Cosmology: Current Thoughts And Future Possibilities Of The Standard Model
In a thought provoking article published in the Royal Astronomical Society journal, Astronomy and Geophysics (Vol 55, Issue 3), Prof Ofer Lahav (UCL) and Dr Michela Massimi (Edinburgh U) pose the intriguing question: when does a negative piece of research data warrant a paradigm shift in currently accepted understanding?
In this particular case the question was posed in a cosmological context and points to anomalous data received from type 1a supernovae, which show that the Universe is expanding at an accelerating rate.
The current ‘ΛCDM’ model (Lamda + Cold Dark Matter) is derived from Einstein’s general theory of relativity (GR), which is widely accepted as a robust description of the current Universe—however, Einstein’s initial hypothesis included the now infamous, ‘cosmological constant’ (CC), which was added to produce a static universe. This was later found to be incorrect, as the accelerating nature of the Universe was in direct conflict with the CC. To overcome this discovery, a modification of GR was necessary with the addition of ‘Dark Energy’ (Λ) and ‘Cold Dark Matter’.
This has proved to be a challenging obstacle for cosmologists to confirm because, as these two entities are ‘dark’ (i.e. invisible), they have been illusive to detect, and remain only speculative modifications to both the ΛCDM model and, by association, GR theory.
So, do they exist or not?
If they are both proved non-existent with current technology should we retain Einstein’s rather successful theory for certain applications, or is a complete paradigm shift necessary, or indeed, inevitable?
Lahav and Massimi state previous cases of the anomalous perihelion of Mercury, as an example of a paradigm shift (Newtonian Gravity (NG) to GR), and the anomalous perihelion of Uranus and subsequent discovery of Neptune, as an example of model retention (NG).
In the case of Mercury a hypothetical planet named, Vulcan, was invoked to explain the anomalies, however it was never discovered. This inevitably led to the derivation of a new improved theory of gravity (GR), and hence a paradigm shift. This is analogous to the dark Universe hypothesis in the sense that if it is not discovered an alternative cosmological theory, and a reworking of GR, will need to be discovered.
The ‘Dark Energy Survey’ is currently searching, along with other programmes, to discover the existence of the dark universe; so, until then it remains unclear how future cosmological models will appear. However, as Lahav points out, ‘we currently have the technological tools to search for the answer’.
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