How was Absolute Zero discovered?

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Johann Mahne

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How was Absolute Zero discovered?
« on: 28/07/2011 15:12:06 »
I've always wondered how the value of -273 deg c was discovered as the coldest possible temperature.
Was it through experiment or from astronomical measurements (spectrometers) or calculated theoretically?

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Offline JP

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How was Absolute Zero discovered?
« Reply #1 on: 28/07/2011 16:23:52 »
It's a theoretical idea.

Temperature is defined as the average kinetic energy of particles making up matter.  Kinetic energy is energy of motion, so it's a measurement of the average motion of a lot of particles.  It makes sense that the lowest possible temperature is when that motion stops.  This was the original idea of absolute zero.

More recently, scientists have learned that small particles can never stop moving because of the rules of quantum mechanics.  Absolute zero can still defined as the temperature where they're moving the least amount possible.

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Offline Phractality

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How was Absolute Zero discovered?
« Reply #2 on: 28/07/2011 17:28:49 »
It was discovered by graphing the relationship among temperature, pressure and volume of gasses. For a constant volume of most gases, the pressure to temperature graph follows a straight line which reaches zero pressure at -273.15°C.
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Offline Mr. Data

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How was Absolute Zero discovered?
« Reply #3 on: 28/07/2011 17:55:28 »
It's a theoretical idea.

Temperature is defined as the average kinetic energy of particles making up matter.  Kinetic energy is energy of motion, so it's a measurement of the average motion of a lot of particles.  It makes sense that the lowest possible temperature is when that motion stops.  This was the original idea of absolute zero.

More recently, scientists have learned that small particles can never stop moving because of the rules of quantum mechanics.  Absolute zero can still defined as the temperature where they're moving the least amount possible.

It was first proposed by Einstein, it has a value of 1/2 \hbar ω. It not a theoretical idea, it's a proven limit on temperatures of systems, free and bound.

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Offline Mr. Data

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How was Absolute Zero discovered?
« Reply #4 on: 28/07/2011 18:00:39 »
I've always wondered how the value of -273 deg c was discovered as the coldest possible temperature.
Was it through experiment or from astronomical measurements (spectrometers) or calculated theoretically?


It was proposed in 1913 using a formula that was develeoped by Max Planck. Einstein used it to describe vibrational energy, and was given as

ε = (hv/ehv/kT-1) + hv/2

hv/2 can be thought of an existing kinetic energy for a system, which means that -273 can never be accomplished. This also means the zero point energy does not actually exist! I've even proposed that Fermi energy equations propose a faulty premise as it requires the idea that the ZP-energy is a real value.
« Last Edit: 28/07/2011 18:02:25 by Mr. Data »

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Offline imatfaal

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How was Absolute Zero discovered?
« Reply #5 on: 28/07/2011 18:11:46 »
from wikipedia
http://en.wikipedia.org/wiki/Absolute_zero
Quote
Limit to the 'degree of cold'

The question whether there is a limit to the degree of cold possible, and, if so, where the zero must be placed, was first attacked by the French physicist Guillaume Amontons in 1702, in connection with his improvements in the air thermometer. In his instrument, temperatures were indicated by the height at which a column of mercury was sustained by a certain mass of air, the volume or "spring" which varied with the heat to which it was exposed. Amontons therefore argued that the zero of his thermometer would be that temperature at which the spring of the air in it was reduced to nothing. On the scale he used, the boiling-point of water was marked at +73 and the melting-point of ice at 51, so that the zero of his scale was equivalent to about −240 on the Celsius scale.

and from the 1911 (ie before the the planck formula you mention)  encyclopedia britannica
http://www.1911encyclopedia.org/Cold
Quote
After J. P. Joule had determined the mechanical equivalent of heat, Lord Kelvin approached the question from an entirely different point of view, and in 1848 devised a scale of absolute temperature which was independent of the properties of any particular substance and was based solely on the fundamental laws of thermodynamics (see Heat and Thermodynamics). It followed from the principles on which this scale was constructed that its zero was placed at - 273°, at almost precisely the same point as the zero of the air-thermometer.
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Offline Mr. Data

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How was Absolute Zero discovered?
« Reply #6 on: 28/07/2011 18:16:40 »
There is no question that the equation and experimental evidence implies the zero point energy limit is not attainable. The reason why is because of:

E = ∫ (Th/Tc - 1) C dT

If the integral here is taken to the Th to Tc, (hot and cold temperatures) then if C is a constant and as Th approaches Tc, E tends to infinity.

