture in the phys.org article. I think this is what the researchers have created.
Mathematically, it boils down to exp(-x/T) being increasing for negative T and decreasing for positive T.
posted by ILuvMath at 10:44 AM on January 4, 2013 [2 favorites]
"I don't usually laugh out loud at work, 2bucksplus. Wish I could favorite you twice!"
Careful, Pistache - if I've learned anything from this thread, it's that adding more favourite to the system means 2bucksplus might end up negative favourited.
posted by Prince Lazy I at 10:51 AM on January 4, 2013 [2 favorites]
Careful, Pistache - if I've learned anything from this thread, it's that adding more favourite to the system means 2bucksplus might end up negative favourited.
posted by Prince Lazy I at 10:51 AM on January 4, 2013 [2 favorites]
We already know quite a bit about "quantum gas." According to my brother, after a gas in a closed space interacts with an observer, its wave function collapses and it takes on a stable vector deriving from one single dealer.
posted by R. Schlock at 10:55 AM on January 4, 2013 [15 favorites]
posted by R. Schlock at 10:55 AM on January 4, 2013 [15 favorites]
DU is right about this being called "journalism", but I'm just going to consider it as further evidence that we live in a universe implemented with signed integer overflow bugs.
posted by atbash at 10:56 AM on January 4, 2013 [1 favorite]
posted by atbash at 10:56 AM on January 4, 2013 [1 favorite]
ILuvMath- bingo. This is a statistical phenomenon operating in a context of a bounded, isolated system. IOW- Infinite free energy is not available in your market area.
posted by Phyllis Harmonic at 10:57 AM on January 4, 2013
posted by Phyllis Harmonic at 10:57 AM on January 4, 2013
Kind of reminds me of Revelation Space, which features spacecraft with stealth devices which are endothermic computers, i.e. They get colder the more computation they perform (cooling down the spaceship makes it harder to detect in space).
posted by EndsOfInvention at 10:58 AM on January 4, 2013 [1 favorite]
posted by EndsOfInvention at 10:58 AM on January 4, 2013 [1 favorite]
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.
Read more at: http://phys.org/news/2013-01-atoms-negative-absolute-temperature-hottest.html#jCp
from the phys.org article linked above
posted by OHenryPacey at 10:59 AM on January 4, 2013
Read more at: http://phys.org/news/2013-01-atoms-negative-absolute-temperature-hottest.html#jCp
from the phys.org article linked above
posted by OHenryPacey at 10:59 AM on January 4, 2013
It's Kelvins all the way down.
posted by weapons-grade pandemonium at 10:59 AM on January 4, 2013 [1 favorite]
posted by weapons-grade pandemonium at 10:59 AM on January 4, 2013 [1 favorite]
Why does it feel like they could have easily come up with a different name for this state of matter but following in the tradition of "teleportation" the quantum folks decided to fuck around and give us "negative kelvin"?
posted by Tell Me No Lies at 11:03 AM on January 4, 2013 [3 favorites]
posted by Tell Me No Lies at 11:03 AM on January 4, 2013 [3 favorites]
I don't care so much for this negative Kelvin, always complaining.
posted by TwelveTwo at 11:14 AM on January 4, 2013
posted by TwelveTwo at 11:14 AM on January 4, 2013
You expect me to understand high school math? Someone explain it with kittens.
posted by Ad hominem at 11:15 AM on January 4, 2013 [3 favorites]
posted by Ad hominem at 11:15 AM on January 4, 2013 [3 favorites]
Negative temperature just means that adding more energy to the system cools it down
posted by empath
Eponysterical.
posted by nathancaswell at 11:17 AM on January 4, 2013
posted by empath
Eponysterical.
posted by nathancaswell at 11:17 AM on January 4, 2013
We already know quite a bit about "quantum gas." According to my brother, after a gas in a closed space interacts with an observer, its wave function collapses and it takes on a stable vector deriving from one single dealer.
posted by R. Schlock at 10:55 AM on January 4 [+] [!]
The Copenhagen interpretation implies quantum entanglement of gas to observer, such that measurement of quantum gas is essentially equivalent to creation of quantum gas, with all the ethical concerns associated from such a derivation.
posted by It's Raining Florence Henderson at 11:21 AM on January 4, 2013 [12 favorites]
posted by R. Schlock at 10:55 AM on January 4 [+] [!]
The Copenhagen interpretation implies quantum entanglement of gas to observer, such that measurement of quantum gas is essentially equivalent to creation of quantum gas, with all the ethical concerns associated from such a derivation.
posted by It's Raining Florence Henderson at 11:21 AM on January 4, 2013 [12 favorites]
To understand negative temperature, you need to know what the definition of temperature is, at least to a scientist. It turns out that the statistical mechanics definition of "temperature" does map to your everyday understanding (at least for things with positive temperature), as it should otherwise why the hell would scientists use the same word for both concepts, but it is a bit confusing.
