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#18737 03/08/07 08:20 PM
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I don't know if there is enough knowledge acquired yet about Bose-Einstein condensates to answer my question, but here it goes....

From what I have read about the subject, I understand that the atoms in such a condensate appear to occupy the same space.

If this is so, is there a limit to the number of atoms that can occupy that same space?
How would this affect the actual matter density of the element in question?


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There is enough information and the number of atoms able to occupy the same space, it would appear, is infinite (whatever that means).

Density-wise it might be a really good way to think about the universe before the Big Bang and Inflation.


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Are you implying that if we were to cool off a really high amount of atoms into a bose-einstein condensate, we could increase mass infinitely leaving the volume to a near zero, therfore creating a gravitational singularity?


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Wow. That's an interesting thought.

I could picture that being used in a sci-fi piece explaining how an advanced civilization manages to build their power sources. Just feed a large enough amount of matter into a condensate until it eventually is big enough to start eating it's own environment with gravity.

Of course, the near-zero temperature would need to be maintained, and that would be pretty tough in something as energetic as a black hole. (It also begs the question, does a black hole evaporate faster when it's hotter? We know it evaporates more and more quickly as it shrinks, and that probably equates to heat somehow.)

(Yes, I know this post probably belongs in the Sci-Fi subject area, but this was where it fit. smile )

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This is weird and confusing.

Isn't it true that protons, neutrons, and electrons, being fermions, cannot form a Bose-Einstein Condensate as they prohibited by the Pauli exclusion principle from occupying the same quantum state? - and that only bosons can do this.

Ok, I found something in Wikipedia:

"Particles composed of a number of other particles (such as protons, neutrons or nuclei) can be either fermions or bosons, depending on their total spin. Hence, many nuclei are in fact bosons. So even though the main three massive subatomic particles i.e. the proton, neutron, and electron are all fermions, it is possible for a single element such as helium to have some isotopes that are fermions (e.g. 3He) and other isotopes that are bosons (e.g. 4He). (3He) is composed of one neutron and two protons [PNP]. Likewise, the deuteron (2H), which is composed of one proton plus one neutron [NP] is a boson, while the triton (3H), which is composed of two neutrons plus one proton [NPN] is a fermion. The deuterium atom composed of three fermions (proton+neutron+electron)is a fermion, while its nucleus [NP] when separated from the electron is a boson."

It's still confusing though!


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Well fermions would create a fermionic condensate
While bose-einstein is called a bosonic condensate
Which both share similar properties

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


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So, MrBiGG78, Dan Summons' statement, below, is wrong?

"No analogous phenomenon occurs for two or more fermions, which are prohibited by the Pauli exclusion principle from occupying the same quantum state"

Dan Summons, Physics Undergrad Student, UOS, Souhampton


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Red ... follow this link:
http://en.wikipedia.org/wiki/Fermionic_condensate

To address the original question ... yes in theory one could create a black hole this way. You might, however, run into a few significant engineering issues on the way there.


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I'm far from being a particle physicist (I just read a lot) and I never implied that Dan Summons is wrong...


Here is the excerpt I would refer to...

"It is far more difficult to produce a fermionic superfluid than a bosonic one, because the Pauli exclusion principle prohibits fermions from occupying the same quantum state. However, there is a well-known mechanism by which a superfluid may be formed from fermions. This is the BCS transition, discovered in 1957 by John Bardeen, Leon Cooper and Robert Schrieffer for describing superconductivity. These authors showed that, below a certain temperature, electrons (which are fermions) can pair up to form bound pairs now known as Cooper pairs. As long as collisions with the ionic lattice of the solid do not supply enough energy to break the Cooper pairs, the electron fluid will be able to flow without dissipation. As a result, it becomes a superfluid.
"

Cooper pairs are bosonic in nature and therfore the Pauli exclusion principle doesn't apply anymore. Therefore, at sufficiently low temperature and high pair density, the pairs may form a Bose-Einstein condensate.


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Thanks for the link MrBiGG78 & DA. I don't mean to flog this, but at first sight, some of the available info looks contradictory. I think I have it at last (don't I?): the fermions first form Cooper pairs, then these are able to form a condensate.


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In some cases what you will find redewenur is that multiple fermions can bind themselves into a collection that is bosonic.

