A day in the life

There is a day-in-the life profile of me in today’s Irish Times, Ireland’s newspaper of record. I’m very pleased with it, I like the title  – Labs, lectures and luring young people into scence  – and the accompanying photo, it looks like I’m about to burst into song! This is a weekly series where an academic describes their working week, so I give a day-to-day description of the challenge of balancing teaching and research at my college Waterford Institute of Technology in Ireland.

Is this person singing?

There is quite  a lot of discussion in Ireland at the moment concerning the role of  institutes of technology vs that of universities. I quite like the two-tier system – the institutes function like polytechnics and tend to be smaller and offer more practical programmes than the universities. However, WIT is something of an anomaly – because it  is the only third level college in a largeish city and surrounding area, it has been functioning rather like a university for many years (i.e. has a very broad range of programmes, quite high entry points and is reasonably research-active). The college is currently being considered for technological university status, but many commentators oppose the idea of an upgrade – there are fears of a domino effect amongst the other 12 institutes, giving Ireland far too many universities.

It’s hard to know the best solution but I’m not complaining – I like the broad teaching portfolio of the IoTs, and there is a lot to be said for a college where you do research if you want to, not because you have to!

Update

I had originally said that the institutes cater for a ‘slightly lower level of student’. Oops! This is simply not true in the case of WIT, given the entry points for many of the courses I teach, apologies Jamie and Susie. Again, I think the points are a reflection of the fact that WIT has been functioning rather like a university simply because of where it is.

A quantum conference at Castletown House

I spent most of the bank holiday weekend at a conference in beautiful Castletown House in County Kildare. Castletown House is well-known as a venue for classical music concerts but I had never been there for a conference before!

Castletown House in Co. Kildare

The conference was Irish Quantum Foundations, this year’s meeting of the Irish Quantum Field Group. Organised by Eoin O’Colgain of the University of Oviedo in conjunction with theoretical physicists at the Dublin Institute for Advanced Studies, the National University of Ireland, Maynooth and Trinity College Dublin, it was most enjoyable.  Of course,  I’m not a quantum theorist (or any other sort of theorist) but as well as many talks on quantum field theory and string theory, there were seminars on recent advances in experimental particle physics and cosmology. You can find the programme and abstracts here – highlights for me were  a seminar on the recent results from the Planck satellite by Steven Gratton of Cambridge University and a talk on recent studies of the internal structure of the proton at LHCb by Ronan McNulty of University College Dublin.

The conference also featured a public science lecture on the Higgs boson by Peter Higgs of Edinburgh University. Yes, the man himself! Peter’s visit to Ireland received quite  bit of media attention and his lecture certainly didn’t disappoint. About 400 young people turned up in Maynooth University late on Friday afternoon to hear him describe how his work in quantum theory led him postulate the existence of the Higgs boson in 1964. Younger colleagues from Edinburgh then described the successful search for the Higgs at the Large Hadron Collider and how the discovery fits into modern physics. It was a very enjoyable outreach event and I think the point, that what once seemed an abstruse piece of theoretical physics went on to become a major lynchpin of modern physics , was well-made. A nice touch was that Professor Higgs was introduced by Dr Brian Dolan, a quantum theorist at Maynooth who informed the assembled students and visitors that he had studied under Higgs as a student at at Edinburgh!

Peter Higgs being congratulated by Dr Fabiola Gianotti of the ATLAS experiment at CERN , on the day of the announcement of the discovery of a Higgs-like particle at the LHC

The last talk of the conference was a memorial lecture in honour of my father, Lochlainn O’Raifeartaigh. The lecture was given by Professor Nathan Seiberg of the Institute of Advanced Studies at Princeton, a very appropriate choice – Nathan is a world-renowned figure in quantum field theory and string theory, particularly for his work in supersymmetry. This work is closely related to that of Lochlainn, in fact several of my father’s last papers were on the Seiberg-Witten model. Nathan gave a superb overview of some new advances in supersymmetry, carefully drawing out the connections between his own work and that of Lochlainn in many instances. Dad always said that he thought his work on supersymmetry breaking was probably his best and it’s good to know that scientific work can live on, just as music and literature do.