Temperature is DEFINED as the partial derivative of the energy of a system with respect to the entropy of the system. So: what the fuck does that mean?
You have a thermodynamic system: a box of gas say. That box of gas has a bunch of properties: for one, the energy in the motion of the gas. I'll just refer to this as the "energy" E of the system (there are lots of other energies I could care about: gravitational potential, chemical, nuclear, but since I'm not dropping this box of gas or blowing it up, I can ignore all that). It also has "entropy," which I'll call S. Entropy is, in my opinion, the most important concept in physics. It is also one of the most slippery. You can think of the entropy as "the number of ways you can rearrange the system and no one would notice the difference." So, a hot box of gas has lots of entropy, because all those particles zipping around can be swapped with each other or have their momentum altered and no one would be able to tell that the system had changed. While a cold box of gas (particles nearly stationary) has low entropy, since if you start altering the momentum of individual particles, the system looks different ("hey, there wasn't a particle moving with high velocity before and now there is!").
I know that definition of entropy sounds REALLY anthrocentric. I'm sorry. It's not on a fundamental level - there are ways of rigorously defining all this stuff that removes what seems like the human element of "not noticing the difference," but when describing science I find myself often having to make certain analogies that may make things seem more arbitrary then they are. If you don't trust that statement, I strongly encourage you to go take a physics course on thermodynamics and stat mech and get your hands dirty with all of this. It's fascinating.
It's important to understand that entropy always increases; which makes sense given it's definition. There are more states with high entropy than low (by definition), so given the opportunity, everything eventually finds itself in a state of high entropy - the probability of not doing so is just insanely low (which is why this field is called statistical mechanics, its all about probability). Now, onto the definition of temperature.
Our day-to-day understanding of temperature is that if something is hot and we touch it to something cold, the cold thing heats up and the hot thing cools down. Let's be specific and say I take my box of hot gas, and touch it to a box of cold gas. We know that, eventually, the two objects will reach the same temperature.
Why does that happen? Well, a little bit of energy leaves the hot gas, reducing it's entropy by some amount. This would violate the 2nd Law of Thermodynamics (entropy always increases), except that the energy enters the cold gas, and increases it's entropy MORE than the hot gas entropy decreases. That is,
Delta S_hot (a negative number) + Delta S_cold (a positive number) > 0.
What this means is that, by adding energy to the cold thing, you've moved up the total S of the universe, because, while there would be more entropy in the hot gas system if it could keep all it's energy to itself, the universe doesn't "care" about maximizing the entropy of a single object. It will find its way to maximize the TOTAL entropy, and to do that it will rob the hot object of energy to feed the cold one, because this transaction wins entropically.
So, how do you tell which object is hot and which object is cold? You compare the two systems and ask: if I remove some energy from one system, how does it's entropy change? Is that entropy change greater or less than the entropy change to the second system if I remove a bit of energy? The "hot" system is the one where:
(Delta S/Delta E)_hot < (Delta S/Delta E)_cold
Which is to say, the entropy increase in the cold system is greater than the entropy loss in the hot system, so energy flows from the hot to the cold because the Universe is a bastard and is always going to increase entropy.
If you turn those "Deltas" into derivatives (which is to say, just ask what happens when you change the system by a tiiiinnyyy amount), and define temperature T as partial S/partial E, you'll see that my (totally obvious) explanation of what a hot object is says that, for these two systems:
T_cold < T_hot.
So I've rediscovered the obvious fact that hot things have a higher temperature than cold things.
But I've learned something. I've learned that the transparent fact (to us) that there is something called temperature and it has something to do with whether I get burned or get frostbite if I touch "hot" or "cold" things has to do with this totally non-intuitive definition in terms of entropy.
So now I can FINALLY describe a negative temperature object.
In day to day life, adding energy to an object INCREASES its entropy. The box of gas, in my previous example, gets more disordered when you add energy. But, just from the equation:
T = partial E/partial S (or in the non-infinitesimal limit) Delta E/Delta S
you can ask, what would happen if you had something that LOST entropy when you added energy? Well, Delta S would be negative for positive Delta E, so T is negative. It's hard to imagine how that would happen, but basically this is saying that there are fewer ways to have high energy than there are to have low energy. This "never" happens in normal life, but the scientists here have found a way to finagle a system that does have this property.
