Origins of the Universe: Alternatives to Inflation

The Origins of the Universe project is designed to advance our understanding of the universe by stimulating theoretical research into mechanisms of cosmogenesis. The Simons Foundation's effort will develop testable predictions about string theory, quantum gravity and inflation. To do so, the foundation has assembled an international group of theoretical physicists to tackle one of the biggest unsolved mysteries in science: what exactly went down at the dawn of the universe around 13.8 billion years ago. Einstein's gravity correctly describes astrophysical and cosmological phenomena at hugely diverse scales and is one of the most successful theories of all time. Yet experiment and observation have raised questions that might require theories beyond Einstein's, including the cosmological constant problem, the lack of fundamental understanding of the accelerated expansion of the universe and the enigma of the beginning of the universe. The Cosmology Beyond Einstein's Theory group will explore these issues. The Research in Modern Inflationary Cosmology group will expand our understanding of inflationary dynamics, providing new insights into the density perturbations seeding structure in the universe as well as into the observational constraints on the theory. A key issue will be non-Gaussianity in the cosmic microwave background fluctuations. The group will develop the underlying theory, with control of quantum gravity effects, including typical string theoretic solutions with classical potential energies and many axion fields. Cumrun Vafa will seek to find the universal features that distinguish the string landscape from the swampland by studying solutions to string equations. He is particularly interested in exploring consequences of these features that may lead to observable predictions for cosmology. The inflationary paradigm — the proposal that our universe underwent an era of rapid acceleration — is the dominant paradigm for explaining many of the observed features of the early universe. However, this evidence also allows for alternatives, and so Kurt Hinterbichler's project seeks to identify, discover, explore and develop possible alternatives to test against inflation. This includes studying and developing the structure of novel effective field theories that may be used in the construction of such scenarios. Alberto Nicolis's project involves a systematic application of effective field theory techniques and of spontaneous symmetry breaking considerations to early universe cosmology, with the goal of understanding the realm of possibilities beyond inflation that on the one hand are well motivated from the quantum field theory standpoint and, on the other hand, are compatible with observations. He will address model-independent questions related to the dynamics of the early universe and their implications for cosmological observables, starting from a quantum field theory, symmetry-based viewpoint, with an emphasis on the consequences of spontaneous symmetry breaking and the Goldstone phenomenon. Such an approach has proven extremely valuable in particle physics, and research in cosmology in the last decade has taught us that it can be extremely valuable there as well. The New Theoretical Avenues for the Early Universe group, under Mark Trodden and Justin Khoury, will explore the range of allowed ideas for the early evolution of the cosmos and expand the theoretical and observational ways to distinguish between such possibilities. An important component is the development of new models of the very early universe that can address the traditional problems of standard big bang cosmology and generate density perturbations consistent with observations. A crucial broad question is that of identifying the symmetries that might underlie early universe cosmology and determining their observational consequences. This approach holds out the hope of model-independent tests for different early-universe scenarios. On a more specific level, new models frequently invoke physics that at least superficially conflict with standard stability criteria of general relativity. This group will explore this theoretical issue by sharpening the connection between the null-energy condition and the standard assumptions of quantum field theory.