In the context of speculative science, it seems reasonable to use cosmology as a framework of ideas that can overlap many fields of science. However, in the main review of cosmology, some attempt was made to constrain the discussion within the scope of what might be called the accepted Big Bang theory. However, based on the previous discussion ‘The Scope of Speculation’ the foundations of this theory may still be quite speculative, if judged by the traditional concept of verified science.
Equally, it might be argued that some aspects of the Big Bang model might now be struggling to keep up with the acquisition of observational data and the apparently never-ending influx of new ideas from the field of theoretical physics.
So what is the status of the Big Bang model?
In its original form, the Big Bang model was thought to have expanded from a singularity of infinite density and zero volume. As such, this singularity was perceived to represent ‘everything’ such that there could be no concept of ‘anything’ existing outside the singularity. Therefore, by definition, the subsequent expansion of this singularity had to contain the essence of ‘everything’ that has or could ever exist in space and time, i.e. the cosmic singularity was the universe in its entirety. However, despite the magnitude of its scope, this original model appears to have been predicated on a quite simple assumption, i.e. the universe could not be a static system, if it conformed to the ideas of general relativity. In essence, the original Big Bang was a gravitational model, which was essentially anchored in the observation of the present-day universe and then reversed in time, analogous to a gravitational collapse back towards some point of infinite density, i.e. the moment of creation.
Note: While this reversal under gravity appears quite a logical description, it is not so clear how this original model could have worked in the forward direction of time to explain the expansion of the universe.
So what changed?
Well, based on the gravitational force of gravity alone, there appears to be no rational mechanism that explains the expansion of the universe, such that it would end up in the homogeneous and isotropic state observed today. Equally, despite its name, the Big Bang expansion of the universe could not be described as an explosion from a single point in space and time, but rather it appeared to represent the uniform expansion of space as a function of time, although the actual process by which space expanded remains a debatable concept to this day. However, putting this issue to one side, a more sophisticated energy-density model began to emerge in the early part of the 20th century, which rested on the formulation of the ‘Friedmann equations’. These equations utilized the physics of Newtonian mechanics, general relativity and thermodynamics to try to explain the expansion of the universe in terms of its energy-density and pressure. However, it had one critical problem, i.e. it did not really fit with the increasingly sophisticated data being amassed by astronomical observations related to the Cosmic Microwave Background (CMB).
So has the Big Bang model been rejected?
From the perspective of today’s world, we might drawn an analogy with the current global financial crisis in which a major bank might be described as an institution that has become ‘too big to fail’. So while the name of the institution may be retained for the reassurance of the general public, its underlying processes are forced to undergo radical reform to better meet the challenges of a brave new world. We might generalize a similar change to the original Big Bang model in terms of two sub-models:
These models are sometimes collectively known as the ‘Concordance Model’, which has already been reviewed. However, for the purpose of this discussion, we shall continue to consider them as providing a two-staged process. The first stage starts with the inflationary model anchored in the idea of some sort of quantum scalar field; while the second stage transitions from the extremely short-lived inflationary period into an energy-density (ΛCDM) model, which is now predicated on two further speculative ideas:
Again, the links above can be used to reference earlier discussions, but the key point to note is that the ideas associated with quantum scalar fields, dark matter and dark energy all remain highly speculative ideas, which essentially exist outside any verified model of particle physics. However, in practice, there are a myriad of different and often opposing hypotheses that this section of discussions cannot even really begin to address. Therefore, the goal of the following discussions will simply try to focus on just a few ideas that appear representative of the challenges to the general model, which have often been forwarded by theoretical physicists, who are well respected in their field of expertise. However, the next discussion will begin by presenting a possibly more sobering assessment of human achievement in space exploration, which might be considered as a yardstick against which verified science could/should be assessed.