Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: DoctorBeaver on 03/01/2009 14:38:45
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I'm reading about Bose-Einstyein Condensates (something I know absolutely zilch about) and the zero point motion of superfluid helium is mentioned. Can someone explain ZPM in idiot language for me, please?
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If you could freeze the vacuum down to absolute zero, you would have initially thought you would have a perfectly frozen motion, with a perfectly frozen system. However, even at absolute zero there is motion. This motion is found to be the energy of the zero-point energy field.
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Ah, I wondered if it was something to do with that. Thank you.
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You're welcome.
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How can you cool a vacuum? Surely you can only cool matter? Something I've also wondered about is how can something be regarded as a vacuum if EM and gravitic energy, plus neutrinos, are flooding through it? Even if you could cool all the matter in a given volume, unless you can shield it from all the EMR, gravitic waves and neutrinos it'll still have a positive energy density - that is, there will still be energy within the volume, regardless of how cold it is. For given regions and periods of time, I wouldn't expect this to change much, but it could vary a lot over interstellar/intergalactic distances.
I don't know much about BECs either.
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"Temperature is defined statistically and not mechanically, so the
statement "T=0" is actually not exactly equivalent to the statement "all
motion ceases." The latter is a pretty good approximation, but there are
important exceptions. For example, quantum mechanical "zero-point motion,"
which allows systems in their "ground" (lowest possible energy) state to
have nonzero probability of being found over extended areas of space.
Thus at T=0 the two atoms of a diatomic molecule (e.g. nitrogen) are not rigidly
separated at some distance from each other, but can be thought of as
undergoing rapid vibration with respect to one another. The entire molecule
also "rotates," even at T=0. In the context of spin systems the mechanical
interpretation of temperature as motion is even more misleading, because
you can get T < 0."
And
"Classicaly speaking ALL MOTION CEASES AT ABSOLUTE ZERO.
2.Zero point Quantum motion is always there.
and that is what prevents collapse in the hypothetical scenario
at absolute zero. For very massive objects, this has to be
supplemented with Pauli repulsion.
3.The third law of thermodynamics, also known as the Nernst
theorem, can be written as BY NO FINITE SERIES OF PROCESSES
IS THE ABSOLUTE ZERO ATTAINABLE. No matter how much patience
and money you have, you can not execute an infinite series of
steps."
And finally
" ZERO-POINT MOTION IN A BOSE-EINSTEIN CONDENSATE has been quantitatively measured for the first time, allowing researchers, in effect, to study matter at a temperature of absolute zero. According to quantum mechanics, objects cooled to absolute zero do not freeze to a complete standstill; instead they jiggle around by some minimum amount. MIT researchers (Wolfgang Ketterle, 617-253-6815) measured such "zero-point motion" in a sodium BEC, a collection of gas atoms that are collectively in the lowest possible energy state (Update 233).
According to Ketterle, "the condensate has no entropy and behaves like matter at absolute zero." The MIT physicists measured the motion (or lack thereof) by taking advantage of the fact that atoms absorb light at slightly lower (higher) frequencies if they are moving away from (towards) the light. To determine these Doppler shifts (100 billion times smaller than those of moving galaxies), the researchers used a technique known as Bragg scattering.
In this technique, atoms absorb photons at one energy from a laser beam and are stimulated by a second laser to emit a photon at another energy which can be shifted upward or downward depending on the atoms' motion towards or away from the lasers. Measuring the range in energies of the emitted photons allowed the researchers to determine the range of momentum values in the condensate. Multiplying this measured momentum spread (Dp) by the size of the condensate (Dx) gave an answer of approximately h-bar (Planck's constant divided by 2p)--the minimum value allowed by Heisenberg's uncertainty relation and quantum physics. While earlier BECs surely harvested this zero-point motion, previous measurements of BEC momentum spreads were done with exploding condensates having energies larger than the zero-point energy. (J. Stenger et al., Physical Review Letters, 7 June 1999.) "
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The temperature of space varies but outer space is said to be around 2.725 Kelvin. That means three degrees above absolute zero. That’s -270.425 degrees Celsius, or --454.761 Fahrenheit.
Isn't the trick to see the absence of energy/motion as 'coldness'?
If seen so wouldn't that make a vacuum automatically 'cold as space'?
