A BEC question


by misogynisticfeminist
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misogynisticfeminist
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#1
Oct27-04, 05:37 AM
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From what I know, the cooling of He-4 atoms causes them to fall into the ground state, making them Bosons. But there's something which confuses me, from what I read, these atoms actually coalesce into one "super-atom". And in quantum theory, it is entirely possible for many atoms to be in one spot at the same time (right?). But why is it that BECs are not the size of atoms?

Or is my understanding of BECs flawed around here?
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James R
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Oct27-04, 08:59 AM
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But why is it that BECs are not the size of atoms?
What makes you think BECs are not the size of atoms?
misogynisticfeminist
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#3
Oct27-04, 09:09 AM
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lol, is that so? then won't it be like too miniscule to be handled or something?

da_willem
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Oct27-04, 09:17 AM
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A BEC question


Quote Quote by James R
What makes you think BECs are not the size of atoms?
Experiments have shown that they are not. Actually the molar volume of liquid He4 at absolute zero is 3.1 times larger than can be calculated from interatomic forces for a static lattice.

About the original question. I looked it up in my thermal physics book where it says "We can say that the quantum zero-point moyion is responsible for the expansion of the molar volume". But if some-one knows the details?!
ZapperZ
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Oct27-04, 09:38 AM
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Quote Quote by misogynisticfeminist
From what I know, the cooling of He-4 atoms causes them to fall into the ground state, making them Bosons. But there's something which confuses me, from what I read, these atoms actually coalesce into one "super-atom". And in quantum theory, it is entirely possible for many atoms to be in one spot at the same time (right?). But why is it that BECs are not the size of atoms?

Or is my understanding of BECs flawed around here?
Y'know, next time you read things like this, please make sure you WRITE down the exact source so that the rest of us can double check to make sure you actually read it correctly?

The misconception here comes from the "super-atom" phrase and the meaning of a boson statistics. When a collection of particles undergoes a BE condensation, it does NOT mean that they become one giant atom. It does however mean that ALL of the particles are now coherent with each other and can be described by a single wavefunction. The coherence caused them to be "entangled" to each other and thus, physically and mathematically not separable. Thus, they are often thought of as one single entity, NOT a single atom!

And no, they all don't have to cramp into the same location in space. This is another misconception. What they can do is be in the SAME quantum state.

Zz.


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