This means that it will take an infinite amount of energy to reach T=0. This is along the same idea's as a system requiring an infinite amount of energy to reach speeds equalling c.

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Offline imatfaal

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« Reply #7 on: 28/07/2011 18:32:41 »
Mr Data could you also explain your variables and notation a bit as well so that those not versed in quantum mechanics can attempt to follow the equations and thus your argument.

As an example
ε = (hv/ehv/kT-1) + hv/2

This looks similar to the average value of a planck oscilator - but it should normally be in terms of Ehat rather than epsilon.  And if we are using greek script then the nu should be a nu

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Offline Mr. Data

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How was Absolute Zero discovered?
« Reply #8 on: 28/07/2011 18:39:15 »
Mr Data could you also explain your variables and notation a bit as well so that those not versed in quantum mechanics can attempt to follow the equations and thus your argument.

As an example
ε = (hv/ehv/kT-1) + hv/2

This looks similar to the average value of a planck oscilator - but it should normally be in terms of Ehat rather than epsilon.  And if we are using greek script then the nu should be a nu



You want me to describe this equation for you? Epsilon is a small number, and refers to a small energy contribution. So let ε=Ef where Ef is zero energy field. Let hv/2 = KE where KE is the kinetic energy wherre h is planks constant and v is the frequency. We have expression here (hv/ehv/kT-1) which just looks like a mess of things, including an ugly exponential that non-mathematicians cannot appreciate easily. Just let this equal an energy, but look at it as an energy that equals zero. However, whilst that is a general limit on the system, the system does not actually have a non-zero energy because hv/2 is not equal to zero. So all in all, the equation above really reads

E = KE = 1/2hv

For an existing energy, and will always exist. It cannot reach zero because it would, again, require an infinite amount of energy.

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Offline Mr. Data

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« Reply #9 on: 28/07/2011 18:41:42 »
You can even set v = ω so that

hbar ω/2 = E for a ZP-field fluctuation.

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Offline JP

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How was Absolute Zero discovered?
« Reply #10 on: 28/07/2011 18:53:41 »
It's a theoretical idea.

Temperature is defined as the average kinetic energy of particles making up matter.  Kinetic energy is energy of motion, so it's a measurement of the average motion of a lot of particles.  It makes sense that the lowest possible temperature is when that motion stops.  This was the original idea of absolute zero.

More recently, scientists have learned that small particles can never stop moving because of the rules of quantum mechanics.  Absolute zero can still defined as the temperature where they're moving the least amount possible.

It was first proposed by Einstein, it has a value of 1/2 \hbar ω. It not a theoretical idea, it's a proven limit on temperatures of systems, free and bound.

Maybe you misunderstood what I mean by theoretical.  Absolute zero is theoretical because no one has ever seen it, nor will they, so it's based on theory work, not on observation or experiment.  But it's on solid foundation, as we know exactly what it means in terms of measurable quantities (energy).

Phractality and Matthew's points are good ones.  The original definition of absolute zero was based on extrapolating from a thermometer.  Modern understanding of it is based on the idea of energy in a system.
« Last Edit: 28/07/2011 18:58:36 by JP »

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Offline Mr. Data

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How was Absolute Zero discovered?
« Reply #11 on: 28/07/2011 18:54:57 »
It's funny you ask what you did though, because I think

ε = (hv/ehv/kT-1) + hv/2

Is an ugly equation anyway, and does not really explain why ε is small, or even should contribute hv/2 (the existing energy). This is why the limit

E = ∫ (Th/Tc - 1) C dT

Is much more appropriate, because it is devised under the impression that it is

E = W = ∫ (Th/Tc - 1) C dT

meaning it is the ''work'' of the system. The work required to reach the limit is unattainable. It would require more energy than in the observable universe!

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Offline Mr. Data

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How was Absolute Zero discovered?
« Reply #12 on: 28/07/2011 18:56:05 »
It's a theoretical idea.

Temperature is defined as the average kinetic energy of particles making up matter.  Kinetic energy is energy of motion, so it's a measurement of the average motion of a lot of particles.  It makes sense that the lowest possible temperature is when that motion stops.  This was the original idea of absolute zero.

More recently, scientists have learned that small particles can never stop moving because of the rules of quantum mechanics.  Absolute zero can still defined as the temperature where they're moving the least amount possible.

It was first proposed by Einstein, it has a value of 1/2 \hbar ω. It not a theoretical idea, it's a proven limit on temperatures of systems, free and bound.