At question time, I asked Nathan about his thoughts on the lack of evidence for supersymmetry at the LHC so far (a lack of evidence that is leading some commentators to declare supersymmerty dead in the water). Like so many theorists, he had a very general overview:

“Even if supersymmetry is not realized in the energy range explored by the LHC, it is still and will always be important.  The impact of supersymmetry on theoretical physics and on mathematics has already been huge and it will continue to be essential…there are many parallels with other theoretical ideas that did not solve the problems they were designed to solve but turned out to be crucial in other contexts.”

Of course this is true – gauge theory in particular is full of examples of  advances that seemed to run into a wall, and were later found to be extremely important in other contexts. (Yang-Mills theory is a good example).

All in all, a superb conference – photos will be available on the conference website soon.

Update

I had a very nice conversation with Peter Higgs on Friday about Lochlainn, he remembered him well and was very complimentary about his work. He also pointed out that Irish students, physicists and engineers were losing out by Ireland’s non-membership of CERN, a point he also made on national TV (see link here, the interview is 20 mins in). I got my photo taken with Peter, but it came out looking like Jackson Pollock painting!

Ireland loses a great physicist

There are sad tidings in Ireland this week with the news that Professor Alex Montwill, Ireland’s best-known particle physicist, has died. Alex was an outstanding  physicist in the field of experimental particle physics and the best teacher I ever had, inspiring generations of physics students with his legendary undergraduate lectures on the physics of the elementary particles and the puzzles of the quantum world. If I can pass on even a morsel of his great knowledge to my own students, my career will have been worthwhile.

Professor Alex Montwill of the UCD particle physics group

The biography below is reproduced from the Institute of Physics

Professor Emeritus of Experimental Physics at UCD, Alex Montwill was one of the first Irish scientists to work at CERN in the late 1950’s. From about that time onwards he was head of the Fundamental Particle research group at UCD which later became members of the European Nuclear Emulsion Collaboration. The collaboration carried out extensive studies in hypernuclear physics and subsequently made the first observation of the creation and decay of a particle containing a charmed quark. Apart from over 40 years’ teaching at UCD,  Alex lectured at City College New York and at the University of Minnesota, Minneapolis. He presented some 150 Science slots on RTE1 radio in 1980’s and 1990’s. He is co-author with Ann Breslin of the book entitled ‘Let there be light’ which was published in 2008 by Imperial College Press. Alex’s hobbies were bridge and chess in both of which he represented Ireland in international competition.

I would like to add: Alex and Ann published a second book ‘ The quantum adventure’ just this year. It’s a fantastic read for anyone with an interest in quantum physics. Also, Alex chose the title ‘The laboratory of the mind‘ for his radio show, a title that gives you a feel for his deep interest in the philosophy of physics, an interest he passed on to generations of students. On a personal note, he knew my father well as a physicist and must have got a shock when I came along and was  a very ordinary student! Yet both Alex and Ann were  extremely supportive of my work in communicating the ideas of physics from the beginning.

As well as the countless students he inspired to take up physics as a career, Alex’s legacy can also be seen in today’s thriving particle physics group at UCD. This group, led by Professor Ronan Mc Nulty, is heavily involved in experiments at the LHCb detector at the Large Hadron Collider; these experiments probe the asymmetry between matter and antimatter, a puzzle of fundamental importance in particle physics.

Finally,  a most interesting ‘life-in-physics’ interview with Alex recorded by Dr Tony Scott on behalf of the IoP is available at:
http://www.iopireland.org/resources/audio/page_50891.html

Ar dheis Dé go raibh a anam

Planck and the inflationary universe

Last week saw the first release of new measurements of the cosmic microwave background by the Planck satellite . There have been many articles and blogposts on the results (see last post), all noting that the data fit well to the standard ‘ΛCDM’ model of a universe containing dark energy (69.2 +- .019 %), dark matter (25.8 ± 0.4%) and ordinary matter (4.82 ± 0.05%). Other results are a slightly revised value of the Hubble constant (67.3 +- 1.2 km/s/MPC) and a revised estimate of the period of expansion (13.8 billion years), aka ‘a new age for the universe’. However, there has been relatively little discussion of the implications of the Planck data for the theory of inflation.

