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Offline Mr. Data

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How was Absolute Zero discovered?
« 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.
 

Offline Bored chemist

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How was Absolute Zero discovered?
« 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.
 

Offline Mr. Data

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How was Absolute Zero discovered?
« 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.
 

Offline Bored chemist

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How was Absolute Zero discovered?
« 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.
 

Offline Mr. Data

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How was Absolute Zero discovered?
« 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.
 

Offline Mr. Data

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How was Absolute Zero discovered?
« 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.
 

Offline Bored chemist

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How was Absolute Zero discovered?
« 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 »
 

Offline Mr. Data

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How was Absolute Zero discovered?
« 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.
 

Offline Bored chemist

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How was Absolute Zero discovered?
« 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.
 

Offline Mr. Data

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How was Absolute Zero discovered?
« 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.
 

Offline Bored chemist

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How was Absolute Zero discovered?
« 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 »
 

Offline Mr. Data

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How was Absolute Zero discovered?
« 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.
 

Offline Mr. Data

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How was Absolute Zero discovered?
« 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?
 

Offline yor_on

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How was Absolute Zero discovered?
« 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.
 

Offline yor_on

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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 »
 

Offline JP

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How was Absolute Zero discovered?
« 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.
 

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.
 

Offline yor_on

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How was Absolute Zero discovered?
« 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 »
 

Offline JP

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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.
 

Offline Mr. Data

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How was Absolute Zero discovered?
« 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 »
 

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.
 

Offline Mr. Data

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How was Absolute Zero discovered?
« 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?
 

Offline Mr. Data

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How was Absolute Zero discovered?
« 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.
 

Offline yor_on

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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 »
 

Offline Mr. Data

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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.
 

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