-273 degree Celcius
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DaveC426913
Valued Senior Member
They start to smear out into a Bose-Einstein Condensate. In essence, they lose their individuality.
Close... "only half-a-billionth of a degree above absolute zero"
At that temperature, the "atoms are a million times slower -- it takes them half a minute to move one inch"
And , "At absolute zero (-273 degrees C or -460 degrees F), all atomic motion comes to a standstill since the cooling process has extracted all the particles' energy."
- all ^above^ quoted(in Blue), and more, from : http://news.mit.edu/2003/cooling
DaveC426913
Valued Senior Member
All this being said, it is important to point out that one does not get stationary, discrete atoms. HUP still applies.
If you mean 150 millikelvin, yes that is possible.
I am fairly certain, rpenner, that the "in lab" - "450 picokelvin temperature of the sodium Bose–Einstein condensate gas" achieved at MIT and the "in lab" - "100 picokelvin temperature achieved at Helsinki University of Technology's Low Temperature Lab in 2009" are, literally, "Orders of magnitude" lower in temperature than "150 millikelvin"...
- the ^above^ quoted(in Blue)from : https://infogalactic.com/info/Orders_of_magnitude_(temperature)
...fairly certain...
...further informative Links :
- http://hypertextbook.com/facts/2001/NehemieCange.shtml
- http://www.neatorama.com/2009/07/15/fun-with-low-temperatures/
- https://ltl.tkk.fi/wiki/LTL/World_record_in_low_temperatures
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Is that on paper or actually , If actually how do you measure ?
If you mean absolute zero, the answer is no. Quantum mechanics prevents anything from cooling down to that extent. Doing so would violate the uncertainty principle, for starters.
It depends on the particular properties of the atoms. If they are bosons, then under appropriate conditions of density and low temperature (but still above absolute zero) they can form a Bose-Einstein condensate.
More basically, atoms just slow down as they get colder. They may form a fluid or a solid, or even a superfluid. In bulk, they may become superconducting, too. In short, there's a lot of interesting physics that goes on at low temperatures.
Negative absolute temperatures have been achieved in the lab. A somewhat paradoxical state of matter: http://physicscentral.com/explore/action/negative-temperature.cfm
Negative temperatures are a case of shifting the goalposts from considering all states to a restricted discussion where a population inversion is physically possible.
Lasers formally are described as optical media in a population inversion so that more sites are ready to fall into a lower state and amplify the light rather than move from a lower state to the higher one and absorb light. Thus you can have negative temperature systems without cryogenics. That's a shifting of the goalposts in that we are talking about atomic internal states rather than all the energy of the atoms.
From later in the same article: “It is important to note that the negative temperature region, with more of the atoms in the higher allowed energy state, is actually warmer than the positive temperature region.”
Here they built a physical system (the environment of the laser trap) where some spots were potential valleys and some were potential hills. At low positive temperature there would be a tendency for atoms to cluster at the bottom of valleys. At high temperature there would be less of a tendency. At infinite temperature, there would be no statistical difference between atom densities in valleys or hills. At low negative temperature there would be a statistical clumping at the peaks of the hills.
They got it that way by literally shifting the goalposts, they turned the valleys into hills.
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I was attempting to illustrate that Absolute Zero is defined as −273.15°C = 0 K so −273°C = 0.15 K = 150 mK, which while expensive to obtain, is much warmer than the state of the art in cryogenic achievements.
While the Celsius scale started as 0°C = freezing, 100°C = boiling, it was redefined in terms of absolute zero and the triple point (1948) of a very specific sample (2005) of distilled water of particular isotopic composition. So now freezing ≈ −0.000089°C = 273.149911 K, boiling ≈ 99.9839°C = 373.1339 K
https://en.wikipedia.org/wiki/Celsius#Common_temperatures
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Then you are siding here with the banned SimonsCat's take on such a thing. I suggest going back and reviewing how it all went in a previous thread from about here:
http://www.sciforums.com/threads/vi...xplain-dark-energy.158695/page-3#post-3431276
exchemist
Valued Senior Member
Q-reeus beat me to it here.
