“Our current understanding of physics allows us to reconstruct the history of the Universe from the first 10-43 seconds of existence.”
Inflation, the consensus model
In recent decades, a very solid foundation has been laid for the Big Bang theory, with evidence gathered in support of the so-called standard model, which is the best up-to-date explanation of the origin, evolution, and current state of the Universe. Although there are many unknowns, our current understanding of physics allows us to reconstruct the history of the Universe from the first 10-43 seconds of existence.
A key component of the standard Big Bang model is the inflation hypothesis, an extremely rapid expansion of the early universe, introduced by Alan Guth in 1981 and originally modified by Andrei Linde, Andreas Albrecht and Paul Steinhardt.
The inflation incorporated into the Big Bang model solves some of the issues presented by this theory, in particular the flatness and horizon problems.
The problem of flatness is a consequence of the fact that, according to the theory of relativity, space can have any degree of curvature and the flatness that we observe could only be explained by extremely fine-tuned—and therefore unlikely—initial conditions. The huge stretch implied by inflation could explain the flatness we see in the Universe.
The so-called horizon problem is that we see that our universe is homogeneous, even between points that apparently could not be in contact. Inflation would explain that they were in contact prior to it.
This has been reason enough for this theory to have been widely accepted in the last forty years. Nevertheless, like any complex physical theory, it is considered incomplete and presents aspects that require a better explanation.
The inflation mechanism has undergone modifications by numerous scientists, giving rise to different proposals to explain the origin of the Universe. Steinhardt and Vilenkin developed the so-called “eternal inflation” model, a mechanism by which an endless succession of universes is produced in the instant of the Big Bang.
Nor has there been a lack of critics, such as Roger Penrose, who describes inflation as science fiction.
The Planck satellite observations: in dispute
The dispute took shape in 2013 with the publication by theoretical physicists Anna Ijjas and Paul Steinhardt of Princeton, and Abraham Loeb of Harvard, of the analysis of the data from the Planck satellite. In the paper, entitled Inflationary paradigm in trouble after Planck2013, the authors say that experimental data disfavors all inflationary scenarios.
Study of the data and its subsequent interpretation in relation to inflation continued, with three new academic papers appearing over the following year, each a replica of the previous. The aforementioned article was followed by Inflatable Paradigm after Planck 2013, by Alan Guth and David Kaiser of MIT, and Yasimuri Nomura of the University of California; and this by Inflatable schism after Planck2013, a paper by the same team as the first. The fourth paper, Inflationary Cosmology after Planck 2013, was by Andrei Linde of Stanford University. The dispute is therefore between the heads of the main research centers.
The proof that fails to appear
Quantum fluctuations in the first moments of the Big Bang should produce distortions in the fabric of space-time that would result in what is known as primordial gravitational waves, and their signatures should be imprinted on the cosmic microwave background radiation. Finding them would therefore lend validity to the inflationary model, thus closing an important chapter of cosmology.
But these waves have not yet been discovered, despite efforts to find them. In January 2015, the team of astronomers from the BICEP2 project, which one year earlier believed it had identified them after comparing the data with those provided by the Planck satellite, retracted its conclusions. What might have been proof of the inflationary theory collapsed?
Pop goes the universe: the argument ignites
The controversy escalates when the debate shifts from the academic setting to the wider media.
Pop goes the universe is the title of the paper published by the trio Ijjas, Steinhard and Loeb in the January 2017 edition of Scientific American. It details different aspects of inflation that they consider difficult to accept, especially the initial conditions required by the theory: “Two improbable criteria have to be satisfied for inflation to start. First, shortly after the big bang, there has to be a patch of space where the quantum fluctuations of spacetime have died down and the space is well described by Einstein’s classical equations of general relativity; second, the patch of space must be flat enough and have a smooth enough distribution of energy that the inflationary energy can grow to dominate all other forms of energy.”
But what undoubtedly fuels the fire in the polemic is the claim that inflationary cosmology cannot be evaluated using the scientific method: “the expected outcome of inflation can easily change if we vary the initial conditions, change the shape of the inflationary energy density curve, or simply note that it leads to eternal inflation and a multi mess […] these features make inflation so flexible that no experiment can ever disprove it.”
