Category Archives: Cosmology (general)

Last day of Quantum Foundations conference at Oxford

Yesterday was the last day of the  Cosmology and Quantum Foundations  conference, a symposium that formed part of the  Establishing the Philosophy of Cosmology project at Cambridge and Oxford.

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There was no workshop in the  morning, but there were two weighty lectures in the afternoon, ‘Inflationary Cosmology as a Laboratory for Primordial Quantum Mechanics’ by Antony Valentini and ‘Relational Quantum Mechanics: Spinfoam Cosmology’  by Carlo Rovelli.

Antony Valentini’s talk was the second installment of his thesis that we should consider the possibility that the quantum equilibrium universe we experience is simply a subset of a much larger ensemble which is deterministic, not in equilibrium, and does not obey the standard rules of quantum probability. In this model, elements of the larger ensemble made a transition  by a process of relaxation on atomic timescales to the quantum equilibrium we see today. Antony hypothesized that observational cosmology might offer a test for his model because any non-equilibrium states remaining before cosmic inflation would have become frozen during this period,  feeding into the cosmic microwave background at the end of inflation. His analysis suggested one explanation for the well-known power deficit in the CMB at long wavelengths in the Planck and WMAP data.  I have no idea what the theoreticians thought of Antony’s hypothesis, but talks like this certainly give the lie to those who accuse physicists of groupthink and of being incapable of thinking outside the box!

Carlo Rovelli then gave the second installment of his talk on his relational view of quantum mechanics (see last post). The main point here was that adding gravity to the analysis is not a complication in the case of the relational interpretation of qt because the model is fundamentally relativistic in nature (gravity is simply a curvature of spacetime in relativity). He went on to describe how the theory leads to the ‘quantum loop’ view of quantum gravity. I am not qualified to comment on the theory, but what I took out of Carlo’s talks is that the only fundamental entities in relational theory are covariant quantum fields -the wavefunction has no physical significance, any more than a mathematical operator.

All this was followed by a round table discussion between, Carlo, Antony, Simon Saunders and David Wallace. For many of us, this was a major highlight of the conference. It was a privilege to hear major proponents of the many-worlds interpretation of quantum theory (Saunders and Wallace) arguing point-by point against the relational view (Rovelli), not to mention pointed interjections from heavyweights in the audience such as John Barrow, Julian Barbour and Joe Silk. During the course of the debate, it struck me that the discussion was in some ways a modern echo of the classic debate between the Heisenberg and Schroedinger interpretations of the quantum world. I could almost see Heisenberg behind Carlo Rovelli’s chair, applauding his emphasis on the discreteness as the key property of the quantum world and his dislike of the wavefunction. In the opposite corner, Schroedinger’s view had much in common with the many-worlds camp because of his dislike of collapsing wavefunctions. Indeed, it has recently been suggested by several authors that Schroedinger’ s later work on quantum interpretation somewhat anticipates the many-worlds view (will dig out references on this).

So a splendid finish to a splendid conference; an important debate on the meaning of quantum theory between leading proponents of alternate modern interpretations of the theory, with echoes of history throughout.

Update

It all happens at Oxford. Strolling past the Sheldonian this evening, I heard the familiar strains of Vivaldi’s Four Seasons. Turns out Nigel Kennedy was giving a concert with the Oxford Philomusica, so I sneaked into the foyer to hear the last few movements. You don’t hear much about Kennedy since he moved to Poland, but his performance was as electric as ever. I timed the applause at over 20 minutes, he certainly hasn’t lost his gift for communicating with the audience. However, the real surprise was the orchestra, it didn’t sound like any college orchestra to me – lovely crisp playing, fantastic articulation in the fast passages, and super pianissimos in the slow passages. Turns out the Oxford Philomusica is a relatively new initiative, a professional orchestra in residence at the university. What a great idea , I’m sure it gives a unique opportunity for the very best of the music students

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Nigel Kennedy at the Sheldonian

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Day II at Oxford

Today was the second day of the  Cosmology and Quantum Foundations  conference, a symposium that forms part of the  Establishing the Philosophy of Cosmology project at Cambridge and Oxford.

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The workshop this morning started with a fascinating talk by Douglas Spolyar  on a model of cosmic inflation that predicts that inflation could happen at relatively low energies. The big advantage of such models that they are testable at the TeV energies, i.e., at accelerators such as the LHC; I need to read the paper before I comment further, but all the talks will soon be available on the conference website.

