Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: chris on 19/03/2010 21:36:07
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If a single atom of a substance were cooled to absolute zero (assuming this were possible), would the electrons become stationary?
Chris
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I dunno about 'stationary'. I think something more like a pseudo-solid 'frozen' shell wave-function, where every point on the surface would be at all probabilities, would make more sense to me (whilst baring in mind that it's impossible).
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If a single atom of a substance were cooled to absolute zero (assuming this were possible), would the electrons become stationary?
Chris
No.
If they "froze out" they would have a known position, energy, time and momentum. That's forbidden by the uncertainty principle. This is the origin of the zero point energy..
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So what's happening when a substance becomes a Bose-Einstein condensate?
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In Bose-Einstein condensates, you put all your particles into the lowest possible energy state. As Bored Chemist stated, this lowest possible energy state is not the same as a zero energy state.
By the way, this is a process that can only happen for a special class of particles called Bosons, since most of the particles that make up everyday matter, Fermions, can't all stack together in the same energy state.
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That's interesting; I thought I read of researchers putting clusters of e.g. caesium atoms, into B-E states by intense cooling?
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Ah--I was thinking of elementary particles and constituents of atoms. Of the elementary particles, only the force-carriers (photons, W/Z bosons and gluons) are bosons. And if you get slightly more complex, protons, neutrons and electrons are all fermions. However, you can add up these basic components to make more complicated particles, you can make things that behave like Bosons. Helium-4 is the most commonly used example. (In quantum-speak, Bosons have integer spin and Fermions have half-integer spin.)
I think that Bosonic fundamental particles should behave like Bosons no matter how small you got (down to the Planck scale, I guess). Bosonic atoms would behave like Bosons unless you tried to look at scales smaller than the atoms, in which case you'd start seeing their constituent particles.
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Yeah, it's weird Chris, and another proof of that matter-wave duality. So even if we can say that matter (fermions) have a matter-wave property there are differences between that, and how it behave as compared to waves (bosons). And it's not as simple as Helium-4 suddenly becomes true bosons as we f.ex expect photons to be.
“When liquid helium is cooled below 2.2 K, a Bose condensate begins to form in the liquid. At these low temperatures, liquid helium behaves as a superfluid having, among other strange properties, zero viscosity. In a superfluid helium, the helium atoms have a volume, and essentially "touch" each other, yet at the same time exhibit strange bulk properties, consistent with a Bose-Einstein condensation.
The latter reveals that they also have a wave-like nature and do not exhibit standard fluid properties, such as friction. For nuclei made of hadrons which are fermions, the same type of condensation does not occur, yet nevertheless, many nuclear properties can only be explained similarly by a combination of properties of particles with volume, in addition to the frictionless motion characteristic of the wave-like behavior of objects trapped in Schroedinger quantum orbitals"
So here those super cooled 'bosons' have a volume right? and therefore they shouldn't be able to be 'super imposed' should they? But if we then look at a ordinary Helium 4 atom.
"“The helium-4 atom… In an actual helium atom, the protons are superimposed in space and most likely found at the very center of the nucleus, and the same is true of the two neutrons. Thus all four particles are most likely found in exactly the same space. Classical images of separate particles thus fail to model known charge distributions in very small nuclei."
So, at room temperature both protons and neutrons are superimposed? And to that that we can add your electrons that we won't be able to pinpoint, and who also can be super positioned, being at two places simultaneously, as well as 'mass less' apparently, under certain circumstances?
It's not a very exact definition, is it? Or, if you like, our definitions are becoming more and more 'exact', but under different circumstances? It depends on how you define this 'exactness' it seems, and what expectations you have of being able to describe it in words.
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Bosons has a integral spin and all can occupy the same state (super imposed) and examples are photons, 4He atoms, gluons. Fermions has a half-integral spin and can only occupy ‘one per state’ (one ‘peg’, one ‘hole’) and examples are electrons, protons, neutrons, quarks, neutrinos
“ The spin-statistics theorem shows that all bosons obey Bose–Einstein statistics, whereas all fermions obey Fermi-Dirac statistics or, equivalently, the Pauli exclusion principle, which states that at most one particle can occupy any given state. Thus, if the photon were a fermion, only one photon could move in a particular direction at a time. This is inconsistent with the experimental observation that lasers can produce coherent light of arbitrary intensity, that is, with many photons moving in the same direction. Hence, the photon must be a boson and obey Bose–Einstein statistics.”