So the condensate isn't the fermions but rather the bosonic bound state of the fermions.


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Yes, I think I got that at last DA. It gets around the Pauli exclusion principle. Thanks.

Thanks again, MrBigg, for your help.

It's not always that the nature of the info is difficult to understand, but when relatively new research is involved, some articles are obsolete (and therefore seem contradictory). As for Dan Summons, it seems that he was right, but what he said was misleading since he made no mention Cooper pairing. This may be because it wasn't achieved until 2003.


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Wow, google your name and you might find yourself quoted on a physics forum! smile

(Yes, original answer was posted 2001 or something like that....back when i was an undergrad)



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Originally Posted By: Durante
Wow, google your name and you might find yourself quoted on a physics forum! smile

It's an honour to have you drop by.


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All,
This is my first post so please go easy on me smile.
Anyhow,
I was thinking that we could really use several concepts here to
create a very nice energy cell; let me know what you think.
Take two BEC's grow them quite large - you will get (I think, this is all brainstorming) at some point a "soft singularity" something that acts like what Steven Hawking calls a black hole, but is not black (SH's black holes do radidate, and eventually evaporate), but more like a pinched off area of space time. (again I'm referencing his Brief History of Time, old but I think has good ideas.) Given that you make two of opposite spin (even a BEC has a spin right? (not sure), can keep them close, the virtual particle pairs they generate and absorb (if they act like SH says singularities do) would hopefully be of opposite charges. And there you have it, a very nice battery with anode and cathode. Now all you need is a way to take advantage of the current flow or whatever energy is cycling through this system. Hmmf. Sure would beat fusion which we know is hard to create here on Earth. I figure its a subtler approach, and sometimes they can be best. I know this is way way out there, but hey maybe some of you can lend a hand?
Thanks!
-Amnion

P.S.
Also if BEC's have a quantum state/spin, perhaps we can entangle them like photons and get some energy flow going with two of them perhaps entangled at "90 degree" angles, sort of like polarized light? Hmmf.


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The amount of energy currently required would make this remarkably inefficient as an energy cell.

Have you looked at the investment required to cool something down to, essentially, absolute zero?


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I didn't before, but thanks for that insight, it helps me think more clearly. Looking at this idea as its taking shape, it seems like its something further off, but I think as it comes closer to reality, we will find that it not so hard to do, but I agree, we will have to build towards this goal, no invention goes from nonexistence to existence without using others' ideas.
Right now laser/evaporative cooling allows us to reach BEC's, superatoms, liquid helium, and other liquid gases get us to BES's, superfluids. IMHO the best place to cool something at the moment is to start this sort of project on the dark side of the moon, or in deep space. These places are always very cold, which is a good start. Then we make it colder via the use of lasers/evaporative cooling, and soon via methods that we haven't thought of yet. Besides, if you are playing with a super high energy reactor, it might be wise to experiment far from Earth, you don't want this going wrong in our backyard. Maybe the Moon is too close, but we don't have the technology right now to jump to a far space and back, so I guess we will have to create our "lab" somewhere on the moon or at first Antarctica.
-A


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Amnion: "the best place to cool something at the moment is to start this sort of project on the dark side of the moon...so I guess we will have to create our "lab" somewhere on the moon"

Remembering, of course, that the moon has day and night, and that there is no permanent 'dark side'.


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Amnion: "..dark side of the moon, or in deep space. These places are always very cold, which is a good start.."

I think you'd be surprised how warm (in a relative sense) these places are. If you put a thermometer is deep space and allowed it to cool (this would take a really long time), and kept it isolated from all sources of light and background radiation, you'd find it would never read cooler than 2.7K.

The first Bose-Einstein Condensate (1995) had a temperature less than 100 billionths of a degree above absolute zero (100 billionths of a degree kelvin) i.e. a lot colder than outer-space!

Thanks,
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Amnion certainly has a point, though, in that the temperature gradient would be small. Would there be vast difference in energy requirements between the following:

(1) Cooling a mass in deep space from 2.7K to 0.2K

(2) Cooling the same mass on Earth from room temperature, to room temperature minus 2.5K


"Time is what prevents everything from happening at once" - John Wheeler
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