Archive for July, 2011

I was just re-reading this post over at Cosmic Variance about a paper by Sean Carroll, which he summarises as:

Our observed universe is highly non-generic, and in the past it was even more non-generic, or “finely tuned.” One way of describing this state of affairs is to say that the early universe had a very low entropy. … The basic argument is an old one, going back to Roger Penrose in the late 1970′s. The advent of inflation in the early 1980′s seemed to change things — it showed how to get a universe just like ours starting from a tiny region of space dominated by “false vacuum energy.” But a more careful analysis shows that inflation doesn’t really change the underlying problem — sure, you can get our universe if you start in the right state, but that state is even more finely-tuned than the conventional Big Bang beginning. We find that inflation is very unlikely, in the sense that a negligibly small fraction of possible universes experience a period of inflation. On the other hand, our universe is unlikely, by exactly the same criterion. So the observable universe didn’t “just happen”; it is either picked out by some general principle, perhaps something to do with the wave function of the universe, or it’s generated dynamically by some process within a larger multiverse. And inflation might end up playing a crucial role in the story. We don’t know yet, but it’s important to lay out the options to help us find our way.

It’s a very nice paper and Sean’s post is also worth a read. What I didn’t notice before was this comment from Peter Coles:

I remember having a lot of discussions with George Ellis way back in the 90s about this issue. I strongly agree that what inflation does is merely to push the fine-tuning problems back to an earlier epoch where they are effectively under the carpet (or beyond the horizon, if you prefer a different metaphor). In fact we were planning to write a sort of spoof of Galileo’s “Dialogue concerning the Two Chief World Systems” featuring characters with names like “Inflatio” and “Anthropicus” …. but never got around to it.

Dear Peter Coles, Please write that paper!!! I’ve been looking through the inflation literature lately and there seems to be an uncomfortably large portion of it devoted to propaganda, arguing that inflation is inevitable and the only possible solution to the problems of the standard hot big bang. A good example is this exchange of papers (one, two and three), where Hollands and Wald face off against Kofman, Linde, and Mukhanov on the issue of whether inflation can explain the low entropy of our universe. The question of whether inflation can be the last word in cosmology (and initial conditions) is in need of clarification.


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A few quick things from around the internet.

1. Our favourite Welsh astrophysicist and supervisor, Geraint Lewis, has been keeping himself busy. He’s appeared on Wikipedia, and even has his own blog: Cosmic Horizons. And he’s presented a lecture titled “The Life of Galaxies on ABC Radio National as part of their Music and the Cosmos event, which manages the most depressing end to a public lecture ever:

They have fuel in their cores which is slowly being used up, and eventually stars will start to turn off. Once they’ve used up all their fuel, they can’t burn any more, they will turn off, they will become black, they will emit no light. At some point in the very dim and distant future there will be one remaining star in our Milky Way galaxy, and at some point that too will run out of fuel and it will become dark and the Milky Way will enter into a night and the night will go on forever.

Well worth a listen.

2. A set of three excellent lectures on gravitational waves from Kip Thorne were delivered as the Pauli Lectures at ETH. Video and audio are available here. The first lecture was for the general public and shows some wonderful recent simulations of colliding black holes. Later lectures were more technical but no less fascinating. I’d almost forgotten how much I like General Relativity.

3. I was recently sent this and I loved it. From herePlan of the City is a new animated film, conceived and directed by Joshua Frankel, about the architecture of New York City blasting off into outer space and resettling on Mars. The film’s visuals are an animated collage combining live action footage, animated elements, illustrations and treated photographs, including photos taken by the Mars rovers Spirit and Opportunity made available to the public domain by the NASA Jet Propulsion Laboratory. Plan of the City was created in collaboration with composer Judd Greensteinand NOW Ensemble, an acclaimed “indie classical” chamber ensemble; the ensemble, including Greenstein, feature prominently in the film as live actors set inside the animated framework.

4. If you’re a sucker for punishment … I was recently invited to give four lectures on the fine-tuning of the universe for intelligent life at the St. Thomas Summer Seminar in Philosophy of Religion in Minnesota. The first and second lectures attempt to cover all of modern physics, astrophysics and cosmology in 2 hours, from the structure of atoms and molecules to planet, star and galaxy formation. The third lecture considers what would happen if we changed the laws of nature. In particular, we find that in many cases, the universe would not be able to evolve and sustain complex, intelligent life. The fourth lecture discusses the multiverse – the idea that the universe that we observe is just one of many, each different. I discuss the most popular multiverse today – the inflationary multiverse – and the challenges that the multiverse faces. The talks are on youtube.

5. Aesop himself couldn’t have invented a fable as obvious as this.

6. If you can get a hold of it, Andy Fabian has written an excellent article titled The Impact of Astronomy, which “assesses the variety and scope of the impact astronomy has on science, technology and society – and why it is so hard to measure”. It describes a number of cases in which astronomy has lead to important advances in other areas, including the development of WiFi and digital cameras.

7. Look at this! And also, a wonderful bit of Fry & Laurie.





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I’m back enjoying the Cambridge life for a fortnight, and already have some cricket lined up. Some comments from a previous post got me thinking …

Cosmic Variance recently polled its readers on what got them interested in science. The most common answer was popular science books, and this was certainly true for me. I discovered the nerdy pleasures of a good book on physics as I finished high school, and still enjoy such books today. Below is a list of some of my favourite cosmology and physics books for the interested layperson, organised alphabetically by author. I obviously don’t agree with everything written in these books, but they all presented the science accurately (to the best of my knowledge) and were thoroughly entertaining.

John Barrow: I’ve read and greatly enjoyed many of Barrow’s writings – New Theories of Everything, Between Inner and Outer Space, Impossibility, Pi in the Sky, The Book of Nothing, The Infinite Book, The Anthropic Principle. He combines mathematics and science seamlessly, loves a good historical anecdote or illustration, and isn’t afraid to wander into regions metaphysical. I think that my personal favourite was “Pi in the Sky”, which was my first introduction to the mind-blowing legacy of Kurt Godel. “New theories of everything” is a great introduction to modern physics and cosmology.

Paul Davies: As with Barrow, I haven’t met a Davies book I haven’t enjoyed – God and the New Physics, The Matter Myth, The Mind of God, The Last Three Minutes, The Goldilocks Enigma. A Davies book will always be wide ranging, from pure mathematics to cosmology to physics to biology. His forays into philosophy are thoughtful, even if I don’t always agree. I’d start with “The Goldilocks enigma” – it’s nominally about the fine-tuning of the universe for intelligent life but gives a very good introduction to modern cosmology and physics along the way. (more…)

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