Laura Mersini then gave a talk on evidence for the multiverse post-Planck. This was a discussion of her thesis that the multiverse should in principle be detectable in the cosmic microwave background because of the phenomena of quantum entanglement and decoherence. She then discussed how in her view the Planck data offers support for the model in terms of the cold spot, the dark flow and other effects. It was a good thorough lecture and I understood a lot more than I did at the Cambridge conference on the philosophy of cosmology last March.  Of course, not all cosmologists agree with her thesis and there was plenty of lively discussion from the audience – as an experimentalist, I really like the way theoreticians constantly challenge each other  during their talks, it’s very interactive!

In the afternoon , it was back to the conference proper for ‘Probability and the multiverse: an Everettian view’, the second installment of Simon Saunder’s discussion of the many-worlds interpretation of quantum theory. I found this a lot more challenging than Monday’s talk, I really need to brush up on my reading on many-worlds. Max Tegmark then gave a talk on ‘Thermodynamics, information and consciousness in a quantum multiverse’, a discussion that was  full of interesting insights and provocative ideas. A central theme of his is that entropy does not always increase, but can in fact decrease on observation. I have heard this idea before but I’ve never been clear whether it is an argument that pertains to entropy as a state of information about a system, or whether it is literally true of physical entropy.  I wanted to ask this at question time, and how one might test the hypothesis,  but time ran out.

[Update: I asked Max this question over coffee. I think the answer is yes to physical entropy and he suggested an experiment that could test the idea; unfortunately, I understood about 5% of what he said, I need to read up on this!]

The last speaker of the day was Carlo Rovelli, who spoke on a new interpretation of quantum theory known as the relationary view, a hypothesis  he put forward in the 1990s. This interpretation of qt  imports a lot of ideas from special relativity, in particular applying the idea of the reference frame of the observer to the measurement problem. Thus, instead of talking about wavefunctions that collapse into one state or another, one has to consider that measurements of systems are made relative to another system – it is the relation between the systems that counts. It was fascinating to hear a description of this intriguing new idea from its creator, and tomorrow he will explain how the new theory gives a description of  quantum gravity. [Writing this, I seem to remember that one of Schrodinger’s own objections to the notion of collapsing wavefunctions involved the problem of observations of the same object from different reference frames, must look this up]

After all that, it was time for the conference dinner. I was lucky enough to be at the same table as Carlo, who is also  the author of the highly regarded book ‘The First Scientist: Anaximander and His Legacy’ and we had a great discussion on the history of science. I have never met a physicist who is not interested in the history of our subject – how things were found out is almost as interesting as the things themselves!

As a bonus, the an after-dinner talk was given by Max Tegmark who posed an intriguing question; what if mathematics is a useful way of describing nature simply because nature *is* mathematics? This question was  first raised by Pythagoras, and Max gave an extremely interesting talk on the subject. So much so that I finally realised who he reminds me of – Richard Feynman!

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I had a quick walk under the Bridge of Sighs before dinner

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Oxford!

I’m at Oxford University this week, at the Cosmology and Quantum Foundations  conference, a symposium that forms part of the recent Establishing the Philosophy of Cosmology project at Cambridge and Oxford.

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Physicists don’t always accept the relevance of philosophy in the study of physics, but there is no question that quantum theory has long posed difficult questions of a philosophical nature, not least the interpretation of the quantum wavefunction. In addition, modern cosmology points towards a universe that was once in an extremely small and dense state,  that may or may not have had a finite beginning. As well as the familiar problems of quantum philosophy, this raises a host of other philosophical problems, such as ‘When did the laws of physics become the laws of physics?’ or ‘Were space and time always there or did emerge with the big bang ?’

The conference started at 9.30 this morning with a workshop on cosmic inflation. First up was Andrew Liddle ; after a brief review of the basic postulate of inflation, Andrew explained how the theory soon provided an explanation for the formation of galactical structure (in terms of quantum fluctuations in the early universe inflated to the perturbations observable in the cosmic background radiation). This explanation has since become a major motivation for the theory. Andrew then described new constraints imposed on inflationary models by the data from the Planck satellite.