Maybe you misunderstood what I mean by theoretical.  Absolute zero is theoretical because no one has ever seen it, nor will they, so it's based on theory work, not on observation or experiment.  But it's on solid foundation, as we know exactly what it means in terms of measurable quantities (energy).

Oh right, well... Let zero point energy equal any definition that makes sense in this case. It is still an experimental fact of a temperature we cannot reach rather than a postulation, it is an axiom.

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Offline imatfaal

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How was Absolute Zero discovered?
« Reply #13 on: 28/07/2011 23:53:09 »
Mr Data - your use of terms is confusing me and I would hazard a guess others as well. 
1. You say firmly that this is not a postulate - but it is an axiom.  In my dictionary they are the same thing - they are the unproven basis of the logical progression from which the argument moves forward.
2. An experimental fact that we cannot do something? 
3. Please spell out the variables/constants you are using - I know it is a pain but it really helps understanding
4. you say epsilon is a very small number -  which I agree is how it is normally used in this area as a dimensionless increment.  However in your equation it clearly must have the same units as energy through dimensional analysis.  And what is omega etc?  BTW we do have greek letters available (click preview to get full editor) and the nu is nice and distinct
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Offline Mr. Data

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How was Absolute Zero discovered?
« Reply #14 on: 29/07/2011 01:41:51 »
Don't hazard a guess for anyone else, unless they speak up. If anyone says to me that the zero-point energy is attainable, I would almost certainly disagree with the lack of experimental evidence. No matter how cold we set our instruments to, one will see that T=0 is very unrealistic. Can you proove this wrong? If you can, I will take back what I said, until then I hope you can appreciate that whatever is confusing you on this, will not naturally imply anyone else.

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Offline imatfaal

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How was Absolute Zero discovered?
« Reply #15 on: 29/07/2011 11:22:53 »
Mr D - experiments failing to reach absolute zero do not show that it is unreachable - merely that we havent reached it yet - it is theory that determines that abs zero is unattainable. 

If anyone says to me that the zero-point energy is attainable, I would almost certainly disagree with the lack of experimental evidence.

You are using zero-point energy and abs zero as interchangeable terms - they are not.  zero-point energy is the prime candidate for the casimir effect, which can be demonstrated in a lab - so there is experimental evidence.  Abs zero was and can still be seen as a classical limit - zpe is a non-classical quantum effect; whilst there are significant links they are not the same thing at all.

you never did explain any of your equations or why you felt they were relevant to the discussion.



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Offline Bored chemist

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How was Absolute Zero discovered?
« Reply #16 on: 29/07/2011 14:46:03 »
I agree that Mr Data's use of symbols is confusing, but it's hardly the point.
He claims that absolute zero is based on some complicated equation drawn up in 1913 but there is documentation to show that it was known about earlier than that. In addition, the equation it framed in terms of the thermodynamic temperature. You can't define that unless you already know about absolute zero.
In short, Mr Data is wrong.
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Offline JP

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How was Absolute Zero discovered?
« Reply #17 on: 29/07/2011 16:47:35 »
To sum it up:

1) In 1702, absolute zero was defined as the lower limit of a thermometer that worked by the expansion or contraction of a volume of air.

2) In 1848, Lord Kelvin came up with a definition from theory based on the motion of molecules (thermodynamics).  Absolute zero would be the point where all motion stopped.

3) In 1913, Einstein and Otto Stern came up with the idea that particle motion can't stop entirely due to quantum mechanics.  This changed the definition of absolute zero slightly to be the point at which the energy of motion of the particles is at a minimum.

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Offline Mr. Data

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How was Absolute Zero discovered?
« Reply #18 on: 29/07/2011 23:29:06 »
I agree that Mr Data's use of symbols is confusing, but it's hardly the point.
He claims that absolute zero is based on some complicated equation drawn up in 1913 but there is documentation to show that it was known about earlier than that. In addition, the equation it framed in terms of the thermodynamic temperature. You can't define that unless you already know about absolute zero.
In short, Mr Data is wrong.

That will be because I've never heard of the other sources.

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Offline Bored chemist

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How was Absolute Zero discovered?
« Reply #19 on: 30/07/2011 15:33:50 »
Then "Don't hazard a guess ".
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Offline Mr. Data

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How was Absolute Zero discovered?
« Reply #20 on: 30/07/2011 17:57:08 »
I was perfectly right in what I said though. Zero Point energy is not a theoretical idea. It's a scientific principle. You cannot reach zero momentum; that would directly violate the UP.

