[neilep (OP)]

Dearest Quantologists,


Absolute Zero is well cold !!Colder than my freezer and that is currently set at -18c (-0.4F) which is.....freezing !!


I found out recently that even at absolute zero quantum thingies still move !!


Look,



"Hi I'm Quanty and I'm moving despite it being rather chilly"




Here is a quantum thingy that I took a photo of with my 1976 SX-70 Polaroid when I set my Freezer to -273.15c just moments ago.
I took video too and it was moving. This is true because I said so.




So, two questions really, why does quantum stuff still move at 0K ? and therefore, should absolute zero be even lower than -273.15c ?








I dunno.....do ewe ?




Hugs and shmishes


mwah mwah


Sheepy
xx

[varsigma]

One thing I noticed about your questions is that absolute zero is a theoretical limit. There's a reason no experiment has been done at absolute zero or 0 deg K.

It has to do with the so-called Planck energy of quantum particles; none of these is ever at 0 deg K, because then it would have no rest energy or ground state. It wouldn't be a particle any more.

[paul cotter]

Surely it would still have mass at 0deg k and hence the energy of e=m(csq)  Does the uncertainty principle apply to low temperatures like this or is it strictly position and momentum?

[alancalverd]

Does the uncertainty principle apply to low temperatures like this or is it strictly position and momentum?

If an object doesn't move, you know its position and momentum exactly. This is forbidden by the indeterminacy principle, regardless of its kinetic energy.

[Eternal Student]

Hi.

    I'm fairly sure we've had some other threads discussing temperature and the sorts of issue that @neilep has raised.

This is a short summary of how I see the current situation.   Note that  (i)  I'm only one person and don't claim any special expertise in this field of study,    (ii)  It is apparent that our notion of temperature is changing, so that whatever is said here will probably change again in a few years.


Summary:

    Historically temperature was understood in many different ways.   One simple approach is that temperature was the thing you measure when you stick a thermometer into something.   Problems with this approach were too numerous to mention.  For example, how do you build a reliable thermometer?   Sticking a thermometer into some liquid is reasonably easy but sticking a thermometer into some solid is often impossible.  How do you ensure you're getting good thermal contact etc?      In the very old days, some things just didn't have a temperature if you couldn't stick a thermometer into it.
     At a later time,  let's say between 1848  (when Lord Kelvin was developing his Kelvin scale) and 2019 (when the weights and measures commitee redefined temperature) it was quite popular to define and consider temperature using a thermodynamic approach.   That actually worked quite well.
    Since May 2019,  international agreement has been to define temperature based on a Kinetic Theory approach.   That's not my fault, it's just what was done by the weights and measures committee and whoever establishes the SI units for Science.   They wanted to improve our definition and undertstanding of temperature and it was thought that basing temperature on this theoretical framework would make it more objective and absolute.   Just to be clear about this - the modern Kelvin scale is NOT the one that Lord Kelvin developed, we kept the name but ditched most of the notions that Lord Kelvin used.

     We have a great model and good understanding for this kinetic theory approach  IF  the substance is an ideal gas.   The trouble is that most things are NOT ideal gases.   We have a few other reasonable classical models for other things but by no means do we have a good classical model for the microscopic behaviour of everything.
     One very important thing to note is that the sort of microscopic mechanics that is used in these models and that the weights and measures committee have declared we MUST use,  are based on classical mechanics and NOT quantum mechanics.    This is a problem because some things are evidently quantum mechanical but we never-the-less have to do some translation into an equivalent classical system when we assign a temperature to that system.   As mentioned already, we have some good classical microscopic models for some things but sometimes we just do not have any such model that we can use.   Overall, the attempt by the weights and measures committee to make temperature more objective and absolute have caused as many problems as they may have hoped to solve.

   Reference:   Spend the time reading Wikipedia's entry for "temperature" and you'll get some idea of how temperature has been redefined.    https://en.wikipedia.org/wiki/Temperature.     That Wikipedia entry has been edited and adjusted since the last time I looked at it about 1 year ago.   As mentioned, it is very likely to keep changing in the near future.


