  Applying the seminal work of Bose in 1924 on what was later known as
Bose-Einstein statistics, Einstein predicted in 1925 that at sufficiently low
temperatures, a macroscopic fraction of constituents of a gas of bosons will
drop down to the lowest available energy state, forming a `giant molecule' or a
Bose-Einstein condensate (BEC), described by a `macroscopic wavefunction'. In
this article we show that when the BEC of ultralight bosons extends over
cosmological length scales, it can potentially explain the origins of both dark
matter and dark energy. We speculate on the nature of these bosons.