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Offline Bored chemist

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« Reply #21 on: 30/07/2011 22:10:56 »
You were "perfectly right" in that you said "It was proposed in 1913", but it was documented nearly half a century earlier and follows from work done in the 1780s.
http://en.wikipedia.org/wiki/Charles's_law

and also from even earlier work going back at least to the work in 1702 by Amontons.

I agree that you can't reach absolute zero.
Nernst pointed that out.
http://en.wikipedia.org/wiki/Third_law_of_thermodynamics
Interestingly, he did so just before 1913.

Zero point energies do exist and, for some systems they are a requirement of the UP.
However, while that's true for a vibrating molecule, it's not true for a lot of particles.
If they are stationary then the uncertainty of the momentum is zero, but, provided that you don't know where they are (ie the uncertainty of the position is infinite), that's not a violation. It applies to the much loved "particle in a box" but not to a free particle.

(if the vibrating molecule stopped vibrating the position of one atom WRT the others would be fixed, and so would its momentum. That's forbidden.)


« Last Edit: 30/07/2011 22:15:49 by Bored chemist »
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Offline Mr. Data

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« Reply #22 on: 31/07/2011 01:21:22 »
Stop, stop stop!

Who said zero-point energies where a fundamental principle? Anything which imposes zero momentum implies an exact spacial coordinate... This is ALWAYS forbidden... who you reading from, englighten me please.

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Offline Mr. Data

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« Reply #23 on: 31/07/2011 01:30:57 »
The concept and workable mechanism behind the experimental evidence behind the zero-point field should be no more complicated than excepting that spacetime, and every planck unit which occupies it, is constantly fuelled with a smallest unit of energy. This energy will at it's lowest energy refer to the kinetic energy of a vibrating energy 1/2 hbar \omega. You cannot have a unit of spacetime reach T=0 as much as you cannot accelerate it to c. Notice that the lowest speed possible will not equal v=0, as much as it's maximum speed will never reach c... everything is always in motion.

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Offline Bored chemist

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« Reply #24 on: 31/07/2011 11:02:48 »
"who you reading from, englighten me please."
My old University notes; probably Atkins or Richards. Anyway, whoever it was I think they had the advantage over you of not saying both
"Zero Point energy is not a theoretical idea. "
implying that it's real and
"This also means the zero point energy does not actually exist! "
saying that it's not.
Perhaps, when you have made up your mind,...
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Offline Mr. Data

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« Reply #25 on: 31/07/2011 17:18:09 »
Ask yourself this. How can the zero point even exist, if no one can ever reach that state? Zero point energy is a real unnattainable limit. It is not an idea, it is a measure of experimental fact.

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Offline Bored chemist

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« Reply #26 on: 31/07/2011 18:39:11 »
Ask yourself this. How can the zero point even exist, if no one can ever reach that state? Zero point energy is a real unnattainable limit. It is not an idea, it is a measure of experimental fact.
You still don't seem sure if it's experimentally real or purely hypothetical.
Incidentally, a good fraction of the nitrogen molecules I am breathing are in the bottom excited vibrational state. Their properties are dependent on the existence of zpe.
You don't have to get to absolute zero to achieve that.
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Offline Mr. Data

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« Reply #27 on: 01/08/2011 03:12:01 »
No, I'm quite sure of what I have said. You simply are not understanding what I telling you. Again, how can a real T=0 (as a temperature exsit) when T=0 cannot be reached? No matter how much cooling energy you pump into your apparatus, there is no way you can ever reach ZPE. There is always energy, always heat attributed to any vibrating energy.

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Offline Bored chemist

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« Reply #28 on: 01/08/2011 06:58:09 »
Try reading this.
As I said before, many or most of the nitrogen molecules I am breathing are in the vibrational ground state.
The only vibrational energy they have is zero point energy.
That's the real world, yet you seem to wan to insist it's not possible.
You seem not to have noticed that, at normal temperatures, most energy is translational.
That's why it's wrong to say "There is always energy, always heat attributed to any vibrating energy."
If it's zpe there's no heat associated with it.
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Offline Mr. Data

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« Reply #29 on: 01/08/2011 18:12:13 »
Lol... are you trying to joke this?

You do realize that the terminology zero point energy is misleading? Ground state energy is something far different than a system achieving zero point energy. It is not called a [zero point] for nothing you know. Zero, the non-existing of temperatures... energy, just as it says on the tin. Except T=0 is never accomplished, and what you have left over is a system with 1/2 hbar omega. You are not gaining energy from a zero point field, it is the energy you have left over when you reach this value of 1/2 hbar omega. It is not caused by a system reaching zero point energy (or by definition T=0) but is caused by the lack of it's ability or work to reach T=0.