What I am fairly confident of is that whatever zero point energy remains in the ground state of a system does not contribute to its temperature, because a temperature >0K implies that heat can be extracted from a body (by placing it in contact with something closer to 0K. Clearly this is impossible if the constituents of the body are all in the ground states of all their degrees of freedom. So at absolute zero the zero point energy remains.
I suppose one might try to argue that the HUP makes it is impossible to determine accurately the temperature, due to uncertainties in the energy. However I would counter that temperature is a bulk property, i.e. of a statistical ensemble of quantum objects, rather than of an individual quantum object, and thus invoking the HUP is not appropriate in such a case.
exchemist
Valued Senior Member
As rpenner says, -273 is not quite absolute zero, which is -273.15C.
If you mean what happens to atoms at absolute zero, they will all be in their ground states, for all the degrees of freedom that they have.
Conversely, at any temperature above absolute zero, a proportion of atoms or molecules will be in excited states, above the ground state. The first degrees of freedom to be excited will be translational motion. Next, as the temperature rises a bit more, rotational states of molecules will start to be excited and then, with a further rise in temperature, molecular vibrations start to be excited as well. At any temperature above absolute zero, there are collisions between molecules due to these motions, whereby energy is continuously exchanged and redistributed statistically among them. This is thermal motion.
But at absolute zero, all this falls back, so that everything is "sleeping" in its ground states. But note that I say sleeping, not dead, because "zero point" motion, which represents the residual energy that remains in ground states, is still there.....
exchemist
Valued Senior Member
Yeah I hate this description actually.
Journos love it for its gosh-wow factor but all it means is a "population inversion", as rpenner has explained.
Temperature appears in the expression - in statistical thermodynamics - for a Boltzmann distribution, which describes how molecules or atoms distribute themselves statistically among the energy levels they can explore.
If you have a simple two energy-state system, such as in a laser, you can represent the inversion (which just means more entities in the upper than the lower) mathematically by plugging a -ve value for T into the expression. In fact, though, the distribution function is intended to apply to a system at thermal equilibrium, which a population inverted system most certainly is not.
So really it seems to me it's a fiddle, from stretching a piece of maths into a zone where it is not strictly applicable. But it makes for nice headlines and contributes to the head-scratching mystique of science (rather unfortunately, in my view
).Sorry about that. I was temporarily distracted from the more reasonable take on the thread by my long-ago memory of when I first ran into the concept of a negative temperature, emerging from calculations of involving entropy while doing student homework in a thermodynamics class: how getting a handle on it improved my comprehension of stuff in general. Careless link.
exchemist
Valued Senior Member
Ah OK. Hope my description brought back happy rather than unhappy memories of that. I recall Stat TD being really cool stuff, but far from easy to grasp properly. I still struggle with the particle interchange business that leads to Fermi-Dirac and Bose-Einstein stats......
Indeed. Probably not a good idea to sidetrack into widespread use of concepts like 'negative energy', 'negative probability', or 'negative frequencies'. Which seem absurd on face value. Given the usual definition of such quantities. Such negative mathematical things do have a legitimate use but require close inspection of how such are defined and the context of actual use.Yeah I hate this description actually.
Journos love it for its gosh-wow factor but all it means is a "population inversion", as rpenner has explained.
Temperature appears in the expression - in statistical thermodynamics - for a Boltzmann distribution, which describes how molecules or atoms distribute themselves statistically among the energy levels they can explore.
If you have a simple two energy-state system, such as in a laser, you can represent the inversion (which just means more entities in the upper than the lower) mathematically by plugging a -ve value for T into the expression. In fact, though, the distribution function is intended to apply to a system at thermal equilibrium, which a population inverted system most certainly is not.
So really it seems to me it's a fiddle, from stretching a piece of maths into a zone where it is not strictly applicable. But it makes for nice headlines and contributes to the head-scratching mystique of science (rather unfortunately, in my view