Andrew’s talk was followed by a seminar by Douglas Spolyar on a new model describing how inflation might have ended (‘supercooled inflation’). I won’t describe it here as part II is due tomorrow. For lunch, we all trooped over to the famous Clarendon lab to hear well-known MIT physicist Max Tegmark give  a rather different sort of talk, ‘The future of life – a cosmic perspective’,  hosted by Oxford’s Future of Humanity Institute. Max’s main thesis was that a cosmological perspective renders existential problems more important, not less. Given that there is a finite chance that mankind is the only conscious life in the universe, if mankind were to die out there would be no-one to observe the universe! It’s a fascinating and provocative argument, and I was pleased to see climate change up there amongst the existentialist risks. However, I wasn’t entirely convinced by Max’s central theme ; apart from the philosophical debate concerning the role of the observer (is he/she really that important?) one wonders are there not more selfish reasons to tackle existential risks (what do I know,  it was an interesting take anyway).

After the Tegmark seminar, it was off to St Anne’s College for the opening of the conference proper. The afternoon session kicked off with a talk by well-known Oxford physicist Simon Saunders on the Many Worlds interpretation of quantum theory. Oxford have a major reputation in this area and I know no better physicist to give an introduction to this topic. It was a fascinating lecture and part II is tomorrow.  After coffee, Max Tegmark gave another excellent talk, this time on The cosmological interpretation of quantum mechanics – unifying the inflationary and quantum multiverses’ (more on this tomorrow).

After dinner with Andrew, I walked around Oxford and took a few photos.There is such fabulous  architecture everywhere you look, no wonder it produces great thinkers. Also, there’s a real thrill in seeing so many locations that are familiar from Inspector Morse , not to mention Lewis.

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The Bodlean (I think)

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The Bridge of Sighs

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The River Thames

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Last day at Cambridge Infinities Conference

Today was the third and last day of the ‘Infinities and Cosmology’ conference at Cambridge (there is also a workshop tomorrow, see website). Yesterday saw quite a heavy schedule, with part II of George Ellis’s ‘Infinites of Age and Size Including Global Topological Issues’, part II of Anthony Aguirre’s ‘Infinite and Finite State Spaces’ and part II of Michael Douglas’s ‘Can We Test the String Theory Landscape?’ (see previous post for an outline of these topics). We also had a fairly technical talk on ‘Singularities and Cosmic Censorship in General Relativity’ by the Cambridge mathematician Mihalis Dafermos: nuts-and-bolts talks like these are great for non-relativists like me because you get to see the mathematical tools used in GR research.

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The logo for the Infinities in Cosmology conference; an artist’s impression of small universes

Today saw part II of Mihalis’s talk and the lecture ‘Infinite Computations and Spacetime’ by Mark Hogarth, a fascinating exploration of new methods of computation by exploiting relativistic spacetime . I won’t attempt to summarize either, but the lectures should soon be available on the conference website.

For me, the highlight of the day was the talk ‘At Home and At Sea in an Infinite Universe: Newtonian and Machian Theories of Motion’ by Simon Saunders,  the well-known Oxford physicist and philosopher of physics. This was a superb discussion of Newton’s cosmology, in particular the paradox of gravitational instability in the Newtonian universe of infinite size and absolute, fixed space. Did Newton realize that our solar system might possess a net acceleration, or did he assume that external gravitational forces somehow cancel out? Drawing on material from Newton’s Principia and his ‘System of the World’,  Professor Saunders argued that Newton assumed the latter, though whether he attributed such a delicate cosmic balancing act to divine intervention or to unknown forces is not clear. (The possibility of a theological argument is not so fanciful as this work was the first mathematical attempt to try to describe the universe as a whole). Later, Professor Saunders suggested that it is likely Newton declined to spend too much time on the question simply because it was untestable.

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Newton’s famous Principia

There were many other interesting points in this fascinating lecture. Viewing the slides shown from Newton’s Principia, I was struck by the equivalence drawn again and again between bodies at rest and in uniform motion. This anticipates Einstein’s special theory of relativity and is again slightly in conflict with Newton’s assumption of a fixed, absolute space, as Simon pointed out. All this hints at a possible difference in Newton’s philosophy towards the universe at large versus motion on local scales – ironic as he was the first scientist to unite terrestrial and celestial motion in a single framework. I won’t comment further, but the lecture left one eager to read Simon’s recent paper on the subject.

