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A celebration of Sir Fred Hoyle at the Royal Astronomical Society

The birth centenary of the noted British astrophysicist Sir Fred Hoyle was celebrated on Friday at the Royal Astronomical Society with a one-day meeting of talks describing Sir Fred’s many contributions to 20th century physics. While he is chiefly remembered in some quarters as the physicist who was ‘wrong on the big bang’, Sir Fred in fact made a number of seminal contributions to modern physics in several fields. Indeed, it was a treat to witness former collaborators and students recall his contribution to stellar evolution, stellar nucleosynthesis, astrobiology and cosmology, to name but a few.

I hadn’t been to the RAS before although I was elected a Fellow a few years ago, and I was stunned by its fantastic location in central London. It is housed in the famous Burlington House on Piccadilly, sharing the premises and courtyard with the Linnean Society, the Geological Society and the Royal Academy of Arts, a stone’s throw from Piccadilly Circus. As luck would have it, the Royal Academy are currently hosting a show of the work of the Chinese artist Weiwei, and his striking ‘Tree Sculpture’ filled the Burlington courtyard.

Burlington house on Piccadilly, housing five learned London societies, including the Royal Academy of Arts

Weiwei’s exhibit ‘Tree Sculpture’ in the Burlington courtyard. The RAS is located on the west wing of the courtyard.

The meeting opened with an introduction by Lord Martin Rees, who gave a comprehensive overview of Sir Fred’s works in a short, a ten-minute talk. This was followed by a description of Hoyle’s contribution to accretion physics by Professor Andrew Fabian of the Institute for Astronomy (IOA) in Cambridge, and talks on Hoyle’s work on nucleosynthesis by Professor Lynden-Bell (IOA) and Professor Malcolm Longair, Director of the Cavendish laboratory.

Professor Jayant Narlikar of the Inter-University Centre for Astronomy and Astrophysics (Pune, India) then gave the talk ‘Fred’s theories and ideas about gravity’. This was a rare treat – as a long term collaborator, Jayant made several important contributions to the development of Hoyle’s steady-state model of the universe (including the development of a new version of the model based on the principle of least action, and the development of the later ‘quasi-steady-state’ model), so it was most interesting to hear his take on the genesis of the steady-state cosmologies of Hoyle and Bondi and Gold.

Hoyle and Narlikar in 1966

Another treat was a talk by Professor Chandra Wickramasinghe of the University of Buckingham, ‘Fred Hoyle and the foundation of astrobiology’. This presented interesting insights into Chandra’s long collaboration with Sir Fred, from their early work on interstellar dust to their famous hypothesis that life on earth was seeded by comets. The latter work essentially founded the modern field of astrobiology, although they are not always credited for this.

Jayant’s talk was followed by a talk on Hoyle’s cosmology by Professor John Barrow of the Department of Applied Mathematics and Theoretical Physics at Cambridge. John gave a superb overview of Hoyle’s steady-state model of the universe, and of the battle royale between Hoyle’s theory group and Martin Ryle’s astronomy group at Cambridge during the 1950s. Most members of the audience were familiar with this story, but John brought out many points that are not well known – not least that the widespread skepticism concerning Hoyle’s hypothesis of the continuous creation of matter was something of a moot point. As demonstrated by Bill McCrea in 1951, a viable steady-state model can be constructed without this assumption. John also reminded the audience that today’s models of cosmic inflation are effectively steady-state cosmologies, and, if the eternal inflationary scenario is right, it is possible that the observed universe is a locally evolving patch in a global ensemble that is in a steady state!

Eternal inflation could give rise to evolving universes embedded in a global steady-state ensemble

I touched on both these points in my own talk ‘Steady-state cosmologies in context‘, although my main aim was to remind the audience that Hoyle’s steady-state model was a reasonable hypothesis at the time – and that the notion of a steady-state universe surfaced in cosmology on many occasions, from Arrhenius to Nernst, from Holmes to MacMillan. Further, not many people know that soon after the emergence of the first evidence for an expanding universe, several physicists considered the possibility of an expanding universe that remains in a steady state due to a continuous replenishment of matter, from Tolman to Einstein, from Schroedinger to Mimura. That said, my main focus was to discuss Einstein’s abandoned attempt at a steady-state model , an unpublished work discovered 2 years ago. (You can find more on Einstein’s attempt at a steady=state model here and here).

Between the two talks on Sir Fred’s cosmology, Nicola Hoyle gave a fascinating description of her personal recollections of her grandfather. It included many intriguing photos and pieces of information I hadn’t seen before. The meeting ended with a talk by Professor John Faulkner of the University of California at Santa Cruz on Sir Fred’s contribution to our understanding of stellar structure and evolution, after which we all trooped off to the beautiful library of Geological Society on the other side of the square for coffee.

All in all, a superb conference in memory of a superb physicist. The meeting was organized by Simon Mitton of Cambridge University. You can find the programme here and slides for my own talk on the ‘Seminars’ page of this blog.

