KALSTER Posted June 20, 2008 Report Share Posted June 20, 2008 First a quote from the NIST page on recent Bose-Einstein Condensate experiments: ” Working at JILA, physicist Carl Wieman's [pronounced wy-man] team has explored tuning the self-interaction of atoms in a BEC. By making a BEC in a particular isotope of rubidium, rubidium-85, and then changing the magnetic field in which the BEC is sitting, the team is able to adjust the wavefunction's self-interaction between repulsion and attraction. If the self-interaction is repulsive, all the parts of the wavefunction push each other away. If it is attractive, they all pull towards each other, like gravity. Achieving a pure BEC in rubidium-85 required the cloud of atoms to be cooled to about 3 billionths of a degree above absolute zero, the lowest temperature ever achieved.Making the self-interaction mildly repulsive causes the condensate to swell up in a controlled manner, as predicted by theory. However, when the magnetic field is adjusted to make the interaction attractive, dramatic and very unexpected effects are observed.The condensate first shrinks as expected, but rather than gradually clumping together in a mass, there is instead a sudden explosion of atoms outward. This "explosion," which actually corresponds to a tiny amount of energy by normal standards, continues for a few thousandths of a second. Left behind is a small cold remnant condensate surrounded by the expanding gas of the explosion. About half the original atoms in the condensate seem to have vanished in that they are not seen in either the remnant or the expanding gas cloud.” They change the properties of the magnetic field trapping the BEC, but how does that affect the forces present in between the constituent atoms? Do they simply tune the field so that it cancels out repulsive forces by destructively interfering with them? Can this only be done with BEC’s because of the uniformity of the wavefunction the atoms collapsed to? Does it mean that the virtual force-carrier particles of each field (van der Waal?) interfere with each other and cancels out? What happens to the energy then, or does it simply revert to the ground zero point energy? What do they mean when they say that “this procedure caused the BEC to implode and shrink beyond detection”? Quote Link to comment Share on other sites More sharing options...
Moontanman Posted June 20, 2008 Report Share Posted June 20, 2008 That's an amazing thing, I wonder what insights will be made from this "Nova" in test tube? It asks a great many questions that beg to be answered. Quote Link to comment Share on other sites More sharing options...
Buffy Posted June 21, 2008 Report Share Posted June 21, 2008 Makes sense to me. I think its hot! YouTube - Cannonball Adderley Sextet- Bossa Nova Nemo http://www.youtube.com/watch?v=PGbWUIxkbQc Jazz is rhythm and meaning, :rolleyes:Buffy Quote Link to comment Share on other sites More sharing options...
Moontanman Posted June 21, 2008 Report Share Posted June 21, 2008 You are no doubt cool Buffy, cool no doubt. Absolute zero cool, BEC cool......:rolleyes: Quote Link to comment Share on other sites More sharing options...
Moontanman Posted June 21, 2008 Report Share Posted June 21, 2008 This is all well and good but what does it have to do with the Bose Einsteinium Condensate Nova? Quote Link to comment Share on other sites More sharing options...
KALSTER Posted June 21, 2008 Author Report Share Posted June 21, 2008 Woop-tee-doo, Bosenova is a play on Bossa Nova. Now any non-hijacking comments? Quote Link to comment Share on other sites More sharing options...
Moontanman Posted June 21, 2008 Report Share Posted June 21, 2008 Woop-tee-doo, Bosenova is a play on Bossa Nova. Now any non-hijacking comments? Duh, where did you park your squad car KALSTER? Quote Link to comment Share on other sites More sharing options...
KALSTER Posted June 21, 2008 Author Report Share Posted June 21, 2008 Duh, where did you park your squad car KALSTER?What is that supposed to mean? My point is that I made a serious post with interesting information and then some "residents" find it amusing to hijack the thread and post videos regarding Bossa Nova on here like children. What the hell? Is this the norm on this forum? Quote Link to comment Share on other sites More sharing options...
Moontanman Posted June 21, 2008 Report Share Posted June 21, 2008 What is that supposed to mean? My point is that I made a serious post with interesting information and then some "residents" find it amusing to hijack the thread and post videos regarding Bossa Nova on here like children. What the hell? Is this the norm on this forum? Sorry dude, I thought you were being sarcastic, you will notice I did make a serious post at the beginning. I thought the BEC Nova was one of the most interesting things I've heard of in long while but I really don't know exactly what to make of it. It really looks like one of those things that will yield far more than it would seem at first blush. Just an oddity now but who knows type of thing. Look at the first laser, who would have predicted when we have now from that humble beginning. What is your take on the BEC Nova? Quote Link to comment Share on other sites More sharing options...
