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Offline Mr. Data

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How was Absolute Zero discovered?
« Reply #75 on: 03/08/2011 14:03:53 »
It seems as though you are saying that temperature is really kinetic energy,and that there is no place where there is no kinetic energy?Ok i'll accept that, since as you say radiation has kinetic energy.
 What do you mean by 10000th of a degree of error?
 What do you mean by quantum fluctuations in space,is this a theory only or has it been measured?
I agree that space cannot be empty as all space has radiation in it.I just meant space without molecules.

By 10,000th of an error, this simply gives us a degree of freedom to allow certain parts of space to be slightly warmer than let us say the X-directionality. It is a smudge-factor.

Now, temperature can be thought of as a kinetic energy, or even the sum of the kinetic energy of the constituents of a macroscopic object. For instance, by theory it is said that a metal becomes hotter when the particles it is made of increase in kinetic energy. The faster they move, the hotter the object becomes.

As for quantum fluctuations, you may want to read this: http://arxiv.org/abs/gr-qc/0401082 - it is our best understanding of the vacuum in context of quantum mechanics.
 

Johann Mahne

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How was Absolute Zero discovered?
« Reply #76 on: 03/08/2011 14:18:55 »
This is all detracting from the OP,but anyway...
 It seems as though the link you gave is saying that the fluctuations can add energy to particles (cosmic rays),but not detract from them?Seems strange to me because if a particle moves through a zone that has a lower energy then it should suck energy away from the particle.Do the fluctuations not average zero?Seems like perpetual motion?
 

Offline JP

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How was Absolute Zero discovered?
« Reply #77 on: 03/08/2011 14:20:02 »
Well JP I've seen two definitions there. Either the 'Casimir force' belongs to matter itself, or to space. As for zero point energy, sure it exists, at least I expect it to do so. As for it needs absolute zero?

Yor_on, what is the meaning of defining absolute zero for a single particle?  Zero-point energy is meaningful and achievable for a single particle, temperature is not.
 

Offline Mr. Data

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« Reply #78 on: 03/08/2011 14:30:48 »
Well JP I've seen two definitions there. Either the 'Casimir force' belongs to matter itself, or to space. As for zero point energy, sure it exists, at least I expect it to do so. As for it needs absolute zero?

Yor_on, what is the meaning of defining absolute zero for a single particle?  Zero-point energy is meaningful and achievable for a single particle, temperature is not.

Well, zero point energy for a particle would be a particle which ceases to exist strictly by the classical definition. Of course, quantum mechanics has something else to say. Even if T=0, a particle will still move. Indeed, large collections of particles will move. Speaking of one particle, is just as rewarding if not simpler than speaking or concentrating on a system with a large amount of particles.
 

Offline Mr. Data

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How was Absolute Zero discovered?
« Reply #79 on: 03/08/2011 14:36:06 »
This is all detracting from the OP,but anyway...
 It seems as though the link you gave is saying that the fluctuations can add energy to particles (cosmic rays),but not detract from them?Seems strange to me because if a particle moves through a zone that has a lower energy then it should suck energy away from the particle.Do the fluctuations not average zero?Seems like perpetual motion?

Take out some qoutations which highlight your incongruities, and we can analyze them.
 

Offline JP

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« Reply #80 on: 03/08/2011 14:45:10 »
Of course, quantum mechanics has something else to say. Even if T=0, a particle will still move. Indeed, large collections of particles will move. Speaking of one particle, is just as rewarding if not simpler than speaking or concentrating on a system with a large amount of particles.

Nope, you can't talk meaningfully about temperature of a single particle.  Temperature is defined for an ensemble of particles and it's properties (such as never reaching T=0) rely on the statistics of many particles.  That's where you keep going wrong when you say you can't reach T=0 for a single particle.  Such a phrase is meaningless. 

Here's a paper on reaching ZPE for a single molecule:
http://prl.aps.org/pdf/PRL/v62/i4/p403_1
 

Offline Mr. Data

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How was Absolute Zero discovered?
« Reply #81 on: 03/08/2011 14:55:08 »
I don't know if I agree with you. Temperature is part of the equation which describes the ZPE for a single quantum oscillator:

ε = hv/(ehv/kT-1) + hv/2

If temperature cannot be defined for a single oscillator, how does it enter the equation?
 

