  Inflation and quintessence can both be described by a single scalar field.
The cosmic time evolution of this cosmon field realizes a crossover from the
region of an ultraviolet fixed point in the infinite past to an infrared fixed
point in the infinite future. This amounts to a transition from early inflation
to late dynamical dark energy, with intermediate radiation and matter
domination. The scaling solution of the renormalization flow in quantum gravity
connects the two fixed points. It provides for the essential characteristics of
the scalar potential needed for the crossover cosmology and solves the
cosmological constant problem dynamically. The quantum scale symmetry at the
infrared fixed point protects the tiny mass of the cosmon and suppresses the
cosmon coupling to atoms without the need of a non-linear screening mechanism,
thereby explaining apparent issues of fine tuning. For a given content of
particles the scaling solution of quantum gravity is a predictive framework for
the properties of inflation and dynamical dark energy.