After the meeting, speakers were treated to dinner at the famous RAS Dining Club, and I rolled back to my hotel through the gardens of Buckingham Palace. On Saturday, I took a hop-on hop-off open bus tour of London and it was a great success. In particular, I caught a young string orchestra rehearsing Correlli and Vivaldi concerti in St Martin in the Fields, and a superbly talented string quartet playing Brahms’s Hungarian Dances in Covent Garden, not to mention a relaxing stroll  along the Embankment in the afternoon sun. I’d forgotten what London can be like on a Saturday afternoon, must visit the RAS more often!

The best way to see London


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A day out (and a solar eclipse) at Maynooth University

I  had a most enjoyable day on Friday at the mathematical physics department of Maynooth University, or NUI Maynooth, to give it its proper title. I was there to attend an international masterclass in particle physics. This project, a few years old, is a superb science outreach initiative associated with CERN, the European Centre for Particle Physics particle in Geneva, home of the famous Large Hadron Collider (LHC). If you live on planet earth, you will probably have heard that a famous particle known as the Higgs boson was recently discovered at the LHC. The idea behind the masterclasses is to give secondary school students the opportunity to “become a particle physicists for a day” by performing measurements on real data from CERN.


The day got off to a great start with a lecture on “Quarks, leptons and the forces of nature” by Dr. Paul Watts, a theoretical physicist at Maynooth. An excellent introduction to the world pf particle physics, I was amused by Paul’s cautious answer to a question on the chances of finding supersymmetric particles at the LHC. What the students didn’t know was that Paul studied under the late Bruno Zumino, a world expert on supersymmetry, and one of the pioneers of the theory. Paul’s seminar was followed by another lecture, “Particle Physics Experiments and the Little Bang” , an excellent a talk on the detection of particles at the LHC by Dr Jonivar Skullerud, another physicist at Maynooth. In between the two lectures. we all trooped outside in the hope of seeing something of today’s solar eclipse . I was not hopeful, given that the sky was heavily overcast until about 9.30. Lo and behold, the skies cleared in time and we all got a ringside view of the event through glasses supplied by Maynooth physics department! Now that’s how you impress visitors to the college… images IMG_20150320_101922

Viewing the eclipse

After lunch we had the workshop proper. Each student was assigned a computer on which software had been installed that allowed them to analyse particle events from the ALICE detector at the LHC (lead ion collisions). Basically, the program allowed the students to measure the momentum and energy of decay products of particles from the tracks produced in collisions, allowing them to calculate the mass of the parent particle and thus identify it. As so often, I was impressed how quickly the students got the hang of the program – having missed the introduction thanks to a meeting, I was by far the slowest in the room. We all then submitted our results, only to find a large discrepancy between the total number of particles we detected and the number predicted by theory! We then all returned to the conference room, and uploaded our results to the control room at the LHC. It was fun comparing our data live with other groups around Europe and discussing the results. Much hilarity greeted the fact that many of the other groups got very different results, and the explanation for that (but what many groups really wanted to know was  whether we got a good look at the eclipse in Ireland). IMG_20150320_154423

Uploading our results via a conference call with the contol room at the LHC, CERN

All in all, a wonderful way for students to get a glimpse of life in the world of the LHC, to meet active particle physics researchers, and to link up with students from other countries. See here for the day’s program.


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Robert Boyle summer school

I spent last weekend at a most enjoyable summer school in honour of Robert Boyle, the Waterford-born Anglo Irish aristocrat who became a major figure in the English scientific revolution. Boyle was extremely well-known in his day for his scientific discoveries, his role in the Royal Society and his discussions on the usefulness of the new scientific method (if he is less well-known today, it may be because his contributions were later eclipsed by the groundbreaking advances of his contemporary, the genius Isaac Newton).


The Irish-born scientist and aristocrat Robert Boyle


Lismore Castle, the birthplace of Robert Boyle

The summer school took place from Thursday 4th to Sunday 7th of July in the Heritage Centre in Lismore, the beautiful town that is the home of Lismore Castle where Boyle was born.  The talks covered a wide range of topics, from the history and philosophy of the scientific revolution to Boyle’s own life and were of huge interest to anyone with an interest in history, science or indeed the history of science.  It was the sort of conference I like best – a small number of inter-disciplinary talks aimed at curious academics and the public alike, with lots of time for questions and long breaks for discussion. Other highlights were an open-air barbecue in Lismore Castle on Friday evening, a re-enactment in costume of some famous Boyle experiments and a tour around the famous Lismore Castle Gardens.


Song and dance in the grounds of Lismore Castle

The festival proper started with a lecture on Thursday evening by Jim Malone, the Robert Boyle professor of medical physics at Trinity College Dublin:  ‘Robert Boyle: Getting to Know the Man from Lismore’. This was a general overview of Ireland’s most famous scientist, from Boyle’s early years in Ireland to his travels in Europe in 1639-45, from the rise of the Royal Society in England to Boyle’s prolific work at Oxford in the period 1655-1668. It was a very appropriate introduction to Boyle’s great contributions to science, medicine, philosophy and theology and there were also many biographical details I hadn’t heard before, not least the astonishing number of awards and honours he turned down – clearly not a scientist motivated by fame or fortune. You can find more on Jim and his lecture on the conference website here.


