The fifth state of matter shows up only below temperatures colder than interstellar space. For a rubidium-87 gas the threshold Tc sits near 170 nano-kelvin, and below it a broad cloud piles into one sharp peak, the condensate fraction following N₀/N = 1 − (T/Tc)³. The reason lies in the de Broglie wavelength: the colder it gets the more that wavelength swells, until it exceeds the spacing between atoms, the matter waves overlap and the atoms can no longer be told apart. Fermions cannot do this, forbidden by the Pauli principle.
The fifth state of matter shows up only below temperatures colder than interstellar space. For a rubidium-87 gas the threshold Tc sits near 170 nano-kelvin, and below it a broad cloud piles into one sharp peak, the condensate fraction following N₀/N = 1 − (T/Tc)³. The reason lies in the de Broglie wavelength: the colder it gets the more that wavelength swells, until it exceeds the spacing between atoms, the matter waves overlap and the atoms can no longer be told apart. Fermions cannot do this, forbidden by the Pauli principle.
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