I calculate that both in the matter-dominated Einstein-deSitter universe, and in the present universe in which the cosmological constant dominates the expansion rate, the observable universe expands at exactly the "escape velocity" of its total mass energy. At present, this expansion is about 985 million radial meters/second, generating about 2.34e+63 cubic meters/second of new vacuum. As the domination of the expansion rate by the cosmological constant continues, the future universe will expand geometrically, approaching the rate of a simple deSitter universe. I think it is also correct that the future ACCELERATION of expansion will be driven by the addition of "new" vacuum space in the future, not by the vacuum space that is already here. If (hypothetically and contra-factually) one posited that future vacuum space will not bring a cosmological constant with it, but the existing vacuum retains its cosmological constant, then the future expansion rate would be at a (declining) Einstein deSitter rate. Which brings me to my first question: What is the motivating source of expansion in an Einstein-deSitter universe? I would appreciate if you would direct me to whatever you see as the most compelling explanation. I have read that an Einstein deSitter universe is analogous to a "cannonball" shot off in a single impulse. That impulse may be "inflaton energy" left over from Inflation. I've also seen it described vaguely as "kinematics". Frankly, I don't see where this massive energy artifact could be hiding in the universe, and continuing to create new vacuum space for us in perpetuity (assuming the universe is flat). I understand the "negative pressure" theory for dark energy, but I haven't seen that described as the source of the original Einstein-deSitter expansion. I note that if the mass/energy of the universe were considered at the level of tiny units (such as atoms), the "escape velocities" of those individual units would result in a total volumetric expansion rate for the universe which exactly equals the observed expansion rate. This raises a second question: is there anything in General Relativity that treats the gravity of mass/energy as ITSELF a motivating source of spatial expansion? For example, if gravitation imposes a stress-energy tensor on the surrounding space, causing geometric curvature, could the same mechanism also cause spatial expansion? I understand that in the Einstein-deSitter model, gravity is treated as a restraint on expansion rather than as a cause of it. But if GR explains gravitation as a cause of expansion, then some important pieces would fit neatly in place. For example, by definition it would cause the universe to perpetually maintain itself exactly at "critical mass", maintaining perfect geometric flatness. If gravitational expansion isn't consistent with GR, might it perhaps be consistent with recent speculation on quantum gravity?