   Anyway, one answer or reply we can offer to the OP is the following:
You just aren't allowed to use a quantum mechanical model for the substance you are trying to assign a temperature to.   You would HAVE to translate the behaviour of your substance into some classical microscopic model.    What you'll then end up with is a temperature that says something about the average kinetic energy per particle, even if it's a total abstraction to imagine that anything like individual classical particles could be found in this substance or thing.
    In your case, despite your assertion that this thing has temperature 0 k, it probably won't be and can't be 0 k.  You probably can't obtain an official temperature of precisely 0 Kelvin unless the zero point energy of your thing actually is 0 and the corresponding classical model would have particles with 0 kinetic energy.

Best Wishes.

(Last edit to fix some spelling errors).

[Eternal Student]

Hi.

    I'd better have some concrete examples of the confusion that exists about temperature and the Wiki entry that I mentioned:

Quantum Mechanics is OK and is used?

At this temperature, matter contains no macroscopic thermal energy, but still has quantum-mechanical zero-point energy as predicted by the uncertainty principle, although this does not enter into the definition of absolute temperature.

[ From the section subtitled "Absoutre Zero",  https://en.wikipedia.org/wiki/Temperature#Absolute_zero ] 

The microscopic description in statistical mechanics is based on a model that analyzes a system into its fundamental particles of matter or into a set of classical or quantum-mechanical oscillators and considers the system as a statistical ensemble of microstates.

[From "Theoretical Foundations",  https://en.wikipedia.org/wiki/Temperature#Theoretical_foundation

No it's not OK and shoudn't be used
The magnitude of the kelvin is now defined in terms of kinetic theory, derived from the value of the Boltzmann constant.

Kinetic theory provides a microscopic account of temperature for some bodies of material, especially gases, based on macroscopic systems' being composed of many microscopic particles, such as molecules and ions of various species, the particles of a species being all alike. It explains macroscopic phenomena through the classical mechanics of the microscopic particles

[From  "Kinetic Theory Approach"  https://en.wikipedia.org/wiki/Temperature#Kinetic_theory_approach ]

But what do we actually use?
Historically, there are several scientific approaches to the explanation of temperature: the classical thermodynamic description based on macroscopic empirical variables that can be measured in a laboratory; the kinetic theory of gases which relates the macroscopic description to the probability distribution of the energy of motion of gas particles; and a microscopic explanation based on statistical physics and quantum mechanics. In addition, rigorous and purely mathematical treatments have provided an axiomatic approach to classical thermodynamics and temperature.

[From  "Theretical Foundations",  https://en.wikipedia.org/wiki/Temperature#Theoretical_foundation

  -  You see, officially we HAVE to use the one in Orange,  Kinetic Theory, especially if we want to specify the temperature in k     BUT  it makes more sense to use some of the other approaches sometimes and so we (physicists) do exactly that -  regardless of what the weights and measures committee may have stipulated.

Overall
     Temperature is a bit of a mess at the moment - but that is only my opinion.
      On the positive side, it's certainly very interesting.   I mean we would want temperature to be some intrinsic property that a body has irrespective of what sort of particles it's made from or what sort of thing that body is.  We might call this "hotness" instead of temperature.  However, it turns out that this thing may not be as intrinsic as we wanted it to be.   The "hotness" of a thing can change even if all you have done is put the thing in a different place or changed something that was external to the thing.
      The quality of hotness refers to the state of material only in a particular locality, and in general, apart from bodies held in a steady state of thermodynamic equilibrium, hotness varies from place to place.

[From https://en.wikipedia.org/wiki/Temperature#Basic_theory]

       
   So, another way to answer the OP from @neilep  is as follows:      The quantum thingy you described does what it does.  Temperature may only be a crude or macroscopic thing you could try to assign and it doesn't stop it from doing what it does.

should absolute zero be even lower than -273.15c ?

    Only if you think you have a better system for describing "hotness".

Best Wishes.