What happens if you touch a "heat bath" of negative temperature material (a heat bath is a theoretical construct in thermodynamics, and defined as "an object of a certain temperature that is so big that you can never remove or add enough energy to noticeably change it's temperature. For example, if I jump into the ocean, the ocean gains energy from me as it cools me down, but you'll never see the temperature of the ocean rise because I jumped in.) Well, if I touch a -T object, energy that flows from me into it would reduce my entropy (as I have positive T), but reduce it's entropy (by definition: gaining energy causes -T objects to reduce in S). However, if energy flows from it into me, I gain entropy AND the -T object gains entropy. So, if the -T object was big enough and stable enough, it would just continue to dump energy into ANY positive T object in thermal contact. Thus, it is "hotter" in our day-to-day understanding of "hot" than every object with positive temperature.
Which implies to me that these objects are massively unstable; you must continually dump energy into the system (by processes low entropy-energy somewhere in your lab apparatus) otherwise your little -T object will just dump all it's energy out and you'll destroy the delicate set-up that allowed you to cheat the normal relation between energy change and entropy change.
Which is not to say that this isn't really cool, or potentially useful. I have no idea, but when I learned about thermodynamics way back when, the only example of -T objects I heard about were magnetic systems that display similar behavior but don't have quite the same cachet of a real box o' gas that likes to give away energy like it's going out of style. So I think this is pretty nifty.
In conclusion, temperature is a land of contrasts.
Also bonehead, they are talking about dark energy, not dark matter. Dark matter is (from all evidence) a totally normal matter density (i.e. it attracts via gravity) with the particular property that it interacts extremely weakly with normal matter. Dark energy is the wacky shit that behaves like a cosmological constant: increasing the expansion of the Universe while maintaining a constant energy density as the volume increases. All evidence and theoretical understanding (granted, we don't have a solution for either) is that they are totally unrelated.
posted by physicsmatt at 11:25 AM on January 4, 2013 [95 favorites]
Temperature is DEFINED as the partial derivative of the energy of a system with respect to the entropy of the system. So: what the fuck does that mean?
You have a thermodynamic system: a box of gas say. That box of gas has a bunch of properties: for one, the energy in the motion of the gas. I'll just refer to this as the "energy" E of the system (there are lots of other energies I could care about: gravitational potential, chemical, nuclear, but since I'm not dropping this box of gas or blowing it up, I can ignore all that). It also has "entropy," which I'll call S. Entropy is, in my opinion, the most important concept in physics. It is also one of the most slippery. You can think of the entropy as "the number of ways you can rearrange the system and no one would notice the difference." So, a hot box of gas has lots of entropy, because all those particles zipping around can be swapped with each other or have their momentum altered and no one would be able to tell that the system had changed. While a cold box of gas (particles nearly stationary) has low entropy, since if you start altering the momentum of individual particles, the system looks different ("hey, there wasn't a particle moving with high velocity before and now there is!").
I know that definition of entropy sounds REALLY anthrocentric. I'm sorry. It's not on a fundamental level - there are ways of rigorously defining all this stuff that removes what seems like the human element of "not noticing the difference," but when describing science I find myself often having to make certain analogies that may make things seem more arbitrary then they are. If you don't trust that statement, I strongly encourage you to go take a physics course on thermodynamics and stat mech and get your hands dirty with all of this. It's fascinating.
It's important to understand that entropy always increases; which makes sense given it's definition. There are more states with high entropy than low (by definition), so given the opportunity, everything eventually finds itself in a state of high entropy - the probability of not doing so is just insanely low (which is why this field is called statistical mechanics, its all about probability). Now, onto the definition of temperature.
Our day-to-day understanding of temperature is that if something is hot and we touch it to something cold, the cold thing heats up and the hot thing cools down. Let's be specific and say I take my box of hot gas, and touch it to a box of cold gas. We know that, eventually, the two objects will reach the same temperature.
Why does that happen? Well, a little bit of energy leaves the hot gas, reducing it's entropy by some amount. This would violate the 2nd Law of Thermodynamics (entropy always increases), except that the energy enters the cold gas, and increases it's entropy MORE than the hot gas entropy decreases. That is,
Delta S_hot (a negative number) + Delta S_cold (a positive number) > 0.
What this means is that, by adding energy to the cold thing, you've moved up the total S of the universe, because, while there would be more entropy in the hot gas system if it could keep all it's energy to itself, the universe doesn't "care" about maximizing the entropy of a single object. It will find its way to maximize the TOTAL entropy, and to do that it will rob the hot object of energy to feed the cold one, because this transaction wins entropically.