All in all, a superb conference. It was interesting that, even with such distinguished speakers, moderators observed time limits strictly in order to allow plenty of time for questions and comments after the talks. In some ways, this was the best part; it’s not often one gets to hear to-and-fro arguments between scientists like John Barrow, George Ellis, Julian Babour and Simon Saunders, in the lecture theatre and over coffee.

Speaking of coffee, one of the best aspects of the conference was the venue. Cambridge’s Department of Applied and Theoretical Physics forms part of its Centre for Mathematical Sciences and is housed in a lovely modern open-plan building, with the smell of coffee and scones wafting throughout the atrium. What other mathematics institute can boast such a setup?  Not DIAS, I’m afraid. Indeed, I’m writing this post in the quiet atrium/canteen (no annoying background music – that wouldn’t be tolerated here). However, I’ve just realised that we are now finished for the day, so I’m off to do some sight-seeing at last.

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The main atrium in the Center for Mathematical Sciences is one big coffee shop, perfect for group discussions of physics, philosophy and mathematics

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The Department of Applied Mathematics and Theoretical Physics forms part of the Centre for Mathematical Sciences at Cambridge

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Infinities at Cambridge

The ‘Infinities and Cosmology’ conference  (see last post) got off to a great start here at Cambridge today. The first surprise was that DAMTP, Cambridge’s Department of Applied Mathematics and Theoretical Physics, is now housed in a beautiful modern building with lots of light, wide open spaces and a great canteen. The building forms part of the new Centre for Mathematical Sciences, most impressive. I couldn’t resist taking a few other photos after breakfast on my way to the conference, nearly missed registration!

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The Department of Applied Maths and Theoretical Physics at Cambridge

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 Clare College (where I’m staying) in the mist at breakfast this morning

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Walking through Clare College on the way to the conference

After registration and coffee, the conference started with a ‘brief introduction’ by John Barrow . This comprised a succinct but comprehensive overview of problems posed by infinities in mathematics, classical physics, quantum physics and particle physics, finishing with a discussion of specific problems in cosmology. There’s nothing quite like an overview like this by an expert, all sorts of connections between diverse phenomena become apparent. I took copious notes which will keep me busy over the next few days. Indeed, I suspect that if no other speaker had turned up, Prof Barrow could have expounded further on the topics he touched on for the duration of the conference.

George Ellis then took the podium for the first installment of his talk ‘Infinities of age and size, including global topology issues’. He set a no-nonsense tone by starting with a pet peeve – that physicists routinely confuse inconceivably large numbers with infinity, a very different beast. He expounded on this theme at length and then set about an interesting argument: that talk of infinities in physical systems is meaningless unless one can verify that they are truly infinite – which cannot be done, as pointed out by David Hilbert. Thus, the hypothesis of an infinite universe is dubious science and dubious philosophy. George then postulated a general test (the Ellis/Hilbert fork) for theories; any hypothesis that no longer works when infinite quantities are replaced by arbitrarily large numbers is bunk!

We were still pondering this opening salvo when Anthony Aguirre took the podium after coffee to talk about ‘Infinite and finite spacetimes’. This started with a succinct review of the ‘initial conditions’ problem in the big bang model, the theory of cosmic inflation and the main inflationary models of today. In particular, Anthony explained why inflation leads naturally to the concept of the multiverse  (essentially, quantum tunneling or equivalent processes are simply far too slow to compete with the still-inflating universe, leading to separate bubble universes). Personally, I once hoped that some mathematician would one day prove that inflation either happened to all or the universe or not at all, but this is looking increasingly unlikely. Anthony then went on to describe the model of eternal inflation and explained how Hoyle’s famous ‘steady-state universe’ could be right after all (at least on the global scale of the multiverse, as he explained in response to a silly question from yours truly).

After lunch, string theorist Michael Douglas presented the first installment of his talk ‘Can we test the sting theory landscape?’. This was the most technical talk so far, nothing less than a brief review of fundamental ideas in string theory and the famous problem of the landscape. A very basic argument Michael made chimed with me, namely that “almost all physical theories have a landscape of possible solutions” (there are dozens of example of this in solid-state physics). After some more general points, Michael went on to address the problem of dark energy, describing how his recent work on the flux vacua hypothesized by Bousso and Polchinski might deliver a mechanism for the cancellation necessary to reduce the quantum energy of the vacuum to the tiny ‘dark energy’ value we see today. I need to read around this area before Michael’s follow-up talk tomorrow so I’ll stop there!