KALSTER Posted June 21, 2008 Author Report Share Posted June 21, 2008 Sorry dude, I thought you were being sarcastic, you will notice I did make a serious post at the beginning. I thought the BEC Nova was one of the most interesting things I've heard of in long while but I really don't know exactly what to make of it. It really looks like one of those things that will yield far more than it would seem at first blush. Just an oddity now but who knows type of thing. Look at the first laser, who would have predicted when we have now from that humble beginning. What is your take on the BEC Nova?Oh, that's ok then:) It is just that Buffy is an administrator:rolleyes:. Thanks for your comments, I share your enthusiasm (obviously), it is a phenomena that defies explanation using current theory. How often does that happen? My take? Well my take would mostly consist of uneducated speculation, hence my misguided post here. Being uneducated I naturally do have my own little hypothesis that might (in my mind) explain a lot of things.:phones: I have an idea that forces might be distinct fractal disturbances of an Einsteinian aether, the magnetic field (consisting of its own brand of fractals) being tuned to destructively interfere with the intermolecular forces of the BEC, but as I said, it is not based on current theory or understanding, which I am after on this thread. You? Quote Link to comment Share on other sites More sharing options...
Moontanman Posted June 21, 2008 Report Share Posted June 21, 2008 Oh, that's ok then:) It is just that Buffy is an administrator:rolleyes:. Thanks for your comments, I share your enthusiasm (obviously), it is a phenomena that defies explanation using current theory. How often does that happen? My take? Well my take would mostly consist of uneducated speculation, hence my misguided post here. Being uneducated I naturally do have my own little hypothesis that might (in my mind) explain a lot of things.:phones: I have an idea that forces might be distinct fractal disturbances of an Einsteinian aether, the magnetic field (consisting of its own brand of fractals) being tuned to destructively interfere with the intermolecular forces of the BEC, but as I said, it is not based on current theory or understanding, which I am after on this thread. You? Well, I'm not exactly a PHD either but I am impressed by it's connection or similarity to larger more real world type systems. How close does it simulate a real Nova? Real world applications would be very interesting but I can't think of any right now. It is fascinating to be sure, I hope more information is forthcoming. Quote Link to comment Share on other sites More sharing options...
KALSTER Posted June 21, 2008 Author Report Share Posted June 21, 2008 Unfortunately, while it does resemble a supernova, it does not yield much energy. Learning the details behind the curtain of uncertainty might yield some surprising discoveries about the nature of matter though:ideamaybenot: Quote Link to comment Share on other sites More sharing options...
Moontanman Posted June 21, 2008 Report Share Posted June 21, 2008 Unfortunately, while it does resemble a supernova, it does not yield much energy. Learning the details behind the curtain of uncertainty might yield some surprising discoveries about the nature of matter though:ideamaybenot: I wonder what would have happened if the BEC had been made of helium3 or deuterium or a mixture of both(assuming it could have been made of them) What might have happened then? Quote Link to comment Share on other sites More sharing options...
KALSTER Posted June 21, 2008 Author Report Share Posted June 21, 2008 I am not sure, but it can't be sustainable IMO. The BEC is cooled to 3 billionths of a degree Kelvin, so any heat gained would destroy the conditions necessary for the Bosenova to occur in the first place. Since I have received no answers to my questions in the OP, I am guessing that the induced switch to an exclusively attractive intermolecular force would not be possible in non-BEC conditions, as the exact required modulation for each molecule would have to be administered individually. This is not a problem for the BEC, as the whole condensate can be thought of as one giant molecule, having collapsed into the same wave function. Quote Link to comment Share on other sites More sharing options...
Moontanman Posted June 22, 2008 Report Share Posted June 22, 2008 I am not sure, but it can't be sustainable IMO. The BEC is cooled to 3 billionths of a degree Kelvin, so any heat gained would destroy the conditions necessary for the Bosenova to occur in the first place. Since I have received no answers to my questions in the OP, I am guessing that the induced switch to an exclusively attractive intermolecular force would not be possible in non-BEC conditions, as the exact required modulation for each molecule would have to be administered individually. This is not a problem for the BEC, as the whole condensate can be thought of as one giant molecule, having collapsed into the same wave function. I know it takes special atoms to make a BEC I was just wondering if either helium3 or deuterium were one of them. If they were and you crowded them together close enough no matter what the temp you should get a reaction that releases large amounts of energy. They did say the core of the BEC was contracted to vanishing. I don't really know enough to really be making any assumptions about this, it was just a stray thought passing through what little gray matter I have floating around in my head:doh: Quote Link to comment Share on other sites More sharing options...
