Energy diagram for Lemaitre's Loitering Model

Newtonian energy diagram for Lemaitre's loitering model -- the total energy is closely matched to the peak of the gravitational energy curve. One might imagine launching a ball from the big bang with just enough energy to reach the hilltop and roll down the other side. The ball almost comes to a standstill at the hilltop, before rolling down the other side.

Notice how the true age is significantly longer than the Hubble time, which was Lemaitre's original motivation for considering this model.

 

Figure: Whittle's (upcoming) undergraduate textbook.