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Back at Cambridge

This week I’m back in Cambridge University, attending  a cosmology conference at  DAMTP, the famous Department of Applied Mathematics and Theoretical Physics. I’m delighted to be back – Cambridge is only a short hop from Dublin and it is such a great place to visit, with its beautiful colleges, bijou shops and lively student life. I arrived late in the afternoon, and walked to the town centre in a light rain; tourists everywhere were complaining about the English weather but I thought the rain and the falling light set the scene perfectly as I walked along past the ancient colleges.

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St John’s College in the rain this evening

This time around I’m staying in Clare College, one of the oldest colleges in the university. Its beautiful front quad is just off Kings’ parade to the front, while the back of the college straddles the River Cam all the way back to the University Library. The rooms are lovely (no tv – wouldn’t have it otherwise). In fact, working at my little desk and watching the rain across the quad makes me feel quite nostalgic, like a student again – perhaps in another universe there is a younger me starting out in this fabulous university .

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Clare College in the daytime

The conference, Infinities and Cosmology,  is not on theoretical or experimental cosmology, but on the philosophy of cosmology. It forms part of a new Oxford-Cambridge initiative  aimed at bringing physicists and philosophers together in order to improve our understanding  of the universe and its origins, from exploring the meaning of the initial singularity to the philosophical implications of theories such as cosmic inflation and the multiverse. This particular conference was organised by John Barrow , Jeremy Butterfield and David Sloan, names that carry a lot of weight in the intersection of physics and philosophy, and visiting speakers include other heavy hitters such as Anthony  Aguirre, Mihalis Dafermos, George  Ellis and Simon  Saunders. You can see the conference program here.

That said, mixing philosophy with physics is not an approach that meets with universal approval – Stephen Hawking once declared that  ‘philosophy is dead’, while Laurence Krauss has also been pretty scathing about the contribution of philosophers to physics.  Both are physicists I hugely respect, but I think this initiative is more about making physicists aware of their deepest assumptions than about  converting philosophers into cosmologists.  Also, those of us with an interest in the history of cosmology notice that scientific progress has often been hindered by unexamined philosophies – from Aristotle’s geocentric model of the solar system to Harlow Shapley’s faith in a single-galaxy model, from Einstein’s assumption of a static universe to the steady-state universe of Hoyle, Bondi and Gold. More recently, I have long suspected that some of the resistance to inflationary models arises from a simple dislike of the exceedingly large numbers involved – an objection that is understandable, but not really tenable from a philosophical point of view.

So I’m not expecting that philosophers will suddenly shine light on well-known problems in big bang physics – it’s more that we physicists can profit by examining the philosophical assumptions we operate under. In general,  scientists  are pretty good at being aware of underlying scientific assumptions, but sometimes a general philosophical viewpoint is often overlooked precisely because it is so widespread. Another  advantage is that philosophy gives us a useful language in which to articulate underlying assumptions.

To give one example, consider the following. The  ‘big bang ‘ model predicts a universe that was once in a hot, tiny, dense state,  expanding and cooling ever since. There is a great deal of evidence to support this model, but it runs into mathematical difficulties as time zero is approached (part of the problem is that we do not have a theory to describe gravity on the smallest or ‘quantum’ scales).  These are technical problems that every cosmologist battles with, but they might one day be resolved, leaving us with a consistent theory of a universe with a definite beginning. In that case, questions that few physicists ever consider become very important:

–          In a universe with a definite beginning, when did the laws of physics becomes the laws of physics?  Were they somehow ‘born’ with the universe, or did they come into being at a later stage. In other words are they emergent, rather than fundamental? If so, what entity or entities did they emerge from?

–          Could it be that space and time themselves are not fundamental but also emergent? In other words, is it possible that space and time were not born with the universe, but are made up of something more fundamental than either? (One clue here is Einstein’s discovery that space and time are not absolute but affected by motion and by gravity).  Could it be that they are non-fundamental as well as non-static?

–          If so, doesn’t this create problems of causality in the case of time?

This is just a flavour of the sort of questions one encounters in the philosophy of cosmology.  Right now, I’d better turn in so I’m wide awake for  tomorrow. In the first lecture, George Ellis, one of the world’s leading theoretical cosmologists, will give a talk ‘Infinites of age and size, including issues in global topology’ .  I suspect I’ll need my wits about me….