modest Posted June 22, 2008 Report Share Posted June 22, 2008 They change the properties of the magnetic field trapping the BEC, but how does that affect the forces present in between the constituent atoms? Do they simply tune the field so that it cancels out repulsive forces by destructively interfering with them? Can this only be done with BEC’s because of the uniformity of the wavefunction the atoms collapsed to? Does it mean that the virtual force-carrier particles of each field (van der Waal?) interfere with each other and cancels out? What happens to the energy then, or does it simply revert to the ground zero point energy? It is called Feshbach resonance. When comparing the magnetic field to the scattering length of two atoms (near the Feshbach resonance): the scattering length (a) can be negative or positive. The original Bose-Einstein condensates were done with rubidium-87 which naturally has a positive atom-atom scattering length. This makes for a stable condensate as is described below. Newer experiments including the Bosenova is done with rubidium-85 which has a negative atom-atom scattering length. By controlling the magnetic field containing the BEC, the condensate can be tuned near the Feshbach resonance, and to either side. This is called BEC-BCS crossover and it is described some here: Feshbach Resonances and the BEC-BCS crossover From BEC to BCSThe interaction between two atoms can be described by the scattering length, shown on the right versus magnetic field close to a Feshbach resonance. On the side where the scattering length is positive, the molecular energy level is lower in energy than the energy of two unbound atoms. The molecular state is thus "real" and stable, and atoms tend to form molecules. If those atoms are fermions, the resulting molecule is a boson. A gas of these molecules can thus undergo Bose-Einstein condensation (BEC). This side of the resonance is therefore called "BEC-side". On the side of the resonance where the scattering length is negative, isolated molecules are unstable. Nevertheless, when surrounded by the medium of others, two fermions can still form a loosely bound pair, whose size can become comparable to or even larger than the average distance between particles. A Bose-Einstein condensate of these fragile pairs is called a "BCS-state", after Bardeen, Cooper and Schrieffer. This is what occurs in superconductors, in which current flows without resistance thanks to a condensate of electron pairs ("Cooper pairs"). Relevant to the Bosenova: If the scattering length is positive (see pic above) then it will make up diatomic molecules with a self-repulsive effect. Conversely, if the scattering length is negative there is an attractive interaction. The theory behind this is complicated. If you’re looking for particulars you can look here: http://www.tcm.phy.cam.ac.uk/~fmm25/Marchetti_LECTURE4.pdf What do they mean when they say that “this procedure caused the BEC to implode and shrink beyond detection”? The method used to image a condensate has only a finite resolution. I assume it imploded to a size which was under the detectable resolution of the equipment. This does not mean it really 'disappeared', nor did the missing rubidium 'disappear' in the sense that it surely is still in the universe following the first law of thermodynamics. The missing condensate probably escaped the magnetic trap - which I gather is odd considering the energy needed to accomplish that. I'd like to thank you Kalster for posting this topic which is very interesting. I am very uneducated when it comes to all things quantum and I enjoy topics such as these that peak my curiosity on that topic. From everything I just read, there is no satisfactory theory or explanation for why this 'explosion' happens. There are many proposals as one can see here, but nothing too solid. Hopefully solving this mystery will provide insights into other things quantum mechanical. ~modest Quote Link to comment Share on other sites More sharing options...
Moontanman Posted June 22, 2008 Report Share Posted June 22, 2008 It is called Feshbach resonance. When comparing the magnetic field to the scattering length of two atoms (near the Feshbach resonance): the scattering length (a) can be negative or positive. The original Bose-Einstein condensates were done with rubidium-87 which naturally has a positive atom-atom scattering length. This makes for a stable condensate as is described below. Newer experiments including the Bosenova is done with rubidium-85 which has a negative atom-atom scattering length. By controlling the magnetic field containing the BEC, the condensate can be tuned near the Feshbach resonance, and to either side. This is called BEC-BCS crossover and it is described some here: Feshbach Resonances and the BEC-BCS crossover Relevant to the Bosenova: If the scattering length is positive (see pic above) then it will make up diatomic molecules with a self-repulsive effect. Conversely, if the scattering length is negative there is an attractive interaction. The theory behind this is complicated. If you’re looking for particulars you can look here: http://www.tcm.phy.cam.ac.uk/~fmm25/Marchetti_LECTURE4.pdf The method used to image a condensate has only a finite resolution. I assume it imploded to a size which was under the detectable resolution of the equipment. This does not mean it really 'disappeared', nor did the missing rubidium 'disappear' in the sense that it surely is still in the universe following the first law of thermodynamics. The missing condensate probably escaped the magnetic trap - which I gather is odd considering the energy needed to accomplish that. I'd like to thank you Kalster for posting this topic which is very interesting. I am very uneducated when it comes to all things quantum and I enjoy topics such as these that peak my curiosity on that topic. From everything I just read, there is no satisfactory theory or explanation for why this 'explosion' happens. There are many proposals as one can see here, but nothing too solid. Hopefully solving this mystery will provide insights into other things quantum mechanical. ~modest I think it's agreat thread too, too bad Buffy thought it was about a dance:alien_dance: ;) :hihi: Quote Link to comment Share on other sites More sharing options...
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