No matter:) where it's 'produced'.
But that's not true, otherwise that would have been enough for creating a BEC anywhere on Earth.
So how can a vacuum transfer heat?
You are correct, we just have to look at all those photons traveling.
somehow they keep of from interacting with the vacuum around them.
But they 'interact' only with 'matter'.
Here is how Wikipedia explains it
http://en.wikipedia.org/wiki/Heat_transfer#Radiation
As for the rest LeeE:)
Don't know.
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What one can notice though, is that even though photons and vacuum won't interact with each other in vacuum.
Vacuum seems to adapt to the heat surrounding itself?
If we had a closed lead box (containing vacuum), would the temperature from the inside of that box adapt to the temperature outside, and would size matter:)
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Hmmm, this is all very interesting.
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Heisenberg's relation: Δx•Δp ≥
h/2
where Δx = indetermination of particle's position; Δp = indetermination of particle's momentum.
If motion stopped completely, than Δp would become zero (if the particle is still, it has a precise value of its momentum: zero) --> Δx would become infinite so the particle could be everywhere. Of course the two things together are inconsistent.
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Nice Lightarrow, do you mean that both those seems to be fulfilled inside a 'ideal vacuum:)
I definitely should try to understand more of what physics see as 'radiation' inside a 'nothing'(ideal vacuum).
This might be of interest for you?
It's a 'reinterpretation' of Bell's Theorem?
In it he argues that Einstein was right after all about 'quantum non-locality.'
Read it, I got to admit that the math is lightyears beyond me :)
But maybe not you.
And SC and Steve and Madidus and Mr. S and....
And then you can explain it ::))
http://arxiv.org/abs/0707.1333
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Heisenberg's relation: Δx•Δp ≥ h/2
where Δx = indetermination of particle's position; Δp = indetermination of particle's momentum.
If motion stopped completely, than Δp would become zero (if the particle is still, it has a precise value of its momentum: zero) --> Δx would become infinite so the particle could be everywhere. Of course the two things together are inconsistent.
Whilst this is a relation to the movement of the zero-point energy field, i must say, it's not at all the main reason. In fact, simply due to finding a massive amount of energy at zero-point is generally considered the reason:
ε=hv/e (hv/kt - 1) + hv/2
Which means, an entire half of the energy of the system (which theoretically is made to reach absolute zero, but currently is unattainable), is found still to exist. So 1/2hv of energy is said to ''vibrate'' at these temperatures.
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Nice Lightarrow, do you mean that both those seems to be fulfilled inside a 'ideal vacuum:)
I definitely should try to understand more of what physics see as 'radiation' inside a 'nothing'(ideal vacuum).
This might be of interest for you?
It's a 'reinterpretation' of Bell's Theorem?
In it he argues that Einstein was right after all about 'quantum non-locality.'
Read it, I got to admit that the math is lightyears beyond me :)
But maybe not you.
And SC and Steve and Madidus and Mr. S and....
And then you can explain it ::))
http://arxiv.org/abs/0707.1333
Oh my giddy little friend, when i saw it contained Clifford Algebra, i hid behind the sofa.
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What!!
Oh Ye of Little Faith, not so I say, not so.
With proper preparations this will be a piece of cake:)
First one just have to wonder, what school should I choose:)
And then, what university (one with lots of girls sounds ok to me:)
And most importantly, will I live long enough to finish the education?
And then ...Onwards to the hall of fame....
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On the other hand
Oh Ye who have ridden into the valley of doom..
Ah, so you found it somewhat daunting?
Good Good, then we are two...
Or is it three?
(I should never have opened that ***ed.pdf:)
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(I should never have opened that ***ed.pdf:)
There are thousands of documents which complexity is far beyond my knowledge (this is one of them) so you're in good company [:)]
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I'm reading about Bose-Einstyein Condensates (something I know absolutely zilch about) and the zero point motion of superfluid helium is mentioned. Can someone explain ZPM in idiot language for me, please?
Do you know the most amazing part of the zero-point energy field equations?
It suggests that everything, from the electron to the quark particle, even to our own composite bodies, to entire galaxies, everything comes from the zero-point field.
If you take the vacuum, and take it to such postulates, it means that there is an intrinsic property of the vacuum which states that this fabric that physical objects lyes on, is in fact a physical fabric itself. It means, in short, that if you removed all of the physical stuff of the vacuum, the vacuum itself would not exist.