So, how do you tell which object is hot and which object is cold? You compare the two systems and ask: if I remove some energy from one system, how does it's entropy change? Is that entropy change greater or less than the entropy change to the second system if I remove a bit of energy? The "hot" system is the one where:
(Delta S/Delta E)_hot < (Delta S/Delta E)_cold
Which is to say, the entropy increase in the cold system is greater than the entropy loss in the hot system, so energy flows from the hot to the cold because the Universe is a bastard and is always going to increase entropy.
If you turn those "Deltas" into derivatives (which is to say, just ask what happens when you change the system by a tiiiinnyyy amount), and define temperature T as partial S/partial E, you'll see that my (totally obvious) explanation of what a hot object is says that, for these two systems:
T_cold < T_hot.
So I've rediscovered the obvious fact that hot things have a higher temperature than cold things.
But I've learned something. I've learned that the transparent fact (to us) that there is something called temperature and it has something to do with whether I get burned or get frostbite if I touch "hot" or "cold" things has to do with this totally non-intuitive definition in terms of entropy.
So now I can FINALLY describe a negative temperature object.
In day to day life, adding energy to an object INCREASES its entropy. The box of gas, in my previous example, gets more disordered when you add energy. But, just from the equation:
T = partial E/partial S (or in the non-infinitesimal limit) Delta E/Delta S
you can ask, what would happen if you had something that LOST entropy when you added energy? Well, Delta S would be negative for positive Delta E, so T is negative. It's hard to imagine how that would happen, but basically this is saying that there are fewer ways to have high energy than there are to have low energy. This "never" happens in normal life, but the scientists here have found a way to finagle a system that does have this property.
What happens if you touch a "heat bath" of negative temperature material (a heat bath is a theoretical construct in thermodynamics, and defined as "an object of a certain temperature that is so big that you can never remove or add enough energy to noticeably change it's temperature. For example, if I jump into the ocean, the ocean gains energy from me as it cools me down, but you'll never see the temperature of the ocean rise because I jumped in.) Well, if I touch a -T object, energy that flows from me into it would reduce my entropy (as I have positive T), but reduce it's entropy (by definition: gaining energy causes -T objects to reduce in S). However, if energy flows from it into me, I gain entropy AND the -T object gains entropy. So, if the -T object was big enough and stable enough, it would just continue to dump energy into ANY positive T object in thermal contact. Thus, it is "hotter" in our day-to-day understanding of "hot" than every object with positive temperature.
Which implies to me that these objects are massively unstable; you must continually dump energy into the system (by processes low entropy-energy somewhere in your lab apparatus) otherwise your little -T object will just dump all it's energy out and you'll destroy the delicate set-up that allowed you to cheat the normal relation between energy change and entropy change.
Which is not to say that this isn't really cool, or potentially useful. I have no idea, but when I learned about thermodynamics way back when, the only example of -T objects I heard about were magnetic systems that display similar behavior but don't have quite the same cachet of a real box o' gas that likes to give away energy like it's going out of style. So I think this is pretty nifty.
In conclusion, temperature is a land of contrasts.
Also bonehead, they are talking about dark energy, not dark matter. Dark matter is (from all evidence) a totally normal matter density (i.e. it attracts via gravity) with the particular property that it interacts extremely weakly with normal matter. Dark energy is the wacky shit that behaves like a cosmological constant: increasing the expansion of the Universe while maintaining a constant energy density as the volume increases. All evidence and theoretical understanding (granted, we don't have a solution for either) is that they are totally unrelated.
posted by physicsmatt at 11:25 AM on January 4, 2013 [95 favorites]
R. Schlock: "We already know quite a bit about "quantum gas." According to my brother, after a gas in a closed space interacts with an observer, its wave function collapses and it takes on a stable vector deriving from one single dealer."
When I first started trading futures many years ago, I told my brother I was trading natural gas futures. His response, "Trading them? Who is buying? I give away natural gas all day long." Wait until I tell him that gas is now trading at negative Kelvin. He will be pissed he didn't short it.
posted by JohnnyGunn at 11:25 AM on January 4, 2013 [1 favorite]
When I first started trading futures many years ago, I told my brother I was trading natural gas futures. His response, "Trading them? Who is buying? I give away natural gas all day long." Wait until I tell him that gas is now trading at negative Kelvin. He will be pissed he didn't short it.
posted by JohnnyGunn at 11:25 AM on January 4, 2013 [1 favorite]
IRFH, I assume you are referring to the now-outdated work of Jens Smaltid and Catharine Deltitte.
posted by Mister_A at 11:25 AM on January 4, 2013 [1 favorite]
posted by Mister_A at 11:25 AM on January 4, 2013 [1 favorite]
I'm an artist type. I know nothing about any of this stuff ... but Negative Kevin would be a hell of a good band name.
posted by philip-random at 11:27 AM on January 4, 2013
posted by philip-random at 11:27 AM on January 4, 2013
Picture one of those air-powered lottery ball machines.
