Before the Big Bang 3: String Theory Cosmology

Before the Big Bang 3: String Theory Cosmology

This series of films explores current views from leading scientists on what may have happened before the big bang.
In our first film in this series we interviewed Abhay Ashtekar the father of loop quantum gravity and loop quantum cosmology to see what it had to say about the nature of the big bang. In this film, we look at some of the approaches inspired by string theory. Here we interview the father of string theory, Gabriele Veneziano, also one of the first to try and apply it to the big bang. But string theory has more than one approach to the issue of what was before the big bang, if anything. So in this film we also interview David Wands, Professor of Cosmology and Director of the Institute of Cosmology and Gravitation at the University of Portsmouth, who has reviewed several string inspired models. Professor Mairi Sakellariadou of King’s College London who specialises in applying quantum gravity models to the early universe. Lastly, Ali Nayeri, who works on a model of the universe known as “string gas cosmology”.
As in our previous films we discuss some of the challenges these theories face, and how they might be experimentally tested. As well as looking at other issues such as is there a mulitverse and did the universe have a beginning?
All of the scientists who were interviewed for the film were given a draft for any corrections or clarifications. All approved it for publication. One additional clarification Mairi Sakellariadou wanted to add was “My discussion about space-time dimensionality refers to the string gas scenario, namely the decompactification of 3 spatial dimensions (the interplay between winding and momentum modes, the duality between large and small spaces).
My paper refers to the brane scenario: within the higher dim bulk, branes of all dim are embedded and as we have shown interactions between branes lead to the decay of higher dim branes while 3dim and 1dim branes remain; one of the former could play the role of our universe while the latter are the so-called cosmic superstrings, the analogues of field theoretical 1dim topological defects, called cosmic strings.”

It should be noted that since this film was made the BICEP results were shown to be consistent with dust from foregrounds, rather than gravity waves. Animations provided by Ali Nayeri and Alex Bennett. Music is from Sigur Ros and is used with permission,

Eva Silverstein | Horizon Physics: Cosmology, Black Holes, and String Theory – 1 of 2

Black hole and cosmological horizons — from which nothing can escape according to classical gravity — play a crucial role in physics. They are central to our understanding of the origin of structure in the universe, but also lead to fascinating and persistent theoretical puzzles. They have become accessible observationally to a remarkable degree, albeit indirectly. These lectures will start by introducing horizons and how they arise in classical gravity (Einstein’s general relativity). In the early universe, the uncertainty principle of quantum mechanics in the presence of a horizon introduced by accelerated expansion (inflation) leads to a beautifully simple, and empirically tested, theory of the origin of structure. Its effects reach us in tiny fluctuations in the background radiation we observe from the time when atoms first formed.

This theory, and the observations, are sensitive to very high energy physics, including effects expected from a quantum theory of gravity such as string theory. Modeling the early universe within that framework helps us better understand the inflationary process and its observational signatures. Analyzing the `big data’ from the early universe — which continues to pour in — is a major effort. This provides concrete tests of theoretical models of degrees of freedom and interactions happening almost 14 billion years ago.

Our understanding breaks down if we push further back in time, or into black hole horizons. This challenges us to determine more precisely how and why our existing theories fail. I will explain these basic puzzles, and conclude with some of the latest results on this question in string theory, which exhibits interesting new effects near black hole horizons.


String Theory

String Theory – Lawrence Krauss and Brian Greene
Professors Lawrence Krauss and Brian Greene discuss Brian Greene’s introduction into the field of String Theory and the educational reasons to how he came to study and popularise the subject with physics in general.