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Cosmic fingerprints at Trinity College Dublin

I was back in my alma mater Trinity College Dublin on Monday evening in order to catch a superb public lecture, ‘ Fingerprinting the Universe’ , by Andrew Liddle, Professor of Astrophysics at the University of Edinburgh. The talk was presented by Astronomy Ireland, Ireland’s largest astronomy club and there was a capacity audience (despite the threat of snow) in the famous Schrödinger lecture theatre in the Fitzgerald Building, Trinity’s physics department.

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Professor Liddle was introduced by David Moore, Chairman of Astronomy Ireland, who also presented an update of the club’s recent activities  (David and I participated in a discussion of the life and science of Sir Isaac Newton on NEWSTALK radio station the evening before, you can hear a podcast of the show here). Anyone with an interest in cosmology will be familiar with Andrew Liddle’s seminal textbook ‘ An Introduction to Modern Cosmology’, (not to mention several other books) and the ensuing lecture certainly didn’t disappoint.

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Starting with a tribute to the work of both Schrödinger and Fitzgerald, Andrew gave a brief outline of today’s cosmology, showing how it has moved from a rather speculative subject to a mature field of study. He attributed this progress to key advances in three main areas: precision observations by satellite, sophisticated theoretical models and high performance computing for both analysis and simulation.

He then described five specific challenges that any successful model of the cosmos must address –  the expanding universe;  the formation of structure (galaxies etc);  the age of the universe; the composition of the universe (baryonic matter, radiation, neutrinos, dark matter and dark energy);  a consistent description of the very early universe (cosmic inflation or alternatives).

As ever, many in the audience were surprised to hear that, while dark energy is estimated to make up about 73% of the mass-energy content of the universe, we have very little idea of the nature of this phenomenon!

In the second part of the lecture, Andrew focused on the cosmic microwave background (CMB), explaining how the study of this ‘fossil radiation’  gives precious information on the early universe,  and in particular describing how tiny non-uniformities (or anisotropies) imprinted on the radiation formed the seeds of today’s galaxies (‘cosmic finger-printing’). There followed a swift description of results of CMB studies by the COBE and WMAP satellite missions, with a reminder that more recent measurements by the European Space Agency’s   PLANCK Satellite Observatory  will be announced next week. He also reminded us how, amongst other triumphs, the theory of inflation gives a very satisfactory explanation for the origin of the variations in the background radiation terms of quantum fluctuations in the very early universe. This link between inflation and galaxy formation is often under-stated in the popular literature; in answer to a query from me question time, Andrew confirmed that non-inflationary explanations for the origins of the observed variations in the microwave background have not been very successful. It’s pretty impressive that inflation can give an explanation for the origin of structure, given that this was not part of the original motivation for the theory.

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The ESA’s PLANCK Satellite will report new measurements of the cosmic microwave background on March 21st this month

All in all, a fantastic talk, well worth the trip; afterwards, we all repaired to a nearby pub for sandwiches and further discussion of the universe over hot ports and Guinness…

P.S. In his discussion of the discovery of the expanding universe, I was pleased to see Professor Liddle refer to the work of Vesto Slipher; it seems that recent historical work on the important contribution of Slipher is finding its way into the mainstream community.

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VM Slipher and the expanding universe

In an earlier post, I mentioned an upcoming  conference in Arizona to celebrate the pioneering work of the American astronomer Vesto Slipher. As mentioned previously, 2012 marks the centenary of Slipher’s observation that light from the Andromeda nebula was Doppler shifted, a finding he interpreted as evidence of a radial velocity for the nebula. By 1917, he had established that the light from many of the distant nebulae is redshifted, i.e. shifted to lower frequency than normal. This was the first  indication that the most distant objects in the sky are moving away at significant speed, and it was an important step on the way to the discovery of the expanding universe.