Let's say you define gravity in terms of the distribution of the lottery balls in the container. You definition states that side of the container where most of the balls tend to gather is the side closest to the source of gravitational attraction. The balls are constantly in motion, but at any given time in your machine, most of the balls tend to gather near the bottom, with a few near the top.
Now let's say you turbocharge the fans in your lottery machine, adding huge amounts of energy so that most of the balls tend to gather at the top of the container, with only a few near the bottom. Using the definition of gravity given above, one could state that you've just created negative gravity.
Of course, gravity hasn't actually been reversed. There's no such thing as negative gravity. Rather, the combination of having an upper bound (the top of the container) and adding huge amounts of energy (the turbocharged fan) causes the system to behave as if it were in a state of negative gravity. It is technically correct, per your definition, to call it negative gravity, but since your definition was not made to take into account a situation such as this, doing so doesn't accurately convey what's going on. It does, however, generate more clicks for your press release.
posted by dephlogisticated at 11:32 AM on January 4, 2013 [8 favorites]
Let's say you define gravity in terms of the distribution of the lottery balls in the container. You definition states that side of the container where most of the balls tend to gather is the side closest to the source of gravitational attraction. The balls are constantly in motion, but at any given time in your machine, most of the balls tend to gather near the bottom, with a few near the top.
Now let's say you turbocharge the fans in your lottery machine, adding huge amounts of energy so that most of the balls tend to gather at the top of the container, with only a few near the bottom. Using the definition of gravity given above, one could state that you've just created negative gravity.
Of course, gravity hasn't actually been reversed. There's no such thing as negative gravity. Rather, the combination of having an upper bound (the top of the container) and adding huge amounts of energy (the turbocharged fan) causes the system to behave as if it were in a state of negative gravity. It is technically correct, per your definition, to call it negative gravity, but since your definition was not made to take into account a situation such as this, doing so doesn't accurately convey what's going on. It does, however, generate more clicks for your press release.
posted by dephlogisticated at 11:32 AM on January 4, 2013 [8 favorites]
Also, an alternative title for this post: We Need To Talk About Kelvin
posted by dephlogisticated at 11:37 AM on January 4, 2013 [5 favorites]
posted by dephlogisticated at 11:37 AM on January 4, 2013 [5 favorites]
Negative Kevin would be a hell of a good band name.
Too late.
posted by Herodios at 11:43 AM on January 4, 2013
Too late.
posted by Herodios at 11:43 AM on January 4, 2013
"Absolute zero"
You keep using that word. I do not think it means what you think it means.
posted by markslack at 12:06 PM on January 4, 2013
You keep using that word. I do not think it means what you think it means.
posted by markslack at 12:06 PM on January 4, 2013
Save me, peer review, because lots of new physics sounds just like "....and then a miracle occurs".
Be a shame if it's all luminiferous aether.
posted by dglynn at 12:08 PM on January 4, 2013
Be a shame if it's all luminiferous aether.
posted by dglynn at 12:08 PM on January 4, 2013
In an ensemble of particles, all of them don't have the same energy, but they follow a certain energy distribution. Normally (for low but positive T), most particles move very little, a few of them move a bit more, and a rare few can be quite fast. If you plot this distribution (a histogram over how many particles have a certain energy), it decreases exponentially with energy. The temperature is the coefficient that tells how quick this decay is.
In the sub-zero experiment, they have managed to reverse this distribution, so there are more particles moving quickly than slowly. It still follows an exponential curve, but now it's an increase instead of a decay. Hence you can fit the distribution to the same equation as usually, but with a negative value for T.
posted by springload at 12:11 PM on January 4, 2013 [2 favorites]
In the sub-zero experiment, they have managed to reverse this distribution, so there are more particles moving quickly than slowly. It still follows an exponential curve, but now it's an increase instead of a decay. Hence you can fit the distribution to the same equation as usually, but with a negative value for T.
posted by springload at 12:11 PM on January 4, 2013 [2 favorites]
yeah, much shorter take away: this result does not break physics (not to take away from the accomplishment of the experimentalists). Absolute Zero still exists, negative temperatures are totally fine with the laws of thermodynamics, this is just a very unusual system that behaves in ways that are extremely counter-intuitive, but completely expected from relatively basic statistical mechanics.
(I'm a theorist, I get to give back-handed compliments to experimentalists by describing their results as "just very unusual" and "completely expected.")
posted by physicsmatt at 12:15 PM on January 4, 2013 [1 favorite]
(I'm a theorist, I get to give back-handed compliments to experimentalists by describing their results as "just very unusual" and "completely expected.")
posted by physicsmatt at 12:15 PM on January 4, 2013 [1 favorite]
Also bonehead, they are talking about dark energy, not dark matter.