Offline JP

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« Reply #82 on: 03/08/2011 15:58:51 »
That's not the equation that described ZPE for a single quantum oscillator.  That's a thermodynamic equation for a collection of them.  The single quantum harmonic oscillator energy is:

E=(N+1/2)hbar*omega, where N=0,1,2,3,4,...

When N=0, you're at the ZPE, which has energy hbar*omega/2.
 

Offline Mr. Data

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« Reply #83 on: 03/08/2011 16:09:16 »
Not according to this:

http://en.wikipedia.org/wiki/Zero-point_energy

''Then in 1913, using this formula as a basis, Albert Einstein and Otto Stern published a paper of great significance in which they suggested for the first time the existence of a residual energy that all oscillators have at absolute zero.''
 

Offline Mr. Data

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« Reply #84 on: 03/08/2011 16:09:48 »
Or maybe I picked it up wrong...
 

Offline Mr. Data

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How was Absolute Zero discovered?
« Reply #85 on: 03/08/2011 16:11:16 »
''the most famous such example of zero-point energy is E={\hbar\omega / 2} associated with the ground state of the quantum harmonic oscillator.''

From the same link. E={\hbar\omega / 2} is just the part of the remaining kinetic energy in the equation given.
 

Offline imatfaal

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How was Absolute Zero discovered?
« Reply #86 on: 03/08/2011 16:13:21 »
Mr D - please learn to read your own sources before contradicting others.  We know you picked it up wrong.  Why are you persisting to try and "answer" these questions when it is quite clear that you haven't even read up to a wikipedia level?
 

Offline Mr. Data

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How was Absolute Zero discovered?
« Reply #87 on: 03/08/2011 16:20:14 »
Mr D - please learn to read your own sources before contradicting others.  We know you picked it up wrong.  Why are you persisting to try and "answer" these questions when it is quite clear that you haven't even read up to a wikipedia level?

The speculations from the equations match those of JP's... after the equation given (which I presented) it simply states that

''According to this expression, an atomic system at absolute zero retains an energy of hν.''

Now, I don't see a great difference here. If you set N = hv/(ehv/kT -1) = 0 then you still end up with the same result.
 

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Offline Mr. Data

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How was Absolute Zero discovered?
« Reply #88 on: 03/08/2011 16:22:11 »
Shrunk
And I think it a bit sanctimonious of you to suddenly challenge my ability to read something. It's a common frequent thing here to see that kind of behaviour - we are all fallible, prone to mistakes. But I don't see you coming down on other people. Perhaps I left a mark with you?
 

Offline imatfaal

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How was Absolute Zero discovered?
« Reply #89 on: 03/08/2011 16:27:51 »
This discussion is quite fascinating but I'm not a scientist so i'm not sure that i understand the implications of absolute zero and kinetic energy of molecules.
  We are told that the universe has an average temperature of 2.7 k.But now i'm confused.Does this average only apply to matter and not space itself?
 If a space probe measures the temperature in space somewhere between our local group of galaxies and the virgo group then what kinetic energy are we taking about? Photons have no mass so they cannot have any kinetic energy?The Cosmic Background radiation cannot have any kinetic energy either.Does this mean that it's not valid to speak of a temperature and that the space probe is returning only the temperature of it's probe?
Johann - the whole of the universe is full of thermal radiation (ie radiation given off by hot objects) that is a relic of three hundred years or so after the big bang.  This radiation, which when emitted by hot hydrogen ions was ultraviolet, has been stretched by the expanding universal so that it has been red-shifted to the microwave band.  All bodies above absolute zero will give off black body radiation - the spectrum they emit is related to the temperature of the the black body; the wavelength of the CMBR is that of a body at 2.75K.  

What that means is that any object colder that 2.75K will on average absorb radiation and warm up (ignore black holes they are weird) and any object warmer than 2.75K will on average emit radiation and cool down; ie the two systems will tend towards equilibrium.  As the entire universe is homogeneously full of this radiation it makes sense to talk of a temperature.  

A probe always measures the temperature of the probe - but we hope that by clever engineering we can ensure that the probe will be in equilibrium with the surroundings.  Other ways to measure temperature rely on the spectrum of radiation the object is emitting and use the black body equation to find the temperature.  
 

