Can quantum gravitational effects influence the entire history of the Universe?

In this work, a flat Friedmann-Robertson-Walker universe with dust and a cosmological constant is quantized. By means of a canonical transformation, the classical Hamiltonian is reduced to that of either a harmonic oscillator or anti-oscillator, depending on whether $\Lambda <0$ or $\Lambda >0$, respectively. In this way, exact solutions to the Wheeler-DeWitt equation can easily be obtained. It turns out that a positive cosmological constant alone may account for an early inflationary regime and a later accelerated expansion phase, with a period of decelerated expansion in between. This suggests that quantum-gravitational effects can influence most of the history or even the entire history of the Universe.