I thought physicmatt was being (uncharacteristically) a dick, until I realized bonehead is a username.
The internet is a strange place.
posted by pickinganameismuchharderthanihadanticipated at 12:20 PM on January 4, 2013 [1 favorite]
I thought physicmatt was being (uncharacteristically) a dick, until I realized bonehead is a username.
The internet is a strange place.
posted by pickinganameismuchharderthanihadanticipated at 12:20 PM on January 4, 2013 [1 favorite]
Dear god, why can't I seem to close tags?
posted by pickinganameismuchharderthanihadanticipated at 12:22 PM on January 4, 2013
posted by pickinganameismuchharderthanihadanticipated at 12:22 PM on January 4, 2013
Hah. Wow, I didn't even realize that is how it parsed.
posted by physicsmatt at 12:24 PM on January 4, 2013
posted by physicsmatt at 12:24 PM on January 4, 2013
I'm not at all an expert, but I'll take a shot at explaining "negative temperature" using just high school math.
If you look at the Boltzmann distribution here , you'll notice that for finite positive temperature, then the distribution is decreasing as energy increases.
You and I went to very different high schools.
posted by slogger at 12:33 PM on January 4, 2013 [3 favorites]
If you look at the Boltzmann distribution here , you'll notice that for finite positive temperature, then the distribution is decreasing as energy increases.
You and I went to very different high schools.
posted by slogger at 12:33 PM on January 4, 2013 [3 favorites]
Without having clicked, I'm going to guess the answer is "journalism".
That's what I thought but I at least hovered over the link to see that it was in Nature. I would imagine they're a little more rigorous then, like, Wired or something.
posted by delmoi at 12:36 PM on January 4, 2013
That's what I thought but I at least hovered over the link to see that it was in Nature. I would imagine they're a little more rigorous then, like, Wired or something.
posted by delmoi at 12:36 PM on January 4, 2013
Dear god, why can't I seem to close tags?
Dear pickinganameismuchharderthanihadanticipated,
Even I don't know that, but you should know that there is forgiveness available.
For five minutes.
-God
posted by benito.strauss at 1:11 PM on January 4, 2013
Dear pickinganameismuchharderthanihadanticipated,
Even I don't know that, but you should know that there is forgiveness available.
For five minutes.
-God
posted by benito.strauss at 1:11 PM on January 4, 2013
Lies, damned lies, and statistics.
Probabilities aren't about reality, they're about the limitations on our knowledge of reality. All fine and good, so long as we remember that.
posted by Twang at 1:34 PM on January 4, 2013
Probabilities aren't about reality, they're about the limitations on our knowledge of reality. All fine and good, so long as we remember that.
posted by Twang at 1:34 PM on January 4, 2013
Lord Kelvin defined the absolute temperature scale in the mid-1800s in such a way that nothing could be colder than absolute zero.
Physics has advanced since the mid-1800s you say? Hmmm.
*strokes chin*
Wolfgang Ketterle, a physicist and Nobel laureate at the Massachusetts Institute of Technology in Cambridge
Can you be someone else with a name like Wolfgang Ketterle?
Y'know, I like to think I'm pretty well accomplished, but you see guys like this doing this kind of work and just - damn. I mean the guy runs a 2:50 marathon. Has 3 kids. Divorced, but I'd think that actually takes up more time. Makes me feel like I'm a slacker for sleeping 3 hours a night.
(I was at a thing a while back talking to a guy about some of the funky things I've done. Not bragging, but I like to tell funny or interesting stories. I was talking about all kinds of stuff. My car in high school. Places I've been. Yeah, it was Chris Cassady. He's probably got a few more interesting things to discuss than I have. I wouldn't worry about tag closing given the level of what's being brought to the table. There are degrees of making an ass of oneself. Plus, one time during sex I called my wife "Frank." Also once I sawr a blimp.)
IANAP but this:
If the balls are, however, at negative temperature, their kinetic energy will already be so large that it cannot increase further. Therefore the balls cannot roll down and stay on top of the hill. The energy boundary therefore renders the system stable!"
makes sense.
But this: Negative temperatures imply negative pressures and open up new parameter regimes for cold atoms, enabling fundamentally new many-body states.
hurts my brain.
What new many-body states? 'Cos this makes it sound pretty radical (high temperature superconductivity f'rinstance. I've read some stuff on the Quantum spin Hall effect and had to go have a little bit of a lie down)
posted by Smedleyman at 1:52 PM on January 4, 2013
Physics has advanced since the mid-1800s you say? Hmmm.
