I did a google search for "boson" and got this Wikipedia entry. Here's the first part of the entry
In particle physics, bosons are subatomic particles that obey Bose–Einstein statistics. Several bosons can occupy the same quantum state. The word boson derives from the name of Satyendra Nath Bose.
Bosons contrast with fermions, which obey Fermi–Dirac statistics. Two or more fermions cannot occupy the same quantum state.
Since bosons with the same energy can occupy the same place in space, bosons are often force carrier particles
How does that relate to the previous post? I don't know. Maybe some of the particles are acting like bosons and are trying to occupy the same quantum state- Bose -Einstein condensate. If so, it is not at absolute zero temperature, which would appear strange. But one thing about quantum mechanics, it is one strange phenomenon.
I've been reading a bit about bosons and fermions. Here's what I was looking for:
Weakly interacting fermions can also display bosonic behavior under extreme conditions, such as in superconductivity.
This could explain why rubidium is used for Bose Einstein condensates. It can act as a boson, presumably.
In 1995, rubidium-87 was used to produce a Bose-Einstein condensate, for which the discoverers won the 2001 Nobel Prize in Physics.
Why does rubidium act like a boson? I can't find anything that answers that question. Perhaps it is this hyperfine structure. At any rate, rubidium has unusual properties which make it useful.