Wheeler's It from Bit Proposal in Loop Quantum Gravity
  As an attempt to realize Wheeler's "it-from-bit proposal" that physics should
be reduced to simple yes-no questions we consider a model of loop quantum
gravity, where the only allowed values of the quantum numbers $j_p$ at the
punctures of the spin network on the spacelike two-surfaces of spacetime are
$0$ and $\frac{1}{2}$. When $j_p=0$, the puncture is in the vacuum, and it does
not contribute to the area of the two-surface, whereas when $j_p=\frac{1}{2}$,
the puncture is in an excited state, and the allowed values of the associated
quantum number $m_p$ are $-\frac{1}{2}$ and $+\frac{1}{2}$. As a consequence,
the spin network used as a model of spacetime is analogous to a system of
particles with spin $\frac{1}{2}$, and every puncture carries exactly one bit
of information. When applied to spacetimes with horizon our model enables us to
find an explicit expression for the partition function of spacetime. Using this
partition function we may, among other things, obtain the Bekenstein-Hawking
entropy law for black holes. When applied to cosmological models with horizon
the partition function predicts a cosmic phase transition in the early
Universe, where the cosmological constant went through a dramatic decrease and
the matter of the Universe was created out of the vacuum.