On Friday morning, Dr Anna-Marie Roos of the University of Lincoln laid out the historical context of Boyle’s work in more detail in her lecture ‘Robert Boyle and Early Modern English Science’. Starting with the work of Sir Francis Bacon, she described the emergence of a new questioning of the wisdom of the ancient Greeks, a new philosophy propagated by the invisible college. She then went on to describe Boyle’s experimentation in the context of complementary investigations by colleagues such as Hooke, Wren and Halley. This talk established a detailed social context for Boyle’s investigations very carefully without in any way detracting from the great work he did. You can find more on Anna-Marie and her lecture on the conference website here.


In the afternoon, Dr Bill Eaton of Georgia Southern University gave the talk ”Boyle in Ireland; Medicine and the Mechanical Philosophy’ where he made a very interesting point on Boyle’s philosophy of science. It turns out that although Boyle spent very little time in Ireland, he did some work on dissection of animal and human cadavers with William Petty in the period 1652 to 1654 in Ireland, experiments that played a very important part in the development of his philosophy of science. Thus, while we associate Boyle’s  scientific work with his later years at Oxford, it is likely that his earlier studies in anatomy in Ireland probably played an important role in in his development as a scientist, particularly in his belief in experimentation to judge the rightness or wrongness of a hypothesis. More on Bill and his lecture here.


Song and dance at the castle barbecue

I had a sore head after the open-air barbecue at Lismore Castle on Saturday morning, but not so sore that I didn’t enjoy the superb lecture ‘For the Glory of God and For the Relief of Man’s Estate’ by Dr Allan Chapman of the University of Oxford. In many ways, this was the perfect sequel to Anna Marie’s earlier talk on historical context (see above), I never tire of Allan’s unique coupling of a huge breadth of historical knowledge with an ability to communicate key historical points in clear, simple language. To pick one important theme, Professor Chapman was at pains to trace the rise of the new philosophy to a number of earlier advances in the 15th and 16th century; from geography (the voyages to the Americas proved Aristotle wrong on many counts) to anatomy (animal dissections showed the ancients to be equally wrong on the innards of living species), from herbal medicine (tried and tested herbal remedies were far superior to ‘cures’ from ancient books) to the discovery of the invisible force of magnetism. It set Boyle’s investigations in a yet wider context and I was particularly struck by Allan’s insight that to Boyle and his colleagues, new instruments such as the microscope were very much the equivalent of new ships for the previous century’s explorers. Another great theme was Allan’s careful analysis of Boyle’s motivation, that each experiment was driven by his dual passion of investigating God’s creation and relieving the suffering of man. Allan analysed the latter in detail, explaining how Boyle and his contemporaries expected the new investigations to help combat the ever-present threat of famine. You can find more on Allan and his lecture on the conference website here.

Professor Chapman’s discussion of Boyle’s concern for the relief of man’s estate set the stage nicely for a more contemporary talk, ‘Plants for the 21st Century’, by Professor Liam Dolan of Oxford University. This was yet another tour-de-force: starting with some astonishing diagrams of plants by Boyle’s contemprary Robert Hooke, Liam went on to describe groundbreaking research in botany today, not least the use of modern genetics to meet the challenge of feeding the world’s growing population in the face of climate change. This was an overview of current attempts to modify plant genes in order to improve the resistance of crucial crops to disaster, for example the synthesis of a new strain of rice that can survive widespread and frequent flooding in Bangladesh. Similar efforts are ongoing to synthesis crops that can survive prolonged drought, a likely consequence of climate change in other parts of the world. It was a superb introduction to the fraught topic of genetic modification and it fitted very well with Boyle’s concern for the  ‘relief of man’s estate’. You can find more on Liam and his lecture here.

All in all, a superb conference in a beautiful setting. There were several other great talks, not least a discussion of Boyle’s contemporary Valentine Greatrakes  by Dr Peter Elmer and a superb talk on ageing and dementia by Professor Ian Roberston. Ireland is home to a great many excellent summer schools on literary figures and traditional musicians, but none on scientists; I suspect this festival will become be a major event in the Irish summer calender in a few years.

P.S. I should say this was the second annual Boyle summer school organised by the CALMAST science outreach group at WIT and by the Lismore Heritage Centre. It was sponsored by Science Foundation Ireland, the Royal Society of Chemistry, the Institute of Chemisty in Ireland, the Institute of Physics in Ireland, the Robert Boyle Foundation,  i-scan, Abbott, Lismore Castle Arts and the Lismore House Hotel.


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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!

British physicist Peter Higgs (R) congra

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.


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!

Hi Res Cormac Higgs


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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.

Image.ashx Image2.ashx

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:

Ar dheis Dé go raibh a anam


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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 Ωk = -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 (ns 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…


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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 Ho (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: Ωk = -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 paperConstraints 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 H0,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 Ωm .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


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