[neilep (OP)]

One thing I noticed about your questions is that absolute zero is a theoretical limit. There's a reason no experiment has been done at absolute zero or 0 deg K.

It has to do with the so-called Planck energy of quantum particles; none of these is ever at 0 deg K, because then it would have no rest energy or ground state. It wouldn't be a particle any more.

Thank you very much for your kind response. How can absolute zero be given a definition and a temperature if it can never be reached ?

[alancalverd]

Carnot efficiency is η = 1 - Tc/Th.

So if the theoretical efficiency of a heat engine is 100%, Tc must be zero. There's the definition!

[neilep (OP)]

Hi.

    I'm fairly sure we've had some other threads discussing temperature and the sorts of issue that @neilep has raised.

This is a short summary of how I see the current situation.   Note that  (i)  I'm only one person and don't claim any special expertise in this field of study,    (ii)  It is apparent that our notion of temperature is changing, so that whatever is said here will probably change again in a few years.


Summary:

    Historically temperature was understood in many different ways.   One simple approach is that temperature was the thing you measure when you stick a thermometer into something.   Problems with this approach were too numerous to mention.  For example, how do you build a reliable thermometer?   Sticking a thermometer into some liquid is reasonably easy but sticking a thermometer into some solid is often impossible.  How do you ensure you're getting good thermal contact etc?      In the very old days, some things just didn't have a temperature if you couldn't stick a thermometer into it.
     At a later time,  let's say between 1848  (when Lord Kelvin was developing his Kelvin scale) and 2019 (when the weights and measures commitee redefined temperature) it was quite popular to define and consider temperature using a thermodynamic approach.   That actually worked quite well.
    Since May 2019,  international agreement has been to define temperature based on a Kinetic Theory approach.   That's not my fault, it's just what was done by the weights and measures committee and whoever establishes the SI units for Science.   They wanted to improve our definition and undertstanding of temperature and it was thought that basing temperature on this theoretical framework would make it more objective and absolute.   Just to be clear about this - the modern Kelvin scale is NOT the one that Lord Kelvin developed, we kept the name but ditched most of the notions that Lord Kelvin used.

     We have a great model and good understanding for this kinetic theory approach  IF  the substance is an ideal gas.   The trouble is that most things are NOT ideal gases.   We have a few other reasonable classical models for other things but by no means do we have a good classical model for the microscopic behaviour of everything.
     One very important thing to note is that the sort of microscopic mechanics that is used in these models and that the weights and measures committee have declared we MUST use,  are based on classical mechanics and NOT quantum mechanics.    This is a problem because some things are evidently quantum mechanical but we never-the-less have to do some translation into an equivalent classical system when we assign a temperature to that system.   As mentioned already, we have some good classical microscopic models for some things but sometimes we just do not have any such model that we can use.   Overall, the attempt by the weights and measures committee to make temperature more objective and absolute have caused as many problems as they may have hoped to solve.

   Reference:   Spend the time reading Wikipedia's entry for "temperature" and you'll get some idea of how temperature has been redefined.    https://en.wikipedia.org/wiki/Temperature.     That Wikipedia entry has been edited and adjusted since the last time I looked at it about 1 year ago.   As mentioned, it is very likely to keep changing in the near future.


   Anyway, one answer or reply we can offer to the OP is the following:
You just aren't allowed to use a quantum mechanical model for the substance you are trying to assign a temperature to.   You would HAVE to translate the behaviour of your substance into some classical microscopic model.    What you'll then end up with is a temperature that says something about the average kinetic energy per particle, even if it's a total abstraction to imagine that anything like individual classical particles could be found in this substance or thing.
    In your case, despite your assertion that this thing has temperature 0 k, it probably won't be and can't be 0 k.  You probably can't obtain an official temperature of precisely 0 Kelvin unless the zero point energy of your thing actually is 0 and the corresponding classical model would have particles with 0 kinetic energy.

Best Wishes.

(Last edit to fix some spelling errors).

WOW...Thank you very much . I will indeed read the Wikipedia article.