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  1. Joined
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    19 Jan '19 04:10
    How slow can an electron go?

    I am particularly interested in why a Bose Einstein Condensate behaves in the way it does. I read that a BEC was predicted before observed by Satyendra Nath Bose. Is that prediction based on a slower electron? I was having a hard time finding out so I figured somebody on here might already know and save me time searching for the answer.
  2. Germany
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    19 Jan '19 10:46
    There is no strict limit on "how slow an electron can go" as long as the uncertainty principle is satisfied.

    A BEC consists of bosons, and electrons are fermions, so electrons cannot Bose-condense except as a part of some composite boson. Bose-Einstein condensation can be explained purely on quantum statistical grounds, it doesn't rely on specific properties of the constituent bosons.
  3. Subscribersonhouse
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    21 Jan '19 04:03
    @kazetnagorra said
    There is no strict limit on "how slow an electron can go" as long as the uncertainty principle is satisfied.

    A BEC consists of bosons, and electrons are fermions, so electrons cannot Bose-condense except as a part of some composite boson. Bose-Einstein condensation can be explained purely on quantum statistical grounds, it doesn't rely on specific properties of the constituent bosons.
    Aren't the Bose condensates in one quantum state, a kind of single atom, quantumly speaking?
  4. Joined
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    21 Jan '19 05:27
    @kazetnagorra said
    There is no strict limit on "how slow an electron can go" as long as the uncertainty principle is satisfied.

    A BEC consists of bosons, and electrons are fermions, so electrons cannot Bose-condense except as a part of some composite boson. Bose-Einstein condensation can be explained purely on quantum statistical grounds, it doesn't rely on specific properties of the constituent bosons.
    What is your source of info? You cannot lower temps to absolute zero so there has to be a limit to electron speed.

    If the electrons of a BEC are not tugging on each other how does a BEC flow upwards seeming to defy gravity? A slower electron would explain this. How can a Boson explain that?
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    21 Jan '19 05:29
    @sonhouse said
    Aren't the Bose condensates in one quantum state, a kind of single atom, quantumly speaking?
    That seems to be a popular theory, but just a theory.
  6. Germany
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    21 Jan '19 16:51
    @metal-brain said
    What is your source of info? You cannot lower temps to absolute zero so there has to be a limit to electron speed.

    If the electrons of a BEC are not tugging on each other how does a BEC flow upwards seeming to defy gravity? A slower electron would explain this. How can a Boson explain that?
    You cannot reach absolute zero, but you can get arbitrarily close to it in principle. In practice, experiments using ultra-cold atoms achieving BEC can reach temperatures below 1 µK. As a source of information, you can consider reading Pethick & Smith's standard text on BECs in dilute atomic vapours.

    Electrons in a BEC (if part of some composite boson) can interact, but that interaction isn't important for the principle of Bose-Einstein condensation, which just relies on the constituent particles being bosons. To understand how it works you need some understanding of basic quantum mechanics. In loose laymen's language: bosons like to be in the same state, and at low temperatures you can get a lot of them in the lowest momentum state.
  7. Subscribersonhouse
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    21 Jan '19 18:19
    @kazetnagorra said
    You cannot reach absolute zero, but you can get arbitrarily close to it in principle. In practice, experiments using ultra-cold atoms achieving BEC can reach temperatures below 1 µK. As a source of information, you can consider reading Pethick & Smith's standard text on BECs in dilute atomic vapours.

    Electrons in a BEC (if part of some composite boson) can interact, b ...[text shortened]... e in the same state, and at low temperatures you can get a lot of them in the lowest momentum state.
    So electrons are a kind of contamination of the Bose, then? Do they interfere with any of the properties of the Bose?
  8. Joined
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    21 Jan '19 21:35
    @kazetnagorra said
    You cannot reach absolute zero, but you can get arbitrarily close to it in principle. In practice, experiments using ultra-cold atoms achieving BEC can reach temperatures below 1 µK. As a source of information, you can consider reading Pethick & Smith's standard text on BECs in dilute atomic vapours.

    Electrons in a BEC (if part of some composite boson) can interact, b ...[text shortened]... e in the same state, and at low temperatures you can get a lot of them in the lowest momentum state.
    That still doesn't explain why a BEC seems to defy gravity and runneth over cup.
  9. Germany
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    22 Jan '19 07:40
    @metal-brain said
    That still doesn't explain why a BEC seems to defy gravity and runneth over cup.
    Massive particles in a BEC are affected by gravity in the same way as ordinary massive particles. I guess "runneth over cup" refers to superfluids in a container, which can run over the cup due to surface tension and the absence of viscosity. It's essentially the same effect that causes water in a cup to curl up at the edges (defying gravity, in your words), on steroids.
  10. Germany
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    22 Jan '19 07:44
    @sonhouse said
    So electrons are a kind of contamination of the Bose, then? Do they interfere with any of the properties of the Bose?
    They are not a contamination. In a BEC of ultra-cold atoms, it is the atoms as a whole that Bose-condense, which includes the nucleus and electrons. The internal structure of the atoms is not important for the principle of Bose-Einstein condensation, as long as the atoms in question are composite bosons.
  11. Joined
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    22 Jan '19 14:38
    @kazetnagorra said
    Massive particles in a BEC are affected by gravity in the same way as ordinary massive particles. I guess "runneth over cup" refers to superfluids in a container, which can run over the cup due to surface tension and the absence of viscosity. It's essentially the same effect that causes water in a cup to curl up at the edges (defying gravity, in your words), on steroids.
    " It's essentially the same effect that causes water in a cup to curl up at the edges"

    Surface tension is caused by the cohesion of water. Isn't it adhesion that causes water in a cup to curl up at the edges? Water has both cohesive and adhesive properties. I thought the two went hand in hand, but perhaps I was mistaken.

    Does a BEC superfluid retain adhesive properties while losing cohesive properties? Why is the BEC clinging to the rim of the cup as it runs over?
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