Conceptual Issues

1As part of a ‘duty of inquirywe might reasonably raise some questions and issues that are speculative in the sense that no definitive answer may yet exist. However, while many people turn to cosmology because they are looking for answers to the ‘big’ questions about the universe, they often find that many standard textbooks tend to shy away from such issues. Therefore, this section will simply highlight a number of initial issues related to the gravitational mass and the energy of universe, primarily in an attempt to widen the perspective of a number of potential cosmological models.

  • The Gravitational Mass of the Universe
    There is an assumption, as per the cosmological principle, that space on the scale of the universe is both homogeneous and isotropic. On this basis, could the theorem of Newton's Shells be used as a mass-gravity model for the universe?

  • The Energy of the Universe
    While we will not actually address the wider issues linked to Friedmann's equation until a later section, we might still consider the issue of the conservation of energy, based on kinetic and potential energy. Basically, if we assume that energy cannot be created or destroyed, where did the energy that drives the universe come from and can we account for all of it? Within the scope of this discussion, there is some initial consideration of the following facets of energy:

For example, if the universe started some finite time ago as a point singularity, it is not so unreasonable to ask whether it had, and still has, a finite size. For it would seem that no matter how great the subsequent expansion of the universe might have been, it must still have some sort of boundary. We might also wish to inquire into the nature of expanding space, as opposed to some form of explosion, in which every cubic metre of the universe is said to be expanding. Although the scope of cosmology appears to describe a number of expansion and contraction models, we might question what ‘force-energy’ is driving the expansion, especially given the current speculation that the expansion of the universe is now accelerating.