Vesto Melvin Slipher (1875-1969)

The conference turned out to be very informative and enjoyable, with lots of interesting presentations from astronomers, historians and science writers. It’s hard to pick out particular talks from such a great lineup, but three highlights for me were Einstein, Eddington and the 1919 Eclipse Expedition by Peter Coles, Georges Lemaitre: A Personal Profile by John Farrell and Slipher’s redshifts as support for de Sitter’s universe? by Harry Nussbaumer. The latter compared the importance of the contributions of Slipher, Hubble, Einstein, De Sitter, Friedmann and Lemaitre (to mention but a few) and was a focal point for the conference. My own talk ‘Who discovered the expanding universe? – an open bus tour’ was quite similar to Harry’s , with some philosophy of science thrown in, while Micheal Way’s talk Dismantling Hubble’s Legacy? also touched on similar ground.  However, there was little danger of overlap since viewpoints and conclusions drawn from the material varied quite widely! You can see the conference program here.

A slide from Peter Cole’s talk on the Eddington eclipse experiment

A slide from John Farrell’s talk showing a postcard from Lemaitre to Slipher, announcing the former’s visit to the Lowell observatory

Harr Nussbaumer, author of ‘The Discovery of the Expanding Universe’,  in action

Front slide of my own presentation

The best aspect of the conference was the question and answer session after each talk. There was quite a divergence of opinion amongst the delegates concerning the relative importance of the various scientists in the story, which made for great discussions (though I suspect that much of the argument arises from differing views concerning the role of the theoretician vs the role of the experimentalist). You can see a list of speakers and abstracts for the talks here and the slides for my own talk are here.

There was plenty of material here for the relativist; indeed, quite a bit of discussion concerned the relative contributions of Friedmann and Lemaitre (told you it was a good conference). In particular, the Israeli mathematician Ari Belenkiy gave a defence of Friedmann’s work in his talk Alexander Friedmann and the Origin of Modern Cosmology, pointing out that the common assertion that Friedmann took no interest in practical matters is simply untrue, given his work in meteorology, and that the relevant astronomical data was not widely available to Europeans at the time. I must admit I share Ari’s view to some extent; I’m always somewhat in awe of a theoretician who describes all possible solutions to a problem (in this case the universe), as opposed to one solution that seems to chime with experiments of the day.

Title slide of Ari’s talk on Friedmann

The conference also included a trip to the Lowell observatory, including a view of the spectrograph used by Slipher for his groundbreaking measurements and a peep through the famous 24-inch Clark telescope which remains in operation to this day. We were also treated to a few scenes from Dava Sobel’s upcoming play based on her book on Copernicus, read by Dava herself and the eminent Harvard science historian Owen Gingerich.

The famous spectograph, perfectly preserved

Slipher’s telescope remains in use today

Dava Sobel and Professor Owen Gingerich reading from her new play at the Lowell observatory

All in all, a superb conference, definitely worth the long trip (Dublin-Chicago-Phoenix-Flagstaff). Earlier in the week, I gave a longer version of my talk at the BEYOND centre at Arizona State University in Phoenix; I was afraid some of the theoreticians in Larry Krauss’s  group might find it a bit equation-free, but they seemed to enjoy it. Larry and Paul Davies have a fantastic operation going on at the BEYOND centre, but I have to say the ambience and surroundings  at Flagstaff are probably more suitable for a European – much nicer weather!

Many thanks to Ari Belenkiy for the photographs. You can find more descriptions of the conference on John Farrell’s Forbes blog, and on Peter Coles’s  In The Dark blog.

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September conference: origins of the expanding universe

A conference next month will celebrate the pioneering work of the American astronomer Vesto Slipher. On September 13-15th, the Lowell Observatory in Flagstaff, Arizona, will host the conference The Origins of the Expanding Universe to commemmorate the hundredth anniversary of Slipher’s measurements of the motion of the distant nebulae; see here for the conference website.

As readers of this blog will know, Slipher observed that the light from many of the distant nebulae was redshifted, i.e. shifted to lower frequency than normal. This was the first  indication that the distant nebulae are moving away at significant speed and it was an important hint that some nebulae are in fact distinct galaxies far beyond our own Milky Way (see cosmology 101 section). A few years later, Edwin Hubble combined Slipher’s redshift results with his own measurements of distance to establish that there is a linear relation between the distance to a galaxy and its rate of recession; the relation became known as Hubble’s law although it probably should be called the Hubble/Slipher law.

The Hubble/Slipher discovery of the recession of the galaxies  was a key step along the road to the discovery of the expanding universe, but the two are not quite the same thing; for the latter, one needs to situate the phenomenon in the context of the general theory of relativity (according to relativity, the galaxies appear to be moving away from one another because space is expanding). The Belgian physicist Georges Lemaitre was the first to make the connection between the relativistic universe and the observed recession of the galaxies, although his contribution is often overlooked. A major thrust of the conference is to explore exactly such distinctions; looking at the lineup, it looks like an intriguing mixture of cosmologists, astronomers and historians.

