Can Quantum Gravitational Effects Influence the Entire History of the Universe?

In this work, a flat Friedmann-Robertson-Walker (FRW) 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.