As we saw in previous posts, the theory of cosmic inflation suggests that the universe underwent an extremely rapid, gigantic expansion in the first fractions of an instant, expanding in volume by a factor of about 10⁷⁸  in the time interval 10⁻³⁶ to 10⁻³² of the first second. Such numbers seem crazy in comparison with the relatively sedate expansion of space observed today (Hubble constant above), but inflation gives a very neat solution to several different problems associated with the big bang model; a lack of magnetic monopoles in the universe, the smoothness of the cosmic microwave background, and the fact that the geometry of space appears to be flat. Best of all, it can be shown that inflation provides a natural explanation for the tiny perturbations in the microwave background that gave rise to today’s galaxies (it is thought that quantum fluctuations in the infant universe were amplified by inflation to become the seeds of today’s galactic structures).

Inflation posits an extremely rapid expansion of space in the first fractions of a second

Inflation has become an extremely successful paradigm in big bang cosmology, and today there are few non-inflationary explanations for the geometry of the universe or the formation of structure. But what exactly was the mechanism of inflation? There are over a hundred distinct models; although the WMAP satellite gave results that are consistent with the general idea, the data did not allow one to discriminate between the different models of inflation. So how about Planck?

The first result is that Planck gives a measurement of Ω_k = -0.0005 +- .07 for the curvature of space. This indicates a universe that is very close indeed to flatness. This result confirms and extends  many complementary measurements of the geometry of the universe and strengthens the case for inflation (essentially, inflation predicts that the universe expanded so quickly that any large-scale curvature was quickly smoothed out, just as a balloon blown up to gigantic proportions will appear flat to an observer). Explaining a spatial curvature that is exactly flat without inflation is extremely difficult as it requires a very special balance between the competing forces of expansion and gravity, so this is an important triumph for inflation.

A second profound result from Planck is that the ‘power’ spectrum of the perturbations in the microwave background has a ‘spectral index’ of 0.96 +-.009. This value, close to 1 but slightly less, is exactly consistent with almost all models of inflation. Best of all, the Planck data allow allow us to separate out two spectral parameters that could not be disentangled before (n_s and r, see here). The upshot is that the new data render some inflationary models very improbable, while others remain possible but with new constraints.

Inflationary models (lines and circles) vs the Planck data; points within dark blue and grey shading represent confidence intervals of 95% and 68% respectively

In particular, many complicated inflationary models such as power-law, double-field, and hybrid-model inflation are now effectively ruled out. (These results are backed by a lack of detection of non-Gaussianity in the CMB spectrum). Instead, the simplest ‘slow-roll single field’ type models are firmly in the frame of possibility (yellow and orange lines for example) . Intriguingly, it seems a Higgs-type field is also a possibility if it is strongly coupled to gravity.

Slow-roll inflation; a slowly decaying potential is required for inflation to end in a manner consistent with the observable universe

All in all, a spectacular vindication for inflation, a theory that was once considered far too contrived to be true. You can find more on this in the official summary of the Planck results here  (p36) or the specific Planck paper ‘Constraints on Inflation’ here.  This is how science progresses; painstaking analysis of models gives predictions that can be compared to emerging data. Many possible scenarios are ruled out, while others remain possible. Overall, it is important not to lose sight of the main result i.e. that the extraordinary phenomenon of cosmic inflation is almost certainly right and the simplest models are looking most likely! (Note that there is a misprint in the summary paper: the text on page 36 should refer to fig 26, not 23 – you saw it here first).

The next step is that more detailed observations by Planck may be able to detect a phenomenon known as B-mode polarization in the microwave background; if so, this could allow us to narrow the inflationary candidates down further, not to mention provide us with the first observation of gravitational waves.

Planck and the cyclic universe

One intriguing alternative to inflation is the ekpyrotic cyclic universe. In this model, the big bang is the result of a collision of two branes in a cyclic universe. Such models can reproduce all the characteristics of a standard big bang universe in a natural way, without the extra premise of inflation and its special initial conditions. As a bonus, the postulate of a big bang in the context of a cyclic universe is very attractive because it sidesteps difficult philosophical questions such as ‘when did the laws of physics become the laws of physics?’ or ‘when did spacetime become spacetime?’