Why can't you understand this? Indeed, why does anyone treat the zero point field as something a particle can reach? You don't freeze an electron down to zero temperature, then expect energy to be left over. You try and make the system reach zero point energy, but as I have shown countless and countless time before, this is impossible.

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Offline Mr. Data

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« Reply #30 on: 01/08/2011 18:14:53 »
If it's zpe there's no heat associated with it.


Which is exactly my point bored chemist. If there is no heat, there is no ZPE. But in all cases, there is an energy and momentum associated to every particle in the universe, so by logical deduction, ZPE is non-existant. You just proved my own case.

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Offline Bored chemist

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« Reply #31 on: 01/08/2011 19:10:23 »
From WIKI
" the energy of the ground state is known as the zero-point energy of the system."

From Mr Data
"Ground state energy is something far different than a system achieving zero point energy."


From Mr Data
"You try and make the system reach zero point energy, but as I have shown countless and countless time before, this is impossible."
In reality, most of the molecules in the air around you are in their vibrational ground states and have the ZPE which you need to account for if you want to explain their spectra.

"You don't freeze an electron down to zero temperature, then expect energy to be left over. "
Ignoring the fact that the first half is impossible, actually I do. Once you get cold (and room temperature will be quite cold enough for a lot of cases) there's not enough energy (on average) to get something out of the ground state. So it sits in the ground state, but as we both agree, it has to be moving in order to comply with the UP. The energy associated with that movement is the ZPE.

I'm sure anyone reading this will come rapidly to their own conclusion

For those who care,
The vibrational frequency of nitrogen is 2331 cm^-1
Equivalent to about 0.29eV
At room temp the mean energy is about 0.026 eV
Boltzmann's law gives n/n(o)= e^-(0.29/0.026)
So about  14 molecules in each million are in the first excited vibrational state.
The rest are in the ground state.
99.985 % are in the state Mr Data says you can't reach.
"You try and make the system reach zero point energy, but as I have shown countless and countless time before, this is impossible."
« Last Edit: 01/08/2011 19:31:51 by Bored chemist »
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Offline Mr. Data

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« Reply #32 on: 01/08/2011 19:47:06 »
You are implying zero point energy is real; this would mean you can freeze your system to absolute temperatures!!!!! This is impossible!

The ground state is simply the lowest energy state for any system, like a longitudinal photon is to mexican hat potential.

In reality, most of the molecules in the air around you are in their vibrational ground states and have the ZPE which you need to account for if you want to explain their spectra.

In what sense? Are you saying molecular objects which perhaps absorb zero point flucuations? This I would agree with. Fluctuations of the zero point energy field however, are not borne from systems which reach zero temperatures.

Ignoring the fact that the first half is impossible, actually I do.

Now you are confusing me!

Yes, the first half is impossible, and this is because no system, no molecular, no atomic, no subatomic system can be frozen to zero temperatures, so explain to me how your sentance makes more sense, than saying a particle does not reach zero temperatures because of the energy left over?

Yes... anyone reading this should come to their own conclusions. It makes absolutely no sense to speak of a zero point energy as an ''existing'' temperature. It is a limit, an unnatainable limit, because:

A) It will require an infinite amount of energy for a system to reach T=0

B) Every particle in the universe always has a momentum (and this is attributed directly to ZPE) - except it is an energy which will stop a system reaching T=0 - the system never actually reaches this mythical limit!!


So perhaps any confusions will be settled on this part:

Once you get cold (and room temperature will be quite cold enough for a lot of cases) there's not enough energy (on average) to get something out of the ground state. So it sits in the ground state, but as we both agree, it has to be moving in order to comply with the UP. The energy associated with that movement is the ZPE.

Right, except the energy associated to the ZPE is nothing but an intrinsic momentum inherent in aboslutely every system! It is just another fancy word, for yet another deceiving model of physics. ZPE does not exist, and can never be reached. Any energy in a system is not a contribution of ZPE in many cases - it is simply a part of the momentum of the system. If you could, however, freeze an object to asbolute zero temperatures first, then somehow revive that particle to some mometum through a contribution of some field, then yes... this would be an energy associated from the movement of a zero point field, keeping in mind a zero point field is exactly how I defined it earlier: It is the zero temperature associated to freezing a quantum system.