All this is highly relevant to my yet-to-be-completed book so after a long, wet summer at WIT, I’m off to sunny Arizona next month!  My own talk is titled ‘Who discovered the expanding universe?’ and I intend to compare and contrast the contributions of various pioneers such as Slipher, Hubble, Humason, Friedmann and Lemaitre. You can see a list of speakers and abstracts for the talks here.

Many thanks to Peter Coles of In the Dark for drawing the conference to my attention.

Update

Going on holiday just as classes start back? Nice job – Ed.

Sigh. I haven’t had a day off all summer and this is not a holiday.

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Astronomy and cosmology at Birr Castle

Yesterday, I travelled to historic Birr Castle in the centre of Ireland in order to catch the end of the annual meeting of the Astronomical Science Group of Ireland. Birr Castle is a great setting for an astronomy meeting –  not only is it a beautiful castle with fantastic grounds, it is also an important landmark in the history of astronomy. The castle was the home of the famous Leviathan, a reflecting telescope that was the largest instrument of its kind in the world for many years. The telescope was built in the 1840s by Lord Parsons, the third Earl of Rosse, and featured  a 72-inch mirror, a marvel of engineering at the time.  He made many important discoveries with the instrument, not least the first observation of the spiral structure of some of the distant nebulae and the detection of stars within the nebulae. Indeed, the Earl was one of the first to propose that the nebulae were entire galaxies distinct from our own, a hypothesis that was not definitely established until Hubble’s measurements with the 100-inch Hooker telescope at Mt Wilson in California.

Birr Castle in Co.Offaly

The Leviathan telescope at Birr castle

There were a great many interesting talks over the two days of the meeting (see program here), but I was there to catch ‘The Search for Polarization Fluctuations in the Cosmic Microwave Background’ by Creidhe O’Sullivan of NUI Maynooth. Creidhe started with a basic overview of the cosmic microwave background (CMB), explaining its importance as evidence in support of the big bang model and describing the measurements of temperature fluctuations in the radiation by the COBE and WMAP satellites. (The CMB is the primordial radiation left over from the time that atoms first began to form. Cosmologists and astronomers spend a great deal of time studying the tiny temperature fluctuations imprinted in the CMB, as this gives information on the density and geometry of the early universe, see the Cosmology 101 section of this blog.)

Creidhe then moved on to explain the study of polarization in the background radiation. The CMB radiation is expected to be polarized because it comprises light that has been scattered by many particles; when light is scattered, it gets polarized into different planes of vibration. (Polaroid sunglasses operate on the same principle; they cut down on light by allowing only light polarised in one plane to pass through). Hence cosmologists search for fluctuations in polarization as well as temperature in the CMB, although the polarization fluctuations are much smaller. Mathematically speaking, the polarization is divided into two modes: electric (E –mode) and magnetic (B-mode) polarisation. E-modes have been detected since 2003; the analysis of these modes has become a major area of research in cosmology. Creidhe gave a superb overview of the instruments used to analyse the E- modes, including the work of her own group with the QuaD experiment at the South Pole.

The QUaD experiment at the South Pole

She finished the talk by explaining that the next big challenge in cosmology is the detection of B–mode polarization in the background radiation. B-modes present a great challenge as they are yet more difficult to detect. The great hope here is that the PlANCK satellite telescope, with its improved resolution. Just as the COBE satellite results were a watershed in our view of the early universe, the resolution of B-mode polarization in the CMB by PLANCK would give yet more support for the big bang model and cosmic inflation, and even offer evidence for the existence of gravity waves.

The Planck satellite telescope

That is not to say terrestrial experiments will not have their place. After Creidhe’s talk, another member of the Maynooth group, Stephen Scully, gave a brief overview of the team’s work on the QUBIC experiment. This is a new type of the bolometric interferometer that will be used in the next generation of terrestrial measurements at the South Pole.

All in all, a most informative afternoon. After the talks, we were shown the site in the castle grounds where a new radiotelescope is to be situated. This will form the Irish node of the international LOFAR astronomy project, bringing Birr castle up to date with modern astronomy – more on this in the next post.

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