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Note from micronesia: please read the thread before making comments about how we have just turned physics on its head. |
On January 05 2013 23:57 Fruscainte wrote:
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 gravity4.
Holy shit.. mass effect anyone?
I have a question though. Since the energy moves from a parts of atoms in the cloud at negative-kelvin to the positive-kelvin atoms in the cloud (from cold to hot, the opposite of what is normal), would the negative-kelvin atoms just continue to get colder and colder with a higher and higher value of negative-kelvin?
edit: Is negative-kelvin actually cold or is it hot? I'm reading negative-kelvin is actually hotter than any value of positive-kelvin since heat will always flow from negative to positive?
Also, does this invalidate the second law of thermodynamics? Is it possible the conditions necessary to reach this negative-kelvin temperature could ever occur naturally in the cosmos?
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I am surprised that this article is atracting so much popular attention. As has been mentioned, there is nothing really special about reaching "negative temperatures", we have been doing it from years. Someone mentioned LASER devices as an example of a popular device which feature negative temperatures.
Conventional wisdom tells us that high temperatures correspond to all states being equally probable. The thermal fluctuations can put atoms into any state. As one lowers the temperature, the atoms cannot access as many states. They prefer to stay in those with low energy (the thermal fluctuations are not enough to access the high energy states). So, "negative temperature" is the situation when the system perfers to be in high energy states instead of the low energy ones. It takes some experimental creativity to come up with such a situation, but it can be done!
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United States24665 Posts
On January 06 2013 13:23 philcorp wrote:
I am surprised that this article is atracting so much popular attention. As has been mentioned, there is nothing really special about reaching "negative temperatures", we have been doing it from years. Someone mentioned LASER devices as an example of a popular device which feature negative temperatures.
Conventional wisdom tells us that high temperatures correspond to all states being equally probable. The thermal fluctuations can put atoms into any state. As one lowers the temperature, the atoms cannot access as many states. They prefer to stay in those with low energy (the thermal fluctuations are not enough to access the high energy states). So, "negative temperature" is the situation when the system perfers to be in high energy states instead of the low energy ones. It takes some experimental creativity to come up with such a situation, but it can be done!
I believe a large mass of particle, influenced by gravity (a star) is another example of this. Adding energy causes the particles to 'orbit' at a higher altitude, slowing them down (as per satellite motion).
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On January 06 2013 13:40 micronesia wrote:
I believe a large mass of particle, influenced by gravity (a star) is another example of this. Adding energy causes the particles to 'orbit' at a higher altitude, slowing them down (as per satellite motion).
This sounds correct. If I add energy to something orbiting, its orbit gets larger. This is probably why they are hyping it up as the same as 'dark energy' (the name for the thing causing the large scale expansion of the universe). I am somewhat weary to make the analogy too certainly, at least without a great deal of thought though. I am not a general relativity guy, but I do recall some weird things about energy not always being conserved in GR, so one has to be a bit careful, I think.
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On January 06 2013 13:14 GGTeMpLaR wrote:Show nested quote +On January 05 2013 23:57 Fruscainte wrote:
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 gravity4.
Holy shit.. mass effect anyone? I have a question though. Since the energy moves from a parts of atoms in the cloud at negative-kelvin to the positive-kelvin atoms in the cloud (from cold to hot, the opposite of what is normal), would the negative-kelvin atoms just continue to get colder and colder with a higher and higher value of negative-kelvin? edit: Is negative-kelvin actually cold or is it hot? I'm reading negative-kelvin is actually hotter than any value of positive-kelvin since heat will always flow from negative to positive? Also, does this invalidate the second law of thermodynamics? Is it possible the conditions necessary to reach this negative-kelvin temperature could ever occur naturally in the cosmos?
This occurs naturally in stars and black holes. Negative-kelvin is hotter than any positive-kelvin. That is:
-1K > 100,000,000K
Because energy will always flow from the negative system to the positive system. In this case, temperature is being described as
T^(-1) = dS/dE
meaning when you find the slope of the line that you get when you graph entropy vs energy, its inverse will be the temperature. I'm sure if you could hold something that was -100k in your hands, and something that was 100,000,000K in your hands, the -100k wouldn't feel nearly as "hot" as the other. But, the -100K would still donate energy to the 100,000,000K system, and therefore it has a higher temperature.
But I suspect that -100K feels as hot as 100K. It's just the movement of energy which differs them for the most part.
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United Kingdom3482 Posts
On January 06 2013 14:47 Chargelot wrote:Show nested quote +On January 06 2013 13:14 GGTeMpLaR wrote:On January 05 2013 23:57 Fruscainte wrote:
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 gravity4.