But dare I say anymore... such systems being frozen is impossible, because as you said, we seem to agree this would violate the Uncertainty Principle.

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Offline Bored chemist

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« Reply #33 on: 01/08/2011 22:18:45 »
You keep talking about fields.
Are you referring to this sort of thing?
"Vacuum energy is the zero-point energy of all the fields in space"
(from http://en.wikipedia.org/wiki/Zero-point_energy  )

If you are talking about the zero point energy of a vacuum then it's clearly not the same as talking about the zero point energy of something concrete- like the nitrogen molecules which are (practically) all in the vibrational ground state.
A vacuum doesn't have a temperature so it's clearly got little or nothing to do with the topic.
Why did you bring it up?
Never mind.
No matter how cold you get a nitrogen molecule, it will vibrate at just the same frequency, and with just the same energy as the ones you are breathing.
That energy- the energy associated with the ground state isn't zero. The atoms have potential and/ or kinetic energy.
They are (as we agree) moving.
The vibrational ground state of a nitrogen molecule has has got energy. It has about 0.15 eV of energy
It will continue to do so no matter what you say in reply to this.
It will also remain the case that you said "Ground state energy is something far different than a system achieving zero point energy." in direct contradiction of the received wisdom.
You also said "No matter how much cooling energy you pump into your apparatus, there is no way you can ever reach ZPE. "
which is nonsense- you just breathed in billions of billions of counter-examples.
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Offline Mr. Data

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« Reply #34 on: 02/08/2011 05:00:32 »
A vacuum doesn't have a temperature so it's clearly got little or nothing to do with the topic.

A vacuum does have a temperature - temperature is measured by the energy which fills the space you measure. There is no such thing as an ''empty space'' in physics, every small part of spacetime is filled with energy. In fact, relativity determines that the vacuum is a physical sheet and that the seperation of energy from any part of spacetime is impossible. So yes, a vacuum does contain a temperature.

I have heard people state that the vacuum does not technically have a temperature because it implies energy, but anyone with a deep understanding of relativity will know that the vacuum is a physical dynamical sheet of bubbling quantum particles - spacetime is the appearance of matter-energy. The two cannot be seperated.

Indeed, the vacuum temperature is best known as the Microwave background temperature also, the left over remnant of the big bang http://arxiv.org/abs/astro-ph/0012222

No matter how cold you get a nitrogen molecule, it will vibrate at just the same frequency

Actually, you cannot make a molecule reach zero temperatures. This would mean the absence of movement, I thought we covered this.

That energy- the energy associated with the ground state isn't zero. The atoms have potential and/ or kinetic energy.
They are (as we agree) moving


Right. The system never reaches zero temperature as this would imply zero momentum. Hence why a zero point energy (zero implying zero temperatures) is just nonesense.

The vibrational ground state of a nitrogen molecule has has got energy. It has about 0.15 eV of energy

I won't deny this. In fact, whatever energy is there, is part of the dynamical system itself. It is the instinsic energy of the system, not something borne from absolute zero temperatures.

You also said "No matter how much cooling energy you pump into your apparatus, there is no way you can ever reach ZPE. "
which is nonsense- you just breathed in billions of billions of counter-examples.


This part is troubling you the most. What is it which makes my statement unclear when I explain this? Zero point energy is the zero point temperatures at which motion should cease to exist. But since energy cannot be frozen to absolute values, then the particle can never reach zero point energy. Zero point energy is just a refusal to be frozen! It doesn't reach T=0, it keeps on trucking because of the UP.

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Offline Bored chemist

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« Reply #35 on: 02/08/2011 07:04:00 »
Sorry for my poor use of language there.
I should have said that a vacuum doesn't have a temperature that we can set to absolute zero, so it has little or nothing to do with the topic.

"Actually, you cannot make a molecule reach zero temperatures. This would mean the absence of movement, I thought we covered this."
Strawman; since I never said you could.
I said "No matter how cold you get a nitrogen molecule, it will vibrate at just the same frequency" which is true.

"Right. The system never reaches zero temperature as this would imply zero momentum. Hence why a zero point energy (zero implying zero temperatures) is just nonesense. "
You keep missing the point.
Even if we could get it to zero it would continue to vibrate with ZPE.