Offline imatfaal

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« Reply #90 on: 03/08/2011 16:38:48 »
Quote
Zero point energy is the zero point temperatures at which motion should cease to exist.
Quote
Hence why a zero point energy (zero implying zero temperatures) is just nonesense.
Quote
You are implying zero point energy is real; this would mean you can freeze your system to absolute temperatures!!!!! This is impossible!
Quote
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.

The reason I have asked you to be more careful is the comments you have made so far in this thread - you will note they are in direct contradiction to what you are now seem to be agreeing with.
 

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Offline Mr. Data

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How was Absolute Zero discovered?
« Reply #91 on: 03/08/2011 16:39:59 »
Shrunk
Quote
Zero point energy is the zero point temperatures at which motion should cease to exist.
Quote
Hence why a zero point energy (zero implying zero temperatures) is just nonesense.
Quote
You are implying zero point energy is real; this would mean you can freeze your system to absolute temperatures!!!!! This is impossible!
Quote
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.

The reason I have asked you to be more careful is the comments you have made so far in this thread - you will note they are in direct contradiction to what you are now seem to be agreeing with.

Elaborate. And note I will be away for the next hour or so, so make it good for my return.
 

Offline JP

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« Reply #92 on: 03/08/2011 16:42:36 »
Now, I don't see a great difference here. If you set N = hv/(ehv/kT -1) = 0 then you still end up with the same result.

The derivation of the ZPE of a single quantum harmonic oscillator is here: http://en.wikipedia.org/wiki/Quantum_harmonic_oscillator

There is a huge difference because: 1) N is an integer for the harmonic oscillator, while N in your above equation isn't, and 2) these are completely different physical situations.  Yours is, from what I recall, an expression for the energy density of a black body radiator.  A quantum harmonic oscillator is completely different.
 

Offline Mr. Data

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How was Absolute Zero discovered?
« Reply #93 on: 03/08/2011 16:42:54 »

Mr D - you really need to understand that absolute zero and zero-point energy are not the same thing. 

I use zero temperatures, or absolute temperatures interchangeably.

http://en.wikipedia.org/wiki/Thermodynamic_temperature

The fact that zero-point energy is the energy remaining in a system at the limit T=0 does not logically imply, nor practically lead to the claim that zpe can only be observed at absolute zero.

Definition of the ZPE  -

''where ''zero-point'' refers to the energy of the system at temperature T=0, or the lowest quantized energy level of a quantum mechanical system.''

So it is stating that energy remains at T=0. You can use temperature interchangeably with energy or motion. As far as the definition is concerned, zero point energy is when temperatures are zero, and motion should no longer exist. It is entirely logical to assume that the zero point is not a factual temperature, since motion is never erradicated. So long as you have motion, your system cannot be said to be absolutely frozen, hence there is a temperature which cannot be quelled.

I don't recall any post claiming that the limit T=0 can be reached.  But whilst we cannot practically reach it - we state with certainty that at T=0 there is still a ground-state oscillation ie the zero point energy.

By what reasoning? If T=0 is never reached, how can speculations be given it is a true ground state? It seems outside the realm of testable physics.

It seems strange one can state with certainty that at T=0 there is still a ground state, if T=0 is never acheived.... think about it.

It is called zero-point energy because i) it would still be there at T=0 ii) you cannot go any lower.

Who says it would still be there, what evidence do you have that reaching T=0 reveals this prediction? Since we cannot reach the state T=0, then it seems redundant to make the speculation energy would still exist. Energy only exists because it cannot reach this state, not the other way around.


Note you never answered any of this. I will also remind you of my conjecture:

Let us not stray from the proposition being made. Zero point energy, the point at which motion should cease, does not. It is evidence enough to state that the definition of zero point energy is misunderstood.

It seems to be a strongly held belief that zero temperatures are reached, but there still remains a motion. This is an oxymoron.

Motion gives rise to temperature, so if there is no ceasing of motion, then how can your system really be called a zero point? In logical conclusion, zero point motion or temperatures (call it what you will) are never achieved.
 

Offline Mr. Data

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How was Absolute Zero discovered?
« Reply #94 on: 03/08/2011 16:43:44 »
Now, I don't see a great difference here. If you set N = hv/(ehv/kT -1) = 0 then you still end up with the same result.

