Fundamental Physics, the Swampland
of Effective Field Theory and Early
Universe Cosmology
Robert Brandenberger
Abstract Cosmological inflation is not the only early universe scenario consistent
with current observational data. I will discuss the criteria for a successful early universe cosmology, compare a couple of the proposed scenarios (inflation, bouncing
cosmologies, and the emergent scenario), focusing on how future observational data
will be able to distinguish between them. I will argue that we need to go beyond
effective field theory in order to understand the early universe, and that principles of
superstring theory will yield a non-singular cosmology.
Keywords Early universe cosmology · String theory
1 Introduction
In this talk I would like to convey three main messages. The first is that the
inflationary scenario is not the only early universe scenario which is consistent
with current observational data. The second message is that the inflationary scenario
does not appear to naturally emerge from superstring theory. On a positive note (and
this is the third message), there are arguments based on fundamental principles of
superstring theory which indicate that the cosmology which emerges from string
theory will be non-singular.
The two past decades have provided us with a wealth of data about the structure
of the universe on large scales. From the point of view of Standard Big Bang
cosmology most of the data cannot be explained. Why is the universe close to
homogeneous and isotropic on scales which at the time of recombination had never
been in causal contact? Why is the universe so close to being spatially flat? These
are the famous horizon and flatness problems of Standard Big Bang cosmology.
We now have detailed measurements of the small amplitude inhomogeneities in
R. Brandenberger ()
Physics Department, McGill University, Montreal, QC, Canada
e-mail: rhb@physics.mcgill.ca
© Springer Nature Switzerland AG 2021
M. B. Paranjape et al. (eds.), Quantum Theory and Symmetries, CRM Series in
Mathematical Physics, https://doi.org/10.1007/978-3-030-55777-5_37
409
of Effective Field Theory and Early
Universe Cosmology
Robert Brandenberger
Abstract Cosmological inflation is not the only early universe scenario consistent
with current observational data. I will discuss the criteria for a successful early universe cosmology, compare a couple of the proposed scenarios (inflation, bouncing
cosmologies, and the emergent scenario), focusing on how future observational data
will be able to distinguish between them. I will argue that we need to go beyond
effective field theory in order to understand the early universe, and that principles of
superstring theory will yield a non-singular cosmology.
Keywords Early universe cosmology · String theory
1 Introduction
In this talk I would like to convey three main messages. The first is that the
inflationary scenario is not the only early universe scenario which is consistent
with current observational data. The second message is that the inflationary scenario
does not appear to naturally emerge from superstring theory. On a positive note (and
this is the third message), there are arguments based on fundamental principles of
superstring theory which indicate that the cosmology which emerges from string
theory will be non-singular.
The two past decades have provided us with a wealth of data about the structure
of the universe on large scales. From the point of view of Standard Big Bang
cosmology most of the data cannot be explained. Why is the universe close to
homogeneous and isotropic on scales which at the time of recombination had never
been in causal contact? Why is the universe so close to being spatially flat? These
are the famous horizon and flatness problems of Standard Big Bang cosmology.
We now have detailed measurements of the small amplitude inhomogeneities in
R. Brandenberger ()
Physics Department, McGill University, Montreal, QC, Canada
e-mail: rhb@physics.mcgill.ca
© Springer Nature Switzerland AG 2021
M. B. Paranjape et al. (eds.), Quantum Theory and Symmetries, CRM Series in
Mathematical Physics, https://doi.org/10.1007/978-3-030-55777-5_37
409