*strokes chin*
Wolfgang Ketterle, a physicist and Nobel laureate at the Massachusetts Institute of Technology in Cambridge
Can you be someone else with a name like Wolfgang Ketterle?
Y'know, I like to think I'm pretty well accomplished, but you see guys like this doing this kind of work and just - damn. I mean the guy runs a 2:50 marathon. Has 3 kids. Divorced, but I'd think that actually takes up more time. Makes me feel like I'm a slacker for sleeping 3 hours a night.
(I was at a thing a while back talking to a guy about some of the funky things I've done. Not bragging, but I like to tell funny or interesting stories. I was talking about all kinds of stuff. My car in high school. Places I've been. Yeah, it was Chris Cassady. He's probably got a few more interesting things to discuss than I have. I wouldn't worry about tag closing given the level of what's being brought to the table. There are degrees of making an ass of oneself. Plus, one time during sex I called my wife "Frank." Also once I sawr a blimp.)
IANAP but this:
If the balls are, however, at negative temperature, their kinetic energy will already be so large that it cannot increase further. Therefore the balls cannot roll down and stay on top of the hill. The energy boundary therefore renders the system stable!"
makes sense.
But this: Negative temperatures imply negative pressures and open up new parameter regimes for cold atoms, enabling fundamentally new many-body states.
hurts my brain.
What new many-body states? 'Cos this makes it sound pretty radical (high temperature superconductivity f'rinstance. I've read some stuff on the Quantum spin Hall effect and had to go have a little bit of a lie down)
posted by Smedleyman at 1:52 PM on January 4, 2013
On preview, I came here to write what physicsmatt wrote. So I won't bother now.
Fun fact: I'm completely lying.
posted by NailsTheCat at 1:52 PM on January 4, 2013 [3 favorites]
Fun fact: I'm completely lying.
posted by NailsTheCat at 1:52 PM on January 4, 2013 [3 favorites]
"This result, described today in Science1, marks the gas’s transition from just above absolute zero to a few billionths of a Kelvin below absolute zero."
So what is the margin of error here? Is there one? How could there not be?
posted by Splunge at 2:28 PM on January 4, 2013
So what is the margin of error here? Is there one? How could there not be?
posted by Splunge at 2:28 PM on January 4, 2013
Sure there is, but going to negative temperature isn't like a rounding error on the thermometer. The system underwent a change in how it reacts to energy input/output, which I imagine isn't something the experimentalists would miss. In some sense, negative temperature is infinitely far away from any positive temperature (i.e., you don't get there just by doing more of what you're doing)
posted by physicsmatt at 2:36 PM on January 4, 2013
posted by physicsmatt at 2:36 PM on January 4, 2013
Probabilities aren't about reality, they're about the limitations on our knowledge of reality. All fine and good, so long as we remember that.
Except lots of VERY REAL things are really just measures of probability for large populations of molecules. pH and antibody affinity spring to mind here.
posted by Kid Charlemagne at 2:41 PM on January 4, 2013 [1 favorite]
Except lots of VERY REAL things are really just measures of probability for large populations of molecules. pH and antibody affinity spring to mind here.
posted by Kid Charlemagne at 2:41 PM on January 4, 2013 [1 favorite]
> In day to day life, adding energy to an object INCREASES its entropy. The box of gas, in my previous example, gets more disordered when you add energy. But, just from the equation:
T = partial E/partial S (or in the non-infinitesimal limit) Delta E/Delta S
you can ask, what would happen if you had something that LOST entropy when you added energy? Well, Delta S would be negative for positive Delta E, so T is negative.
As cool as their finding is, they've been scooped. T<0 has already been observed by every disgruntled kid who's been asked to put energy into his room so as to bring it to a less disordered state.
posted by Westringia F. at 3:00 PM on January 4, 2013
T = partial E/partial S (or in the non-infinitesimal limit) Delta E/Delta S
you can ask, what would happen if you had something that LOST entropy when you added energy? Well, Delta S would be negative for positive Delta E, so T is negative.
As cool as their finding is, they've been scooped. T<0 has already been observed by every disgruntled kid who's been asked to put energy into his room so as to bring it to a less disordered state.
posted by Westringia F. at 3:00 PM on January 4, 2013
Probabilities aren't about reality, they're about the limitations on our knowledge of reality. All fine and good, so long as we remember that.
Interesting you say that. It marks a division in perspective that I've often thought about. To me, randomness is reality. As an electrical engineer, and an analog one at that, I find the essential fact of noise is inescapable. Of course the modern way is to think like a computer engineer, to think about bits, and there isn't much room for true randomness there. You can't even make truly random things when you want to in that world.