Holy shit.. mass effect anyone? I have a question though. Since the energy moves from a parts of atoms in the cloud at negative-kelvin to the positive-kelvin atoms in the cloud (from cold to hot, the opposite of what is normal), would the negative-kelvin atoms just continue to get colder and colder with a higher and higher value of negative-kelvin? edit: Is negative-kelvin actually cold or is it hot? I'm reading negative-kelvin is actually hotter than any value of positive-kelvin since heat will always flow from negative to positive? Also, does this invalidate the second law of thermodynamics? Is it possible the conditions necessary to reach this negative-kelvin temperature could ever occur naturally in the cosmos? This occurs naturally in stars and black holes. Negative-kelvin is hotter than any positive-kelvin. That is: -1K > 100,000,000K Because energy will always flow from the negative system to the positive system. In this case, temperature is being described as T^(-1) = dS/dE meaning when you find the slope of the line that you get when you graph entropy vs energy, its inverse will be the temperature. I'm sure if you could hold something that was -100k in your hands, and something that was 100,000,000K in your hands, the -100k wouldn't feel nearly as "hot" as the other. But, the -100K would still donate energy to the 100,000,000K system, and therefore it has a higher temperature. But I suspect that -100K feels as hot as 100K. It's just the movement of energy which differs them for the most part.
I'm certainly no expert at biology but if your hand could actually hold either of those things without melting and you could differentiate between two very high temperatures surely the -100K object would feel much hotter because your nerves are basically sensing the heat transfer which would be greater for the -100K object.
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Physician
United States4146 Posts
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It has been done before in other systems: http://en.wikipedia.org/wiki/Negative_temperature
The simplest example is a laser. Any laser has some atoms at negative temperature if you use entropic definition of temperature.
In the paper presented in OP it is done in a different system (and involves motional degrees of freedom), which is cool and might be very useful, but not the first time negative temperature was achieved.
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On January 06 2013 13:40 micronesia wrote:Show nested quote +On January 06 2013 13:23 philcorp wrote:
I am surprised that this article is atracting so much popular attention. As has been mentioned, there is nothing really special about reaching "negative temperatures", we have been doing it from years. Someone mentioned LASER devices as an example of a popular device which feature negative temperatures.
Conventional wisdom tells us that high temperatures correspond to all states being equally probable. The thermal fluctuations can put atoms into any state. As one lowers the temperature, the atoms cannot access as many states. They prefer to stay in those with low energy (the thermal fluctuations are not enough to access the high energy states). So, "negative temperature" is the situation when the system perfers to be in high energy states instead of the low energy ones. It takes some experimental creativity to come up with such a situation, but it can be done! I believe a large mass of particle, influenced by gravity (a star) is another example of this. Adding energy causes the particles to 'orbit' at a higher altitude, slowing them down (as per satellite motion).
Adding energy and causing a slower larger orbit does not mean the the object in orbit prefers the higher energy state because it wants to have a lower, faster orbit with a higher kinetic energy. You also have to take into account the binding energy of the total system of the satellite object and the star. Causing a system to be more tightly bound cause a release of energy overall, including potential, so the lower orbit is actually a lower energy system.
On January 06 2013 15:16 imallinson wrote:Show nested quote +On January 06 2013 14:47 Chargelot wrote:On January 06 2013 13:14 GGTeMpLaR wrote:On January 05 2013 23:57 Fruscainte wrote:
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 gravity4.
Holy shit.. mass effect anyone? I have a question though. Since the energy moves from a parts of atoms in the cloud at negative-kelvin to the positive-kelvin atoms in the cloud (from cold to hot, the opposite of what is normal), would the negative-kelvin atoms just continue to get colder and colder with a higher and higher value of negative-kelvin? edit: Is negative-kelvin actually cold or is it hot? I'm reading negative-kelvin is actually hotter than any value of positive-kelvin since heat will always flow from negative to positive? Also, does this invalidate the second law of thermodynamics? Is it possible the conditions necessary to reach this negative-kelvin temperature could ever occur naturally in the cosmos? This occurs naturally in stars and black holes. Negative-kelvin is hotter than any positive-kelvin. That is: -1K > 100,000,000K Because energy will always flow from the negative system to the positive system. In this case, temperature is being described as T^(-1) = dS/dE meaning when you find the slope of the line that you get when you graph entropy vs energy, its inverse will be the temperature. I'm sure if you could hold something that was -100k in your hands, and something that was 100,000,000K in your hands, the -100k wouldn't feel nearly as "hot" as the other. But, the -100K would still donate energy to the 100,000,000K system, and therefore it has a higher temperature. But I suspect that -100K feels as hot as 100K. It's just the movement of energy which differs them for the most part. I'm certainly no expert at biology but if your hand could actually hold either of those things without melting and you could differentiate between two very high temperatures surely the -100K object would feel much hotter because your nerves are basically sensing the heat transfer which would be greater for the -100K object.
The reason that the heat transfers faster and the negative object feels hotter is because there are more molecules in higher energy states that any positive temperature could yield. There is really nothing special about negative temperature other than the fact that the higher energy states are filled before the lower ones. This is actually pretty special, but the end result is something that can be thought of in the classical sense of actually comparing temperature by touch as negative being hotter that positive.
