[neilep (OP)]

Salutations Academians,


As a sheepy I of course know everything there is to know about......being a sheep. Ewe would think and expect this knowledge to include all there is to know about Absolute Zero, I mean, it's obvious isn't it ? Sheep= Absolute Zero knowledge. Blatant !! Surprisingly and astonishingly though I am somewhat lacking in that regard.




Take a look at Kelvin the Fridge/Freezer



Kelvin The Fridge Freezer Just Moments Ago

As ewe can see one of Kelvins USP's is that he can attain the temperature of Absolute Zero ! But Absolute Zero is impossible to attain yes ? Whilst I consider what actions to take can someone please inform me of how is it known the temperature of Absolute zero if that temperature is impossible to reach ?



whajafink ?




husg and shmishes






mwah mwah xxxxx








neil





"johnny"
"yes, sheepy"
"have ewe finished with your legal team ? I need some litigation advice about a freezer"
"yep, they're all yours "
"thanks Johnny, are we still on for performing at Wembley ?"
"see ewe on stage sheepy"


 

[alancalverd]

I drew two lines on a map, one going northish from Oxford and one eastish from Carlisle, so now I know exactly where Newcastle is but I don't have enough fuel to get there.

US TV inteviewer: "How did you find New York, Your Majesty?"
HMQ: "No problem. I  think the pilot had been there a few times."

[neilep (OP)]

I drew two lines on a map, one going northish from Oxford and one eastish from Carlisle, so now I know exactly where Newcastle is but I don't have enough fuel to get there.

US TV inteviewer: "How did you find New York, Your Majesty?"
HMQ: "No problem. I  think the pilot had been there a few times."

well, I'm convinced ! 

[paul cotter]

It is extrapolated from thermodynamic theory, I wouldn't remember offhand but I could look it up if needed.

[alancalverd]

True. The Carnot cycle determines the efficiency of an ideal engine that takes heat from a hot source and exhausts it to a cold source, and results in the very simple equation
η = 1-T_C/T_H
where it is presumed that there is some absolute scale of temperature T.
Then in principle we can measure the efficiency of a real heat engine or some process that mimics the Carnot cycle, and thus project where T_C → 0 . We then set the triple point of water at a convenient level (say 273.15K) and we have defined a practical temperature scale with an absolute physical basis.

PS by all means try this at home, but it's a lot more difficult than driving to Newcastle or even flying to New York!

[Deecart]

You can reach lower than 0 Kelvin temperature.

A temperature below absolute zero: Atoms at negative absolute temperature are the hottest systems in the world

Date:
    January 4, 2013
Source:
    Max-Planck-Gesellschaft
Summary:
    On the absolute temperature scale, which is used by physicists and is also called the Kelvin scale, it is not possible to go below zero – at least not in the sense of getting colder than zero kelvin. According to the physical meaning of temperature, the temperature of a gas is determined by the chaotic movement of its particles – the colder the gas, the slower the particles. At zero kelvin (minus 273 degrees Celsius) the particles stop moving and all disorder disappears. Thus, nothing can be colder than absolute zero on the Kelvin scale. Physicists have now created an atomic gas in the laboratory that nonetheless has negative Kelvin values. These negative absolute temperatures have several apparently absurd consequences: although the atoms in the gas attract each other and give rise to a negative pressure, the gas does not collapse – a behavior that is also postulated for dark energy in cosmology.

[Eternal Student]

Hi and welcome @Deecart

You can reach lower than 0 Kelvin temperature.

   Yes.   For complicated things like a collection of atoms (or molecules) where you can have a population inversion of the energy levels that their electrons occupy.   It's all complicated and it may not help the OP understand what temperature is or absolute 0 is supposed to be.
   I'm not an expert:  To the best of my knowledge, it's fairly arbitrary to assign a temperature < 0,  it's just that the usual equations of state (e.g.  PV=nRT for an ideal gas) continue to hold if you do.
    There's another discussion on this forum "What is temperature" which would probably just love to have the idea of negative temperatures put into it.    (Temperature is usually considered to be the average kinetic energy of a molecule in the gas and... that can't be negative).
   See:   https://www.thenakedscientists.com/forum/index.php?topic=80604.0      for the other thread - but it is long and has been going for a while.   There'll be no harm in just joining the discussion, I don't think anyone can expect you to read all that has gone before.

Best Wishes.

[evan_au]

how is it known the temperature of Absolute zero if that temperature is impossible to reach ?

Most of the responses so far have focused on the "impossible to reach" part of the question.
I'll start addressing the "how was the temperature of Absolute zero known" part of the question.

One of the ways that the significance of Absolute Zero was inferred was through Charles' Law about ideal gases:
V α T , where:
- V is the volume of the gas
- T is the temperature of the gas

If you draw a graph of volume of a sample of gas vs temperature (on some scale), it forms a straight line. If you extrapolate that line way back to low temperatures, you would predict that around −273.15 Celsius  or −459.67 Fahrenheit, the volume of your gas would seem to drop to zero!
- This extrapolation seemed to apply for many gases and many pressures
- So it seemed that there was something special about this temperature - and it came to be known as "Absolute Zero"

In practice, real gases condensed to a liquid (and mostly, a solid) well before they reached this temperature
- But with the understanding that temperature represents the average kinetic energy of a molecule came the realization that at Absolute Zero, the kinetic energy of the gas molecules would drop to zero (if you ignore quantum effects).

https://en.wikipedia.org/wiki/Ideal_gas
https://en.wikipedia.org/wiki/Absolute_zero