Assume the fabric of space-time is a volume with a boundary. (this seems to be a possibility). The same way that gravity can be modeled as curvature in space-time around an object, the derivative of which creates a force over other objects close by and pulls them closer, the assumption that space-time is a volume with a boundary means that the fabric of space-time might also have a curvature caused by the boundary. This curvature would be stronger the closer we get to the boundary, and it would have the same effect of gravity on the objects inside. It would cause a pulling force towards the boundary which we observe as the acceleration of expansion of the material universe. Could this effect explain the dark energy? Like in a cup of coffee, the foam formed on the surface tends to move and accelerates towards the boundary of the surface because of the force on it caused by the tension at the surface boundary.