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I must say I am intrigued by the notion that dark matter may not obey the laws of thermodynamics+entropy
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On January 06 2013 18:12 a176 wrote:
I must say I am intrigued by the notion that dark matter may not obey the laws of thermodynamics+entropy
What makes you think that?
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So i'm just a chemist and i thing i don't really get this so tell me if i'm wrong:
They created a state of some Atoms in an special environment where they behave the opposite they should at positive temperature, and so they calculate that the atoms have a negative temperature?
So my Problem with this whole thing is: They get a lot of energy into the System (with the Laser) but then the Atoms got less than no energy?
EDIT.: this helped for understanding: http://en.wikipedia.org/wiki/Negative_temperature
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United Kingdom3482 Posts
On January 06 2013 17:42 ZackAttack wrote:Show nested quote +On January 06 2013 15:16 imallinson wrote:On January 06 2013 14:47 Chargelot wrote:On January 06 2013 13:14 GGTeMpLaR wrote:On January 05 2013 23:57 Fruscainte wrote:
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 gravity4.
Holy shit.. mass effect anyone? I have a question though. Since the energy moves from a parts of atoms in the cloud at negative-kelvin to the positive-kelvin atoms in the cloud (from cold to hot, the opposite of what is normal), would the negative-kelvin atoms just continue to get colder and colder with a higher and higher value of negative-kelvin? edit: Is negative-kelvin actually cold or is it hot? I'm reading negative-kelvin is actually hotter than any value of positive-kelvin since heat will always flow from negative to positive? Also, does this invalidate the second law of thermodynamics? Is it possible the conditions necessary to reach this negative-kelvin temperature could ever occur naturally in the cosmos? This occurs naturally in stars and black holes. Negative-kelvin is hotter than any positive-kelvin. That is: -1K > 100,000,000K Because energy will always flow from the negative system to the positive system. In this case, temperature is being described as T^(-1) = dS/dE meaning when you find the slope of the line that you get when you graph entropy vs energy, its inverse will be the temperature. I'm sure if you could hold something that was -100k in your hands, and something that was 100,000,000K in your hands, the -100k wouldn't feel nearly as "hot" as the other. But, the -100K would still donate energy to the 100,000,000K system, and therefore it has a higher temperature. But I suspect that -100K feels as hot as 100K. It's just the movement of energy which differs them for the most part. I'm certainly no expert at biology but if your hand could actually hold either of those things without melting and you could differentiate between two very high temperatures surely the -100K object would feel much hotter because your nerves are basically sensing the heat transfer which would be greater for the -100K object. The reason that the heat transfers faster and the negative object feels hotter is because there are more molecules in higher energy states that any positive temperature could yield. There is really nothing special about negative temperature other than the fact that the higher energy states are filled before the lower ones. This is actually pretty special, but the end result is something that can be thought of in the classical sense of actually comparing temperature by touch as negative being hotter that positive.
I knew that. I was only talking about which would theoretically feel hotter to touch.
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I'm not a science buff ... but holy shit. Thanks for posting this.
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All you wondering out there; second law only says zero can't be reached.
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Looks like they can't call it aboslute zero anymore.
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Okay, I'm just a dumb biologist, but I'm confused...
I think what we have here are low-entropy (eg. crystalline) states that only occur at high temperature, and so as you add heat the system's entropy decreases. That means it's "happier" at high energies, which is the unusual property that makes this possible. That much is okay, I think...
But why do they then dump heat onto anything they come in contact with? Working forward, you'd assume they're going to want to pull as much as they can from whatever's around them because they're stable at higher energies... right?
What am I missing?
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What are the practical implications for a discovery like this?
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United Kingdom3482 Posts
On January 06 2013 21:31 Belisarius wrote:
Okay, I'm just a dumb biologist, but I'm confused...
I think what we have here are low-entropy (eg. crystalline) states that only occur at high temperature, and so as you add heat the system's entropy decreases. That means it's "happier" at high energies, which is the unusual property that makes this possible. That much is okay, I think...
But why do they then dump heat onto anything they come in contact with? Working forward, you'd assume they're going to want to pull as much as they can from whatever's around them because they're stable at higher energies... right?
What am I missing?
I don't think that its necessarily low entropy. The scale for temperature is defined by change in thermal energy divided by change in entropy so for a negative temperature you need one to decrease as the other increases. I don't know enough about it to know which is the one decreasing in this experiment.
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On January 06 2013 00:08 IntoTheWow wrote:
I guess it depends on how you define temperature.
If you release these atoms from their arrangement, you would not get heat transfering to them, but from them.
Exactly. Its a definitional game thats being played. It's neat, but nothing groundbreaking and the terminology/pop sci hype around it is outright misleading.
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EPT