Re, The vibrational ground state of a nitrogen molecule has has got energy. It has about 0.15 eV of energy
you said
"I won't deny this."
I think you  already did.
"No matter how much cooling energy you pump into your apparatus, there is no way you can ever reach ZPE"


And, as another example,
"Zero-point energy is the energy that remains when all other energy is removed from a system. This behaviour is demonstrated by, for example, liquid helium. As the temperature is lowered to absolute zero, helium remains a liquid, rather than freezing to a solid, owing to the irremovable zero-point energy of its atomic motions. (Increasing the pressure to 25 atmospheres will cause helium to freeze.)" from
http://www.calphysics.org/zpe.html
« Last Edit: 02/08/2011 07:14:54 by Bored chemist »
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Offline Mr. Data

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« Reply #36 on: 02/08/2011 07:23:25 »
Strawman; since I never said you could.
I said "No matter how cold you get a nitrogen molecule, it will vibrate at just the same frequency" which is true.


When you said no matter how cold we make a nitrogen molecule, I thought you were implying our limit of T=0. Of course, this is impossible.

Even if we could get it to zero it would continue to vibrate with ZPE.


But we can't which is my point in its entirity. So how do we destinguish vibrational energy from zero point energy? To know the latter, surely a system first needs to reach T=0?

"Zero-point energy is the energy that remains when all other energy is removed from a system.

What?

If you remove the energy system in question, then what are you cooling down to T=0? By remove, what is meant here? You remove a peice of energy (or simply move it from one place to another) vacuum fluctuations take its place; that isn't zero point energy as we are taught by the reasoning of a zero temperature... Though that seems to be a popular answer. By effect, that is simply just another kinetic system which has taken the place of our previous system. No need for superfluous names like zero point energy, or temperatures.

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« Reply #37 on: 02/08/2011 07:24:32 »
You're link says this:

Quantum mechanics predicts the existence of what are usually called ''zero-point'' energies for the strong, the weak and the electromagnetic interactions, where ''zero-point'' refers to the energy of the system at temperature T=0

I thought me and you covered this has to be fundamentally incorrect?

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« Reply #38 on: 02/08/2011 09:08:58 »
Due to quantum fluctuations there can be no 'zero point' for anything. And that one is also Heisenberg's uncertainty principle as far as I know. 'Space' from a QM point of view is in a constant 'shivering', never at rest as the Casimir effect show us.

What we call 'zero' is a place where I expect everything to be at rest, and?
That doesn't seem to exist. Which is weird.
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« Reply #39 on: 02/08/2011 09:10:08 »
As it actually, if lifted up to a principle, states.

There is no universal 'ground state'.
==

Although, locally we have one, 'c'.
And if 'chopped up', we come to the Plank scale in where we can't chop it up any more, as far as I understand :) as that is where the distance travelled by light in one Planck time becomes one Planck length. And we can't make it any better than that.
« Last Edit: 02/08/2011 14:23:37 by yor_on »
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Offline JP

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« Reply #40 on: 02/08/2011 16:33:05 »
Yor_on, the term zero-point energy is a technical term referring to the energy of the ground state of a quantum mechanical system.  As you say, in most cases it can't be at zero energy.  It's called zero-point because it's as close as you can get.

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Offline Bored chemist

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« Reply #41 on: 02/08/2011 19:33:26 »
""Zero-point energy is the energy that remains when all other energy is removed from a system.

What?

If you remove the energy system in question, then what are you cooling down to T=0? By remove, what is meant here?"
You didn't spot the word "other" there did you?

It's the energy left behind because you can't remove it from the system even at absolute zero (it doesn't matter that you can't get there. The ZPE would still be present if you did).

Can I ask you why you think that you need to compress liquid helium before it will solidify?
The textbooks all say it's down to ZPE; but you don't believe in that.
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« Reply #42 on: 02/08/2011 22:19:02 »
In which cases can it be in a 'zero ground state' JP?

How is that defined.
==

If you refer to T=0 then it's not possible.
Well, as far as I know?
« Last Edit: 02/08/2011 22:25:48 by yor_on »
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« Reply #43 on: 03/08/2011 00:07:18 »
Yor_on, you're looking at it backwards.  Temperature is not a fundamental property.  It's something that emerges when you look at the average kinetic energy of many particles.  It doesn't make sense to talk about fundamental properties of a single particle in terms of average values of many. 

Zero-point energy is a fundamental property of a single particle or quantum system.  Zero-point energy of a quantum system is the lower limit on the energy it can have.  This may or may not be easily achievable, but it exists, and you can achieve it in certain cases.  The classic example is a simple harmonic oscillator.  Classically, it behaves like a spring: if you give it energy it oscillates, but if it has zero energy it remains stationary.  Quantum mechanically it's always oscillating a little, no matter how much energy you take out.

