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,
Before the big bang 2 – Conformal Cyclic Cosmology explained
The conventional view that time began at the big bang is often said to be based on what is known as Penrose Hawking singularity theorems. In our last film, Abhay Ashtekar and Ivan Agullo argued that a singularity is replaced with a bounce in quantum gravity. In this film, we interview Sir Roger Penrose, one of the authors of the conventional narrative who presents an alternative view which he calls CCC (Conformal Cyclic Cosmology). In CCC the big bang is not the ultimate beginning but it did not arise from a bounce; instead the universe rescales itself, losing track of how big it is as massive particles disappear (and hence the ability to measure space and time) in the remote future. This cyclic behaviour may be extended to the infinite past and future.
Whilst Roger Penrose and Vahe Gurzadyan’s claim that there was evidence for CCC in the CMB (Cosmic Microwave Background) was not accepted by the wider community, what’s less well known is that a new team led by Prof Krzysztof Meissner (University of Warsaw, CERN) has claimed a confirmation of CCC in a new study. We discuss this with Professors Penrose and Meissner and put to them many questions regarding this new model.
The film is intended for a lay audience that has an interest in cosmology and the origin of the big bang. The interviewees were asked to check a draft of the film to make sure they had not been taken out of context in the edit and there are no scientific mistakes.
Animation credits: Big bang/expanding universe animation: Alex Bennett
Colliding galaxies: NASA
For more material read Roger Penrose’ book Cycles of Time: amazon.co.uk/Cycles-Time-Extraordinary-View-Universe/dp/0099505940
Technical paper on CCC from the Journal of Physics: iopscience.iop.org/1742-6596/229/1/012013
Paper claiming circles in the CMB: link.springer.com/article/10.1140%2Fepjp%2Fi2013-13022-4
Paper denying circles in the CMB: arxiv.org/abs/1012.1305
Meissner’s paper claiming confirmation of circles: arxiv.org/pdf/1307.5737.pdf
Ted Newman’s paper on CCC: arxiv.org/abs/1012.1305
Sean Carroll’s article on CCC and debating William Lane Craig: preposterousuniverse.com/blog/2010/12/07/penroses-cyclic-cosmology/ preposterousuniverse.com/blog/2012/09/25/let-the-universe-be-the-universe/
William Lane Craig podcast on CCC: reasonablefaith.org/truth-free-will-and-cosmology
Before the Big Bang 1 – Loop Quantum Cosmology Explained
What happened before the big bang? It’s one of the most popular questions in astronomy. When the observable universe is smaller than an atom our classical theory of gravity, Einstein’s theory of General Relativity, breaks down and needs to be modified with a theory that can also accommodate the physics of the sub atomic world, quantum mechanics. Armed with a quantum theory of gravity cosmologists may be able to tackle the question of what happened before the big bang. Loop quantum cosmology is considered one of the most promising candidates for such a theory. In this film we interview some of the leading scientists in the field to explain this exciting theoretical development. We ask what happened before the big bang? Is there a multiverse? Why was the entropy of the universe so low in the past? Could the Planck spacecraft anomalies be signs of the pre big bang universe? How do we test these ideas? Should we accept the claims that the universe really has a beginning? In some sections of the film there is CGI animation to help visualise the evolution of the universe. These are for illustrative purposes only and should not be taken too literally. For example, the big bang is not an explosion from a single point and a quantum bridge would not really look like a tunnel; the universe is 4-dimensional, not 2- or even 3-dimensional, so these images are simply to assist the explanation.
All of the video was shot by us on a Sony VG900 full frame video camera. Other images were provided by:
Opening photos: our teacher and friend Roger Wesson (European Southern Observatories)
Eternal inflation animation: Anthony Aguirre & Nina McCurdy (University of Santa Cruz), Joel Primack and Nancy Abrams
Hourglass universe, continuous space time and Big Bang Observer animations: Alex Bennett
Spin foam animation: Thomas Thiemann (FAU Erlangen -Nurnberg), Middle Science Communication (Potsdam), Exozet (Potsdam)
Gamma Ray Burst: European Southern Observatories Black hole simulation: William East (Princeton University)
Thanks to Sabine Hossenfelder at Backreaction blog. Thanks also to Marcus at physicsforums.com
Music is “Shot in the Head” by Moby and is used with permission.
Source material is embedded within the video; click pause to read more details.
The content of the final version of the film was checked and approved by the interviewees. Many thanks to both of them: Abhay Ashtekar (Penn State University) Ivan Aguillo (Cambridge University)
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.