It must be comforting to live in the ordered world of a computer engineer. Still, I've learned to embrace the ambiguity that goes along with accepting noise.
posted by Chuckles at 3:25 PM on January 4, 2013
Interesting you say that. It marks a division in perspective that I've often thought about. To me, randomness is reality. As an electrical engineer, and an analog one at that, I find the essential fact of noise is inescapable. Of course the modern way is to think like a computer engineer, to think about bits, and there isn't much room for true randomness there. You can't even make truly random things when you want to in that world.
It must be comforting to live in the ordered world of a computer engineer. Still, I've learned to embrace the ambiguity that goes along with accepting noise.
posted by Chuckles at 3:25 PM on January 4, 2013
Negative Kevin would be a hell of a good band name.
Too late.
To be clear, I did say Negative Kevin ... not Kelvin. I don't even know anyone named Kelvin.
posted by philip-random at 7:16 PM on January 4, 2013
Well, this article I found a month or two back doesn't see so fringe-science any more. If you can induce a population inversion in a magnetic core, you can extract energy from the ambient environmental heat.
Maybe the Steorn guys weren't wrong after all?
posted by MikeWarot at 9:44 PM on January 4, 2013
Maybe the Steorn guys weren't wrong after all?
posted by MikeWarot at 9:44 PM on January 4, 2013
I don't really know what this headline means, and I didn't read the full article, but I'm not above extrapolating from my misunderstanding of it to all sorts of outlandish ideas from other pop science articles I half remember reading years ago.
posted by moss at 10:37 AM on January 5, 2013
posted by moss at 10:37 AM on January 5, 2013
NOVA did a nice documentary on the history of cold as a scientific concept. It culminates in a neato experiment that uses series of cold gasses and friggin lasers to create a Bose-Einstein condensate.
posted by ian1977 at 11:17 AM on January 5, 2013
posted by ian1977 at 11:17 AM on January 5, 2013
Save me, peer review, because lots of new physics sounds just like "....and then a miracle occurs".
Be a shame if it's all luminiferous aether.
It's the anti-phlogistons that make it possible to go into the negative Kelvins.
posted by Philofacts at 1:09 PM on January 5, 2013
Be a shame if it's all luminiferous aether.
It's the anti-phlogistons that make it possible to go into the negative Kelvins.
posted by Philofacts at 1:09 PM on January 5, 2013
Probabilities aren't about reality, they're about the limitations on our knowledge of reality. All fine and good, so long as we remember that.
But this is a quantum mechanics thread... That's not true at all. There are no "hidden variables." In quantum mechanics, when you know the probability of a certain outcome, you know all you can know.
posted by OnceUponATime at 4:40 AM on January 6, 2013
But this is a quantum mechanics thread... That's not true at all. There are no "hidden variables." In quantum mechanics, when you know the probability of a certain outcome, you know all you can know.
posted by OnceUponATime at 4:40 AM on January 6, 2013
It's the anti-phlogistons that make it possible...
You say this, but if you treat phlogistons as having a molecular weight of -16, a charge of +2 and so forth, the theory actually starts to work pretty well. The big advantage of oxygen is that it gets rid of the whole negative mass thing.
posted by Kid Charlemagne at 3:57 PM on January 6, 2013
You say this, but if you treat phlogistons as having a molecular weight of -16, a charge of +2 and so forth, the theory actually starts to work pretty well. The big advantage of oxygen is that it gets rid of the whole negative mass thing.
posted by Kid Charlemagne at 3:57 PM on January 6, 2013
If the balls are, however, at negative temperature, their kinetic energy will already be so large that it cannot increase further.
Huh huh. You said "balls." You have large cold balls. Or hot, energetic balls. I'm not sure. /butthead
I adore physics, but this is yet another example of a thread that rapidly outpaces (like, by, oh, two comments or so in) my dim layman knowledge of even the basics. It's where I go into Chevy Chase mode and mutter, "It was my understanding that there was to be no math."
posted by Skot at 4:49 PM on January 6, 2013
Huh huh. You said "balls." You have large cold balls. Or hot, energetic balls. I'm not sure. /butthead
I adore physics, but this is yet another example of a thread that rapidly outpaces (like, by, oh, two comments or so in) my dim layman knowledge of even the basics. It's where I go into Chevy Chase mode and mutter, "It was my understanding that there was to be no math."
posted by Skot at 4:49 PM on January 6, 2013
The likelyhood of there being math is P=1. Please adjust your understanding accordingly.
posted by humanfont at 6:55 PM on January 6, 2013
posted by humanfont at 6:55 PM on January 6, 2013
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