[neilep (OP)]

Is it  " reasonable " to assume that if the universe continues to expand forever to a point where all things are so far apart from each other and that there eventually becomes an end to all things active ie: no new galaxy's, stars, black holes, planets, BK Whoppers  ?  etc etc etc......and that everything is necrotic !!....that...then....and only then will absolute zero be the ultimate end ?

Or is Absolute Zero 100% certifiably an impossibility !! ?

[Karen W.]

Remember the polor bear thread.. talking about the fact that there would never be absolute zero.. Was it George who answered that.. I cannot remember..! I will try to find it!

[another_someone]

Even black holes are reputedly emitting hawkins radiation.

As for how thinly spread out the universe is, that could lead to a situation where the average temperature is asymptoticly approaching zero, but approaching is not the same thing as reaching, and that in any case will only be an average (is assumes no lumpiness in the universe - and the universe is remarkably lumpy).

[Karen W.]

Thanks George ..This search engine is making me mad.. I know what topic I wanted but it will not find it using any of the words I know were in the topic!! Frustrating...errrrgh

[neilep (OP)]

Even Black holes eventaully evaporate away over aeons and aeons.........one day.....there wiill be nothing...and even " nothing " will not exist !...I just then expect all will become a  "solid hunk" of absolute zero necrosis !....it may be a cascade effect as I don't expect it will all wink out in one go !..........I am just speculating of course !!

[another_someone]

Even Black holes eventaully evaporate away over aeons and aeons.........one day.....there wiill be nothing...and even " nothing " will not exist !...I just then expect all will become a  "solid hunk" of absolute zero necrosis !....it may be a cascade effect as I don't expect it will all wink out in one go !..........I am just speculating of course !!

How can it be nothing?

If there is something there, then how do you expect to get nothing out of something?

You may be spreading it thiner and thiner, but spreading it thiner does not make less of it - it is still there, just spread over a larger area/volume.

[neilep (OP)]

Even Black holes eventaully evaporate away over aeons and aeons.........one day.....there wiill be nothing...and even " nothing " will not exist !...I just then expect all will become a  "solid hunk" of absolute zero necrosis !....it may be a cascade effect as I don't expect it will all wink out in one go !..........I am just speculating of course !!

How can it be nothing?

If there is something there, then how do you expect to get nothing out of something?

You may be spreading it thiner and thiner, but spreading it thiner does not make less of it - it is still there, just spread over a larger area/volume.

I see your point !....DOH !!.......but perhaps 'nothing ' is not prerequiste for Absolute Zero !!?

[another_someone]

I see your point !....DOH !!.......but perhaps 'nothing ' is not prerequiste for Absolute Zero !!?

Strictly speaking, absolute zero implies zero kinetic energy (i.e. everything is absolutely stationary with respect to everything else).

Even if an atom only gets to collide with another atom once every 10 years, or once every 1 million years - it still means those collisions take place, and so the temperature might be some small fraction of a millionth of a degree kelvin, but crucially, it will still not be absolutely zero.

To us, used to temperatures of around 300 kelvin, that might seem like almost absolute zero; but to someone who is used to temperatures of a million kelvin, even 300 kelvin might like almost absolute zero, and to someone used to 1 millionth of a kelvin, the difference between 1 millionth kelvin and half a millionth kelvin will still be significant.

[DoctorBeaver]

I remember reading a sci-fi story a few years ago where scientists were trying to attain absolute zero. When they managed it all the atoms started falling apart.

Would that happen or is just the fancy of a sci-fi author? I would imagine that to attain absolute zero, even the carrier particles would have to stop moving. Surely if that happens then atomic forces would cease and everything would indeed come apart. Then again, if the atoms were falling apart, that implies movement which means they could not be at absolute zero so they'd stop falling apart.  []

[Soul Surfer]

Everything cannot be still even at the absolute zero of temeperature.  The universe contains a lot of fermions  ie particles with half interger spin like electrons protons and neutrons.  Quantum mechanics states that only two fermions of opposite spin can occupy the same energy level in any atom or substance this means that atoms have residual energy and molecules are moving about even at absolute zero temeperature.

[DoctorBeaver]

Everything cannot be still even at the absolute zero of temeperature.  The universe contains a lot of fermions  ie particles with half interger spin like electrons protons and neutrons.  Quantum mechanics states that only two fermions of opposite spin can occupy the same energy level in any atom or substance this means that atoms have residual energy and molecules are moving about even at absolute zero temeperature.

