[Paper Review] The big-bang theory: construction, evolution and status

Jean–Philippe Uzan|arXiv (Cornell University)|Jun 20, 2016

History and Developments in Astronomy4 citations

TL;DR

This paper traces the historical construction, evolution, and current status of the big-bang model, emphasizing its foundation in general relativity and its validation through diverse cosmological observations. It highlights the model’s predictive power for nucleosynthesis, cosmic microwave background, large-scale structure, and expansion history, while acknowledging unresolved issues like dark matter and dark energy.

ABSTRACT

Over the past century, rooted in the theory of general relativity, cosmology has developed a very successful physical model of the universe: the {\em big-bang model}. Its construction followed different stages to incorporate nuclear processes, the understanding of the matter present in the universe, a description of the early universe and of the large scale structure. This model has been confronted to a variety of observations that allow one to reconstruct its expansion history, its thermal history and the structuration of matter. Hence, what we refer to as the big-bang model today is radically different from what one may have had in mind a century ago. This construction changed our vision of the universe, both on observable scales and for the universe as a whole. It offers in particular physical models for the origins of the atomic nuclei, of matter and of the large scale structure. This text summarizes the main steps of the construction of the model, linking its main predictions to the observations that back them up. It also discusses its weaknesses, the open questions and problems, among which the need for a dark sector including dark matter and dark energy.

Motivation & Objective

• To trace the historical development of the big-bang model from its roots in general relativity to its current observational status.
• To clarify the distinction between physical cosmology (observational, theory-driven) and Cosmology (philosophical, holistic), especially regarding the universe’s origins and fine-tuning.
• To evaluate the robustness of the standard model by testing its underlying assumptions, such as the Copernican principle, distance duality, and field equations.
• To assess the role of dark matter and dark energy as components of the 'dark sector' despite no direct detection, and to examine the theoretical challenges they pose.
• To emphasize the importance of testing model hypotheses beyond parameter precision, including relativistic effects and non-linear structure formation.

Proposed method

• Uses historical and theoretical analysis to reconstruct the step-by-step development of the big-bang model from general relativity.
• Applies abductive reasoning to infer the most likely cosmological scenario from observations, distinguishing it from deduction and induction.
• Reviews observational constraints from the cosmic microwave background, large-scale structure, and supernova data to validate the model’s predictions.
• Tests fundamental assumptions such as the equivalence principle, isotropy, homogeneity, and the distance duality relation using cosmological surveys.
• Analyzes the role of N-body simulations and perturbation theory in modeling non-linear structure formation, while accounting for relativistic corrections.
• Evaluates extensions of general relativity (e.g., scalar-tensor theories) as phenomenological tools, treating them as toy models rather than physical theories.

Experimental results

Research questions

• RQ1 How did the big-bang model evolve from Einstein’s general relativity to become the standard model of cosmology?
• RQ2 To what extent do current observations support the assumptions of the standard model, such as the Copernican principle and the form of the Einstein field equations?
• RQ3 What are the key observational tests that validate the big-bang model’s predictions on nucleosynthesis, CMB anisotropy, and large-scale structure?
• RQ4 Why is the existence of dark matter and dark energy necessary despite their lack of direct detection, and what do they imply about the limits of current physics?
• RQ5 How do theoretical extensions of general relativity, such as scalar-tensor theories, affect cosmological predictions, and what constraints do observations place on them?

Key findings

• The big-bang model has been robustly validated by a wide range of observations, including the cosmic microwave background, large-scale structure, and Type Ia supernovae, which constrain the expansion history and matter content.
• No deviations from general relativity or the standard model have been detected in large-scale tests of the field equations, the equivalence principle, or the distance duality relation.
• The model successfully predicts the primordial abundances of light elements (e.g., helium-4, deuterium), consistent with observations from big-bang nucleosynthesis.
• The observed isotropy and homogeneity of the universe on large scales support the Copernican principle, though its validity on the largest scales remains under investigation.
• Despite high-precision measurements of cosmological parameters, the physical origin of the cosmological constant and the nature of dark matter remain unresolved theoretical problems.
• Theoretical extensions of general relativity, such as scalar-tensor theories, have been tested but do not yet provide a better fit than the standard model, and are largely considered phenomenological toy models.