The derivation of the ZPE of a single quantum harmonic oscillator is here: http://en.wikipedia.org/wiki/Quantum_harmonic_oscillator

There is a huge difference because: 1) N is an integer for the harmonic oscillator, while N in your above equation isn't, and 2) these are completely different physical situations.  Yours is, from what I recall, an expression for the energy density of a black body radiator.  A quantum harmonic oscillator is completely different.

Thank you for the link. I will take back what I said about the equation. I admit it is based on a flaw, an incorrect application.
 

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Offline JP

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How was Absolute Zero discovered?
« Reply #95 on: 03/08/2011 16:46:32 »
Shrunk
Quote
Zero point energy is the zero point temperatures at which motion should cease to exist.
Quote
Hence why a zero point energy (zero implying zero temperatures) is just nonesense.
Quote
You are implying zero point energy is real; this would mean you can freeze your system to absolute temperatures!!!!! This is impossible!
Quote
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.

The reason I have asked you to be more careful is the comments you have made so far in this thread - you will note they are in direct contradiction to what you are now seem to be agreeing with.

Elaborate. And note I will be away for the next hour or so, so make it good for my return.

Oh, you'll be away for more than an hour, I think, as this response makes it clear you don't have any desire to be civil on this forum: something you've been warned about in the past.
 

Offline Bored chemist

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How was Absolute Zero discovered?
« Reply #96 on: 03/08/2011 20:48:10 »
You really do keep missing the point.

You say "It seems to be a strongly held belief that zero temperatures are reached, but there still remains a motion. This is an oxymoron."
Nope, it's the truth.

You can't remove the vibrational energy from a nitrogen molecule. It's not that you can't get it cold enough, it's that there is no lower energy state for it to be in.
The ground state is the lowest you can get. There's still energy associated with it.
Cooling it further doesn't make sense ( all you could do would be to reduce the fraction of molecules in any excited state.)

Once you get a nitrogen molecule into the vibrational ground state (as most of them are).
1 you cannot take any more vibrational energy out of it because, to do that you would have to move it to a lower energy state and, since it's in the ground state, there isn't one.
2 It will therefore stay in that ground state no matter how far you cool it (including, in principle, to zero)
Yet, because the ground state has a vibrational energy of about 0.15 eV, it still has quite a lot of energy. (Very roughly, the same energy as something glowing red hot)
That energy is the zero point energy of the system.
It's prefectly real.
It's the sort of thing that stops helium freezing unless you compress it.
« Last Edit: 03/08/2011 20:50:00 by Bored chemist »
 

Offline Soul Surfer

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How was Absolute Zero discovered?
« Reply #97 on: 04/08/2011 23:47:59 »
BC one thing that this discussion shows how many people do not understand that we live in a dynamic universe and it is this residual vibrational energy that actually holds the atoms in molecules together.  Also this dynamic energy gets greater as you look further inside the atom the electrons in atoms have much greater energies corresponding to optical to x ray frequencies and the quarks inside the neucleons have so much energy that there is more energy in their motion than their rest masses.
 

Offline imatfaal

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« Reply #98 on: 05/08/2011 00:32:35 »
To an extent SoulSurfer - but the fact that the bound system has a lower energy than its constituent parts, ie that energy is needed to separate the stable system (the binding energy), does not logically entail the fact that the lowest energy is not zero.  In other words it is not obvious from the fact that energy is required to break either molecular or nuclear bonding that these systems must have a ground state that is not zero.  Strong bonds are the lowest energy state - not an energy rich state.  Whether you can make the connexion between vibrational energy and the quantum chromodynamic binding energy of quarks and gluons is beyond me - but it seems to be explaining non-classical matters in a far too classical a manner
 

Offline Bored chemist

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« Reply #99 on: 05/08/2011 06:57:14 »
My personal opinion is that this thread largely shows that Mr data doesn't know what he is talking about to an extent that is verging on trolling.
I cite this excerpt as evidence for that opinion
"Let us not stray from the proposition being made. Zero point energy, the point at which motion should cease, does not. It is evidence enough to state that the definition of zero point energy is misunderstood.

It seems to be a strongly held belief that zero temperatures are reached, but there still remains a motion. This is an oxymoron.

Motion gives rise to temperature, so if there is no ceasing of motion, then how can your system really be called a zero point? In logical conclusion, zero point motion or temperatures (call it what you will) are never achieved."

Other evidence is plentiful, as cited by Imatfaal earlier

 

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