If you build your way back up to temperature, not reaching absolute zero tells you that if you have many such particles, they can't all be at their zero-point energy at once.  One of them might be, but all of them can't be.

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Offline Mr. Data

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« Reply #44 on: 03/08/2011 02:48:50 »
Yor_on, the term zero-point energy is a technical term referring to the energy of the ground state of a quantum mechanical system.  As you say, in most cases it can't be at zero energy.  It's called zero-point because it's as close as you can get.

Exactly. It is the closest we can get to zero temperatures, hence zero point energy is a misnomer - a great misunderstanding is applied to this, as we can see, Bored Chemist seems confident that I have somehow a misunderstanding.

I understand exactly what zero point temperatures imply, and I know fine well that reaching T=0 is impossible, so zero point energy as it is defined is never actually reached. It is a mythology.

As I said, zero point energy is just a fancy name for a refusal to reach T=0, so zero point temperatures do not really exist.
« Last Edit: 03/08/2011 02:52:28 by Mr. Data »

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Offline Mr. Data

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« Reply #45 on: 03/08/2011 02:51:34 »
In which cases can it be in a 'zero ground state' JP?

How is that defined.
==

If you refer to T=0 then it's not possible.
Well, as far as I know?
In which cases can it be in a 'zero ground state' JP?

How is that defined.
==

If you refer to T=0 then it's not possible.
Well, as far as I know?


Ground state is the lowest energy state - note also that this implies by the UP that T does not equal 0. Never does. Hence zero point temperatures does not exist.

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Offline Mr. Data

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« Reply #46 on: 03/08/2011 02:57:15 »
""Zero-point energy is the energy that remains when all other energy is removed from a system.

What?

If you remove the energy system in question, then what are you cooling down to T=0? By remove, what is meant here?"
You didn't spot the word "other" there did you?

It's the energy left behind because you can't remove it from the system even at absolute zero (it doesn't matter that you can't get there. The ZPE would still be present if you did).

Can I ask you why you think that you need to compress liquid helium before it will solidify?
The textbooks all say it's down to ZPE; but you don't believe in that.

I never made any statements on compressing liquid helium. Did I?

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« Reply #47 on: 03/08/2011 02:59:40 »
Bored, you said ZPE would still be presentt if I did remove all energy from a peice of spacetime, but I think this is a speculation at best, since there is no experimental evidence to varify that. As I said, you cannot make a bit of spacetime suit the idea of an ''empty space'' - all of it is filled with quantum fluctuations.

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« Reply #48 on: 03/08/2011 03:31:18 »
I'm not looking at it any specific way JP, more than saying that there is no ground state that I know of. But you state that there is, if I got you right? Maybe you are referring to defining a system as being in arbitrarily defined 'ground state'? Or maybe it is a theoretical definition of some other kind. What I did reading you was to go out on the net trying to find such a state in our universe? But it wasn't there :) But just as you can define space as a macroscopic ground state I presume that you can do so with a lot of other 'states' too.

That is, if you don't know that 'state' to exist, and can show me how to see it?
==

A harmonic oscillator can not be at absolute zero, as far as I know, other than theoretically.

We will never reach that state. To me 'c', and absolute zero, is a symmetry of kind, defining boundaries of our universe. It also has to do with 'scales' of other kinds, as the Planck scale, which to me also becomes boundaries defining where our limit of knowing goes. We know they should 'exist', but just as we won't pass, or even reach, 'c', not by normal motion of invariant mass anyway, so we won't get to absolute zero. They remind me very much of constants' all of them. Well, I suppose they are constants too :)
« Last Edit: 03/08/2011 03:58:28 by yor_on »
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« Reply #49 on: 03/08/2011 03:39:02 »
I'm not looking at it any specific way JP, more than saying that there is no ground state that I know of. But you state that there is, if I got you right? Maybe you are referring to defining a system as being in arbitrarily defined 'ground state'? Or maybe it is a theoretical definition of some other kind. What I did reading you was to go out on the net trying to find such a state in our universe? But it wasn't there :) But just as you can define space as a macroscopic ground state I presume that you can do so with a lot of other 'states' too.

That is, if you don't know that 'state' to exist, and can show me how to see it?


I think you've hit it on the button. No states can be made to reach T=0, so saying it should exist even when energy is not present seems decieving. I think I make a good arguement to say zero point temperatures don't actually exist. Also you are right about ground state, that can even apply to a macroscopic system, it could even apply to the universe as a whole! In fact, the entire universe according to current belief, is very much in a ground state.