Reply and rejoinder
This paper stirred things up among the supporters of inflation, who within a few months brought together 33 leading scientists, including several Nobel laureates, who signed a reply that was published on the Scientific American website. Despite the reputation of the signatories, they did not respond convincingly to the opposing arguments and placed much emphasis on an emotional approach: a large number of accumulated papers and supporters that bring together the theory. The authors of the article once again replied by the same media. Ultimately, this fresh row brought nothing new.
Not everything in the universe origin debate is science
It is understandable that inflation theorists, many of whom spent most of their careers working on inflationary models, have a great attachment to these theses. The emotional side is undoubtedly enhanced by the fact that Steinhardt was one of the early proponents of inflation and that he now argues against it by proposing another model, a cyclic Universe.
If we look at the Spanish saying No hay peor cuña que la de la misma madera (there’s no worse wedge than that of the same wood, which roughly means there’s no worse enemy than a former friend), we must take into consideration the opinion of Andrew Liddle of the University of Edinburgh, who points out that both theories are similar, as they share many of the mathematical tools used and yield similar results when observations like the cosmic microwave background are applied.
As Sabine Hossenfelder of the Frankfurt Institute of Advanced Studies sees it, “the ideological convergence around inflation is indicative of a culture that’s become overly risk-averse in its publishing, hiring and funding practices”.
Paradigm shift: bounce versus bang
The idea of a cyclic or oscillating universe goes back to time immemorial. However, it has only been able to have mathematical support from the theory of relativity.
The Big Bang model assumes the beginning of the Universe starting from a point that is small enough for quantum fluctuations in energy to be of great importance. And to arrive at the uniform Universe we know, inflation is needed, an expansion so great that it would completely smooth the distortions and unevenness between different points.
Proponents of cyclic models thus try to avoid the existence of a point as the beginning of the Universe, assuming that in each cycle there is a period of expansion and another of contraction, and that in the transition from one cycle to the next, it does not become small enough for quantum fluctuations to distort the homogeneity of the Universe. This is the proposal shown to us in Pop goes the universe: “there seem to be two logical possibilities. Either the universe had a beginning, which we commonly dub the “big bang,” or there was no beginning and what has been called big bang was actually a “big rebound,” a transition from some preceding cosmological phase to the present expanding phase.”
The cyclic Universe of Ijjas and Steinhardt continues its path
In January 2018, Anna Ijjas published a research paper describing a mechanism by which a cosmic bounce could occur without becoming smaller than the Planck length. A hypothetical energy source stops the contraction and gently reverses it to expand long before the Universe is reduced to the point where the effects of quantum gravity are significant.
In the summer of 2019, Ijjas and Steinhardt published a paper entitled A new kind of cyclical universe in Physics Letters B, in which they presented the conclusions of their latest work, where they assure that “the resulting cosmology not only solves the homogeneity, isotropy, flatness and monopole problems and generates a nearly-scale invariant spectrum of density perturbations, but it also addresses a number of age-old cosmological issues that big bang inflationary cosmology does not.”
In September last year, it was announced that the Simons Foundation had granted funding to continue in this line.
Universe origin debate remains
The next step in this exciting debate should come from experimental observational astrophysics and cosmology. Primordial gravitational waves have long been sought and their detection would provide evidence for the inflationary model. Otherwise, says Marc Kamionkowski of Johns Hopkins University—who has not taken part in the dispute—if 10 years from now they have not been detected, they would have to abandon the current inflation model.
The cyclic model theory predicts that the dark energy that is driving the current accelerated expansion should decline, which may be detectable in future experiments. We shall have to wait and see.
Scientific models versus philosophical thinking
Philosophy represents the intellectual approach that aims to understand the whole and therefore the concept of the Universe is a typical philosophical concept. It seems logical to compare the analysis of the origin of the Universe that is debated in scientific terms with the corresponding one in philosophical terms.
Physics and cosmology provide insight into the structures and dynamics of nature. How a system evolves from one state to another. But they cannot ultimately tell us why the whole system exists or why it is endowed with the particular order it manifests. Physics can never tell us how we get from absolute nothingness (a state with no space or time, no matter, no energy, no wave function or field, nothing physical at all) to something that has a particular order. There is no physics of “absolutely nothing”.
In a definitive sense, philosophy and theology cannot answer these questions either, at least not adequately. But they can propose arguments that provide consistent and intelligent preliminary answers to this question that are less inadequate than the alternatives.