During his presentation at Cambridge last week (see last post), Professor Paul Shellard mentioned that the new Planck data render many cyclic models, including the ekpyrotic universe, a lot less likely. At question time, I asked him what aspect of the new data disfavours the cyclic theories; it seems the lack of non-Gaussianities in the CMB spectrum rules out the conversion mechanism required by most cyclic models. However, Paul also suggested that the cyclic theorists would no doubt overcome this temporary setback by tweaking their models! I haven’t found much on this in the Planck papers so more on this later…

Ancient light at Cambridge University

I stayed on in Cambridge today in order to catch a series of seminars on the exciting new measurements of primordial light from the early universe – the  PLANCK satellite measurements of the cosmic microwave background. The Institute of Astronomy here hosted talks by three PLANCK team leaders all associated with Cambridge: Professor George Efstathiou, Director of the Kavli Institute of Cosmology (seen on tv worldwide yesterday), Dr Anthony Challoner of the Department of Applied Maths and Physics, and Professor Paul Shellard, Director of the Centre for Theoretical Cosmology at Cambridge. This was not an occasion to be missed and it didn’t disappoint. (See here for an introduction to the cosmic background radiation and its importance in big bang cosmology).

Map of the cosmic microwave background as measured by the PLANCK  satellite (2013). Image from ESA

There were three separate talks; Professor Efstathiou gave a general overview of the results, Anthony Challoner presented a talk on PLANCK mapping of dark matter by gravitational lensing, and Paul Shellard discussed the implications of the new results for physics beyond the standard cosmological model.

Professor Efstathiou started by explaining why the new measurements were of much greater sensitivity than those of the previous satellite WMAP. One reason is that PLANCK has detectors at both low and high frequencies; the latter (at over 100 GHz) is particularly useful for overcoming problem of  galactic emissions. (A great deal of this kind of work is about subtracting out a large foreground signal comprising emissions from the universe over billions of years). A consistent theme of George’s talk was that the new measurements are sufficiently precise to stand alone, rather than relying on complementary data from astrophysics. For example, a slight tension between the PLANCK measurements of dark energy (below) and data from recent supernova observations may indicate that the latter have larger uncertainties than previously estimated.

A comparison of the resolution of images of the background radiation captured by the COBE satellite (1992), the WMAP satellite (2002) and the PLANCK satellite (2013). Photo from ESA.

I won’t try and summarize the full talk but the main results (in case you haven’t been reading the news) are:

1. The new data are in close agreement with the standard ΛCDM inflationary big bang model; the data fit extremely well to the standard 6 -parameter model  (no evidence of new parameters), although the results suggest some slight adjustments to the following parameters:

2. A revised value for the Hubble constant H_o (the expansion parameter): 67.3 +- 1.2 km/s/MPC, at the lower end of previous estimates

3. A new constraint on the curvature parameter: Ω_k = -0.0005 +- .07 (zero to you and me)

4. A revised estimate of the dark energy contribution: 69.2 ± 1.0%

5. A revised estimate for the dark matter content of the universe:  25.8 ± 0.4%

6. A revised estimate for the ordinary matter content of the universe:  4.82 ± 0.05%

7. A revised ‘age’ estimate for the universe of 13.8 billion years

7. A ‘spectral index’ of 0.96, closely in agreement with simple models of inflation

This last result is one of the most important; as it says in the conclusions of the paper ‘Constraints on Inflation’ (paper XXII of the PLANCK results) , “The simplest inflationary models have passed an exacting test with the Planck data”.

The results are published as a series of 18 papers on the ArXiv, and you can find the summary paper here . Two important anomalies previously seen in the WMAP data remain; an asymmetry between the ‘northern’ and ‘southern’ hemispheres, and the famous cold spot

                           New estimate of the Hubble constant (Planck collaboration, ESA)

 The power spectrum of the cosmic microwave background (PLANCK collaboration, ESA)

George finished by emphasizing a number of caveats; something of a mismatch at low multipoles, the problem of degeneracy (see below) and the lack of a clear signal of B-mode polarization; he is hopeful that the latter may be forthcoming next year.