Well, that told me!  [:I]

[another_someone]

Everything cannot be still even at the absolute zero of temeperature.  The universe contains a lot of fermions  ie particles with half interger spin like electrons protons and neutrons.  Quantum mechanics states that only two fermions of opposite spin can occupy the same energy level in any atom or substance this means that atoms have residual energy and molecules are moving about even at absolute zero temeperature.

Can you not circumvent this in some way by the use of cooper pairs to convert the fermions into bosons?

[neilep (OP)]

Everything cannot be still even at the absolute zero of temeperature.  The universe contains a lot of fermions  ie particles with half interger spin like electrons protons and neutrons.  Quantum mechanics states that only two fermions of opposite spin can occupy the same energy level in any atom or substance this means that atoms have residual energy and molecules are moving about even at absolute zero temeperature.

Can you not circumvent this in some way by the use of cooper pairs to convert the fermions into bosons?

What has Henry & Tommy Cooper go to do with this ?

Ok..enough jesting !...THANK you very much..this is all very interesting stuff !

[Bored chemist]

Henry Cooper and Tommy Cooper can only occupy the same space if they are spinning in oposite directions.
More importantly, I think that if you have a cooper pair it can be "unpaired" again with the release of energy. That makes it a kind of excited state so it's not at absolute zero. Of course I may be talking rubbish here because it isn't really my field.

[another_someone]

More importantly, I think that if you have a cooper pair it can be "unpaired" again with the release of energy. That makes it a kind of excited state so it's not at absolute zero. Of course I may be talking rubbish here because it isn't really my field.

This is an interesting issue, since it asks whether temperature is the measure of all energy, or only kinetic energy.

I remember some time ago someone claimed they had reached a negative absolute temperature, as they had reduced kinetic energy to within a fraction of a degree, and then aligned the spins of the atoms, so reducing the energy even further to a level that would be less than if all the kinetic energy had vanished.  I have not seen that claim repeated lately []

More relevantly, if one includes all the energy within a state as part of its temperature, then one has to include the potential temperature release that could come about by fusing two hydrogen atoms - which means that no element other than iron could even get close to absolute zero temperature.  I don't really think that scenario stands up to actual practical application.

Thus, whether cooper pairs might release energy when unpaired is not really in my view an issue, only what their actual kinetic energy at that time is.

Cooper pairs aside, atomic Bose-Einstein condensates are another case where a collections of fermions can behave as if they are bosons.

[Bored chemist]

You make a good point that temperature needs to be properly defined for this question to make sense.
It's perfectly possible for something to have several temperatures at the same time.
BTW, can you get a Bose Einstein condensate from fermions or do you need bosons? I thought that was why it was difficult to get 3He to form a superfluid compared to 4He.

[another_someone]

BTW, can you get a Bose Einstein condensate from fermions or do you need bosons? I thought that was why it was difficult to get 3He to form a superfluid compared to 4He.

Yes, you need bosons, which is why He⁴ is easier than He³, but the point is that even He⁴, although it is a boson, is composed of protons, neutrons, and electrons, which are all fermions.

[DoctorBeaver]

- which means that no element other than iron could even get close to absolute zero temperature.

What is so special about iron?

[another_someone]

Elements lighter than iron can release energy by fusion, while those that are heavier than iron can release energy by fission; hence iron is the element with the least nuclear energy.

[lightarrow]

I remember some time ago someone claimed they had reached a negative absolute temperature, as they had reduced kinetic energy to within a fraction of a degree, and then aligned the spins of the atoms, so reducing the energy even further to a level that would be less than if all the kinetic energy had vanished.  I have not seen that claim repeated lately []

I don't know that, but I know that negative temperatures do exists. It's explained even in Zemansky's Thermodynamics:
temperature can be defined as:
T = ∂U/∂S
where U is the internal energy and S is the entropy.

In lasers, when the system is in "population inversion":
http://en.wikipedia.org/wiki/Population_inversion
the temperature so defined is negative, since U increases while S decreases (because of the more ordered state given by the population inversion).

Said simply: you increase the energy of the lasing system making atom's electrons go up to higher energy levels. But in this way, when a lot of them are in these higher states, the system is more ordered, so the total entropy is lower.
So, during that process, ∂U is positive (U increases) while ∂S is negative (S decreases).
So T is negative.

In this case, however, the system is not colder than a 0°K system, but, actually,  hotter!
http://math.ucr.edu/home/baez/physics/ParticleAndNuclear/negativeTemperature.html