Even Einstein once postulated from his mathematical assertions, ''Before relativity, we thought that if you removed all the matter and energy from the vacuum, spacetime would continue to exist. We now know this not to be true.''
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Even Einstein once postulated from his mathematical assertions, "Before relativity, we thought that if you removed all the matter and energy from the vacuum, spacetime would continue to exist. We now know this not to be true"
I'd go along with the idea that energy creates it's own space to exist within but I haven't been able to formulate a logical argument to support it. And sort of related to this is; how can space expand if space (vacuum) consists of nothing? That is, how can space expand when there is nothing to expand?
Of course, I'm not saying that it doesn't, just that there would appear to be more to space than meets the eye (or telescope/spectrograph etc)
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Very Nice..
My own unqualified guess (for now:)is that we have mass and acceleration.
Mass is what defines space, acceleration is something very 'local' compared to other types of mass.
If mass defines spacetime then motion, distance, (3D) and time seems to be something following of mass?
But I'm not really happy with this as it is like saying 'this is it' but without being able to explain any of the other phenomena, but I can't see time without mass?
How about this:)
A vacuum with only one thing in, our at one G accelerating rocket, it would act the same way as gravity and it would have 'time'.
As that is the only way for any object to move a distance.
The acceleration would 'guarantee' our movement here.
Would spacetime become 'bigger' due to its acceleration.
(In fact, would it move at all???)
Would acceleration be any guarantee for that?
According to that 'elevator'
Then we take our earth and do the same.
Would that spacetime be 'smaller' as the Earth would be stationary?
Or would it be 'bigger'
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Even Einstein once postulated from his mathematical assertions, "Before relativity, we thought that if you removed all the matter and energy from the vacuum, spacetime would continue to exist. We now know this not to be true"
I'd go along with the idea that energy creates it's own space to exist within but I haven't been able to formulate a logical argument to support it. And sort of related to this is; how can space expand if space (vacuum) consists of nothing? That is, how can space expand when there is nothing to expand?
Of course, I'm not saying that it doesn't, just that there would appear to be more to space than meets the eye (or telescope/spectrograph etc)
Do you really want my scientific opinion, or do people here want to flout it with the highest impunity, whilst superfluously invalidating the science behind the pipe works. If people here want to learn the sciences here, lessons are the least of their worries.
Taking for granted the work being shown would be a good start. I am not harsh, nor am i **** in giving the work for other people to learn, but i will not be here to be taken a fool of... i have better things to do.
Yoron, that was not personal. You are here to learn, but to many fall into this place hoping that i will take hold of their personal pet-theories and answer them. Science needs to be rigorous and scintifically-experimental.
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Nah, don't worry about me:)
I've been called worse..
You are quite correct in that I see it as a learning experience.
And that my definitions will change as I learn.
But I believe it is the same with us all here.
We all have kept the ability to adapt intact.
And we all have our own 'ideas'.
At least that's my impression.
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Btw: LeeE :)
The idea behind matter being 'space' is strange, but if you consider that space seems to contain energy all by itself that both allows for 'virtual particles' that do affects spacetime
http://en.wikipedia.org/wiki/Vacuum_fluctuation#Manifestations
As well as spontaneous matter creation according to
http://www.infidels.org/library/modern/mark_vuletic/vacuum.html
Then it seems to me that space is something more than just a vacuum.
But if you is like me you probably knew this already.
But due to the male predisposition for 'one thing at a time', you know :) what differs us from females.
You, as I had when writing about BEC, kind of forgotten those evidence.
But in my case I have a friend more:)
Mr Alzheimer ::)))
No, not really, but it feels so at times.
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Hmm...
Do you really want my scientific opinion...
I wasn't asking for it, just making a comment.
...whilst superfluously invalidating the science behind the pipe works.
What has plumbing got to do with this?
nor am i **** in giving the work for other people to learn
Does that mean you do not have a 4-star teaching rating?
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I apologize. Yesterday i was just a bit hyped up with the way another member spoke to me. Sorry again, it wasn't supposed to be directed at you in such a way.
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Np [:)]
It's all coals off a duck's back to me.
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But yet, i was wrong, very fuc@ing wrong. I am very sorry for this.