Anthony Challoner then gave a talk on ‘Full-sky Mapping of Dark Matter with PLANCK’, a description of the mapping of dark matter by PLANCK using the technique of gravitational lensing. The point here is that one cannot get everything from the ‘power’ spectrum above because of the problem of degeneracy; aspects of the  spectrum can be reproduced with different values of H_0, Ω_m etc . Luckily, gravitational lensing is sensitive to the geometry of the universe and to the growth of structure, and so allows an independent method of the determination of Ω_m .I won’t attempt to summarize Anthony’s talk but the main result is that the gravitational lensing results from PLANCK are very much consistent with the parameters derived from the power spectrum.

Finally, Professor Paul Shellard gave a talk ‘ Beyond the Standard Paradigm’. This lecture discussed possible signs of physics beyond the standard cosmological model in the new PLANCK measurements (for example, hints of support for non-inflationary models of the infant universe). The first point of interest is that the famous ‘spectral index’ of the power spectrum is close but not equal to one (0.96), just as expected for inflation. More specifically, probing the shape of the power spectrum gives a powerful tool for selecting or rejecting models. A shape that is decidedly non-Gaussian would effectively rule out ‘slow roll’ inflation, the simplest model.  On the other hand, a closely Gaussian shape would rule out two-field inflationary models, and impose serious constraints on most non-inflationary models. The new result: almost no deviations from Gaussianity, at least within a factor of one in a million. This places important new restraints on models such as cosmic strings,  global textures etc. It seems the result also makes ekpyrotic cyclic models a lot less likely (something to do with the mechanism proposed by most cyclic models, must look this up). Finally, another result was a clear lack of evidence for a fourth generation of neutrinos (was anyone really expecting otherwise?)

All in all, some fantastic results, I’m glad I was here to hear the exciting news at firsthand.  At the end, Paul Shellard joked that one can now read the initials SWH in the PLANCK spectrum (some people claimed that Stephen Hawking’s initials were clearly visible in the WMAP spectrum). It was a fun way to finish the morning’s seminars, but I couldn’t see really it! The main overview paper is here and you can access the full set of papers here.

What I thought was the Institute of Astronomy at Cambridge (actually the library)

The real Institute of Astronomy; not quite as majestic but buzzing with activity

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.

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.

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.

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

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

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!

The Department of Applied Maths and Theoretical Physics at Cambridge

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

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!

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.

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 .

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….

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.

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.

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.

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.

Mid-term in Chamonix

Last week was mid-term and I had a few days skiing in Chamonix in the French Alps. Chamonix lies in the shadow of Mont Blanc, the highest of the Alpine peaks, and the area is famous for its challenging snowsports and mountain climbing. It was surprisingly easy to get to (1 hr 30 mins from Geneva airport) and the skiing certainly didn’t disappoint.

I stayed with my brother and his family in a tiny chalet in Les Praz, a small village just outside the town of Chamonix. The great advantage of this village is that it offers easy access to La Flègere, a large ski area on the opposite side of the valley to the crowds at Chamonix. We had one day’s skiing out of Flegère, another at Argentière, the next resort along the valley, and the final day at Le Tour, further down the valley again.

The village of Les Praz in Chamonix

The skiing was great in each case; lots of snow, steep pistes  and clear skies almost every afternoon. An extra thrill was the fact that one could ski over the Swiss border and have lunch in Switzerland. Of the three resorts, Flegère was my favourite; plenty of trees, nice unpisted runs under the lifts and not too many people.

The lonely skier

That said, I retain my preference for skiing in Austria. One reason is that, like many French resorts, Chamonix has relatively few gondolas, a large number of button lifts  and uncovered chairlifts. Button lifts are quite tiring on the feet after a while, while exposed chairlifts can get very cold – a concern at altitudes above 1500 m where the midday temperature is often below -10 degrees Celsius. In Austria, almost all the main resorts have installed a healthy distribution of small, efficient gondolas and covered chairlifts (in the latter case, the chairs are heated by solar panels in the plastic cover). There were also far fewer restaurants and cafes on the Chamonix slopes, which I found quite surprising for such a famous resort (coffee breaks are important for the tired skier). So while the French are justifiably proud of their resorts, I still prefer Austria!

All in all a very good ski holiday, highly recommended…