Adam joined Queen Mary as a PhD student a year after I did and it’s been great sharing an office with him over the past few years. Although we haven’t yet written a paper together we’ve thrown a lot of ideas around so hopefully we can work together on something soon. When it comes to listing the names I imagine he will be arguing for alphabetical order!

Adam will be taking up his fellowship in the University of Nottingham from October 2011.

The slides for the talk are available as a pdf or through the embedded widget below. My style for talks is heavily skewed towards minimalist slides with lots of verbal explanation so without having me beside you to guide you through them they might be hard to understand. Perhaps one day I will get around to recording the audio for a talk as well.

Slideshare:

The talk is supposed to be based on our last paper (which will soon appear in JCAP by the way), but with limited time I think I will have to speed through it pretty quickly. As a lot of the paper draws in techniques and results from string theory, I might have to gloss over those to.

The audience is going to be large (at least 50 people), with a mix of postgrads, postdocs and faculty from across the UK. And with a varied mix of theoretical and observational cosmologists, I am finding it difficult to find the right level to pitch the talk at.

To make things a little harder, I have written the talk using Beamer, which is a very impressive presentation class for LaTeX. But I have never used it before, so I am constantly dipping in to the userguide to find out how to do things that in OpenOffice would be simple. That said, I really like being able to incorporate equations into my presentation with no fuss at all, as opposed to the tortuous methods needed in other programs.

With any luck I will be able to overcome these problems before next Tuesday, so here’s hoping the train to Portsmouth gets us there on time!

Bernard introduced the idea of the multiverse, after having plugged the new book and thanked all the contributors. With only thirty minutes allotted to each speaker there wasn’t enough time for a detailed explanation, but he explained some of the different multiverse ideas, in particular using this picture by Max Tegmark to illustrate the hierarchy of multiverse structures. With time running out (and some quite surprising heckling when he asked for some leeway), Bernard had to race through the history of physics on one slide, imploring us to consider it as “an artistic journey”.

The main thrust of the later sections was that throughout history science has expanded the realm of its applicability, from the Earth, to the Solar System, to the galaxy and beyond. The next step in this progression will be to extend our thinking beyond the particle horizon to consider what might lie beyond.

George Ellis immediately made clear that he was not enamoured of the multiverse as a scientific investigation, but later conceded that as a philosophical idea it might have merit as an explanation. But he insisted that it cannot make any predictions and at least currently is not verifiable. In one particularly insightful comment he destroyed notions of using statistics to show how probable a multiverse must be, countering that these statistical analyses presuppose the existence of the multiverse by virtue of their nature. If there is only one universe, then a statistical analysis has nothing useful to say about this one data point!

Prof Ellis also showed how much extrapolation must take place by considering the past light cone of our observable universe, at first filling the whole wall, but then being reduced in stages to a small lonely triangle surrounded by the unobservable region beyond. The idea that we can talk knowledgeably about these regions was rejected, as was the tendency of scientists to talk about “infinity” as he put it. He implored scientists not to open the door to a topic that cannot be verified, insisting that it would lead to a rush of similarly unverifiable ideas claiming scientific validity (presumably referring to ID/creationism).

Paul Davies spoke last and started by lamenting that most discussions of this type revolved around choosing between ignorance, a multiverse, or Intelligent Design as an explanation for the universe’s existence. He quoted the famous “turtles all the way down” explanation of the universe, but expanded it to include a god/multiverse as a “super-levitating turtle”, a description which also appears in his new book. This certainly brought a few chuckles from the audience, but the deeper argument was that it would be more intellectually pleasing to not have to resort to any outside cause to explain the universe and it’s “bio-friendliness”.

The second half of the talk then turned to an explanation of this helpful property of the universe using the uncertainty inherent in a time-reversible quantum mechanical description of the universe. I can’t say I followed exactly what was meant, and Paul Davies freely admitted that Mike Duff called this part of the talk “mumbo-jumbo”. The main idea was that the universe should be considered as an information processor, with the maximum amount of processing possible determined by the volume and hence changing with time. Weird things should happen if something exceeds this processing power, although what would constitute weird wasn’t mentioned. On top of this the universe would be in a feedback loop in which observers shape the course of physical laws in the past, with ever greater precision leading on from “better” observations. This would not be causality violating but rather a later decision would give context to earlier events as in the delayed choice experiment of Wheeler. In this way the tower of turtles would be turned into a turtle loop in which the existence of the universe explains itself. As Davies noted in response to a question, this kind of closed loop history is familiar in any time-travelling story, with no external influence needed to set the events in motion (for example in the film Twelve Monkeys).

After the three talks there was an audience Q&A session, with most of the questions being quite considered and helpful. There was however the usual feature of events like this, where someone stood up and complained that his paper on similar ideas had been censored by the powers-that-be on the arXiv. Paul Davies actually took up this poin, agreeing that sometimes physicists are afraid of questioning the basis on which they rely on physical laws.

All in all it was a good night, with some nice food and wine afterwards and a few of us headed to a local to continue the discussion.

On the night of the launch there are going to be three speakers, Bernard himself, Paul Davies and George Ellis, with Chris Isham chairing. Unfortunately the event is by invitation only and is now fully booked. I will try to give an outline of the talks here on Friday, if I can keep up. Hopefully there will be an interesting discussion, and of course some food for the starving grad students!