Is religious tradition, creatio ex nihilo, complementary to scientific explanation
The idea of divine creation, as developed in the Jewish-Christian and Islamic religious tradition, creatio ex nihilo, is complementary to scientific explanation (and therefore to any cosmology and quantum physics that can provide explanations about the early stages of our universe), because it simply provides an explanation or foundation for the existence and basic order of what the sciences propose and discover.
The philosophical proposition of creatio ex nihilo is the existence of a self-existent and self-explanatory cause, the Creator, who is the fundamental source of being and order, in whom all existing things participate. As such, this Creator is not another entity or process in the Universe that can be detected and isolated from other physical causes or entities. It is causally different from them because without Him there would be nothing.
The Creator, first cause, “is the foundation or ground of secondary causes, but secondary causes are also real in themselves, which means that natural phenomena can be genuinely explained by laws of nature”.
Creation is not a temporal event, but a relationship, a relationship of ultimate dependence. Therefore, the ’cause’ applied to God should not be conceived as a physical force or an interaction, as it is in physics, but in terms of a relationship of dependence that is always present. Therefore, the Creator is always sustaining or preserving, all that exists.
In his essay Thomas Aquinas on Creation and Science, William E. Carroll says, “Thomas Aquinas thinks that this philosophical understanding of creation prescinds from any question of the world’s temporality. Contrary to many in his own day, and in our day, he thinks that an eternal, created universe is intelligible.
Thus, contemporary cosmological theories that employ a multiverse hypothesis or an infinite series of big bangs do not challenge the fundamental feature of what it means to be created, that is, the complete dependence upon God as cause of existence. An eternal universe would be no less dependent upon God than a universe that has a beginning of time. To be created out-of-nothing does not mean that a created Universe must be temporally finite. *
Bioethics Observatory – Institue of Life Sciences
Catholic University of Valencia
 cfr. John Auping Birch, El origen y la evolución del Universo, 2016 ISBN 978-607-417-070-2
 Anna Ijjas, Paul J. Steinhardt & Abraham Loeb, Inflationary paradigm in trouble after Planck2013 – 1 June 2013 – arXiv 1304.2785v2
 Alan H. Guth, David I. Kaiser & Yasunori Nomura, Inflationary Paradigm after Planck 2013 – 14 Jan 2014 – arXiv 1312.7619v2
 Anna Ijjas, Paul J. Steinhardt & Abraham Loeb, Inflationary schism after Planck2013 – 27 Feb 2014 – arXiv 1402.6980v1
 Andrei Linde, Inflationary Cosmology after Planck 2013, Stanford University – 9 Mar 2014 – arXiv 1402.0526v2
 Ron Cowen, Gravitational waves discovery now officially dead – 30 January 2015 – Nature News & Comment (https://www.nature.com/news/gravitational-waves-discovery-now-officially-dead-1.16830)
 Anna Ijjas, Paul J. Steinhardt & Abraham Loeb, Pop goes the universe – Scientific American, January 2017 32-39
 Guth, A. et al., A Cosmic Controversy – Scientific American. Posted on scientificamerican.com February 2017.
 Jake Hebert, Ph.D., Big Bang Blowup at Scientific American, The Institute for Creation Research – May 29, 2017
 Marcus Woo, Did the Universe Start with a Bounce Instead of a Bang? – NOVA December 14, 2016
 Jess Romeo, Can Physicists Rewrite the Origin Story of the Universe? – UNDARK – 12 Sep 2019
 Anna Ijjas, Space-time slicing in Horndeski theories and its implications for non-singular bouncing solutions – arXiv 1710.05990v2 27 Jan 2018
 Anna Ijjas & Paul J.Steinhardt, A new kind of cyclic universe – Physics Letters B 28 June 2019
 Staff Writers, New initiative to explore origin and future of Universe – SPACE DAILY Sep 23, 2019
 Anil Ananthaswamy, Search intensifies for primordial gravitational waves – Science Writer PNAS May 14, 2019
 Evandro Agazzi, The Universe as a Philosophical Problem – Interdisciplinary Encyclopedia of Religion and Science 1991
 William R. Stoeger, SJ, God, physics and the Big Bang, The Cambridge Companion to Science and Religion 2010
 Creation Ex Nihilo and the Sciences: An Interview with Yonghua Ge, Interface March 29, 2019
 William R. Stoeger, SJ, op. cit.
 William E. Carroll, Thomas Aquinas on Creation and Science Intercollegiate Review · Modern Age October 11, 2016