Concordance Model

Possibly the two most salient questions regarding the concordance model is who believes it and why. First, in response to the `who`, it is probably true to say that the majority of cosmologists working in this field would probably support the basic tenets of this model, but not necessarily all its conclusions. Second, considering the `why`, it is assumed that the supporters of the model would simply say that there is sufficient evidence to convinced them that this model is on the right track.

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While noting the implication of general support for the concordance model, let us also summarise 3 key aspects of the current model, which although compatible with some observations, invoke new ideas that extend beyond the baseline of standard particle physics:

  1. Inflation is a hypothesis that might explain why the Universe has evolved as we now see it. However, it requires a concept of ultra-high energy physics that is not verified or even necessarily understood.

  2. The evolution of the large-scale structures of the universe seems to require the existence of a new type of matter, which does not interact with normal matter. Again, the existence of this matter has not been verified, only inferred from various galactic anomalies. However, it does have a name, i.e. Cold Dark Matter (CDM).

  3. Observations now suggest that the universe is not only expanding, but this expansion is now accelerating, which suggests some causative agent. So far, the nature of this agent is unverified, not understood and referenced via several different names. To some it is the cosmological constant; while others refer to it as dark energy or possibly vacuum energy or even zero point energy.

So while the weight of authority undoubtedly supports the current model, the previous summary does appear to highlight a level of speculation underpinning this model, which has led some to question, not only its interpretations, but the scientific principles underpinning its development:

"Astronomy can never be a hard-core physics discipline, because the Universe offers no control experiment, i.e. with no independent checks it is bound to be highly ambiguous and degenerate. For example, while superluminal motion can be explained by Special Relativity, data on the former can never on their own be used to establish the latter. This is why traditionally astrophysicists have been content with (and proud of) their ability to use known physical laws and processes established in the laboratory to explain celestial phenomena. Cosmology is not even astrophysics: all the principal assumptions in this field are unverified (or unverifiable) in the laboratory, and researchers are quite comfortable with inventing unknowns to explain the unknown. How then could, after fifty years of failed attempt in finding dark matter, the fields of dark matter and now dark energy have become such lofty priorities in astronomy funding, to the detriment of all other branches of astronomy? "

This statement was not written by a marginalized amateur trying to push his own unsubstantiated theory, but rather a respected professor of physics at the University of Alabama, Dr. Richard Lieu. The full article can be read by following the title link: ΛCDM cosmology, from which the next extract is also taken:

"Cosmologists should not pretend to be mainstream physicists, because there is only one irreproducible Universe and control experiments are impossible. The claim to overwhelming evidence in support of dark energy and dark matter is an act of exaggeration, which involves heavy selection of evidence and an inconsiderate attitude towards alternative models with fewer (or no) dark components. When all evidence are taken into account, it is by no means clear that ΛCDM wins by such leaps and bounds."

Please accept that the goal of this discussion is not to try and discredit the concordance model, but neither is it a goal to simply accept statements, as fact, without carrying out some level of inquiry. So, initially, it will be assumed that the experts qualified to discuss the ΛCDM model fall into 1 of 2 camps, i.e. for or against. While possibly too much of a generalisation, we might initially assume that the ‘for’ camp will naturally focus on all the upside observational evidence that support their position, while the ‘against’ want to cite all the anomalies, no matter how obscure. So, while this overview may lack any authority, it will try to look at both sides of the argument, simply because the ΛCDM model is just what its name suggests, i.e. a model, and not, as yet, a statement of verified fact. So on this basis we will continue with what might appear to be a number of questioning statements, but which may encapsulate some of the central issues of the current model:

  • The ΛCDM model requires some form of prerequisite and additional inflationary model as, in isolation; the ΛCDM model cannot explain the expansion of the observed universe from a cosmic singularity of zero dimensions and infinite density.

  • The ΛCDM model is predicated on normal matter only constituting 4% of the universe with the remaining 96% described in terms of 23% cold dark matter and 73% dark energy; the exact nature of both are essentially unknown and unverified.

  • However, the ΛCDM model aligns to the idea of a basic `big bang` model, which is said to explain the cosmic microwave background observations, as well as the large-scale structural and supernovae observations of an accelerating expanding universe. As such, it is the simplest known model that is in general agreement with observed phenomena.

The next 2 sub-sections of this introduction are intended to provide an initial insight of the key concepts that will be expanded on throughout the overall discussion of the ΛCDM concordance model: